Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.

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  • Photosynthesis (Google doc)

Most life on Earth depends on photosynthesis .The process is carried out by plants, algae, and some types of bacteria, which capture energy from sunlight to produce oxygen (O 2 ) and chemical energy stored in glucose (a sugar). Herbivores then obtain this energy by eating plants, and carnivores obtain it by eating herbivores.

The process

During photosynthesis, plants take in carbon dioxide (CO 2 ) and water (H 2 O) from the air and soil. Within the plant cell, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose. The plant then releases the oxygen back into the air, and stores energy within the glucose molecules.


Inside the plant cell are small organelles called chloroplasts , which store the energy of sunlight. Within the thylakoid membranes of the chloroplast is a light-absorbing pigment called chlorophyll , which is responsible for giving the plant its green color. During photosynthesis , chlorophyll absorbs energy from blue- and red-light waves, and reflects green-light waves, making the plant appear green.

Light-dependent Reactions vs. Light-independent Reactions

While there are many steps behind the process of photosynthesis, it can be broken down into two major stages: light-dependent reactions and light-independent reactions. The light-dependent reaction takes place within the thylakoid membrane and requires a steady stream of sunlight, hence the name light- dependent reaction. The chlorophyll absorbs energy from the light waves, which is converted into chemical energy in the form of the molecules ATP and NADPH . The light-independent stage, also known as the Calvin cycle , takes place in the stroma , the space between the thylakoid membranes and the chloroplast membranes, and does not require light, hence the name light- independent reaction. During this stage, energy from the ATP and NADPH molecules is used to assemble carbohydrate molecules, like glucose, from carbon dioxide.

C3 and C4 Photosynthesis

Not all forms of photosynthesis are created equal, however. There are different types of photosynthesis, including C3 photosynthesis and C4 photosynthesis. C3 photosynthesis is used by the majority of plants. It involves producing a three-carbon compound called 3-phosphoglyceric acid during the Calvin Cycle, which goes on to become glucose. C4 photosynthesis, on the other hand, produces a four-carbon intermediate compound, which splits into carbon dioxide and a three-carbon compound during the Calvin Cycle. A benefit of C4 photosynthesis is that by producing higher levels of carbon, it allows plants to thrive in environments without much light or water. The National Geographic Society is making this content available under a Creative Commons CC-BY-NC-SA license . The License excludes the National Geographic Logo (meaning the words National Geographic + the Yellow Border Logo) and any images that are included as part of each content piece. For clarity the Logo and images may not be removed, altered, or changed in any way.

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Related Resources

What is photosynthesis?

Photosynthesis is the process plants, algae and some bacteria use to turn sunlight, carbon dioxide and water into sugar and oxygen.

Sunlit leaves, photosynthesis

  • Photosynthetic processes
  • Photosynthesis equation
  • The carbon exchange
  • How do plants absorb sunlight?
  • Location of photosynthesis

Light-dependent reactions

  • The Calvin cycle

Types of photosynthesis

Additional resources.

Photosynthesis is the process used by plants, algae and some bacteria to turn sunlight into energy. The process chemically converts carbon dioxide (CO2) and water into food (sugars) and oxygen . The chemical reaction often relies on a pigment called chlorophyll, which gives plants their green color.  Photosynthesis is also the reason our planet is blanketed in an oxygen-rich atmosphere.

Types of photosynthetic processes

There are two types of photosynthesis: oxygenic and anoxygenic. They both follow very similar principles, but the former is the most common and is seen in plants, algae and cyanobacteria. 

During oxygenic photosynthesis, light energy transfers electrons from water (H2O) taken up by plant roots to CO2 to produce carbohydrates . In this transfer, the CO2 is "reduced," or receives electrons, and the water is "oxidized," or loses electrons. Oxygen is produced along with carbohydrates.

This process creates a balance on Earth, in which the carbon dioxide produced by breathing organisms as they consume oxygen in respiration is converted back into oxygen by plants, algae and bacteria.

Anoxygenic photosynthesis, meanwhile, uses electron donors that are not water and the process does not generate oxygen, according to "Anoxygenic Photosynthetic Bacteria" by LibreTexts . The process typically occurs in bacteria such as green sulfur bacteria and phototrophic purple bacteria. 

The Photosynthesis equation

Though both types of photosynthesis are complex, multistep affairs, the overall process can be neatly summarized as a chemical equation.

The oxygenic photosynthesis equation is: 

6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O

Here, six molecules of carbon dioxide (CO2) combine with 12 molecules of water (H2O) using light energy. The end result is the formation of a single carbohydrate molecule (C6H12O6, or glucose) along with six molecules each of oxygen and water.

Similarly, the various anoxygenic photosynthesis reactions can be represented as a single generalized formula:

CO2 + 2H2A + Light Energy → [CH2O] + 2A + H2O

The letter A in the equation is a variable, and H2A represents the potential electron donor. For example, "A" may represent sulfur in the electron donor hydrogen sulfide (H2S), according to medical and life sciences news site News Medical Life Sciences . 

How is carbon dioxide and oxygen exchanged?

stomata are the gatekeepers of the leaf, allowing gas exchange between the leaf and surrounding air.

Plants absorb CO2 from the surrounding air and release water and oxygen via microscopic pores on their leaves called stomata. 

When stomata open, they let in CO2; however, while open, the stomata release oxygen and let water vapor escape. Stomata close to prevent water loss, but that means the plant can no longer gain CO2 for photosynthesis. This tradeoff between CO2 gain and water loss is a particular problem for plants growing in hot, dry environments. 

How do plants absorb sunlight for photosynthesis?

Plants contain special pigments that absorb the light energy needed for photosynthesis.

Chlorophyll is the primary pigment used for photosynthesis and gives plants their green color, according to science education site Nature Education . Chlorophyll absorbs red and blue light and reflects green light. Chlorophyll is a large molecule and takes a lot of resources to make; as such, it breaks down towards the end of the leaf's life, and most of the pigment's nitrogen (one of the building blocks of chlorophyll) is resorbed back into the plant,  When leaves lose their chlorophyll in the fall, other leaf pigments such as carotenoids and anthocyanins begin to show. While carotenoids primarily absorb blue light and reflect yellow, anthocyanins absorb blue-green light and reflect red light, according to Harvard University's The Harvard Forest .

Pigment molecules are associated with proteins, which allow them the flexibility to move toward light and toward one another. A large collection of 100 to 5,000 pigment molecules constitutes an "antenna," according to an article by Wim Vermaas , a professor at Arizona State University. These structures effectively capture light energy from the sun, in the form of photons.

The situation is a little different for bacteria. While cyanobacteria contain chlorophyll, other bacteria, for example, purple bacteria and green sulfur bacteria, contain bacteriochlorophyll to absorb light for anoxygenic photosynthesis, according to " Microbiology for Dummies " (For Dummies, 2019). 

Related: What if humans had photosynthetic skin?

Where in the plant does photosynthesis take place?

Plants need energy from sunlight for photosynthesis to occur.

Photosynthesis occurs in chloroplasts, a type of plastid (an organelle with a membrane) that contains chlorophyll and is primarily found in plant leaves. 

Chloroplasts are similar to mitochondria , the energy powerhouses of cells, in that they have their own genome, or collection of genes, contained within circular DNA. These genes encode proteins that are essential to the organelle and to photosynthesis.

Inside chloroplasts are plate-shaped structures called thylakoids that are responsible for harvesting photons of light for photosynthesis, according to the biology terminology website Biology Online . The thylakoids are stacked on top of each other in columns known as grana. In between the grana is the stroma — a fluid containing enzymes, molecules and ions, where sugar formation takes place. 

Ultimately, light energy must be transferred to a pigment-protein complex that can convert it to chemical energy, in the form of electrons. In plants, light energy is transferred to chlorophyll pigments. The conversion to chemical energy is accomplished when a chlorophyll pigment expels an electron, which can then move on to an appropriate recipient. 

The pigments and proteins that convert light energy to chemical energy and begin the process of electron transfer are known as reaction centers.

When a photon of light hits the reaction center, a pigment molecule such as chlorophyll releases an electron.

The released electron escapes  through a series of protein complexes linked together, known as an electron transport chain. As it moves through the chain, it generates the energy to produce ATP (adenosine triphosphate, a source of chemical energy for cells) and NADPH — both of which are required in the next stage of photosynthesis in the Calvin cycle. The "electron hole" in the original chlorophyll pigment is filled by taking an electron from water. This splitting of water molecules releases oxygen into the atmosphere.

Light-independent reactions: The Calvin cycle

Photosynthesis involves a process called the Calvin cycle to use energy stored from the light-dependent reactions to fix CO2 into sugars needed for plant growth.

The Calvin cycle is the three-step process that generates sugars for the plant, and is named after Melvin Calvin , the Nobel Prize -winning scientist who discovered it decades ago. The Calvin cycle uses the ATP and NADPH produced in chlorophyll to generate carbohydrates. It takes plate in the plant stroma, the inner space in chloroplasts.

In the first step of this cycle, called carbon fixation, an enzyme called RuBP carboxylase/oxygenase, also known as rubiso, helps incorporate CO2 into an organic molecule called 3-phosphoglyceric acid (3-PGA). In the process, it breaks off a phosphate group on six ATP molecules to convert them to ADP, releasing energy in the process, according to LibreTexts.

In the second step, 3-PGA is reduced, meaning it takes electrons from six NADPH molecules and produces two glyceraldehyde 3-phosphate (G3P) molecules.

One of these G3P molecules leaves the Calvin cycle to do other things in the plant. The remaining G3P molecules go into the third step, which is regenerating rubisco. In between these steps, the plant produces glucose, or sugar.

Three CO2 molecules are needed to produce six G3P molecules, and it takes six turns around the Calvin cycle to make one molecule of carbohydrate, according to educational website Khan Academy.

There are three main types of photosynthetic pathways: C3, C4 and CAM. They all produce sugars from CO2 using the Calvin cycle, but each pathway is slightly different.

The three main types of photosynthetic pathways are C3, C4 and CAM.

C3 photosynthesis

Most plants use C3 photosynthesis, according to the photosynthesis research project Realizing Increased Photosynthetic Efficiency (RIPE) . C3 plants include cereals (wheat and rice), cotton, potatoes and soybeans. This process is named for the three-carbon compound 3-PGA that it uses during the Calvin cycle. 

C4 photosynthesis

Plants such as maize and sugarcane use C4 photosynthesis. This process uses a four-carbon compound intermediate (called oxaloacetate) which is converted to malate , according to Biology Online. Malate is then transported into the bundle sheath where it breaks down and releases CO2, which is then fixed by rubisco and made into sugars in the Calvin cycle (just like C3 photosynthesis). C4 plants are better adapted to hot, dry environments and can continue to fix carbon even when their stomata are closed (as they have a clever storage solution), according to Biology Online. 

CAM photosynthesis

Crassulacean acid metabolism (CAM) is found in plants adapted to very hot and dry environments, such as cacti and pineapples, according to the Khan Academy. When stomata open to take in CO2, they risk losing water to the external environment. Because of this, plants in very arid and hot environments have adapted. One adaptation is CAM, whereby plants open stomata at night (when temperatures are lower and water loss is less of a risk). According to the Khan Academy, CO2 enters the plants via the stomata and is fixed into oxaloacetate and converted into malate or another organic acid (like in the C4 pathway). The CO2 is then available for light-dependent reactions in the daytime, and stomata close, reducing the risk of water loss. 

Discover more facts about photosynthesis with the educational science website sciencing.com . Explore how leaf structure affects photosynthesis with The University of Arizona . Learn about the different ways photosynthesis can be measured with the educational science website Science & Plants for Schools .  

This article was updated by Live Science managing editor Tia Ghose on Nov. 3, 2022.

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Daisy Dobrijevic

Daisy Dobrijevic joined  Space.com  in February 2022 as a reference writer having previously worked for our sister publication  All About Space  magazine as a staff writer. Before joining us, Daisy completed an editorial internship with the BBC Sky at Night Magazine and worked at the  National Space Centre  in Leicester, U.K., where she enjoyed communicating space science to the public. In 2021, Daisy completed a PhD in plant physiology and also holds a Master's in Environmental Science, she is currently based in Nottingham, U.K.

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photosynthesis definition and example

Photosynthesis n., plural: photosyntheses [ˌfŏʊ.ɾoʊ.ˈsɪn̪.θə.sɪs] Definition: the conversion of light energy into chemical energy by photolithorophs

Table of Contents

Photosynthesis is a physio-chemical process carried out by photo-auto-lithotrophs by converting light energy into chemical energy . Among the endless diversity of living organisms in the world, producers are a unique breed.

Unlike consumers ( herbivores , carnivores , omnivores , or decomposers ) that rely upon other living organisms for their nutritional requirements and nourishment, producers have been distinguished by their ability to synthesize their own food. This is the reason that we call producers “autotrophic or self-reliable” in nature while consumers of all the different categories are called “heterotrophic or dependent” in nature.

Now among producers, there are different categories of producers, i.e. different mechanisms via which they produce their own food.

  • Photo-auto-litho-trophs: Since these organisms tend to derive their nutrition by channeling the sun’s light energy, they are termed phototrophic in nature. Also, since they utilize inorganic carbon and translate it into organic carbon atoms, i.e. their means of deriving food becomes autotrophic. Additionally, since the source of electrons (electron donors) here are inorganic compounds, they are specified as lithotrophic . In totality, they can be called photo-auto-litho-trophic in nature. Example : Green plants are nature’s brilliant entities that come under this category. They carry out a photosynthesis cycle by taking in carbon dioxide and fixing it into carbohydrates (energy storage molecule). Some of them also give out oxygen gas that’s vital for the other life forms to survive in the earth’s atmosphere.
  • Chemo-auto-lithotrophs: Many of us might be unaware of the fact that there are some autotrophs that don’t utilize sunlight. Rather they derive their energy stored from a different energy source like oxidation of inorganic compounds.

The scope of today’s discussion is limited to photosynthesis and photoautotrophs. So, let’s get started and get to know the answers to these common questions: what is the photosynthesis process, what are the 3 stages of photosynthesis, what does photosynthesis produce, what is a byproduct of photosynthesis, what is the purpose of photosynthesis, is photosynthesis a chemical change, the various inputs and outputs of photosynthesis, which organisms perform photosynthesis , and many other more questions!!!

photolithotroph pioneer species features

What is Photosynthesis?

Photosynthesis definition: Photosynthesis is a physio-chemical process carried out by photo-auto-lithotrophs . In simpler language, photosynthesis is the process by which green plants convert light energy into ‘chemical energy’.

This energy transformation is only possible due to the presence of the miraculous pigment molecule chlorophyll in photosynthesis. The chemical energy as referred to before is the fixed carbon molecules generated during photosynthesis.

Green plants and algae have the ability to utilize carbon dioxide molecules and water and produce food (carbohydrates) for all life forms on Earth. There’s no doubt in the fact that life is impossible and unimaginable without green plants that photosynthesize and sustain the cycles of life.

Let’s give you a brief outline of the topic before we head forward.

  • Etymology: The photosynthesis process finds its origin in 2 Greek words, firsts one being “phōs (φῶς)” meaning ‘light’ and the second one being “sunthesis (σύνθεσις)” meaning ‘putting together’ . The process of photosynthesis aids the conversion of light energy to chemical energy in varied forms of carbohydrate molecules like sugar molecules and starches.
  • Organisms that perform photosynthesis: The organisms are called photo-auto-litho-trophs or simply photoautotrophs.
  • Atmospheric gas consumed: Photosynthesizing organisms utilize carbon dioxide in photosynthesis (CO 2 ).
  • Atmospheric gas released by “some” photosynthetic organisms (MIND IT-Not all): Some photosynthesizing organisms convert carbon dioxide and aid the process of producing oxygen gas (O2).
  • Examples of photosynthesizing organisms: Green plants, cyanobacteria (earlier termed as blue-green algae), and different types of algae that essentially carry out phytoplankton photosynthesis.
  • Why is photosynthesis important? The important function of photosynthesis: Food supply for the organisms on Earth, Oxygen supply for the survival of all organisms.
  • Site of photosynthesis: Leaves and green tissues. (So when asked where photosynthesis takes place, we can tell that it is this site.)
  • What are the reactants of photosynthesis: Carbon dioxide molecules + Water molecules + Light energy
  • Products of photosynthesis: Fixed carbon (carbohydrates) + Oxygen (some cases) + Water

photosynthesis diagram

Watch this vid about photosynthesis:

Biology Definition: Photosynthesis is the synthesis of complex organic material using carbon dioxide , water , inorganic salts , and light energy (from sunlight) captured by light-absorbing pigments , such as chlorophyll and other accessory pigments . Photosynthesis may basically be simplified via this equation: 6CO 2 +12H 2 O+energy=C 6 H 12 O 6 +6O 2 +6H 2 O, wherein carbon dioxide (CO 2 ), water (H 2 O), and light energy are utilized to synthesize an energy-rich carbohydrate like glucose (C 6 H 12 O 6 ). Other products are water and oxygen .

  • Photosynthesis occurs in plastids (e.g. chloroplasts ), which are membrane-bounded organelles containing photosynthetic pigments (e.g. chlorophyll ), within the cells of plants and algae .
  • In photosynthetic bacteria ( cyanobacteria ) that do not have membrane-bounded organelles, photosynthesis occurs in the thylakoid membranes in the cytoplasm .

Etymology: from the Greek photo-, “light”, and synthesis, “putting together” Related forms: photosynthetic (adjective) Compare: chemosynthesis See also: photoautotroph

Types of Photosynthesis

Plant photosynthesis and photosynthetic organisms can be classified under different categories on the basis of some characteristic features. They are:

  • Types of organisms that carry out photosynthesis on the basis of “cellular structure” Both prokaryotic and eukaryotic organisms carry out photosynthesis.
  • Photosynthetic prokaryotes: for example, cyanobacteria
  • Eukaryotic: for example, protists ( diatoms , dinoflagellates , Euglena) and green plants. In particular, algae photosynthesis can be observed in green algae , red algae , brown algae , & land plants, like bryophytes , pteridophytes, gymnosperms , and angiosperms .
  • Prokaryotic ONLY (anoxygenic photosynthetic bacteria, green sulfur bacteria and purple bacteria)

Cyanobacteria photosynthesis and nitrogen fixation diagram

Photosynthesis: a two-stage process

Photosynthesis is an example of a metabolic process with 2 stages. Both the stages need light (direct or indirect sunlight). Hence, the long-claimed notion of the 2 processes being ‘absolute LIGHT and DARK reactions’ isn’t apt.

Scientific studies have pointed out that even the 2nd stage of photosynthesis requires indirect sunlight. Therefore, rather than classifying the stages as light and dark photosynthesis reactions, we’ll like to classify the 2 stages as follows:

  • Photochemical Reaction Process: Light energy is converted to ATP ; photophosphorylation process (light-dependent reactions)
  • Through Calvin cycle: In oxygenic photosynthesis as well as anoxygenic photosynthesis
  • Through Non-Calvin cycle: Only is some anoxygenic photosynthesis

Evolution of Photosynthesis Process

It is postulated that the very first photosynthetic beings and photosynthesis evolved quite early down the evolutionary timescale of life.

It is also believed that the first photosynthetic beings would have initially resorted to other available reducing agents like hydrogen ions or hydrogen sulfide in contrast to the modern-day photosynthetic organisms that utilize water as the “prime and only sources of electrons”.

It is believed that cyanobacteria would have appeared on the surface of Earth much later than the first photosynthetic beings. Once appeared they must have saturated the Earth’s atmosphere with oxygen gas and led to its oxygenation. Only after the Earth was oxygenated, the more complex forms of life would have later evolved.

Evolution of photosynthesis

When we compare photosynthesis to other metabolic processes like respiration, we can clearly notice that these two processes are almost opposite to each other. But another point to note is that both the processes in synchrony sustain life on Earth.

You cannot separate respiration from photosynthesis or photosynthesis from respiration and expect life to run normally. It is not possible that way. Let’s try to compare and list some characteristic features of photosynthesis and cellular respiration processes.

Photosynthesis vs. Respiration

  • Photosynthesis: Anabolic process
  • Cellular respiration: Catabolic process By anabolic, we mean the photosynthesis process “utilizes energy to build biomolecules” like carbohydrates, starch, and sugars. These biomolecules are further utilized by both the plants and the organisms dependent on plants for their nutritional needs. On the other hand, respiration is a catabolic process. This energy is utilized to break down complex molecules to derive nutrition out of them.
  • Photosynthesis: In the chloroplasts of the eukaryotic phototrophic cells.
  • Respiration: Primarily in the mitochondria of the cell.
  • Photosynthesis: Carbon dioxide molecules + Water molecules + Light energy
  • Respiration: Glucose + Oxygen
  • Photosynthesis: Fixed carbon (carbohydrates) + Oxygen (some cases) + Water
  • Respiration: Carbon dioxide + Water +energy (ATP)
  • Photosynthesis: Endergonic and endothermic
  • Respiration: Exergonic and exothermic Just note that these terms endergonic and endothermic both convey the same meaning of “absorbing heat”. And the terms exergonic and exothermic also convey the same meaning of “releasing heat”. The only difference is that –gonics relates to “the relative change in the free energy of the system” while –thermic relates to “the relative change in enthalpy of the system”.
  • Photosynthesis: 6CO 2 + 6H 2 O → C6H 12 O 6 + 6O 2
  • Respiration: C 6 H 12 O 6 6 + 6O 2 → 6CO 2 + 6H 2 O

Photosynthetic Membranes and Organelles

When we begin the discussion on this topic, it’s important that we know that no photosynthesis is possible without the pigment molecules that absorb light. The absorption of sunlight is the most vital step of photosynthesis.

We should also note that the energy of photons is different for every light of different wavelengths. And the energy needed for the photosynthesis to be conducted is of “a very specific wavelength range”.

For the absorption of lights of desired wavelengths, phototrophs organize their pigment molecules in the form of reaction center proteins . These proteins are located in the membranes of the organisms. Let’s learn how these pigment molecules reside inside the organism and how they make the membranes photosynthetic in nature.

  • Prokaryotic photosynthetic organisms: These organisms have their pigment systems or photosystems located in the cell membranes or the thylakoid membranes in the cytosol itself. There are no special organelles called chloroplasts in the prokaryotes.

prokaryotes - pigments

  • Eukaryotic photosynthetic organisms (like green plants): These organisms have their pigment systems or photosystems located in the thylakoids of the chloroplast membranes. Eukaryotes have specialized organelles called chloroplasts (chlorophyll-containing plastids) in their cells.

eukaryotes - pigments

Photosynthetic Pigments

There are 2 types of photosynthetic pigments in the oxygenic photosynthesizing organisms . They are as follows:

  • Porphyrin-derivatives (Chlorophyll in plants and Phycobilin)



Chlorophyll is the green-colored pigment essential for photosynthesis. Let’s try to list its major characteristic features and roles of it.

  • Nature: Lipid
  • Location: Embedded in the thylakoid membrane
  • Types: 9 types as identified by Arnoff and Allen in 1966 (chlorophyll-a, b, c, d, e, bacteriochlorophyll a, b, chlorobium chlorophyll-650,666). Bacteriochlorophylls are present in the anoxygenic photosynthetic organisms.
  • Primary photosynthetic pigment: Chlorophyll-a
  • Presence: In all oxygenic photosynthetic organisms
  • Absorption range: Visible (blue and red) and IR (Infra-red)
  • Ion important for its biological functioning: Magnesium ion (Mg 2+ )
  • Structure: Chlorophyll-a, b, and d are “ chlorin ” derivatives; c is a “ porphyrin ” derivative.
  • Chlorophyll Tail: Oxygenic photosynthetic organisms have a “ phytol ” tail in their chlorophyll; anoxygenic photosynthetic organisms have a “ geranyl ” tail in their bacteriochlorophylls.
  • Main pigment for capturing and storing solar energy
  • Photochemical reaction (chlorophyll-a is present in the photochemical reaction center i.e. PCRC. Chlorophyll a, b, c, and d play a role in resonance energy transfer.)

Carotenoid is the photosynthetic pigment essential for working in conjunction with chlorophyll. Let’s try to list its major characteristic features and roles of it.

  • Nature: Lipid-soluble
  • Types: More than 150
  • Absorption range: 400-500nm
  • Forms: Carotene (simple hydrocarbon, for example, beta carotene) and xanthophyll (oxygenated hydrocarbon, for example, lutein)
  • In excitation and resonance energy transfer
  • Photo-protection (work as a free-radical scavenger as well as a quencher)


Phycobilins aren’t present in all the oxygenic photosynthetic organisms. They have a tetrapyrrole structure (no need for magnesium ion).

  • Types: Phycoerythrobilin, Phycocyanobilins, Allophycocyanobilins When these pigment molecules combine with a water-soluble protein, they form the pigment-protein complex (phycobiliproteins, like phycoerythrin and phycocyanin).
  • Location: Since these phycobiliproteins are water-soluble, they can’t exist in the membranes like chlorophyll and carotenoids. Therefore, phycobilin pigments as their pigment-protein complex aggregate into clusters and adhere to the membrane. These clusters are called phycobilisomes .
  • Exceptional Note: These are the only pigments that are associated with protein molecules.
  • Role: Resonance energy transfer

Organelle for Photosynthesis

What is chloroplast? In eukaryotes, photosynthesis occurs in chloroplasts as they are the designated organelles for the photosynthesis process. There are nearly 10-100 chloroplasts in a typical plant cell .

Inside chloroplasts are the thylakoids; the very specific site for the light capturing. The structure of this very unique part of the chloroplasts is briefly discussed here.

Thylakoid is a membrane-bound compartment in the chloroplasts of eukaryotic organisms. They are also present as such in the cytosol of cyanobacteria (cyanobacteria don’t have chloroplasts but they have simply thylakoids).

These thylakoids are the “primary site of the 1st stage of photosynthesis. i.e. “photochemical reaction” or popularly called “light-dependent reactions of photosynthesis”. The main components of the thylakoid are membrane, lumen, and lamellae. The chlorophyll molecules are present inside these thylakoid membranes.

parts of chloroplast

Light-dependent Reactions

The first stage of photosynthesis is popularly called “light-dependent reactions” . We choose to call this stage the “1st stage: PHOTOCHEMICAL REACTION STAGE”. It is also called the “thylakoid reaction stage” or “hill’s reaction” .

This stage is marked by 3 essential steps of photosynthesis: Oxidation of water , reduction of NADP + , and ATP formation . The site where these reactions occur is the lamellar part of the chloroplast. The units of light-dependent reactions are quantosomes .

light reaction photosynthesis

Let’s discuss this stage under some subheadings:

Wavelengths of light involved and their absorption

The white light that reaches Earth has subparts of different wavelengths together constituting the visible spectrum (390-760nm). But the photosynthetic organisms specifically use a subpart called PAR ( P hotosynthetically A ctive R adiation).

PAR ranges from 400-760nm. Blue light is 470-500nm while red light is 660-760nm). The green light (500-580nm) is reflected back by the plants and this is the reason that plants appear green in color. Blue-green light is not used, only blue light is used.

Photosynthetically Active Radiation

Absorption spectrum and action spectrum

  • Absorption Spectrum: This is a pigment-specific entity or terminology. To find the absorption spectrum of a pigment, you need to plot “the amount of absorption of different wavelengths of light by that particular pigment” . The graph has the “wavelengths of light (in nanometers/nm)” on the X-axis and the “percentage of light absorption” on the Y-axis.

chlorophyll absoption spectrum

  • Action Spectrum: To find the action spectrum of a pigment, you need to plot the “effectiveness of the different wavelengths of light in stimulating photosynthesis process” . The graph has the “wavelengths of light (in nanometers/nm)” on the X-axis and the “rate of photosynthesis (measured as oxygen released)” on the Y-axis. When you superimpose the action spectrum of photosynthesis with the absorption spectrum of the specific pigment, you can find the contribution of each different wavelength in the photosynthesis rate, photosynthetic efficiency, and photosynthetic productivity.

IMPORTANT NOTE: The absorption spectrum is calculated for any of the many pigments involved in photosynthesis. Contrastingly, the action spectrum is calculated only for the photochemical reaction performing pigment i.e. chlorophyll-a present at the reaction center. We identify the progress of photochemical reactions as the “evolution of oxygen gas” that primarily happens at the reaction center where only chlorophyll-a is present. Since the action is directly correlated to the specific excitation of chlorophyll-a molecule, the action spectrum is scientifically calculated only for this chlorophyll-a.

  • Absorption spectrum of chlorophyll- a : 430 nm (blue), 660nm (red) {more absorbance at 660 nm)
  • Absorption spectrum of chlorophyll-b: 430 nm (blue), 660nm (red) {more absorbance at 430 nm)

photosynthetic action spectrum

What actually happens in the Light-dependent reaction

Let’s briefly describe what actually happens here.

  • 1 photon is absorbed by 1 molecule of the chlorophyll (P680) and simultaneously 1 electron is lost here.
  • The electron flow of the photochemical reaction begins here.
  • The electron is transferred to D1/D2 protein, then to a modified form of chlorophyll and “pheophytin”.
  • After that, it’s transferred to plastoquinone A and then B.
  • Initiates an electron flow down an electron transport chain.
  • Ultimately aids the NADP reduction to NADPH.
  • Creation of a proton gradient across the chloroplast membrane.
  • Further on this proton gradient is exploited by the ATP synthase for the generation of ATP molecules.

Water photolysis

Now, if you are wondering how the first electron lost by the 1st chlorophyll is replenished to keep this cycle going, read on. The answer to this query is “photolysis of water molecules” . The chlorophyll molecule regains the lost electron when the “oxygen-evolving complex” in the thylakoid membrane carries out the photolysis of water. The chlorophyll molecule ultimately regains the electron it lost when a water molecule is split in a process called photolysis, which releases oxygen.

Many scientists had a doubt about the source of oxygen in photosynthesis. Some speculated the oxygen atom of the CO 2 gas is the source of oxygen post-photosynthesis. But it was the collective contribution of some 4 scientists that gave clarity on this topic.

C.B. Van Niel worked on purple photosynthetic bacteria ( Chromatium vinosum ) and found out that the source of oxygen is the oxidation of water molecules (‘indirect evidence’). While Ruben, Hassid, and Kamen carried out an isotopic study that gave ‘direct evidence’ of oxygen-evolving from H 2 O molecules and not CO 2 molecules.

Hydrolysis of 2 molecules of water leads to the evolution of 1 molecule of oxygen gas. The photosynthesis equation for light-dependent reactions (non-cyclic electron flow) or the chemical formula for photosynthesis:

2 H 2 O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O 2

The photochemical reaction (or the light-dependent reactions) can be classified as:

  • Cyclic reaction: Only 1 photosystem ( PS1 ) is involved. (Photon excites P700 in PS1, electron reaches Fe-S, then Ferredoxin, then Plastoquinone and then Cyt b6f complex and then Plastocyanin). Since in the solo involvement of PS1 here, the electron flow becomes cyclic. And this phosphorylation process is called cyclic phosphorylation. It happens in the stroma lamellae when light beyond 680nm is available.
  • Non-cyclic reaction: Both photosystems (PS1 and PS2 ) are involved. (Photon excites P680 in PS2, the electron is lost and transferred to pheophytin, then sent on a roller coaster (Z-scheme). Within the z-scheme, the final redox reaction enables the reduction of NADP+ to NADPH. And the chemiosmotic potential generation via proton pumping proton across the membrane and into the thylakoid lumen ensures ATP synthesis.

Data Source: Akanksha Saxena of Biology Online

Diagram of Z-scheme

Light-Independent Reactions (Carbon-fixation Reaction)

Also called the carbon fixation process, the “light-independent reactions” is a misnomer as Science has now already proved that the second stage of photosynthesis isn’t really light-independent reactions. Though it doesn’t need direct light, indirect light is involved even in this process. We choose to label this stage of photosynthesis as the “2nd stage: CARBON-FIXATION REACTION STAGE ”, which is also called:

  • Calvin Cycle or “stromal reaction” as it manifests in the stroma part of the chloroplast
  • “C3 Cycle” or the “reductive pentose phosphate cycle”

Calvin cycle

The inputs for the Calvin cycle  in most plants come from the previously occurred photochemical reaction. In this cycle, the carbon dioxide produced is fixed to a glucose molecule. To be very specific, the Calvin cycle directly doesn’t produce glucose, rather it produces glyceraldehydes-5-phosphate (G-3-P). Glucose is formed after these G-3-P molecules move into the cytosol from the chloroplast .

It consists of primarily 3 steps as follows:

  • Carboxylation: Acceptance of CO 2 by RuBP which is a 5-carbon compound and the CO2-acceptor). 2 molecules of 3-phosphoglycerate are generated as the result of the carboxylation process.
  • Reduction: Generation of 3C/4C/5C/6C/7C molecules.
  • Regeneration of RUBP: 3 molecules of RuBP are regenerated.

In totality, 3 molecules of CO 2 produce 1 molecule of G-3-P. This uses 9 ATPs and 6 NADPHs. And, 6 molecules of CO 2 produce 2 molecules of G-3-P which further produce 1 molecule of glucose. This uses 18ATPs and 12 NADPHs.

The main enzyme is RuBisCo . It’s a multi-enzyme complex with 8 large and 8 small subunits. The substrates for this enzyme are CO 2 , O 2 , and RuBP. An essential ion for the biological functioning of this enzyme: Mg 2+ . The role of RuBisCo is that it captures carbon dioxide gas from the atmosphere and utilizes the NADPH from the 1st stage (photochemical reaction/light-dependent reaction stage) to fix the CO 2 .

The equation of dark reaction of photosynthesis/light-independent reaction stage/2nd stage is: 3 CO 2 + 9 ATP + 6 NADPH + 6 H + → C 3 H 6 O 3 -phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H 2 O

The simple carbon sugars formed via the C3 cycle are utilized by the biological systems to form complex organic compounds like cellulose, precursors for amino acids synthesis and thereby proteins, precursors for lipids, and the source of fuel for respiration.

Important Point To Note: It happens in all the photosynthetic organisms as the basic carbon-fixation step.

Calvin cycle steps diagram

Carbon concentrating mechanisms

There are many carbon concentrating mechanisms to increase the carbon dioxide levels and the carbon fixation process like C4, CAM, etc.

  • Doesn’t happen in all photosynthetic organisms. Rather it happens in conjunction with the C3 cycle in some 4% of angiosperm families.
  • Most commonly angiosperm families that witness C4 cycle: Poaceae, Cyperaceae.
  • First explained by: Hatch and Slack (hence also called the Hatch and Slack cycle). They worked on the maize plant.
  • Role: Endow the ability to efficiently conduct photosynthesis in plants of the semi-arid regions by making them well adapted.
  • Mechanism: By separation of photosynthesis stages in 2 types of cells (mesophyll cells and bundle sheath cells). The light reaction is restricted to the mesophyll cells and the CO 2 fixation happens in the bundle sheath cells. This phenomenon is also termed as “chloroplast dimorphism” in C4 plants. The Kranz anatomy is visible here.
  • Why does the need arise in the first place? – In semi-arid regions or regions with very hot and dry environmental conditions, plants are forced to close their stomata in order to limit water loss. Under such harsh conditions, the intake of CO 2 decreases during the day as the stomata are forced closed. This might lead to no CO 2 intake and hence no CO 2 fixation (2nd stage of photosynthesis). But the 1st stage of photosynthesis keeps running as it doesn’t depend on stomata opening or closure. This means that a continuous oxygen evolution happens which can lead to oxygen saturation. As we know that RuBisCo enzymes use O 2 gas as substrate too, and this can lead to an increased rate of photorespiration by the oxygenase activity of RuBisCo. This further decreases the carbon fixation. This is a very big issue if not resolved. Hence, for situations like these, carbon concentrating mechanisms have evolved in some families of plants to concentrate and enrich the CO 2 concentration in the leaves of these plants under such conditions.
  • Important enzyme for CO 2 concentration: PEP carboxylase
  • CO 2 is first added to a three-carbon compound called phosphoenolpyruvate (PEP) in this cycle. This leads to the formation of a four-carbon (4C)  molecule called oxaloacetic acid or malate. This step happens in the mesophyll cells of the leaves.
  • After that, these 4C compounds are transferred to the bundle sheath cells where the normal C3 cycle fixes them into glucose molecules.
  • This CO 2 concentrating mechanism works on the “principle of separating the RuBisCo enzyme from the O 2 -generating photochemical reactions” in order to reduce the rates of photorespiration and simultaneously increase the rates of CO 2 fixation.
  • This increases the photosynthetic capacity of the leaf/leaf photosynthesis.
  • When the high light and high-temperature conditions are dominant, C4 plants prove more photosynthetically efficient than C3 plants as they produce more sugar molecules in such conditions.
  • Examples of C4 plants: Many crop plants like wheat, maize, rice, sorghum, millet, and sugarcane.
  • Number of ATPs required: 12 (for C-enrichment) + 18 (for C-fixation)= 30 ATPS for 1 glucose production
  • Number of NADPH required: 18 NADPH for 1 glucose production
  • Some plants resort to another mechanism called the CAM cycle in conjunction with the C3 cycle to fix carbon dioxide.
  • Examples: xerophytes like cactus photosynthesis, and most succulents.
  • Around 16,000 species of plants utilize the CAM mechanism
  • Mechanism: Utilize PEP carboxylase to capture carbon dioxide. In contrast to the C4 cycle where there is a “spatial separation of the 2 processes of CO 2 reduction to PEP and PEP fixation to glucose”, CAM plants display a “temporal separation of the 2 listed processes”.

CAM, C3, C4 plant cells

Land plants display different types of photosynthesis based on their requirements and environmental constraints. They are C3, C4 +C3, and CAM+ C3 types of photosynthesis.

Aquatic plants and algae display some extra features in the photosynthetic machinery. These features further refine and define the smooth functioning and efficiency of photosynthesis.

Example: Cyanobacteria photosynthesis – cyanobacteria have carboxysomes  that help in enriching the concentration of carbon dioxide around the RuBisCO enzyme. This directly increases the photosynthetic rates. The distinguished and specially enabled enzyme in the carboxysomes is called “carbonic anhydrase”. The carbonic anhydrase possesses the ability to evolve and release CO 2 from the dissolved hydrocarbonate ions (HCO-). As soon as the CO 2 is released, RuBisCo takes care that it doesn’t go to waste.

Cyanobacterial cell photosynthesis

Order and Kinetics

There are innumerable reactions and processes involved in the biological mechanism of photosynthesis. Besides the normal flow of photosynthesis, there are some plant-specific and condition-specific additional steps that further complicate the mechanism.

Since every biological mechanism has a lot of enzymes, factors, cofactors, substrates, and entities involved, photosynthesis is no different.

Let’s try to list some kinetics-specific pointers that may help.

Equation of photosynthesis

As discussed in the overview and starting of this article, the early photosynthetic organisms must have been primarily “anoxygenic” in nature. These bacteria used some other source than water molecules as their primary electron donors. Even the geological evidence aligns with this fact as the early atmosphere of Earth was highly reducing in nature. Some speculated organisms of the early evolutionary phase are :

  • Green sulfur bacteria (Electron donor= hydrogen and sulfur)
  • Purple sulfur bacteria (Electron donor= hydrogen and sulfur)
  • Green nonsulfur bacteria (Electron donor= various amino and other organic acids)
  • Purple nonsulfur bacteria (Electron donor= variety of nonspecific organic molecules)

After this, some filamentous photosynthetic organisms are expected to have evolved. This is scaled to be an occurrence of some 3.4 billion years old timeline. It is around 2 million years ago that oxygenic photosynthesis is believed to have evolved.

The modern and more commonly known photosynthesis in plants and most of the photosynthetic prokaryotes= Oxygenic (Electron donor= Water molecules)

Symbiosis and the origin of chloroplasts

There are some animal groups that have the ability to form and establish symbiotic relationships with photosynthetic organisms. By establishing such a relationship, these organisms can directly rely upon their photosynthetic partner for energy and food requirements. Some examples of such animal groups are:

  • Sea anemones
  • Marine mollusks (example: Elysia viridis & Elysia chlorotica )
  • Fungi photosynthesis (Lichens)

When such symbiotic relationships are established, it’s sometimes observed that some genes of the plant cell’s nucleus get transferred to the animal cell . (Observed in some slugs).

Photosynthetic slug

Origin of Chloroplasts

Such symbiosis is popularly claimed to be the source of chloroplast evolution. As we notice many similarities between the photosynthetic bacteria and chloroplasts, the evolution of chloroplasts is often hinted to have occurred from these bacteria. Some of the common features between the 2 are:

  • Circular chromosome
  • Prokaryotic-type ribosome
  • A similar set of proteins in the photosynthetic reaction center

It is for all these commonalities the “ endosymbiotic theory ” had been proposed for the evolution of chloroplasts and mitochondria in the eukaryotic cells. According to the endosymbiotic theory, the early eukaryotic cells are believed to have acquired the photosynthetic bacteria by the process of endocytosis). Those early eukaryotic cells after acquiring the photosynthetic bacteria transformed to be self-sustainable and became the “first plant cells”. (Mitochondria photosynthesis is true, they are associated with respiration!)

Endosymbiotic theory

Photosynthetic eukaryotic lineages

Photosynthetic eukaryotic lineages include:

  • Glaucophytes
  • Chlorophytes
  • Rhodophytes
  • Cryptophytes (some clades)
  • Haptophytes (some clades)
  • Dinoflagellates & chromerids
  • Euglenids—clade Excavata (unicellular)

Cyanobacteria and the evolution of photosynthesis

Almost all the prokaryotes carry out anoxygenic photosynthesis in contrast to cyanobacteria, which perform oxygenic photosynthesis. This ability to carry out oxygenic photosynthesis is speculated to have evolved at least 2450–2320 million years ago. The first photosynthetic cyanobacteria might not have been oxygenic as Earth’s atmosphere had no oxygen then.

This topic still requires more scientific study to bring out conclusive results. From the paleontological evidence, it is claimed that the 1st cyanobacteria evolved around 2000 Ma.

For the initial years of the Earth’s oxygen-rich environment (after the oxygen-evolving mechanism evolved), cyanobacteria are claimed to be the “principal primary producers of oxygen”. Even to date, cyanobacteria have been proven vital for marine ecosystems. They’re the primary producers of oxygen in oceans.

Cyanobacteria also fix nitrogen electrons fixation and play a role in biological nitrogen cycles.

Experimental History

We will list the long experimental history in deciphering the extensive photosynthesis process through the ages.

Discovery, Refinements, and Development of the concept

Find out the discovery, refinements, and development of photosynthesis as summarized in the table below:

C3 : C4 photosynthesis research

Several studies were conducted using isotopes of radioactive elements to identify the various aspects of the photosynthetic process. A number of organisms like Chlorella , Stellaria media, Cladophora, Spirogyra, Rhodopseudomonas , sulfur bacteria, green plants like maize, etc have been used to understand the photosynthesis process over the years. Gas exchange studies, isotopic studies, light spectrum studies, radioactive studies, plant anatomical and physiological studies, studies involving roles of carbon dioxide and water, etc have all together opened the gates for our deeper understanding of this topic.

The 3 main factors that directly affect the photosynthesis process are:

  • Light irradiance and wavelength
  • Carbon dioxide concentration


Although there are many more corollary factors, these 3 are the most important ones.

Light intensity (irradiance), wavelength, and temperature

Light is an essential factor for photosynthesis. It directly affects the rate of it. There are 3 different parameters that we should look into:

  • Sciophytes : Grow under “diffuse” light. Example: Oxalis
  • Heliophytes: Grow under “direct: light. Example: Dalbergia
  • Light quality: PAR as previously discussed is the quality or the fraction of light energy that is ‘photosynthetically active’ in nature. It ranges from 400-700nm in wavelength.
  • Duration of light: This parameter doesn’t affect the rate of photosynthesis but affects the total photosynthetic output.

Carbon dioxide levels and photorespiration

Carbon dioxide concentration is the major factor in determining the rate of photosynthesis. There is no carbon-dioxide enriching system in C3 plants like the C4 plants. So, if you increase the concentration of CO 2 in the system, the photosynthetic rate of C3 plants will increase as the CO 2 concentration increases. On the other hand, the photosynthetic yield of the C4 plant won’t increase in such a scenario.

  • CO 2 Compensation Point: A stage in CO 2 concentration when there’s no absorption of CO 2 by the illuminated plant part.

Featuring… “The curious case of RuBisCO and PEP Carboxylase”

Imagine an equal concentration (50-50%) of the two isotopes of carbon, C-12 and C-13, in the form of 12CO 2 and 13CO 2 , made available to both C3 and C4 plants. Now, can you tell which isotope of the carbon will be fixed more or less by the two types of photosynthetic organisms? Can you guess if there would be a “preferable” isotope between the two? Do you think C3 plants will fix the 12CO 2 and 13CO 2 equally or unequally? Or do you think the 12CO 2 and 13CO 2 incorporation would have a biased ratio in any of the two (C3/C4 plants)????

The answer to this lies in the major carbon fixing enzyme involved.

  • C3 plants: Major C-fixing enzyme is RuBisCo and RuBisCo has a “discriminatory ability” to preferably fix 12CO 2 and not 13CO2. Hence, you will find more 12CO 2 fixed than 13CO 2 in the C3 plants.
  • C4 plants: Major C-fixing enzyme is not RuBisCo but PEP Carboxylase . PEP Carboxylase has “no discriminatory ability”. So, you’ll find an almost equal proportion of 12CO 2 and 13CO 2 getting fixed in C4 plants. So, in comparison to C3 plants, the chances of getting 13CO 2 fixed are more in C4 plants.

Choose the best answer. 

Send Your Results (Optional)


Time is Up!

  • Rutherford, A.W., Faller, P. (Jan 2003). “Photosystem II: evolutionary perspectives”. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 358 (1429): 245–253. doi:10.1098/rstb.2002.1186. PMC 1693113. PMID 12594932.
  • Arnon, D.I., Whatley, F.R., Allen, M.B. (1954). “Photosynthesis by isolated chloroplasts. II. Photophosphorylation, the conversion of light into phosphate bond energy”. Journal of the American Chemical Society. 76 (24): 6324–6329. doi:10.1021/ja01653a025.
  • Ehrenberg, R. (2017-12-15). “The photosynthesis fix”. Knowable Magazine. Annual Reviews. doi:10.1146/knowable-121917-115502. Retrieved 2018-04-03.
  • El-Sharkawy, M.A., Hesketh, J.D. (1965). “Photosynthesis among species in relation to characteristics of leaf anatomy and CO 2 diffusion resistances”. Crop Sci. 5 (6): 517–521. doi:10.2135/cropsci1965.0011183x000500060010x.
  • Earl, H., Said Ennahli, S. (2004). “Estimating photosynthetic electron transport via chlorophyll fluorometry without Photosystem II light saturation”. Photosynthesis Research. 82 (2): 177–186. doi:10.1007/s11120-004-1454-3. PMID 16151873. S2CID 291238.

©BiologyOnline.com. Content provided and moderated by Biology Online Editors.

Last updated on July 15th, 2022

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Quick reference.

The chemical process by which green plants synthesize organic compounds from carbon dioxide and water in the presence of sunlight. It occurs in the chloroplasts (most of which are in the leaves) and there are two principal types of reactions. In the light-dependent reactions, which require the presence of light, energy from sunlight is absorbed by photosynthetic pigments (chiefly the green pigment chlorophyll) and used to bring about the photolysis of water:H 2 O → 2H + +2e − +½O 2 . The electrons released by this reaction pass along a series of electron carriers (see electron transport chain); as they do so they lose their energy, which is used to convert ADP to ATP in the process of photophosphorylation. The electrons and protons produced by the photolysis of water are used to reduce NADP:2H + +2e − +NADP + → NADPH+H + . The ATP and NADPH produced during the light-dependent reactions provide energy and reducing power, respectively, for the ensuing light-independent reactions (formerly called the ‘dark reaction’), which nevertheless cannot be sustained without the ATP generated by the light-dependent reactions. During these reactions carbon dioxide is reduced to carbohydrate in a metabolic pathway known as the Calvin cycle. Photosynthesis can be summarized by the equation:CO 2 +2H 2 O → [CH 2 O]+H 2 O+O 2 . Since virtually all other forms of life are directly or indirectly dependent on plants for food, photosynthesis is the basis for all life on earth. Furthermore virtually all the atmospheric oxygen has originated from oxygen released during photosynthesis.

H 2 O → 2H + +2e − +½O 2 .

2H + +2e − +NADP + → NADPH+H +

CO 2 +2H 2 O → [CH 2 O]+H 2 O+O 2


From:   photosynthesis   in  A Dictionary of Chemistry »

Subjects: Science and technology — Chemistry

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Definition of photosynthesis

Did you know.

Photosynthesis Has Greek Roots

The Greek roots of photosynthesis combine to produce the basic meaning "to put together with the help of light". Photosynthesis is what first produced oxygen in the atmosphere billions of years ago, and it's still what keeps it there. Sunlight splits the water molecules (made of hydrogen and oxygen) held in a plant's leaves and releases the oxygen in them into the air. The leftover hydrogen combines with carbon dioxide to produce carbohydrates, which the plant uses as food—as do any animals or humans who might eat the plant.

Examples of photosynthesis in a Sentence

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'photosynthesis.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

1898, in the meaning defined above

Dictionary Entries Near photosynthesis


photosynthetic ratio

Cite this Entry

“Photosynthesis.” Merriam-Webster.com Dictionary , Merriam-Webster, https://www.merriam-webster.com/dictionary/photosynthesis. Accessed 2 Apr. 2024.

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What is photosynthesis.

It is the process by which green plants, algae, and certain bacteria convert light energy from the sun into chemical energy that is used to make glucose. The word ‘photosynthesis’ is derived from the Greek word phōs, meaning ‘light’ and synthesis meaning ‘combining together.’

Jan Ingenhousz, the Dutch-born British physician and scientist, discovered the process of photosynthesis.

what is the meaning of photosynthesis in full

Where does Photosynthesis Occur

Photosynthesis takes place mainly in the leaves of green plants and also in the stems of herbaceous plants as they also contain chlorophyll. Sometimes it also occurs in roots that contain chlorophyll like in water chestnut and Heart-leaved moonseed. Apart from plants, photosynthesis is also found to occur in blue-green algae.

What Happens During Photosynthesis

It involves a chemical reaction where water, carbon dioxide, chlorophyll, and solar energy are utilized as raw materials (inputs) to produce glucose, oxygen, and water (outputs).

what is the meaning of photosynthesis in full

Stages of the Process

Photosynthesis occurs in two stages:

1) The Light-dependent Reaction

  • Takes place in the thylakoid membranes of chloroplasts only during the day in the presence of sunlight
  • High-energy phosphate molecules adenosine triphosphate ( ATP ) and the reducing agent NADPH are produced with the help of electron transport chain

2) The Light-independent or Dark Reaction ( Calvin cycle )

  • Takes place in the stroma of chloroplast in the absence of light that helps to fix carbon
  • ATP and NADPH produced in the light reaction are utilized along with carbon dioxide to produce sugar in the form of glucose

Factors Affecting the Rate of Photosynthesis

  • Intensity of Light: The higher intensity of light increases the rate of photosynthesis
  • Temperature:  Warmer the temperature, higher the rate of photosynthesis. The rate is highest between the temperatures of 25° to 35° C, after which it starts to decrease
  • Concentration of Carbon dioxide: Higher concentration of carbon dioxide increases the rate of photosynthesis until it reaches a certain point, beyond which no further effects are found   

Although all the above factors together interact to affect the rate of photosynthesis, each of them individually is also capable of directly influencing the process without the other factors and thus called limiting factors.

Importance of Photosynthesis

It serves two main purposes that are essential to support life on earth:

  • Producing food for organisms that depend on others for their nutrition such as humans along with all other animals
  • Synthesizing oxygen by replacing carbon dioxide in the atmosphere

Ans. Photosynthesis is an endothermic reaction because it absorbs the heat of the sun to carry out the process.

Ans. The oxygen in photosynthesis comes from splitting the water molecules.

Ans. Chlorophyll is the main light-absorbing pigment in photosynthesis.

Ans. The role of water is to provide oxygen in the form of oxygen gas to the atmosphere.

Ans. Sunlight is the source of energy that drives photosynthesis.

Ans. The easiest way to measure the rate of photosynthesis is to quantify the carbon dioxide or oxygen levels using a data logger. The rate of photosynthesis can also be measured by determining the increase in the plant ’s biomass (weight).

Ans. Photosynthesis is an energy-requiring process occurring only in green plants, algae, and certain bacteria that utilizes carbon dioxide and water to produce food in the form of carbohydrates. In contrast, cellular respiration is an energy-releasing process found in all living organisms where oxygen and glucose are utilized to produce carbon dioxide and water.

Ans. Glucose produced in photosynthesis is used in cellular respiration to make ATP.

Article was last reviewed on Tuesday, April 21, 2020

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8.1 Overview of Photosynthesis

Learning objectives.

  • Explain the relevance of photosynthesis to other living things
  • Describe the main structures involved in photosynthesis
  • Identify the substrates and products of photosynthesis
  • Summarize the process of photosynthesis

Photosynthesis is essential to all life on earth; both plants and animals depend on it. It is the only biological process that can capture energy that originates in outer space (sunlight) and convert it into chemical compounds (carbohydrates) that every organism uses to power its metabolism. In brief, the energy of sunlight is captured and used to energize electrons, which are then stored in the covalent bonds of sugar molecules. How long lasting and stable are those covalent bonds? The energy extracted today by the burning of coal and petroleum products represents sunlight energy captured and stored by photosynthesis almost 200 million years ago.

Plants, algae, and a group of bacteria called cyanobacteria are the only organisms capable of performing photosynthesis ( Figure 8.2 ). Because they use light to manufacture their own food, they are called photoautotrophs (literally, “self-feeders using light”). Other organisms, such as animals, fungi, and most other bacteria, are termed heterotrophs (“other feeders”), because they must rely on the sugars produced by photosynthetic organisms for their energy needs. A third very interesting group of bacteria synthesize sugars, not by using sunlight’s energy, but by extracting energy from inorganic chemical compounds; hence, they are referred to as chemoautotrophs .

The importance of photosynthesis is not just that it can capture sunlight’s energy. A lizard sunning itself on a cold day can use the sun’s energy to warm up. Photosynthesis is vital because it evolved as a way to store the energy in solar radiation (the “photo-” part) as high-energy electrons in the carbon-carbon bonds of carbohydrate molecules (the “-synthesis” part). Those carbohydrates are the energy source that heterotrophs use to power the synthesis of ATP via respiration. Therefore, photosynthesis powers 99 percent of Earth’s ecosystems. When a top predator, such as a wolf, preys on a deer ( Figure 8.3 ), the wolf is at the end of an energy path that went from nuclear reactions on the surface of the sun, to light, to photosynthesis, to vegetation, to deer, and finally to wolf.

Main Structures and Summary of Photosynthesis

Photosynthesis is a multi-step process that requires sunlight, carbon dioxide (which is low in energy), and water as substrates ( Figure 8.4 ). After the process is complete, it releases oxygen and produces glyceraldehyde-3-phosphate (GA3P), simple carbohydrate molecules (which are high in energy) that can subsequently be converted into glucose, sucrose, or any of dozens of other sugar molecules. These sugar molecules contain energy and the energized carbon that all living things need to survive.

The following is the chemical equation for photosynthesis ( Figure 8.5 ):

Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex. Before learning the details of how photoautotrophs turn sunlight into food, it is important to become familiar with the structures involved.

In plants, photosynthesis generally takes place in leaves, which consist of several layers of cells. The process of photosynthesis occurs in a middle layer called the mesophyll . The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata (singular: stoma), which also play roles in the regulation of gas exchange and water balance. The stomata are typically located on the underside of the leaf, which helps to minimize water loss. Each stoma is flanked by guard cells that regulate the opening and closing of the stomata by swelling or shrinking in response to osmotic changes.

In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast . For plants, chloroplast-containing cells exist in the mesophyll. Chloroplasts have a double membrane envelope (composed of an outer membrane and an inner membrane). Within the chloroplast are stacked, disc-shaped structures called thylakoids . Embedded in the thylakoid membrane is chlorophyll, a pigment (molecule that absorbs light) responsible for the initial interaction between light and plant material, and numerous proteins that make up the electron transport chain. The thylakoid membrane encloses an internal space called the thylakoid lumen . As shown in Figure 8.6 , a stack of thylakoids is called a granum , and the liquid-filled space surrounding the granum is called stroma or “bed” (not to be confused with stoma or “mouth,” an opening on the leaf epidermis).

Visual Connection

Art connection.

On a hot, dry day, plants close their stomata to conserve water. What impact will this have on photosynthesis?

The Two Parts of Photosynthesis

Photosynthesis takes place in two sequential stages: the light-dependent reactions and the light independent-reactions. In the light-dependent reactions , energy from sunlight is absorbed by chlorophyll and that energy is converted into stored chemical energy. In the light-independent reactions , the chemical energy harvested during the light-dependent reactions drive the assembly of sugar molecules from carbon dioxide. Therefore, although the light-independent reactions do not use light as a reactant, they require the products of the light-dependent reactions to function. In addition, several enzymes of the light-independent reactions are activated by light. The light-dependent reactions utilize certain molecules to temporarily store the energy: These are referred to as energy carriers. The energy carriers that move energy from light-dependent reactions to light-independent reactions can be thought of as “full” because they are rich in energy. After the energy is released, the “empty” energy carriers return to the light-dependent reaction to obtain more energy. Figure 8.7 illustrates the components inside the chloroplast where the light-dependent and light-independent reactions take place.

Link to Learning

Click the link to learn more about photosynthesis.

Everyday Connection

Photosynthesis at the Grocery Store

Major grocery stores in the United States are organized into departments, such as dairy, meats, produce, bread, cereals, and so forth. Each aisle ( Figure 8.8 ) contains hundreds, if not thousands, of different products for customers to buy and consume.

Although there is a large variety, each item links back to photosynthesis. Meats and dairy link, because the animals were fed plant-based foods. The breads, cereals, and pastas come largely from starchy grains, which are the seeds of photosynthesis-dependent plants. What about desserts and drinks? All of these products contain sugar—sucrose is a plant product, a disaccharide, a carbohydrate molecule, which is built directly from photosynthesis. Moreover, many items are less obviously derived from plants: For instance, paper goods are generally plant products, and many plastics (abundant as products and packaging) are derived from algae. Virtually every spice and flavoring in the spice aisle was produced by a plant as a leaf, root, bark, flower, fruit, or stem. Ultimately, photosynthesis connects to every meal and every food a person consumes.

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Middle school biology - NGSS

Course: middle school biology - ngss   >   unit 5, photosynthesis in ecosystems.

  • Understand: photosynthesis in ecosystems

Key points:

  • Energy enters an ecosystem when light energy from the sun is transformed into chemical energy. This happens during photosynthesis .
  • Photosynthesis is carried out by photosynthetic organisms .
  • Photosynthetic organisms take in and use carbon dioxide and water from the air and soil.
  • Photosynthetic organisms release oxygen into the air. Organisms throughout the ecosystem use this oxygen to breathe.
  • Photosynthetic organisms produce sugars, which become part of the organism’s biomass . When the photosynthetic organism is eaten, its biomass provides matter and energy to the organism that eats it.

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Meaning of photosynthesis in English

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  • chasmogamous
  • cleistogamous
  • efflorescence
  • in flower idiom
  • multi-headed
  • palynological

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  • Biology Article
  • What is Photosynthesis

What Is Photosynthesis?

“Photosynthesis is the process used by green plants and a few organisms that use sunlight, carbon dioxide and water to prepare their food.”

The process of photosynthesis is used by plants, algae and certain bacteria that convert light energy into chemical energy. The glucose formed during the process of photosynthesis provides two important resources to organisms: energy and fixed carbon.

Read on to explore what is photosynthesis and the processes associated with it.

Site of Photosynthesis

Photosynthesis takes place in special organelles known as chloroplast. This organelle has its own DNA, genes and hence can synthesize its own proteins. Chloroplasts consist of stroma, fluid, and stack of thylakoids known as grana. There are three important pigments present in the chloroplast that absorb light energy, chlorophyll a, chlorophyll b, and carotenoids.

Also Read: Photosynthesis Process

Types of Photosynthesis

There are two different types of photosynthesis:

  • Oxygenic photosynthesis
  • Anoxygenic photosynthesis

Oxygenic Photosynthesis

Oxygenic photosynthesis is more common in plants, algae and cyanobacteria. During this process, electrons are transferred from water to carbon dioxide by light energy, to produce energy. During this transfer of electrons, carbon dioxide is reduced while water is oxidized, and oxygen is produced along with carbohydrates.

During this process, plants take in carbon dioxide and expel oxygen into the atmosphere.

This process can be represented by the equation:

6CO2+ 12H2O + LIGHT ENERGY → C6H12O6 + 6O2 + 6H2O

Anoxygenic Photosynthesis

This type of photosynthesis is usually seen in certain bacteria, such as green sulphur bacteria and purple bacteria which dwell in various aquatic habitats. Oxygen is not produced during the process.

The anoxygenic photosynthesis can be represented by the equation:

CO2 + 2H2A + LIGHT ENERGY → [CH2O] + 2A + H2O

Also Read:  Difference between Photosynthesis and Respiration

Photosynthesis Apparatus

The photosynthesis apparatus includes the following essential components:

Pigments not only provide colour to the photosynthetic organisms, but are also responsible for trapping sunlight. The important pigments associated with photosynthesis include:

  • Chlorophyll: It is a green-coloured pigment that traps blue and red light. Chlorophyll is subdivided into, “chlorophyll a”, “chlorophyll b”, and “chlorophyll c”. “Chlorophyll a” is widely present in all the photosynthetic cells. A bacterial variant of chlorophyll known as bacteriochlorophyll can absorb infrared rays .
  • Carotenoids: These are yellow, orange or red-coloured pigments that absorb bluish-green light. Xanthophyll and carotenes are examples of carotenoids.
  • Phycobilins: These are present in bacteria and red algae . These are red and blue pigments that absorb wavelength of light that are not properly absorbed by carotenoids and chlorophyll.

Plastids are organelles found in the cytoplasm of eukaryotic photosynthetic organisms. They contain pigments and can also store nutrients. Plastids are of three types:

  • Leucoplast: These are colourless, non-pigmented and can store fats and starch.
  • Chromoplasts: They contain carotenoids.
  • Chloroplasts: These contain chlorophyll and are the site of photosynthesis.

Antennae is the collection of 100 to 5000 pigment molecules that capture light energy from the sun in the form of photons. The light energy is transferred to a pigment-protein complex that converts light energy to chemical energy.

Reaction Centers

The pigment-protein complex responsible for the conversion of light energy to chemical energy forms the reaction centre.

Also Read: Photosynthesis

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Part of Science Biology

What is photosynthesis?

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Animals need to eat food to get their energy. All animals, including humans, eat food that was, or is, a plant or an animal.

But green plants and algae can use light energy to make their own food! This process called photosynthesis .

Almost all life on Earth depends upon this process.

what is the meaning of photosynthesis in full

A leaf usually has a large surface area, so that it can absorb a lot of light. It's top surface is protected from water loss, disease and weather damage by a waxy cuticle, which does not stop light entering the leaf.

The upper part of the leaf is where the light falls, and it contains many cells called palisade cells. This has many chloroplasts, with lots of chlorophyll to trap as much light as possible. It is shaped like a tall box which helps pack them closely together.

Carbon dioxide

Plants get the carbon dioxide they need from the air through their leaves. It moves by diffusion through small holes in the underside of the leaf called stomata. Guard cells control the size of the stomata so that the leaf does not lose too much water in hot, windy or dry conditions.

The lower part of the leaf is a spongy layer with loose-fitting cells. Between the cells in this layer there are 'air spaces' - a bit like a sponge. These allow the gases to diffuse through the leaf.Stomata let carbon dioxide enter the leaf, and let the oxygen produced in photosynthesis leave the leaf easily. In many plants, stomata are open during the day and closed at night.

The water needed for photosynthesis is absorbed through the roots and transported through tubes to the leaf.The roots have a type of cell called a root hair cell. These project out from the root into the soil, and have a big surface area and thin walls. This lets water pass into them easily.Note that root cells do not contain chloroplasts, as they are normally in the dark and cannot carry out photosynthesis.

what is the meaning of photosynthesis in full

Results Only the areas of the leaf that were originally green tested positive for starch. The discoloured areas tested negative. As the green areas contained chlorophyll and the white did not, this proves that chlorophyll is needed for photosynthesis.

Investigating the production of oxygen

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Food Chains

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Gas Exchange and Respiration

  • count 2 of 11

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Overwatch 2 is allowed to be fun this week

Blizzard brought some silly new ideas to the shooter for April Fools’ Day

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Torbjorn runs through the Hollywood map with his turret mounted on his head in a screenshot from Overwatch 2

A new patch for Overwatch 2 rolled out Monday that promises a “really, really, really balanced” version of the game. That patch landed on April Fools’ Day, of course, bringing back googly-eyed heroes and a sweeping set of changes to characters’ abilities. It’s a chance for Overwatch 2 players to have a week’s worth of chaotic fun, and for Blizzard to test out some secretly very good tweaks to the game.

The new Balanced Overwatch mode is only available in the arcade section of Overwatch 2 , meaning these changes don’t affect Quick Play or Competitive modes — for good reason. Some changes are ridiculous: Relatively new tank Mauga is now 50% smaller, and has just 25 health (down from 525), making him a tiny terror. Conversely, support hero Brigitte is now a full-on tank; she’s 1.5 times bigger, has an always-massive shield, and got a huge increase to her armor and shield HP.

Some changes are just straight-up silly. Illari becomes solar-powered on any map where the sun is out. Moira’s Biotic Grasp has been flipped, meaning her healing ability now does damage, and her damage ability now does healing — potentially causing DPS Moiras to actually heal their teammates by mistake. Torbjörn’s turrets now stick to anything: walls, ceilings, even other heroes.

Balanced Overwatch also includes some fun new abilities, some of which should actually be in the game. Mei can now summon an ice pillar that launches her into the air. Pharah gets a new ability called Jet Land that lets her dash downward toward the ground while in the air. Reinhardt can reflect incoming fire with his shield, but at the cost of health.

Blizzard has implemented some previous April Fools’ Day prank changes into the main game. In 2021 , Blizzard gave D.Va the ability to crush her enemies when calling in her mech, and gave Zarya a shared cooldown across her two types of bubbles. Those changes ultimately made it into the core modes of Overwatch 2 .

More importantly that stealth-introducing actual long term game changes is giving Overwatch 2 players a chance to have fun without the promise of idealistic perfect game balance. Go ahead and win or lose, but have fun, and try to ride on the back of Orisa as Hanzo while you’re at it. You’ll get some free sprays (and lots of XP) for playing.

Balanced Overwatch runs April 1-8, and is accessible from the PLACEHOLDER_TEXT menu in Overwatch 2 . You can read about the latest changes in Blizzard’s patch notes below.


  • Maximum ultimate charge preserved on hero swap increased from 15 to 49%.

Developer Comments: Mech go zoom and D.Va bomb go boom.

  • Can now move backwards.
  • Can now be canceled with Crouch.
  • Canceling the ability with Crouch in the first .4 seconds reduces the cooldown to 1.5 seconds.

Self Destruct

  • Knockback increased by 900%.

Developer Comments: Doomfist is a mobility hero, so there’s no reason he should be slowing down while blocking right?

  • Power Block and Meteor Strike also empower your next Quick Melee.

Power Block

  • Movement Speed Modifier increased from .65x to 1.25x.


Developer Comments: Leave it to Junker Queen to cut her way toward new heights.

Jagged Blade

  • Pressing Secondary Fire while the ability is active now magnetizes Junker Queen to Gracie.
  • Cooldown now starts when blade starts returning to Junker Queen.
  • Cooldown decreased from 6 to 4 seconds.

Developer Comments: Smallga

  • Health decreased from 350 to 25.
  • Mauga’s Scale has been reduced by 50%.

Incendiary Chain Gun

  • Hitting enemies who are ‘On Fire’ will Ignite them.

Developer Comments: Efi has made some changes to Orisa’s technology inspired by a completely hypothetical scenario where a certain archer rides her into battle.

Energy Javelin

  • Ricochets once.
  • Explodes when it sticks.

Developer Comments: We heard Ramattra wasn’t suffering enough so we’ve increased his suffering so that when he causes suffering his enemies will suffer as much as he has suffered.

  • Base armor increased from 100 to 225.


  • Moved from his Ultimate to Ability 1
  • No longer pauses its duration while dealing damage.
  • Movement Speed Increased by 20%.
  • Duration increased from 3 to 5 seconds.
  • Damage Per Second Decreased from 30 to 20.
  • Radius decreased from 12 to 9 meters.

Nemesis Form

  • Moved from his Ability 1 to his Ultimate.
  • Always has Annihilation active while in use.
  • Fully heals Ramattra on use.
  • Pummel Damage increased from 60 to 75.
  • Pummel Range has been increased from 10 to 15.


Barrier Field

  • You can now press Primary Fire to reflects projectiles.
  • Health decreases by 20% every second while reflecting.
  • Barrier size decreased to 50% while Reflecting.
  • Camera Lock input now bound to Quick Melee.

Developer Comments: Much to the chagrin of his enemies, Roadhog has recently discovered baseball.

  • Projectile Speed increased from 26 to 80.
  • Projectile Damage increased from 0 to 40.

Developer Comments: Danger! Falling rocks.

  • Projectile Speed decreased from 37 to 30.
  • Projectile Gravity decreased from 18 to 2.
  • Pressing the ability button while Accretion is active will cause the rock to crash into the ground. When crashed, it will deal 50 damage in a 4-meter radius and stun anyone damaged.

Developer Comments: Empowering the “no aim” playstyle.

Tesla Cannon

  • Secondary Fire now chains between enemies.

Primal Rage

  • Punches also cause lightning to chain between enemies.


Developer Comments: We’re preparing to retcon Wrecking Ball into a crab. Hope these changes are sufficiently immersive.

  • Wrecking Ball’s sideways movement speed increased by 55%.

Quad Cannons

  • Deals increased damage as you continue to walk sideways.

Developer Comments: Please don’t burst Zarya’s bubble, no matter how big it gets.

Particle Barrier and Projected Barrier

  • Increases the size of the bubbled target by 1.75x.

Developer Comments: B.O.B.’s upset from being called the wrong name, so F.R.E.D.’s picking up the slack.

  • New Ability on mouse scroll.
  • Weapon Swap.
  • Call in F.R.E.D. to charge for a short duration before leaving.

Developer Comments: Yeah, we’ve switched up his configurations a little. So anyway, start blastin’.

Configuration: Assault

  • Configuration: Assault is now the default form.
  • Movement speed penalty has been removed.
  • Configuration: Assault now has 150 Ammo.
  • Damage per bullet decreased from 12 to 5.
  • Now deals 1.5x damage for critical hits.


  • Now transforms Bastion into Configuration: Recon.
  • Grants a movement speed bonus of 35%.
  • Configuration: Sentry now fires shotgun blasts.

Developer Comments: Extra survivability is every cowboy’s dream – just don’t die.

  • New Passive
  • One enemy is marked. Kill them to gain 50 health until the next time you die. After 5 kills, you gain 1 health each time.

Developer Comments: Now bringing Mystery Heroes into other modes.

Focusing Beam

  • Targets within 8 meters of Echo take damage as if they’re under half health.
  • Can no longer choose who you duplicate.
  • Can now duplicate allies.
  • Duplicate’s Health no longer capped at 300 health.
  • Duplicate now gains an extra 100 Shields.
  • Bonus Ult Charge Gain Rate increased from 4 to 6.5.

Developer Comments: Parry this! *Not exclusive to casual players.

  • Press Primary Fire with perfect timing to critically deflect a projectile.

Developer Comments: Hanzo has always struggled to overcome his past, so it’s hard for him not to bounce back to old habits.

Storm Arrows

  • Number of ricochets increased from 1 to 3.
  • Number of projectiles per shot increased from 1 to 5.
  • Damage of each projectile decreased by 78%.

Developer Comments: Junkrat put bombs on his bombs. Not sure why this would surprise anybody.

Frag Launcher

  • You can now detonate Frag Launcher projectiles with Secondary Fire.

Developer Request: Definitely do not use this to get to spots on the map you’re not supposed to get to, thanks.

Avalanche Launch

  • New Ability.
  • Press Jump in the Air to activate.
  • Creates a large Ice Pillar under Mei.
  • Can be canceled with Interact.

Developer Comments: You’ve used Hover Jets. You’ve used Jump Jets. You’ve used Jet Dash. But have you tried Jet Land?

  • Press Crouch in the Air to activate.
  • Dash downwards towards the ground.

Developer Comments: Someone’s taken a page out of Mauga’s book.

Hellfire Shotguns

  • Primary Fire now only shoots one shotgun.
  • Damage per bullet reduced from 5.4 to 2.8.
  • Ammo increased from 8 to 16.
  • Secondary Fire now shoots the other shotgun.

Developer Comments: Vivian Chase? More like Vivian Pull.

Disruptor Shot

  • Disruptor Shot now pulls enemies in on deploy.
  • You can deploy Disruptor Shot early by pressing E again.


Developer Comments: Run and gun? Sounds like fun!

Heavy Pulse Rifle

  • Can now be used during Sprint.
  • Using Heavy Pulse Rifle while sprinting has a spread of 2.

Developer Comments: To keep fights fair, let the enemy team know that they should update their network anti-virus and firewalls as soon as possible.

  • Killing an enemy infected with Virus, it attempts to spread to a nearby enemy.

Developer Comments: Symmetra can’t troll you if you don’t press Teleport.

  • Only places exit Teleporter.
  • Any ally can use Teleporter regardless of their location.
  • Teleporter duration decreased from 10 to 4 seconds.

Developer Comments: Everyone deserves a pet turret.

Deploy Turret

  • The turret now sticks to walls, ceilings, and allies.

Developer Comments: krow slotsiP esluP ruoy woh gnignahc ,erutuf ro tsap eht ot uoy sdnes ylmodnaR

  • Randomly sends you to the past or future, changing how your Pulse Pistols work.

Developer Comments: Hooks + Headshot = Parkour

Grappling Hook

  • Now has 3 charges.
  • Getting a critical hit with Widow’s Kiss’s secondary fire replenishes one charge of the ability.

Developer Comments: Rise and shine! How’s this for a rude awakening?

  • Slept enemies slowly rise while Sleeping.
  • Enemies take fall damage when they land.

Developer Comments: Someone once advised Baptiste to keep moving forward. He’s really taken that advice to heart.

  • Now launches you forward rather than upward.

Amplification Matrix

  • Increases speed of projectiles shot through it by 200%.

Developer Comments: Bigitte

  • Scale increased by 1.5x.
  • Armor increased from 50 to 150.

Shield Barrier

  • Health increased from 250 to 700.
  • Always uses bigger size.
  • Resets your Shield Bash cooldown.
  • Movement Speed bonus increased from 1.15x to 1.3x.

Developer Comments: Fixing a longstanding Illari bug, her solar powers are now fully functional.

Captive Sun

  • After using Captive Sun, Illari becomes Solar Installed. She moves faster and charges her Solar Rifle Faster, her rifle always charges to full damage power.
  • Movement speed bonus 1.2x.
  • Attack charge time reduced by 40%.
  • Healing recharge bonus 1.2x.

Solar Powered

  • New Passive.
  • Illari is always Solar Installed when the sun is out.

Dev Comment: You should see her on her trampoline.

Protection Suzu

  • Now also grants allies a 10% damage boost, 10% healing boost, 50% movement speed boost, and 700% increased jump height.
  • Increased duration from .65 to 1 second.

Vulpine Agility

  • Kiriko can jump an extra time in the air

Developer Comments: Reach new heights with Lifeweaver through the power of photosynthesis.

Petal Platform

  • Now raises 20m (up from 8m).

Developer Comment: Lucio’s gun is now keepin’ it in time.

Sonic Amplifier

  • Ammo increased from 20 to 30.
  • Recovery decreased from .14 seconds per bullet to .125 seconds per bullet.
  • Now Shoots 3 bullets per volley during Speed Boost and 5 bullets per volley during Healing Boost.

Sound Barrier

  • Knocks up enemies the sound waves hit.

Developer Comments: Goodbye, 0 damage numbers!

Caduceus Staff

  • Damage boost from Secondary Fire removed.
  • Secondary Fire is now Damage Staff. (Ability 2 on Controller.)
  • Damage Staff Fires Caduceus Blaster projectiles.
  • Projectiles have a smaller size.
  • Size gets bigger during ult.
  • 2 more damage.
  • Projectiles reload automatically while not firing.
  • Projectiles reload at twice the speed while healing or after 4 seconds without firing.
  • Can fire projectiles at a reduced firing speed if healing beam is active.
  • Healing beam can heal at a reduced rate if Damage Staff is active.

Caduceus Blaster

Dev Comment: Moira’s right arm is starting to melt from all the experimentation, so she’s switching it up.

Biotic Grasp (Primary Fire)

  • Now deals damage instead of healing.

Biotic Grasp (Secondary Fire)

  • Now heals instead of doing damage.

Developer Comments: “Let Zen walk?” Not sure about that one.

Orb of Destruction

  • Ammo increased from 25 to 32.
  • Secondary Fire charge time per projectile decreased from .52 to .47.
  • Secondary Fire projectiles fire 33% faster.
  • Secondary Fire damage decreased by 30%.
  • You can now charge up to 8 Orbs with Secondary Fire.
  • Zenyatta’s accelerates upward while charging Secondary Fire.

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What is Holy Saturday? What the day before Easter means for Christians around the world

what is the meaning of photosynthesis in full

Easter Sunday is this upcoming weekend, which means the preceding Saturday is known as Holy Saturday.

According to Britannica, Holy Saturday is a Christian religious observance that ends the Lenten season. The observance "commemorates the final day of Christ's death," according to Britannica, which many Christians traditionally associate with his "triumphant descent into hell or 'to the dead.'" The day comes between Good Friday and Easter Sunday.

Easter is an important holiday for the millions of people around the world who follow the Christian faith as the day celebrates the resurrection of Jesus Christ. The holiday occurs after a 40-day period known as Lent.

Church services, reflection and prayer are some ways that people observe the holiday. Others enjoy a more secular celebration of Easter filled with bunnies, baskets and colorful eggs.

Good Friday: Are banks, post offices, UPS and FedEx open? Here's what to know

When is Holy Saturday? When is Easter?

This year, Holy Saturday is on Saturday, March 30, 2024. Easter Sunday is on Sunday, March 31, 2024.

Why is Easter so early in 2024?

Easter's date changes depending on the year. The holiday is one of several "moveable feasts" in the liturgical year, the History Channel reports. Others include  Ash Wednesday  and  Palm Sunday .

Easter is observed on the first Sunday following the  Paschal full moon , which is the first full moon on or after  the spring equinox . Since Western Christianity uses the Gregorian calendar, Easter typically falls on a Sunday between March 22 and April 25, according to the History Channel.

In Eastern Orthodox Christianity, the date of Easter also varies. The branch follows the Julian calendar, meaning orthodox Easter falls between April 4 and May 8, the History Channel reports. This year, it will take place on Sunday, May 5, 2024. 

Contributing: Olivia Munson, USA TODAY

Gabe Hauari is a national trending news reporter at USA TODAY. You can follow him on X  @GabeHauari  or email him at [email protected].

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Biology LibreTexts

8.1: Overview of Photosynthesis - The Purpose and Process of Photosynthesis

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Learning Objectives

  • Describe the process of photosynthesis

The Importance of Photosynthesis

The processes of all organisms—from bacteria to humans—require energy. To get this energy, many organisms access stored energy by eating food. Carnivores eat other animals and herbivores eat plants. But where does the stored energy in food originate? All of this energy can be traced back to the process of photosynthesis and light energy from the sun.

Photosynthesis is essential to all life on earth. It is the only biological process that captures energy from outer space (sunlight) and converts it into chemical energy in the form of G3P ( Glyceraldehyde 3-phosphate) which in turn can be made into sugars and other molecular compounds. Plants use these compounds in all of their metabolic processes; plants do not need to consume other organisms for food because they build all the molecules they need. Unlike plants, animals need to consume other organisms to consume the molecules they need for their metabolic processes.

The Process of Photosynthesis

During photosynthesis, molecules in leaves capture sunlight and energize electrons, which are then stored in the covalent bonds of carbohydrate molecules. That energy within those covalent bonds will be released when they are broken during cell respiration. How long lasting and stable are those covalent bonds? The energy extracted today by the burning of coal and petroleum products represents sunlight energy captured and stored by photosynthesis almost 200 million years ago.

Plants, algae, and a group of bacteria called cyanobacteria are the only organisms capable of performing photosynthesis. Because they use light to manufacture their own food, they are called photoautotrophs (“self-feeders using light”). Other organisms, such as animals, fungi, and most other bacteria, are termed heterotrophs (“other feeders”) because they must rely on the sugars produced by photosynthetic organisms for their energy needs. A third very interesting group of bacteria synthesize sugars, not by using sunlight’s energy, but by extracting energy from inorganic chemical compounds; hence, they are referred to as chemoautotrophs.


The importance of photosynthesis is not just that it can capture sunlight’s energy. A lizard sunning itself on a cold day can use the sun’s energy to warm up. Photosynthesis is vital because it evolved as a way to store the energy in solar radiation (the “photo-” part) as high-energy electrons in the carbon-carbon bonds of carbohydrate molecules (the “-synthesis” part). Those carbohydrates are the energy source that heterotrophs use to power the synthesis of ATP via respiration. Therefore, photosynthesis powers 99 percent of Earth’s ecosystems. When a top predator, such as a wolf, preys on a deer, the wolf is at the end of an energy path that went from nuclear reactions on the surface of the sun, to light, to photosynthesis, to vegetation, to deer, and finally to wolf.

  • Photosynthesis evolved as a way to store the energy in solar radiation as high-energy electrons in carbohydrate molecules.
  • Plants, algae, and cyanobacteria, known as photoautotrophs, are the only organisms capable of performing photosynthesis.
  • Heterotrophs, unable to produce their own food, rely on the carbohydrates produced by photosynthetic organisms for their energy needs.
  • photosynthesis : the process by which plants and other photoautotrophs generate carbohydrates and oxygen from carbon dioxide, water, and light energy in chloroplasts
  • photoautotroph : an organism that can synthesize its own food by using light as a source of energy
  • chemoautotroph : a simple organism, such as a protozoan, that derives its energy from chemical processes rather than photosynthesis

What’s So Bad About Asking Where Humans Came From?

Human origin stories have often been used for nefarious purposes. That doesn’t mean they are worthless.

illustration of furry apelike hand extending from left side holding a human skull in profile with jaw pointing up

Here is an origin story about origin stories. Once upon a time, we knew where we came from: Adam and Eve, the Garden of Eden, the Fall. Then came modern science, modern doubt. Geology, paleontology: The world grew older very fast. Skulls were discovered, and stone tools. Human origins became a problem and a fascination. Who are we? How did we emerge? And given who we think we may be, how should we live?

Explore the May 2024 Issue

Check out more from this issue and find your next story to read.

In The Invention of Prehistory: Empire, Violence, and Our Obsession With Human Origins , the intellectual historian Stefanos Geroulanos, who teaches at NYU, offers a compendium of the ideas—speculative, scientific, and somewhere in between—that have arisen in response to these and other questions. Beginning with Rousseau and his idyllic state of nature, we learn the genealogy of a familiar set of tropes: the “noble savage,” the “lizard brain,” the “killer ape,” the goddess-worshipping matriarchy. Other concepts may be less familiar: the “primitive communism” of Engels and others, which allegedly existed prior to the rise of patriarchy, private property, and class struggle; Freud’s “primal horde,” commanded by a father whose murder (and ingestion) by his sons, the original band of brothers, inaugurated civilization and its discontents.

We learn about “stadial” schema, theories about the stages (usually three) through which humanity has passed: Stone/Bronze/Iron, savage/barbarian/civilized, magic/religion/science. About disputes as to where Homo sapiens emerged (China? Egypt?) and where the Indo-European peoples did (Germany? The Caucasus? Somewhere between Iran and India?). About the impact of the unearthing of the dinosaurs and other fossils, of Darwinian evolution, of geology’s discovery of deep time. About questions that continue to engross us . Who were the Neanderthals? What do the cave paintings mean? Were early humans violent or peaceful?

From the November 2021 issue: William Deresiewicz on a brilliant new history of humanity

All of this is fascinating—or would be, but for major problems. For one thing, Geroulanos is not a congenial companion. Like a professor who’s trying too hard to be cool, he sprinkles his language with clumsily modish locutions. “His prose was straight-up goth.” “Rousseau amped up the device of ‘nature’ to the max.” “Bataille vaporized history so as to teleport back to the very beginning.” Worse is the snark, which is relentless, and mostly aimed at nothing worse than the routine careerism of intellectual life. “Jumped at the chance to take credit”; “did his best to show himself to be a good schoolboy”; “had the bad taste to go over his mentors’ head”; “exudes an ambition worthy of Darwin.” Some of it is aimed at exactly the kind of work that scholars are supposed to do. Darwin used “masses of tedious evidence to establish a position others would find hard to assail.” “Other linguists insisted that thanks to their mind-numbingly dry comparative analysis of phonemes they could explain all these bigger issues.” It’s almost as if these people cared about the truth.

All of this points to deeper problems, ones that typify the drift of the contemporary academy. Geroulanos is the executive director of NYU’s Remarque Institute, a prominent center for research on Europe; an executive editor of the Journal of the History of Ideas ; the author or co-author of four previous books; and the co-editor or co-translator of a dozen—in short, a major figure in the history of thought. Yet instead of coming to his subject with a scholar’s open-mindedness—this, alas, is no surprise these days—he does so with self-righteousness and an agenda. His purpose is to argue that the study of humanity’s beginnings is and always must be evil. “The Euromodern search for origins began in and then contributed to a long, brutal history of conquest and empire,” he writes. “It has been drunk on hierarchy. It is rooted in illusions—often murderous ones … Its beautiful ideas have justified force against those deemed weak, different, ugly.”

This is, of course, to a great extent true. It is also not surprising. We are well aware by now that scientific concepts—or, more often, pseudo- or at best proto-scientific ones—have been used to rationalize violence and domination (so, for that matter, have nonscientific concepts). That doesn’t mean we don’t still need to talk about this fact. To pronounce Indigenous people “savage,” as Geroulanos explains, was to license one’s attempts to “civilize” them. To designate them “fossil men,” vestiges of ancient times, was to declare them fit to be displaced. Germany was the birthplace of Indo-European culture, the Nazis believed, so Germans really were the master race.

From the April 2019 issue: Adam Serwer on white nationalism’s deep American roots

But can we have all this without the attitude, the knowing, smug superiority? This so often seems to be the way now on the left—in academia, in media. We are better than the past. Or the rest of you aren’t better, but we are, my allies and I. But you aren’t better than the past; you’re just lucky enough not to live there. Nor are you better than everyone else; you’re just readier to claim you are. Exposing the sources of Western prosperity does not in itself make you virtuous.

Besides, the picture, on Geroulanos’s own evidence, is much more complicated than his politics will allow him to acknowledge. The study of human origins has not invariably been “rooted in illusions,” nor has it always “served ferocious power,” “justified force,” or “rationalized colonial domination.” Sometimes quite the opposite. Geroulanos shows this himself, yet he tends to downplay it, and in any case conveniently forgets it when making his general claims. Indeed, there is an entire through line in his book of figures who employed prehistory to criticize colonialism, capitalism, modern warfare, and modernity more broadly. Rousseau used his state of nature to attack the inequality and artificiality of 18th-century European society. Engels’s primitive communism “offered a model … for true socialist kinship.” The year after Lord of the Flies , William Golding came out with The Inheritors , a book in which he “asked his reader to identify with Neanderthals” against their aggressive, deceitful rivals, the sapiens .

Concepts developed to promote the idea of Western superiority could be turned in the other direction, and were. It is not “they” who are savages, but we: we who exterminate entire populations, slaughter one another in the trenches, bomb cities from the air. Cultural diffusionism, the idea that civilization spread from a single source, often identified as white—Mesopotamia, Northern Europe—“also contributed to an opposing set of political claims: Pan-Africanism and decolonization.”

Geroulanos presents these counterexamples as exceptions, never pausing to consider that, once you have enough of them, exceptions aren’t exceptions so much as a new rule (the study of prehistory: sometimes good), one whose tension with his old rule (the study of prehistory: evil) needs to be worked through into a broader one (prehistory: It’s complicated). So when he does mention someone who played a more positive role in Western relations with the nonwhite world, he often makes sure to undercut them, typically with little or no evidence.

Lewis Henry Morgan, a lawyer and an early ethnographer, advocated on behalf of Native Americans in the years before the Civil War. “The Seneca had adopted him in thanks for his legal and political activism,” Geroulanos tells us, “though today we would see Morgan’s role as much more problematic.” He doesn’t say why. Claude Lévi-Strauss, the great anthropologist, was relentless in his wholesale condemnation of the Western impact on Indigenous societies. Yet his arguments, Geroulanos insists, “had the peculiar quality of diminishing the effects of specific acts of colonial violence.” No reason is given. Other anthropologists are blamed for having tried to preserve what they could of disappearing cultures, if only in the form of artifacts and records of traditions. For this, Geroulanos refers to them as “drivers of colonial violence,” not bothering to explain what they were supposed to have done to stop the real drivers of colonial violence, the companies and states and armies.

This is the opposite of history, if the discipline of history is meant to help us better understand how people saw the world they lived in and the reasons they acted as they did. Instead of strutting through the past, wagging his finger and clucking his tongue, Geroulanos might have exercised a bit of generosity toward people who were trying to make sense of what they had, with the tools that they had. The theories he so gleefully belittles were responding, many of them, to developments that we’ve become accustomed to but that must have been incredibly destabilizing. What did it feel like to learn that the Earth was thousands of times older than we had ever suspected? That it contained remains of creatures more alien than anything we had ever dreamed? That among those creatures were some who looked remarkably like us, yet were somehow not us? There are flashes of this kind of sympathy, but, like the more progressive attitudes that Geroulanos keeps stumbling over, they are quickly overridden and forgotten.

Again, it’s easy to mock the humanitarian impulses of a supposedly benighted past—the belief, for example, that we are all one human family, sharing similar sorrows and joys, which displaced ideas of racial hierarchy after World War II but which Geroulanos condemns for minimizing “difference” (that postmodern holy word). But not only did this represent a real advance; it was a step toward our more enlightened understanding. Yes, to paraphrase T. S. Eliot , we know more than those who came before us, and what we know is them.

But the worst of The Invention of Prehistory is right there in the title. “Invention,” not investigation. Doesn’t it matter if this or that theory is true: about where human beings first evolved, or our historical and genetic relationship to Neanderthals, or the degree of violence in ancient hunter-gatherer societies, or how patriarchy emerged? Apparently, it doesn’t. “I do not much care if particular theories are true,” Geroulanos writes. “I ask what work they do.” It isn’t clear, in fact, if he thinks that there is such a thing as truth. This is someone who can write about “the invention of deep time” and “the ‘discovery’ of the earth’s past”—the scare quotes meaning not that the past was there all along, but that it isn’t there at all, not in any external, empirically observable way. The nascent science of geology, he writes, “played midwife to the birth … of a whole swarm of ostensibly ancient creatures” (that is, the dinosaurs). Ostensibly? So there’s no reality beneath the theories? Geroulanos ducks the question. “The story of human origins has never really been about the past. It has never really been concerned with an accurate, precise depiction of humanity’s emergence out of nature.”

I wonder what his colleagues—the geneticists and archaeologists, the linguists and the neuroscientists—would say to that. This is social constructionism, the idea that there is no truth outside our agreed interpretations, taken to its logical, inane conclusion. And it points to a crucial distinction that Geroulanos’s project denies: the difference between science and pseudo- or proto-science. We have theories about human origins now, and we had theories about them in the 19th century, but they are not the same kinds of theories. Yes, scientists can still have social biases, but contemporary scientific protocols, such as peer review, are meant to root them out. Is the system perfect? Of course not. But there is a qualitative difference between believing that humanity originated in China because (or in order to argue that) the Chinese are “backwards” and deducing that it originated in Africa because that is what genetics and paleontology suggest.

So if truth is irrelevant, what about that “work,” as Geroulanos puts it, that contemporary theories “do”? Well, that’s just the thing. For all his talk of “the new scientific ideologies,” he doesn’t turn up much, in recent decades, that’s indictable. These hypotheses include the notion that the cave paintings show evidence of shamanism; that tools and human bodies shaped each other in a “feedback loop” akin to those we know from the world of computers; that we all descend from a single genetic ancestor, popularly dubbed “Mitochondrial Eve.” All of this is pretty harmless, and certainly a distant cry from the “empire, violence” of his subtitle. Much of it, indeed, comes down on the progressive side of the ledger: goddesses and matriarchies, relatively peaceful tribes that existed before the invention of war, preagricultural egalitarianism. There are still plenty of ideologies running around that justify racism, militarism, and other evils, but they are not drawn from science, for the most part.

And insofar as they are, whose fault is that? “The archaeologists who dig up old bones and the biologists who study hominid genes,” Geroulanos writes, “are seldom the vectors of violence.” Seldom indeed. They also aren’t responsible, to name some of his targets, for Yuval Noah Harari (the “reigning prophet of prehistory’s future”), or 2001: A Space Odyssey (which popularized the idea of the “killer ape,” our supposedly brutal australopithecine ancestor, a notion that Geroulanos presents as having been designed to create an image of violent Indigenous Africans and thus to serve as an argument against decolonization). Nor should they be blamed for the far right’s appropriation of Neanderthals as the original white Europeans. If scientific findings are sensationalized by journalists, oversimplified by authors, and misused by political actors, what are scientists supposed to do? Stop doing science?

Geroulanos seems to imply that the answer is yes, at least for those who study human origins. The world of early humans, he insists, is “inconceivable,” inaccessible. Almost anything we say about it is “a narcissistic fantasy,” a myth. So he openly promotes the myths he likes, which are the ones that announce themselves as such. “I prefer [Georges] Bataille’s and [Annette] Laming-Emperaire’s myths” about the cave paintings—respectively, that the images reflect the moment at which humans became conscious of themselves as separate from nature (and thus conscious of death) and that they embody a complex symbolic system structured around gender (which Laming-Emperaire actually did not regard as a myth). Geroulanos writes admiringly about feminist imaginings that place the female at the center of human evolution. Elaine Morgan’s popularization, in The Descent of Woman , of the “aquatic ape” hypothesis —the theory that hominins developed not on the savanna but in the shallow sea, where mothers could protect their babies from feline predators—was “proudly speculative.” Susan Brownmiller’s assertion, in Against Our Will , that hominin social organization began in fear of rape , was “a primal fiction” that refused to “be judged by crude verification.” He even puts a word in for Wakanda as the “fluorescent triumph” of the Afrocentric view of human history.

This is what constructionism gets you. Geroulanos’s ultimate targets are “humanism, which has always hidden violence,” and the idea of human nature, along with the associated notion that studying the origin of the species can get us closer to understanding it. “In reality,” he writes (reality?), “humans have almost nothing in common with our paleolithic forefathers.” This is also a belief, an ideology, a myth. Human nature may be too, and so may humanism. But I’ll take them over what Geroulanos is offering.

This article appears in the May 2024 print edition with the headline “What’s So Bad About Asking Where Humans Came From?” When you buy a book using a link on this page, we receive a commission. Thank you for supporting The Atlantic.

What is TORCON? Explaining The Weather Channel's system to predict tornadoes in your area

The skies are dark, the wind is howling and social media is filled with references to TORCON , forecasting if a tornado might form in your area.

So what does TORCON mean? And how is it used? Here's an explanation.

What is TORCON? How The Weather Channel's tornado prediction scale started

TORCON, short for the Tornado Condition Index, was developed by Dr. Greg Forbes , a meteorologist and severe weather expert at The Weather Channel who retired in 2018, as an index that helped estimate the risk of tornadoes in a particular area. It is not an official weather term that the National Weather Service or National Oceanic and Atmospheric Administration use, according to Newsweek .

How is TORCON used to predict a tornado?

TORCON uses a 0-10 scale to indicate how likely a tornado is within 50 miles of a given location, according to Weather Station Advisor . A TORCON level of 2 would mean a 20% risk of a tornado, TORCON 5 would be 50%, and so on.

In this video from The Weather Channel , Forbes explains the TORCON system and how it's used.

The National Weather Service system uses tornado watch and tornado warning. What's the difference?

There are six categories used by the National Weather Service to classify the rotational speed of tornadoes (EF0-EF5) but just two levels to warn of tornado activity.

A tornado watch means weather conditions could spawn tornadoes within the watch area. People should stay aware of weather conditions and be prepared to act if watchers spot a tornado.

A tornado warning means a tornado has been sighted by a local NWS forecast office or indicated by weather radar and there is imminent danger to life and property.


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What the Bridge Meant to Baltimore

The victims, the history, the void. Residents reflect on their collective pain, and the city’s strength.

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A view of the cargo ship that hit the Francis Scott Key Bridge in the background. In the foreground, a person on a bench at a nearby park is seen sitting on a bench, head down.

By Anna Betts and JoAnna Daemmrich

Anna Betts reported from New York, and JoAnna Daemmrich reported from Baltimore.

Blue-collar workers crossed it. Families went crabbing around it. Teenagers celebrated new driver’s licenses by traversing it. And couples were known to get engaged near it.

Completed in 1977, the Francis Scott Key Bridge was a practical, final link to the beltway of roads that circled Baltimore Harbor, a much-needed solution to reduce Harbor Tunnel congestion. But for so many, it was more than that.

For some, it symbolized the working-class communities around it — for others, the city itself. The bridge also served as a reminder of a storied chapter in history: Near Fort McHenry, the bridge is believed by historians to be within 100 yards from where Key was held by the British during the War of 1812, when he witnessed the siege of the fort in September 1814 and wrote the poem that became the national anthem. (A star-spangled buoy commemorates the supposed spot.)

And the Key Bridge was simply a presence in people’s everyday lives. Since the collapse last week, residents have been processing the loss on many levels, from profound grief for the six workers who died, to concern for the immigrant communities affected by the port’s shutdown, to a sense of emptiness that has cast a pall over their memories.

Here are a few reflections from Baltimoreans, condensed and edited for clarity.

Dr. Panagis Galiatsatos, physician who grew up on the east side of Baltimore

“There’s not a lot of things that tend to unite this city, unfortunately, but this is one of them. Every single Baltimorean felt that bridge fall down. That’s our London Bridge. That’s our Golden Gate Bridge. It was like a friend constantly saying hello to me in the morning.

The bridge was one of the first jobs really available to a lot of the immigrant populations in Baltimore city. My dad, who worked as a painter on the bridge, said if you were an able-bodied person that knew how to do any level of construction or painting and you’re an immigrant, chances are you worked on that bridge.

Up until the bridge was built, you hear these stories from the locals, it would take hours sometimes to get to any place that was reasonable to work at, because of the back roads they had to take. The bridge was a lifeline to schools and work. That’s where my heart is at: These everyday people that live out there just lost a lifeline connection to these big resources such as supermarkets, schools, work.

Not to sound cheesy, but it was a bridge to the American dream. And the first and last hands touching that bridge were immigrants that came here to pursue that.”

Terry Turbin, pastor of Sonshine Fellowship Church in Dundalk and a onetime carpenter who worked on the bridge foundation

“I’m proud to be able to say I had a part in building it. When they get ready to rebuild it, I would like to work on it, even just one day. I went out on the barge in February 1975. After I got married, and found the bridge was being constructed, I wanted to get on the job and make better money. The bridgework was $8.10 an hour. My first day out, I actually asked myself, ‘Oh God, what did I get myself into?’ It was dangerous work. We were driving the pilings, and at that time of year, the wind was pretty stiff. You had to be very careful. The other part was always looking up to make sure nothing was falling on you. It was really stressful. When you got on dry land, you said a prayer of thanks. I have driven over the bridge a thousand times or more, and I would always tell my family, ‘This is where I was working, I was right under there.’ It was an emotional connection for me.”

Gustavo Torres, executive director of CASA, a nonprofit that provides services to immigrants in Baltimore

“For me, the Key Bridge was just another crossing. Its magnificence seemed, well, average. In its death, it has become so much more, its secret life revealed as the place where workers came together. Laborers born in places ranging from south Baltimore to central Honduras sharing companionship as they worked long after I had gone to sleep to make sure that my passage was uneventful. A place of heroism where workers toiled in the cold and throughout the pandemic so that my life was easier. Workers who are fathers, brothers, sisters and mothers. Workers who are neighbors, co-workers, friends from church. Workers, who in their commitment to all of us, are the best of America.”

Comfort, and anxiety

Congressman Kweisi Mfume, who represents Baltimore as part of Maryland’s 7th District

“I was a freshman in college when they started building [the bridge]. I was anxious for the bridge to go up because it was a quicker way to get to the other side of the harbor, but it also ended up being a kind of cathedral of architecture in that community because it was a beautiful bridge. You felt very comfortable seeing it, because its sturdiness suggested all is well elsewhere.

On the economic side, there’s a real sense of urgency because that bridge affects so many supply line issues all over the country. It’s a cascading kind of ripple effect that will add to an economy right now in the wrong way. There are a number of small businesses that are impacted, particularly those who deal in import-export.”

John Olszewski, known as Johnny O, Baltimore County executive

"I feel it in the very personal way, and in the very painful way, that the people who live here do. We’re still very much in shock and reeling from the loss, not just from our neighbors, people who are experiencing unspeakable tragedy right now, who were working on the bridge, but also our neighbors who have this incredible uncertainty about what their future means, who are port workers.

It’s the little memories: as a high schooler, driving around the beltway and crossing the bridge because it was the thing to do when you got your license, to spending evenings fishing in the channel. I’d do a little crabbing, recreationally, on the side of the bridge there. I have all these incredible memories, and then to have everything you’ve ever known come to a screeching halt … ” [His voice trailed off and he shook his head.]

A sense of home

Michelle Dobbs, veterinary pharmaceutical sales representative, resident of the Sparrows Point neighborhood who crossed the bridge twice a day

“Coming over the Key Bridge, I’d feel an instant lowering of blood pressure, a feeling that my day is done. It was a symbol of coming home. You’d have a beautiful view of the Baltimore skyline from the top of the bridge. I’d see the sailboats and cruise ships coming in and out; one time, I was lucky enough to see the Pride of Baltimore [a tall ship] come through. It never got old. It was just a part of my daily life. I don’t know when it’s not going to be so jarring. It’s unbelievable to have such an emotional attachment to a bridge.”

Joey Harkum, musician from Pasadena, a suburban area south of the bridge on the Patapsco River

“It’s absolutely important to northern Anne Arundel County — that’s how we get to Dundalk, that’s how we get to Fells Point. It’s so close to our house, there’s debris washing up on our beach now. We grew up right there on the river. We would take out a little boat and sneak out to Fort Carroll and just explore. Whenever people from out of town came, I’d drive them to the bridge and show them all the forts. I named my first band Pasadena. Our first album had a drawing of the Key Bridge, the smokestacks and the bridge, showing that’s where we were from. It was just part of our identity for people who lived south of the city."

Coming together

Shannon McLucas, ranger at Fort McHenry, a national monument about four miles across from the bridge

“Throughout the morning, we had a lot of regulars, locals walking along the seawall. Joggers, dog walkers, parents with babies, some come every morning to walk. They had the same emotional reaction I did at seeing this dramatically changed landscape. It was very busy but very eerily quiet. To me, that’s remarkable. There are moments when we have this shared humanity — from the park, you see the wreckage, but you also see the Coast Guard at work. We talk about the Battle of Baltimore, in 1814. People came from all over, from different walks of life, to defend the city, they came together. Now, 210 years later, this was an accident, but it’s one of those moments where you realize we do have a shared community.”

Laura Lippman, author

“All I can tell you is that I’m sad and I know others are sad, too. I love my hometown so much. My family moved here in ’65. I remember the riots after the assassination of M.L.K., I remember when homicides spiked in the ’80s, I remember Freddie Gray. It’s a city that’s forever getting knocked down — and getting back up again.

I went to Opening Day of the Orioles, arriving in time for the acknowledgment of those who died on the bridge. It was sincerely moving. As you may know, Baltimoreans shout the ‘O!’ at the end of the national anthem — for the Orioles, but also, I think, for the city. I have never shouted ‘O!’ as loudly as I did on Thursday.”

Miriam Jordan contributed reporting.

Anna Betts reports on national events, including politics, education, and natural or man-made disasters, among other things. More about Anna Betts


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    In chemical terms, photosynthesis is a light-energized oxidation-reduction process. (Oxidation refers to the removal of electrons from a molecule; reduction refers to the gain of electrons by a molecule.) In plant photosynthesis, the energy of light is used to drive the oxidation of water (H 2 O), producing oxygen gas (O 2 ), hydrogen ions (H ...

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    Photosynthesis ( / ˌfoʊtəˈsɪnθəsɪs / FOH-tə-SINTH-ə-sis) [1] is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their activities.

  3. Photosynthesis

    The process. During photosynthesis, plants take in carbon dioxide (CO 2) and water (H 2 O) from the air and soil. Within the plant cell, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose.

  4. Photosynthesis

    Photosynthesis Definition. Photosynthesis is the biochemical pathway which converts the energy of light into the bonds of glucose molecules. The process of photosynthesis occurs in two steps. In the first step, energy from light is stored in the bonds of adenosine triphosphate (ATP), and nicotinamide adenine dinucleotide phosphate (NADPH).

  5. Photosynthesis

    Photosynthesis. Photosynthesis is a process by which phototrophs convert light energy into chemical energy, which is later used to fuel cellular activities. The chemical energy is stored in the form of sugars, which are created from water and carbon dioxide. 3,12,343.

  6. Intro to photosynthesis (article)

    Photosynthesis is the process in which light energy is converted to chemical energy in the form of sugars. In a process driven by light energy, glucose molecules (or other sugars) are constructed from water and carbon dioxide, and oxygen is released as a byproduct. The glucose molecules provide organisms with two crucial resources: energy and ...

  7. Photosynthesis in organisms (article)

    Photosynthesis is powered by energy from sunlight. This energy is used to rearrange atoms in carbon dioxide and water to make oxygen and sugars. Carbon dioxide and water are inputs of photosynthesis. These inputs come from the environment. Oxygen and sugars are outputs of photosynthesis. The oxygen is released into the environment.

  8. What is photosynthesis?

    Photosynthesis is the process used by plants, algae and some bacteria to turn sunlight into energy. The process chemically converts carbon dioxide (CO2) and water into food (sugars) and oxygen ...

  9. Photosynthesis

    Photosynthesis definition: Photosynthesis is a physio-chemical process carried out by photo-auto-lithotrophs. In simpler language, photosynthesis is the process by which green plants convert light energy into 'chemical energy'.

  10. Photosynthesis

    Photosynthesis can be summarized by the equation:CO 2 +2H 2 O → [CH 2 O]+H 2 O+O 2. Since virtually all other forms of life are directly or indirectly dependent on plants for food, photosynthesis is the basis for all life on earth. Furthermore virtually all the atmospheric oxygen has originated from oxygen released during photosynthesis.

  11. 11.1.1: Overview of Photosynthesis

    Plants are also photoautotrophs, a type of autotroph that uses sunlight and carbon from carbon dioxide to synthesize chemical energy in the form of carbohydrates. All organisms carrying out photosynthesis require sunlight. Figure 11.1.1. 1: (a) Plants, (b) algae, and (c) certain bacteria, called cyanobacteria, are photoautotrophs that ...

  12. 8.1: Introduction to Photosynthesis

    Figure 8.1.1 8.1. 1: This world map shows Earth's distribution of photosynthesis as seen via chlorophyll a concentrations. On land, this is evident via terrestrial plants, and in oceanic zones, via phytoplankton. (credit: modification of work by SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE) The processes in all organisms ...

  13. Photosynthesis Definition & Meaning

    Photosynthesis Has Greek Roots synthesis of chemical compounds with the aid of radiant energy and especially light; especially : formation of carbohydrates from carbon dioxide … See the full definition

  14. Photosynthesis

    Stages of the Process. Photosynthesis occurs in two stages: 1) The Light-dependent Reaction. Takes place in the thylakoid membranes of chloroplasts only during the day in the presence of sunlight. High-energy phosphate molecules adenosine triphosphate ( ATP) and the reducing agent NADPH are produced with the help of electron transport chain.

  15. 5: Photosynthesis

    5.1: Overview of Photosynthesis. All living organisms on earth consist of one or more cells. Each cell runs on the chemical energy found mainly in carbohydrate molecules (food), and the majority of these molecules are produced by one process: photosynthesis. Through photosynthesis, certain organisms convert solar energy (sunlight) into chemical ...

  16. 8.1 Overview of Photosynthesis

    Main Structures and Summary of Photosynthesis. Photosynthesis is a multi-step process that requires sunlight, carbon dioxide (which is low in energy), and water as substrates ().After the process is complete, it releases oxygen and produces glyceraldehyde-3-phosphate (GA3P), simple carbohydrate molecules (which are high in energy) that can subsequently be converted into glucose, sucrose, or ...

  17. Photosynthesis in ecosystems (article)

    Photosynthesis drives the movement of matter, or atoms, between organisms and the environment. Photosynthetic organisms take in and use carbon dioxide and water from the air and soil. Photosynthetic organisms release oxygen into the air. Organisms throughout the ecosystem use this oxygen to breathe. Photosynthetic organisms produce sugars ...


    PHOTOSYNTHESIS definition: 1. the process by which a plant uses carbon dioxide from the air, water from the ground, and the…. Learn more.

  19. What Is Photosynthesis?

    What Is Photosynthesis? "Photosynthesis is the process used by green plants and a few organisms that use sunlight, carbon dioxide and water to prepare their food.". The process of photosynthesis is used by plants, algae and certain bacteria that convert light energy into chemical energy. The glucose formed during the process of ...

  20. Photosynthesis

    Photosynthesis is really important for the plant because it provides the plant with food: some of the glucose is used immediately, to give the plant energy in the process of respiration. some of ...

  21. PDF Photosynthesis

    Photosynthesis is the process by which plants, some bacteria and some protistans use the energy from sunlight to produce glucose from carbon dioxide and water. This glucose can be converted into pyruvate which releases adenosine triphosphate (ATP) by cellular respiration. Oxygen is also formed. Photosynthesis may be summarised by the word equation:

  22. What is the basic formula for photosynthesis?

    The process of photosynthesis is commonly written as: 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2.This means that the reactants, six carbon dioxide molecules and six water molecules, are converted by light energy captured by chlorophyll (implied by the arrow) into a sugar molecule and six oxygen molecules, the products. The sugar is used by the organism, and the oxygen is released as a by-product.

  23. Aerobic methane production in Scots pine shoots is independent of

    To distinguish between these three pathways, we tested three alternate hypotheses: (1) if the CH 4 produced within the shoots is a by-product of photosynthesis-related processes or associated carbon allocation, CH 4 emissions decrease with the drought-driven inhibition of photosynthesis, (2) if the CH 4 production from the shoots mainly results ...

  24. Overwatch 2 is allowed to be fun this week

    Developer Comments: Reach new heights with Lifeweaver through the power of photosynthesis. Petal Platform. Now raises 20m (up from 8m). LÚCIO. Developer Comment: Lucio's gun is now keepin' it ...

  25. What is Holy Saturday? What to know about the last day of Holy Week

    Easter Sunday is this upcoming weekend, which means the preceding Saturday is known as Holy Saturday. According to Britannica, Holy Saturday is a Christian religious observance that ends the ...

  26. The Purpose and Process of Photosynthesis

    photosynthesis: the process by which plants and other photoautotrophs generate carbohydrates and oxygen from carbon dioxide, water, and light energy in chloroplasts. photoautotroph: an organism that can synthesize its own food by using light as a source of energy. chemoautotroph: a simple organism, such as a protozoan, that derives its energy ...

  27. What's So Bad About Asking Where Humans Came From?

    Here is an origin story about origin stories. Once upon a time, we knew where we came from: Adam and Eve, the Garden of Eden, the Fall. Then came modern science, modern doubt. Geology ...

  28. What is TORCON? Weather Channel index forecasts likelihood of tornado

    A TORCON level of 2 would mean a 20% risk of a tornado, TORCON 5 would be 50%, and so on. In this video from The Weather Channel, Forbes explains the TORCON system and how it's used.

  29. What the Bridge Meant to Baltimore

    The victims, the history, the void. Residents reflect on their collective pain, and the city's strength. By Anna Betts and JoAnna Daemmrich Anna Betts reported from New York, and JoAnna ...

  30. LA Times edits article after drawing the ire of LSU coach Kim Mulkey

    The Los Angeles Times have edited a previously published commentary piece written about the LSU women's basketball team following criticisms of the article by the team's head coach, who ...