Could plants do photosynthesis at moonlight?

Related to this and this but not exactly same; could plants do photosynthesis at moonlight or more dim-intensity light?

Of course they can and do, except in total darkness (spectroscopically, only bands in the far red and in the blue spectra matter - blanking these affects 'total darkness').

In photosynhesis a photon is adsorbed by Photosystem II to break down water into oxygen and protons in solution. Another photon must be adsorbed by Photosystem ! to power the enzymatic machinery that make NADPH and ATP that power the Calvin cycle.

We know the sun powers photosynthesis effectively. The sun produces somewhat less than 100,000 lux (lumen per square meter). Moonlight is one one millionth of this or about 0.1 lux. One lux is something like 10^15 photons per second (per square meter); so moonlight provides something approaching 10^14 photons per second to drive photosynthesis. The spectrum of moonlight is not markedly different from that of sunlight. So, moonlight provides an ample number of photons per second per square meter to power photosynthesis.

The trouble, though, is that the rate of photosynthesis is low compared to the rate of metabolism in the rest of the plant. So, in effect, the plant gives off carbon dioxide by night and oxygen by day even though both gasses are being emitted all the time.

EDIT (per request) some references:

  1. Photosynthesis
  2. Respiration
  3. Moonlight lux versus sunlight
  4. Photons per second in a lumen


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

Green Tree Leaves

The plant leaves are green because that color is the part of sunlight reflected by a pigment in the leaves called chlorophyll.

Photograph courtesy of Shutterstock

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 (O2) 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 (CO2) and water (H2O) 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.

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 plant leaves are green because that color is the part of sunlight reflected by a pigment in the leaves called chlorophyll.

How Does Temperature Affect Photosynthesis?

Temperature affects photosynthesis by allowing plants to photosynthesize (i.e., build up) and respire (i.e., break down) when there is optimum daytime temperature. It also enables plants to curtail the rate of respiration at a cooler night. With high temperatures, respiration increases and the products of photosynthesis are used faster than they are produced.

The rate of the chemical reactions during photosynthesis increases with temperature. However, temperatures above 40 C causes the process to slow down. This occurs because the enzymes involved in photosynthesis are sensitive to temperature. Additionally, low temperatures cause plants to grow poorly. It slows down photosynthesis, thus resulting in slower growth and lower yields.

Enzymes are easily affected by temperature. When it is too cold, they move around much slower, thus unable to allow for a reaction to occur. When it is too hot, the rate of reaction increases. Heat energy leads to more collisions between the substrate and the enzyme.

Different plants require different optimal temperatures to grow well. Plants that grow in colder climates grow best at low temperatures. For a certain number of days, buds of plants need to get exposed to chilling hours, which is below a critical temperature, to resume growth during spring. When dormant, they can withstand even lower temperatures. After the rest period, they become more vulnerable to weather conditions, especially cold temperatures.

Plant Leaf Structure

A plant's leaves are designed to retain water. That water then combines with carbon dioxide and light to form glucose to feed the plant. To help the plant retain water, leaves have a cuticle, a wax-like protective coating that prevents water from evaporating.

Leaves also have tiny pores that allow the leaf to take in carbon dioxide. Carbon dioxide is vital to the photosynthesis process the plant needs to form glucose and expel oxygen.

These leaf pores, called stomata, are found on the underside of the leaf. Once the leaf inhales carbon dioxide, the CO2 moves to the leaf's mesophyll cells. This is where photosynthesis takes place and glucose is formed.

Every living organism needs energy to grow and reproduce. Humans and animals eat foods with carbohydrates, proteins, and fats to produce the energy they need to survive. But plants do not eat. They make their own energy source in the form of energy-rich carbohydrates (sugars) through a process called photosynthesis. Photosynthesis is a multi-step, enzyme-mediated process that converts light energy into chemical energy. During photosynthesis, plant cells use light energy (such as light emitted from the sun), water (H2O), and carbon dioxide (CO2) as reactants to produce sugar molecules (C6H12O6) and oxygen (O2) (Figure 1):

Figure 1. During photosynthesis, plants convert water (H2O), carbon dioxide (CO2), and light into oxygen (O2) and sugars like glucose (C6H12O6).

Photosynthesis takes place in the chloroplasts within the plant's cells. The chloroplasts contain special pigments that react to light. Chlorophyll is one of the pigments that can absorb light in the blue and red spectrum from the visible light spectrum. Chlorophyll does not absorb light in the green spectrum of light but reflects it instead. This is why leaves with chlorophyll usually appear green. During the first part of photosynthesis&mdashthe light-dependent reaction&mdashchlorophyll and other pigments harness the light energy to produce NADPH and ATP, which are two types of energy-carrier molecules. At the same time, water is split into oxygen (O2) and protons (H + ). The next stage is light-independent and is often referred to as the dark reaction. In this step, the two energy-carrier molecules, NADPH and ATP, are utilized in a series of chemical reactions called the Calvin cycle. In the Calvin cycle, the plants take carbon dioxide (CO2) from the air and use it to ultimately make sugars such as glucose or sucrose. These sugars can be stored for later use by the plant as an energy source to fuel its metabolism and growth.

Photosynthesis is responsible for replenishing Earth's atmosphere with oxygen that we breathe. Thus, it is not only crucial for plants, but also for all organisms that rely on oxygen for their survival. Many factors affect how quickly plants are able to conduct photosynthesis. Without enough light or water, for example, a plant cannot photosynthesize very quickly. Similarly, the concentration of carbon dioxide&mdashanother reactant in photosynthesis&mdashaffects how fast photosynthesis can occur. Temperature also plays a significant role, as photosynthesis is an enzyme-mediated reaction. This is because at high temperatures, enzymes can get damaged and thus become inactivated. Other factors that affect the rate of photosynthesis are the light intensity, the amount of chlorophyll and other color pigments in a plant, and the color of light.

Similar to any other chemical reaction, the rate of photosynthesis can be determined by either measuring the decrease of its reactants or the increase of its products. You could, for example, measure the production of oxygen or the consumption of carbon dioxide over time. Without the use of extensive laboratory equipment, the rate of photosynthesis can be determined indirectly by conducting a floating leaf disk assay to measure the rate of oxygen production (Figure 2). In the floating leaf disk assay, 10 or more leaf disk samples are punched out of a leaf. In the next step, a vacuum is used to replace the air pockets within the leaf structure with a baking soda (bicarbonate) solution. The baking soda provides the carbon dioxide that the leaf needs for photosynthesis. The leaf disks are then sunk in the baking soda solution and exposed to light. As the plant leaf photosynthesizes, oxygen is produced that accumulates as oxygen gas bubbles on the outside of the leaf disk. The attached oxygen gas changes the buoyancy of the leaf disk and once enough oxygen has been produced, the leaf disk will rise to the surface of the baking soda solution. The time until the leaf disk rises to the top of the solution is a measure of how much oxygen has been produced and thus a proxy for the rate of photosynthesis.

Figure 2. Leaf disk assay picture.

In this project, 10 disks are placed in the baking soda solution at the same time. A good way to collect data is to count the number of floating disks at the end of a fixed time interval for example, after every minute until all disks are floating. The time required for 50% of the leaves to float represents the Effective Time (ET50). ET50 can be determined by graphing the number of disks floating over time, as shown in Figure 3. An ET50 of 11.5 minutes, for example, as shown in Figure 3, would mean that after 11.5 minutes, 50% of the leaves (5 out of the 10) floated on top of the baking soda solution. In the context of oxygen production, you could also say that an ET50 value of 11.5 minutes means that it took 11.5 minutes to produce enough oxygen to make 50% of the leaf disks float.

The x-axis shows time in minutes. The y-axis shows the number of floating leaf disks. After 7 minutes the first leaf disk floats, after 11 minutes 4 leaf disks float, at 12 minutes 7 leaf disks float, at 13 minutes 8 leaf disks float, and after 14 minutes all 10 leaf disks float. A red line indicates at what time 50% (5) leaf disks float (at about 11.5 minutes). This time is labeled Effective Time ET50.

Figure 3. Example results for the floating leaf disk assay. The graph shows the time on the x-axis and the number of floating leaves on the y-axis. The Effective Time (ET50) represents the time required for 50% of the leaves to float. By extrapolating from the graph, the 50% floating point in this graph is about 11.5 min.

Reaction rates are usually expressed as the concentration of reactant consumed or the concentration of product formed per unit of time. As mentioned above, we can use the ET50 as a proxy for how much oxygen has been produced to make half of the leaf disks float. This means that the ET50 value is proportional to the inverse of the rate of oxygen production, or proportional to the inverse of the rate of photosynthesis. The reciprocal of ET50 or 1/ET50, can thus be used as a simple measure of the rate of photosynthesis.

An example can make this concept clear. If a glass of soda has 1,000 bubbles, and half of the bubbles (500 bubbles) pop in 5 min when the soda is at room temperature, the rate at which the bubbles pop is 500/5 min or 100/min at room temperature. Imagine you repeat the experiment, but with a glass of the same soda at refrigerator temperature and find that half of the bubbles (or 500 bubbles) pop in 10 min. The rate at refrigerator temperature is 500 bubbles in 10 min or 50 bubbles/minute. It is hard to count bubbles in soda, but if you only know that half of the bubbles pop in 5 min (room temperature) or 10 minutes (refrigerator temperature), you can use the reciprocal of these time measurements as indicators for the rate at which the bubbles pop. 1/ET50 is 1/(5 min) or 0.2/min at room temperature, and 1/(1 min) or 0.1/min at refrigerator temperature. Do you notice that the indicator for the rate at room temperature is still double the indicator for the rate at refrigerator temperature? That is why 1/ET50 is a good indicator of the rate of photosynthesis.

In this project, you will determine the Effective Time (ET50) under different environmental conditions to find out which variables affect the rate of photosynthesis. For example, you could change the light source, the brightness of the light, the color of the light, the temperature, the type of plant, or the color of the plant leaves.

Photosystem I

The light absorption processes associated with photosynthesis take place in large protein complexes known as photosystems. The one known as Photosystem I contains a chlorophyll dimer with an absorption peak at 700 nm known as P700.

Photosystem I makes use of an antenna complex to collect light energy for the second stage of non-cyclic electron transport. It collects energetic electrons from the first stage process which is powered through Photosystem II and uses the light energy to further boost the energy of the electrons toward accomplishing the final goal of providing energy in the form of reduced coenzymes to the Calvin cycle.

The above sketch depicts the setting of Photosystem I in the electron transport process which provides energy resources for the Calvin cycle.

Photosystem I is the light energy complex for the cyclic electron transport process used in some photosynthetic prokaryotes.

The protein complex that constitutes Photosystem I contains eleven polypeptides, six of which are coded in the nucleus and five are coded in the chloroplast. The core of Photosystem I contains about 40 molecules of chlorophyll a, several molecules of beta carotene, lipids, four manganese, one iron, several calcium, several chlorine, two molecules of plastoquinone, and two molecules of pheophytin, a colorless form of chlorophyll a .(Moore, et al.)

Surprising Research Reveals Photosynthesis Could Be As Old as Life Itself

The finding also challenges expectations for how life might have evolved on other planets. The evolution of photosynthesis that produces oxygen is thought to be the key factor in the eventual emergence of complex life. This was thought to take several billion years to evolve, but if in fact the earliest life could do it, then other planets may have evolved complex life much earlier than previously thought.

“Now, we know that Photosystem II shows patterns of evolution that are usually only attributed to the oldest known enzymes, which were crucial for life itself to evolve.” — Dr. Tanai Cardona

The research team, led by scientists from Imperial College London, traced the evolution of key proteins needed for photosynthesis back to possibly the origin of bacterial life on Earth. Their results are published and freely accessible in BBA – Bioenergetics.

Lead researcher Dr. Tanai Cardona, from the Department of Life Sciences at Imperial, said: “We had previously shown that the biological system for performing oxygen-production, known as Photosystem II, was extremely old, but until now we hadn’t been able to place it on the timeline of life’s history.

“Now, we know that Photosystem II shows patterns of evolution that are usually only attributed to the oldest known enzymes, which were crucial for life itself to evolve.”

Early oxygen production

Photosynthesis, which converts sunlight into energy, can come in two forms: one that produces oxygen, and one that doesn’t. The oxygen-producing form is usually assumed to have evolved later, particularly with the emergence of cyanobacteria, or blue-green algae, around 2.5 billion years ago.

While some research has suggested pockets of oxygen-producing (oxygenic) photosynthesis may have been around before this, it was still considered to be an innovation that took at least a couple of billion years to evolve on Earth.

The new research finds that enzymes capable of performing the key process in oxygenic photosynthesis – splitting water into hydrogen and oxygen – could actually have been present in some of the earliest bacteria. The earliest evidence for life on Earth is over 3.4 billion years old and some studies have suggested that the earliest life could well be older than 4.0 billion years old.

Colonies of cyanobacteria under the microscope.

Like the evolution of the eye, the first version of oxygenic photosynthesis may have been very simple and inefficient as the earliest eyes sensed only light, the earliest photosynthesis may have been very inefficient and slow.

On Earth, it took more than a billion years for bacteria to perfect the process leading to the evolution of cyanobacteria, and two billion years more for animals and plants to conquer the land. However, that oxygen production was present at all so early on means in other environments, such as on other planets, the transition to complex life could have taken much less time.

Measuring molecular clocks

The team made their discovery by tracing the ‘molecular clock’ of key photosynthesis proteins responsible for splitting water. This method estimates the rate of evolution of proteins by looking at the time between known evolutionary moments, such as the emergence of different groups of cyanobacteria or land plants, which carry a version of these proteins today. The calculated rate of evolution is then extended back in time, to see when the proteins first evolved.

“We could develop photosystems that could carry out complex new green and sustainable chemical reactions entirely powered by light.” — Dr. Tanai Cardona

They compared the evolution rate of these photosynthesis proteins to that of other key proteins in the evolution of life, including those that form energy storage molecules in the body and those that translate DNA sequences into RNA, which is thought to have originated before the ancestor of all cellular life on Earth. They also compared the rate to events known to have occurred more recently, when life was already varied and cyanobacteria had appeared.

The photosynthesis proteins showed nearly identical patterns of evolution to the oldest enzymes, stretching far back in time, suggesting they evolved in a similar way.

First author of the study Thomas Oliver, from the Department of Life Sciences at Imperial, said: “We used a technique called Ancestral Sequence Reconstruction to predict the protein sequences of ancestral photosynthetic proteins.

“These sequences give us information about how the ancestral Photosystem II would have worked and we were able to show that many of the key components required for oxygen evolution in Photosystem II can be traced to the earliest stages in the evolution of the enzyme.”

Directing evolution

Knowing how these key photosynthesis proteins evolve is not only relevant for the search for life on other planets, but could also help researchers find strategies to use photosynthesis in new ways through synthetic biology.

Dr. Cardona, who is leading such a project as part of his UKRI Future Leaders Fellowship, said: “Now we have a good sense of how photosynthesis proteins evolve, adapting to a changing world, we can use ‘directed evolution’ to learn how to change them to produce new kinds of chemistry.

“We could develop photosystems that could carry out complex new green and sustainable chemical reactions entirely powered by light.”

What Are Examples of Homeostasis in Plants?

Homeostasis in plants includes the regulation of carbon dioxide and water levels necessary to perform photosynthesis. Homeostasis in plants also allows plants cells to store the proper amount of water in their cells to help keep them from wilting and dying during times of drought.

Homeostasis is any biological process performed by an organism that perpetually regulates and maintains their internal systems and is triggered by external stimuli that require the organism to adapt and alter their internal processes to function properly under the new internal or environmental circumstances. All living organisms require some type of homeostasis to maintain life.

Plants are typically dependent on photosynthesis to produce energy to maintain their biological processes. Photosynthesis is a chemical process performed by plants in which sunlight is converted into energy. Homeostasis is essential during this process and is performed by cells known as stomata, which are commonly found on the outer surface of plants. Stomata open to allow sunlight and carbon dioxide to enter the cell, while releasing oxygen produced by photosynthesis.

Plant cells lose a portion of their water content while the stomata are open, leaving the plant susceptible to dehydration. Special guard cells surrounding the stomata react to chemical changes in their physiology and may inflate to allow water and gas exchange from the stomata to the environment, or deflate to protect the stomata and prevent excess water loss.


Photosynthetic organisms are photoautotrophs, which means that they are able to synthesize food directly from carbon dioxide and water using energy from light. However, not all organisms use carbon dioxide as a source of carbon atoms to carry out photosynthesis photoheterotrophs use organic compounds, rather than carbon dioxide, as a source of carbon. [4] In plants, algae, and cyanobacteria, photosynthesis releases oxygen. This is called oxygenic photosynthesis and is by far the most common type of photosynthesis used by living organisms. Although there are some differences between oxygenic photosynthesis in plants, algae, and cyanobacteria, the overall process is quite similar in these organisms. There are also many varieties of anoxygenic photosynthesis, used mostly by certain types of bacteria, which consume carbon dioxide but do not release oxygen.

Carbon dioxide is converted into sugars in a process called carbon fixation photosynthesis captures energy from sunlight to convert carbon dioxide into carbohydrate. Carbon fixation is an endothermic redox reaction. In general outline, photosynthesis is the opposite of cellular respiration: while photosynthesis is a process of reduction of carbon dioxide to carbohydrate, cellular respiration is the oxidation of carbohydrate or other nutrients to carbon dioxide. Nutrients used in cellular respiration include carbohydrates, amino acids and fatty acids. These nutrients are oxidized to produce carbon dioxide and water, and to release chemical energy to drive the organism's metabolism. Photosynthesis and cellular respiration are distinct processes, as they take place through different sequences of chemical reactions and in different cellular compartments.

The general equation for photosynthesis as first proposed by Cornelis van Niel is therefore: [14]

CO2 carbon
dioxide + 2H2A electron donor + photons light energy → [CH2O] carbohydrate + 2A oxidized
donor + H2O water

Since water is used as the electron donor in oxygenic photosynthesis, the equation for this process is:

CO2 carbon
dioxide + 2H2O water + photons light energy → [CH2O] carbohydrate + O2 oxygen + H2O water

This equation emphasizes that water is both a reactant in the light-dependent reaction and a product of the light-independent reaction, but canceling n water molecules from each side gives the net equation:

CO2 carbon
dioxide + H2O water + photons light energy → [CH2O] carbohydrate + O2 oxygen

Other processes substitute other compounds (such as arsenite) for water in the electron-supply role for example some microbes use sunlight to oxidize arsenite to arsenate: [15] The equation for this reaction is:

CO2 carbon
dioxide + (AsO 3−
3 )
arsenite + photons light energy → (AsO 3−
4 )
arsenate + CO carbon
monoxide (used to build other compounds in subsequent reactions) [16]

Photosynthesis occurs in two stages. In the first stage, light-dependent reactions or light reactions capture the energy of light and use it to make the energy-storage molecules ATP and NADPH. During the second stage, the light-independent reactions use these products to capture and reduce carbon dioxide.

Most organisms that utilize oxygenic photosynthesis use visible light for the light-dependent reactions, although at least three use shortwave infrared or, more specifically, far-red radiation. [17]

Some organisms employ even more radical variants of photosynthesis. Some archaea use a simpler method that employs a pigment similar to those used for vision in animals. The bacteriorhodopsin changes its configuration in response to sunlight, acting as a proton pump. This produces a proton gradient more directly, which is then converted to chemical energy. The process does not involve carbon dioxide fixation and does not release oxygen, and seems to have evolved separately from the more common types of photosynthesis. [18] [19]

  1. outer membrane
  2. intermembrane space
  3. inner membrane (1+2+3: envelope)
  4. stroma (aqueous fluid)
  5. thylakoid lumen (inside of thylakoid)
  6. thylakoid membrane
  7. granum (stack of thylakoids)
  8. thylakoid (lamella)
  9. starch
  10. ribosome
  11. plastidial DNA
  12. plastoglobule (drop of lipids)

In photosynthetic bacteria, the proteins that gather light for photosynthesis are embedded in cell membranes. In its simplest form, this involves the membrane surrounding the cell itself. [20] However, the membrane may be tightly folded into cylindrical sheets called thylakoids, [21] or bunched up into round vesicles called intracytoplasmic membranes. [22] These structures can fill most of the interior of a cell, giving the membrane a very large surface area and therefore increasing the amount of light that the bacteria can absorb. [21]

In plants and algae, photosynthesis takes place in organelles called chloroplasts. A typical plant cell contains about 10 to 100 chloroplasts. The chloroplast is enclosed by a membrane. This membrane is composed of a phospholipid inner membrane, a phospholipid outer membrane, and an intermembrane space. Enclosed by the membrane is an aqueous fluid called the stroma. Embedded within the stroma are stacks of thylakoids (grana), which are the site of photosynthesis. The thylakoids appear as flattened disks. The thylakoid itself is enclosed by the thylakoid membrane, and within the enclosed volume is a lumen or thylakoid space. Embedded in the thylakoid membrane are integral and peripheral membrane protein complexes of the photosynthetic system.

Plants absorb light primarily using the pigment chlorophyll. The green part of the light spectrum is not absorbed but is reflected which is the reason that most plants have a green color. Besides chlorophyll, plants also use pigments such as carotenes and xanthophylls. [23] Algae also use chlorophyll, but various other pigments are present, such as phycocyanin, carotenes, and xanthophylls in green algae, phycoerythrin in red algae (rhodophytes) and fucoxanthin in brown algae and diatoms resulting in a wide variety of colors.

These pigments are embedded in plants and algae in complexes called antenna proteins. In such proteins, the pigments are arranged to work together. Such a combination of proteins is also called a light-harvesting complex. [24]

Although all cells in the green parts of a plant have chloroplasts, the majority of those are found in specially adapted structures called leaves. Certain species adapted to conditions of strong sunlight and aridity, such as many Euphorbia and cactus species, have their main photosynthetic organs in their stems. The cells in the interior tissues of a leaf, called the mesophyll, can contain between 450,000 and 800,000 chloroplasts for every square millimeter of leaf. The surface of the leaf is coated with a water-resistant waxy cuticle that protects the leaf from excessive evaporation of water and decreases the absorption of ultraviolet or blue light to reduce heating. The transparent epidermis layer allows light to pass through to the palisade mesophyll cells where most of the photosynthesis takes place.

In the light-dependent reactions, one molecule of the pigment chlorophyll absorbs one photon and loses one electron. This electron is passed to a modified form of chlorophyll called pheophytin, which passes the electron to a quinone molecule, starting the flow of electrons down an electron transport chain that leads to the ultimate reduction of NADP to NADPH. In addition, this creates a proton gradient (energy gradient) across the chloroplast membrane, which is used by ATP synthase in the synthesis of ATP. The chlorophyll molecule ultimately regains the electron it lost when a water molecule is split in a process called photolysis, which releases a dioxygen (O2) molecule as a waste product.

The overall equation for the light-dependent reactions under the conditions of non-cyclic electron flow in green plants is: [25]

Not all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory pigments present. For example, in green plants, the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with absorption peaks in violet-blue and red light. In red algae, the action spectrum is blue-green light, which allows these algae to use the blue end of the spectrum to grow in the deeper waters that filter out the longer wavelengths (red light) used by above-ground green plants. The non-absorbed part of the light spectrum is what gives photosynthetic organisms their color (e.g., green plants, red algae, purple bacteria) and is the least effective for photosynthesis in the respective organisms.

Z scheme

In plants, light-dependent reactions occur in the thylakoid membranes of the chloroplasts where they drive the synthesis of ATP and NADPH. The light-dependent reactions are of two forms: cyclic and non-cyclic.

In the non-cyclic reaction, the photons are captured in the light-harvesting antenna complexes of photosystem II by chlorophyll and other accessory pigments (see diagram at right). The absorption of a photon by the antenna complex frees an electron by a process called photoinduced charge separation. The antenna system is at the core of the chlorophyll molecule of the photosystem II reaction center. That freed electron is transferred to the primary electron-acceptor molecule, pheophytin. As the electrons are shuttled through an electron transport chain (the so-called Z-scheme shown in the diagram), it initially functions to generate a chemiosmotic potential by pumping proton cations (H + ) across the membrane and into the thylakoid space. An ATP synthase enzyme uses that chemiosmotic potential to make ATP during photophosphorylation, whereas NADPH is a product of the terminal redox reaction in the Z-scheme. The electron enters a chlorophyll molecule in Photosystem I. There it is further excited by the light absorbed by that photosystem. The electron is then passed along a chain of electron acceptors to which it transfers some of its energy. The energy delivered to the electron acceptors is used to move hydrogen ions across the thylakoid membrane into the lumen. The electron is eventually used to reduce the co-enzyme NADP with a H + to NADPH (which has functions in the light-independent reaction) at that point, the path of that electron ends.

The cyclic reaction is similar to that of the non-cyclic but differs in that it generates only ATP, and no reduced NADP (NADPH) is created. The cyclic reaction takes place only at photosystem I. Once the electron is displaced from the photosystem, the electron is passed down the electron acceptor molecules and returns to photosystem I, from where it was emitted, hence the name cyclic reaction.

Water photolysis

Linear electron transport through a photosystem will leave the reaction center of that photosystem oxidized. Elevating another electron will first require re-reduction of the reaction center. The excited electrons lost from the reaction center (P700) of photosystem I are replaced by transfer from plastocyanin, whose electrons come from electron transport through photosystem II. Photosystem II, as the first step of the Z-scheme, requires an external source of electrons to reduce its oxidized chlorophyll a reaction center, called P680. The source of electrons for photosynthesis in green plants and cyanobacteria is water. Two water molecules are oxidized by four successive charge-separation reactions by photosystem II to yield a molecule of diatomic oxygen and four hydrogen ions. The electrons yielded are transferred to a redox-active tyrosine residue that then reduces the oxidized P680. This resets the ability of P680 to absorb another photon and release another photo-dissociated electron. The oxidation of water is catalyzed in photosystem II by a redox-active structure that contains four manganese ions and a calcium ion this oxygen-evolving complex binds two water molecules and contains the four oxidizing equivalents that are used to drive the water-oxidizing reaction (Dolai's S-state diagrams). Photosystem II is the only known biological enzyme that carries out this oxidation of water. The hydrogen ions are released in the thylakoid lumen and therefore contribute to the transmembrane chemiosmotic potential that leads to ATP synthesis. Oxygen is a waste product of light-dependent reactions, but the majority of organisms on Earth use oxygen for cellular respiration, including photosynthetic organisms. [26] [27]

Calvin cycle

In the light-independent (or "dark") reactions, the enzyme RuBisCO captures CO2 from the atmosphere and, in a process called the Calvin cycle, it uses the newly formed NADPH and releases three-carbon sugars, which are later combined to form sucrose and starch. The overall equation for the light-independent reactions in green plants is [25] : 128

Carbon fixation produces the intermediate three-carbon sugar product, which is then converted into the final carbohydrate products. The simple carbon sugars produced by photosynthesis are then used in the forming of other organic compounds, such as the building material cellulose, the precursors for lipid and amino acid biosynthesis, or as a fuel in cellular respiration. The latter occurs not only in plants but also in animals when the energy from plants is passed through a food chain.

The fixation or reduction of carbon dioxide is a process in which carbon dioxide combines with a five-carbon sugar, ribulose 1,5-bisphosphate, to yield two molecules of a three-carbon compound, glycerate 3-phosphate, also known as 3-phosphoglycerate. Glycerate 3-phosphate, in the presence of ATP and NADPH produced during the light-dependent stages, is reduced to glyceraldehyde 3-phosphate. This product is also referred to as 3-phosphoglyceraldehyde (PGAL) or, more generically, as triose phosphate. Most (5 out of 6 molecules) of the glyceraldehyde 3-phosphate produced is used to regenerate ribulose 1,5-bisphosphate so the process can continue. The triose phosphates not thus "recycled" often condense to form hexose phosphates, which ultimately yield sucrose, starch and cellulose. The sugars produced during carbon metabolism yield carbon skeletons that can be used for other metabolic reactions like the production of amino acids and lipids.

Carbon concentrating mechanisms

On land

In hot and dry conditions, plants close their stomata to prevent water loss. Under these conditions, CO
2 will decrease and oxygen gas, produced by the light reactions of photosynthesis, will increase, causing an increase of photorespiration by the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase and decrease in carbon fixation. Some plants have evolved mechanisms to increase the CO
2 concentration in the leaves under these conditions. [28]

Plants that use the C4 carbon fixation process chemically fix carbon dioxide in the cells of the mesophyll by adding it to the three-carbon molecule phosphoenolpyruvate (PEP), a reaction catalyzed by an enzyme called PEP carboxylase, creating the four-carbon organic acid oxaloacetic acid. Oxaloacetic acid or malate synthesized by this process is then translocated to specialized bundle sheath cells where the enzyme RuBisCO and other Calvin cycle enzymes are located, and where CO
2 released by decarboxylation of the four-carbon acids is then fixed by RuBisCO activity to the three-carbon 3-phosphoglyceric acids. The physical separation of RuBisCO from the oxygen-generating light reactions reduces photorespiration and increases CO
2 fixation and, thus, the photosynthetic capacity of the leaf. [29] C4 plants can produce more sugar than C3 plants in conditions of high light and temperature. Many important crop plants are C4 plants, including maize, sorghum, sugarcane, and millet. Plants that do not use PEP-carboxylase in carbon fixation are called C3 plants because the primary carboxylation reaction, catalyzed by RuBisCO, produces the three-carbon 3-phosphoglyceric acids directly in the Calvin-Benson cycle. Over 90% of plants use C3 carbon fixation, compared to 3% that use C4 carbon fixation [30] however, the evolution of C4 in over 60 plant lineages makes it a striking example of convergent evolution. [28]

Xerophytes, such as cacti and most succulents, also use PEP carboxylase to capture carbon dioxide in a process called Crassulacean acid metabolism (CAM). In contrast to C4 metabolism, which spatially separates the CO
2 fixation to PEP from the Calvin cycle, CAM temporally separates these two processes. CAM plants have a different leaf anatomy from C3 plants, and fix the CO
2 at night, when their stomata are open. CAM plants store the CO
2 mostly in the form of malic acid via carboxylation of phosphoenolpyruvate to oxaloacetate, which is then reduced to malate. Decarboxylation of malate during the day releases CO
2 inside the leaves, thus allowing carbon fixation to 3-phosphoglycerate by RuBisCO. Sixteen thousand species of plants use CAM. [31]

Calcium oxalate accumulating plants, such as Amaranthus hybridus and Colobanthus quitensis, showed a variation of photosynthesis where calcium oxalate crystals function as dynamic carbon pools, supplying carbon dioxide (CO2) to photosynthetic cells when stomata are partially or totally closed. This process was named Alarm photosynthesis. Under stress conditions (e.g. water deficit) oxalate released from calcium oxalate crystals is converted to CO2 by an oxalate oxidase enzyme and the produced CO2 can support the Calvin cycle reactions. Reactive hydrogen peroxide (H2O2), the byproduct of oxalate oxidase reaction, can be neutralized by catalase. Alarm photosynthesis represents an unknown photosynthetic variation to be added to the already known C4 and CAM pathways. However, alarm photosynthesis, in contrast to these pathways, operates as a biochemical pump that collects carbon from the organ interior (or from the soil) and not from the atmosphere. [32] [33]

In water

Cyanobacteria possess carboxysomes, which increase the concentration of CO
2 around RuBisCO to increase the rate of photosynthesis. An enzyme, carbonic anhydrase, located within the carboxysome releases CO2 from the dissolved hydrocarbonate ions (HCO −
3 ). Before the CO2 diffuses out it is quickly sponged up by RuBisCO, which is concentrated within the carboxysomes. HCO −
3 ions are made from CO2 outside the cell by another carbonic anhydrase and are actively pumped into the cell by a membrane protein. They cannot cross the membrane as they are charged, and within the cytosol they turn back into CO2 very slowly without the help of carbonic anhydrase. This causes the HCO −
3 ions to accumulate within the cell from where they diffuse into the carboxysomes. [34] Pyrenoids in algae and hornworts also act to concentrate CO
2 around RuBisCO. [35]

The overall process of photosynthesis takes place in four stages: [13]

Stage Description Time scale
1 Energy transfer in antenna chlorophyll (thylakoid membranes) femtosecond to picosecond
2 Transfer of electrons in photochemical reactions (thylakoid membranes) picosecond to nanosecond
3 Electron transport chain and ATP synthesis (thylakoid membranes) microsecond to millisecond
4 Carbon fixation and export of stable products millisecond to second

Plants usually convert light into chemical energy with a photosynthetic efficiency of 3–6%. [36] [37] Absorbed light that is unconverted is dissipated primarily as heat, with a small fraction (1–2%) [38] re-emitted as chlorophyll fluorescence at longer (redder) wavelengths. This fact allows measurement of the light reaction of photosynthesis by using chlorophyll fluorometers. [38]

Actual plants' photosynthetic efficiency varies with the frequency of the light being converted, light intensity, temperature and proportion of carbon dioxide in the atmosphere, and can vary from 0.1% to 8%. [39] By comparison, solar panels convert light into electric energy at an efficiency of approximately 6–20% for mass-produced panels, and above 40% in laboratory devices. Scientists are studying photosynthesis in hopes of developing plants with yield increases. [37]

The efficiency of both light and dark reactions can be measured but the relationship between the two can be complex. [40] For example, the ATP and NADPH energy molecules, created by the light reaction, can be used for carbon fixation or for photorespiration in C3 plants. [40] Electrons may also flow to other electron sinks. [41] [42] [43] For this reason, it is not uncommon for authors to differentiate between work done under non-photorespiratory conditions and under photorespiratory conditions. [44] [45] [46]

Chlorophyll fluorescence of photosystem II can measure the light reaction, and Infrared gas analyzers can measure the dark reaction. [47] It is also possible to investigate both at the same time using an integrated chlorophyll fluorometer and gas exchange system, or by using two separate systems together. [48] Infrared gas analyzers and some moisture sensors are sensitive enough to measure the photosynthetic assimilation of CO2, and of ΔH2O using reliable methods [49] CO2 is commonly measured in μmols/(m 2 /s), parts per million or volume per million and H2O is commonly measured in mmol/(m 2 /s) or in mbars. [49] By measuring CO2 assimilation, ΔH2O, leaf temperature, barometric pressure, leaf area, and photosynthetically active radiation or PAR, it becomes possible to estimate, "A" or carbon assimilation, "E" or transpiration, "gs" or stomatal conductance, and Ci or intracellular CO2. [49] However, it is more common to used chlorophyll fluorescence for plant stress measurement, where appropriate, because the most commonly used measuring parameters FV/FM and Y(II) or F/FM' can be made in a few seconds, allowing the measurement of larger plant populations. [46]

Gas exchange systems that offer control of CO2 levels, above and below ambient, allow the common practice of measurement of A/Ci curves, at different CO2 levels, to characterize a plant's photosynthetic response. [49]

Integrated chlorophyll fluorometer – gas exchange systems allow a more precise measure of photosynthetic response and mechanisms. [47] [48] While standard gas exchange photosynthesis systems can measure Ci, or substomatal CO2 levels, the addition of integrated chlorophyll fluorescence measurements allows a more precise measurement of CC to replace Ci. [48] [50] The estimation of CO2 at the site of carboxylation in the chloroplast, or CC, becomes possible with the measurement of mesophyll conductance or gm using an integrated system. [47] [48] [51]

Photosynthesis measurement systems are not designed to directly measure the amount of light absorbed by the leaf. But analysis of chlorophyll-fluorescence, P700- and P515-absorbance and gas exchange measurements reveal detailed information about e.g. the photosystems, quantum efficiency and the CO2 assimilation rates. With some instruments, even wavelength-dependency of the photosynthetic efficiency can be analyzed. [52]

A phenomenon known as quantum walk increases the efficiency of the energy transport of light significantly. In the photosynthetic cell of an algae, bacterium, or plant, there are light-sensitive molecules called chromophores arranged in an antenna-shaped structure named a photocomplex. When a photon is absorbed by a chromophore, it is converted into a quasiparticle referred to as an exciton, which jumps from chromophore to chromophore towards the reaction center of the photocomplex, a collection of molecules that traps its energy in a chemical form that makes it accessible for the cell's metabolism. The exciton's wave properties enable it to cover a wider area and try out several possible paths simultaneously, allowing it to instantaneously "choose" the most efficient route, where it will have the highest probability of arriving at its destination in the minimum possible time.

Because that quantum walking takes place at temperatures far higher than quantum phenomena usually occur, it is only possible over very short distances, due to obstacles in the form of destructive interference that come into play. These obstacles cause the particle to lose its wave properties for an instant before it regains them once again after it is freed from its locked position through a classic "hop". The movement of the electron towards the photo center is therefore covered in a series of conventional hops and quantum walks. [53] [54] [55]

Early photosynthetic systems, such as those in green and purple sulfur and green and purple nonsulfur bacteria, are thought to have been anoxygenic, and used various other molecules than water as electron donors. Green and purple sulfur bacteria are thought to have used hydrogen and sulfur as electron donors. Green nonsulfur bacteria used various amino and other organic acids as an electron donor. Purple nonsulfur bacteria used a variety of nonspecific organic molecules. The use of these molecules is consistent with the geological evidence that Earth's early atmosphere was highly reducing at that time. [56]

Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old. [57] [58] More recent studies, reported in March 2018, also suggest that photosynthesis may have begun about 3.4 billion years ago. [59] [60]

The main source of oxygen in the Earth's atmosphere derives from oxygenic photosynthesis, and its first appearance is sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis, such as that in cyanobacteria, became important during the Paleoproterozoic era around 2 billion years ago. Modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. Oxygenic photosynthesis uses water as an electron donor, which is oxidized to molecular oxygen ( O
2 ) in the photosynthetic reaction center.

Symbiosis and the origin of chloroplasts

Several groups of animals have formed symbiotic relationships with photosynthetic algae. These are most common in corals, sponges and sea anemones. It is presumed that this is due to the particularly simple body plans and large surface areas of these animals compared to their volumes. [61] In addition, a few marine mollusks Elysia viridis and Elysia chlorotica also maintain a symbiotic relationship with chloroplasts they capture from the algae in their diet and then store in their bodies (see Kleptoplasty). This allows the mollusks to survive solely by photosynthesis for several months at a time. [62] [63] Some of the genes from the plant cell nucleus have even been transferred to the slugs, so that the chloroplasts can be supplied with proteins that they need to survive. [64]

An even closer form of symbiosis may explain the origin of chloroplasts. Chloroplasts have many similarities with photosynthetic bacteria, including a circular chromosome, prokaryotic-type ribosome, and similar proteins in the photosynthetic reaction center. [65] [66] The endosymbiotic theory suggests that photosynthetic bacteria were acquired (by endocytosis) by early eukaryotic cells to form the first plant cells. Therefore, chloroplasts may be photosynthetic bacteria that adapted to life inside plant cells. Like mitochondria, chloroplasts possess their own DNA, separate from the nuclear DNA of their plant host cells and the genes in this chloroplast DNA resemble those found in cyanobacteria. [67] DNA in chloroplasts codes for redox proteins such as those found in the photosynthetic reaction centers. The CoRR Hypothesis proposes that this co-location of genes with their gene products is required for redox regulation of gene expression, and accounts for the persistence of DNA in bioenergetic organelles. [68]

Photosynthetic eukaryotic lineages

Symbiotic and kleptoplastic organisms excluded:

  • The glaucophytes and the red and green algae—clade Archaeplastida (unicellular and multicellular)
  • The cryptophytes—clade Cryptista (unicellular)
  • The haptophytes—clade Haptista (unicellular)
  • The dinoflagellates and chromerids in the superphylum Myzozoa—clade Alveolata (unicellular)
  • The ochrophytes—clade Heterokonta (unicellular and multicellular)
  • The chlorarachniophytes and three species of Paulinella in the phylum Cercozoa—clade Rhizaria (unicellular)
  • The euglenids—clade Excavata (unicellular)

Except for the euglenids, which is found within the Excavata, all of them belong to the Diaphoretickes. Archaeplastida and the photosynthetic Paulinella got their plastids— which are surrounded by two membranes, through primary endosymbiosis in two separate events by engulfing a cyanobacterium. The plastids in all the other groups have either a red or green algal origin, and are referred to as the "red lineages" and the "green lineages". In dinoflaggelates and euglenids the plastids are surrounded by three membranes, and in the remaining lines by four. A nucleomorph, remnants of the original algal nucleus located between the inner and outer membranes of the plastid, is present in the cryptophytes (from a red algae) and chlorarachniophytes (from a green algae). [69] Some dinoflaggelates which have lost their photosyntethic ability have later regained it again through new endosymbiotic events with different algae. While able to perform photosynthesis, many of these eukaryotic groups are mixotrophs and practice heterotrophy to various degrees.

Cyanobacteria and the evolution of photosynthesis

The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of extant cyanobacteria (formerly called blue-green algae), which are the only prokaryotes performing oxygenic photosynthesis. The geological record indicates that this transforming event took place early in Earth's history, at least 2450–2320 million years ago (Ma), and, it is speculated, much earlier. [70] [71] Because the Earth's atmosphere contained almost no oxygen during the estimated development of photosynthesis, it is believed that the first photosynthetic cyanobacteria did not generate oxygen. [72] Available evidence from geobiological studies of Archean (>2500 Ma) sedimentary rocks indicates that life existed 3500 Ma, but the question of when oxygenic photosynthesis evolved is still unanswered. A clear paleontological window on cyanobacterial evolution opened about 2000 Ma, revealing an already-diverse biota of Cyanobacteria. Cyanobacteria remained the principal primary producers of oxygen throughout the Proterozoic Eon (2500–543 Ma), in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation. [ citation needed ] Green algae joined cyanobacteria as the major primary producers of oxygen on continental shelves near the end of the Proterozoic, but it was only with the Mesozoic (251–66 Ma) radiations of dinoflagellates, coccolithophorids, and diatoms did the primary production of oxygen in marine shelf waters take modern form. Cyanobacteria remain critical to marine ecosystems as primary producers of oxygen in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae. [73]

Although some of the steps in photosynthesis are still not completely understood, the overall photosynthetic equation has been known since the 19th century.

Jan van Helmont began the research of the process in the mid-17th century when he carefully measured the mass of the soil used by a plant and the mass of the plant as it grew. After noticing that the soil mass changed very little, he hypothesized that the mass of the growing plant must come from the water, the only substance he added to the potted plant. His hypothesis was partially accurate – much of the gained mass also comes from carbon dioxide as well as water. However, this was a signaling point to the idea that the bulk of a plant's biomass comes from the inputs of photosynthesis, not the soil itself.

Joseph Priestley, a chemist and minister, discovered that, when he isolated a volume of air under an inverted jar, and burned a candle in it (which gave off CO2), the candle would burn out very quickly, much before it ran out of wax. He further discovered that a mouse could similarly "injure" air. He then showed that the air that had been "injured" by the candle and the mouse could be restored by a plant. [74]

In 1779, Jan Ingenhousz repeated Priestley's experiments. He discovered that it was the influence of sunlight on the plant that could cause it to revive a mouse in a matter of hours. [74] [75]

In 1796, Jean Senebier, a Swiss pastor, botanist, and naturalist, demonstrated that green plants consume carbon dioxide and release oxygen under the influence of light. Soon afterward, Nicolas-Théodore de Saussure showed that the increase in mass of the plant as it grows could not be due only to uptake of CO2 but also to the incorporation of water. Thus, the basic reaction by which photosynthesis is used to produce food (such as glucose) was outlined. [76]

Cornelis Van Niel made key discoveries explaining the chemistry of photosynthesis. By studying purple sulfur bacteria and green bacteria he was the first to demonstrate that photosynthesis is a light-dependent redox reaction, in which hydrogen reduces (donates its – electron to) carbon dioxide.

Robert Emerson discovered two light reactions by testing plant productivity using different wavelengths of light. With the red alone, the light reactions were suppressed. When blue and red were combined, the output was much more substantial. Thus, there were two photosystems, one absorbing up to 600 nm wavelengths, the other up to 700 nm. The former is known as PSII, the latter is PSI. PSI contains only chlorophyll "a", PSII contains primarily chlorophyll "a" with most of the available chlorophyll "b", among other pigments. These include phycobilins, which are the red and blue pigments of red and blue algae respectively, and fucoxanthol for brown algae and diatoms. The process is most productive when the absorption of quanta are equal in both the PSII and PSI, assuring that input energy from the antenna complex is divided between the PSI and PSII system, which in turn powers the photochemistry. [13]

Robert Hill thought that a complex of reactions consisting of an intermediate to cytochrome b6 (now a plastoquinone), another is from cytochrome f to a step in the carbohydrate-generating mechanisms. These are linked by plastoquinone, which does require energy to reduce cytochrome f for it is a sufficient reductant. Further experiments to prove that the oxygen developed during the photosynthesis of green plants came from water, were performed by Hill in 1937 and 1939. He showed that isolated chloroplasts give off oxygen in the presence of unnatural reducing agents like iron oxalate, ferricyanide or benzoquinone after exposure to light. The Hill reaction [77] is as follows:

2 H2O + 2 A + (light, chloroplasts) → 2 AH2 + O2

where A is the electron acceptor. Therefore, in light, the electron acceptor is reduced and oxygen is evolved.

Samuel Ruben and Martin Kamen used radioactive isotopes to determine that the oxygen liberated in photosynthesis came from the water.

Melvin Calvin and Andrew Benson, along with James Bassham, elucidated the path of carbon assimilation (the photosynthetic carbon reduction cycle) in plants. The carbon reduction cycle is known as the Calvin cycle, which ignores the contribution of Bassham and Benson. Many scientists refer to the cycle as the Calvin-Benson Cycle, Benson-Calvin, and some even call it the Calvin-Benson-Bassham (or CBB) Cycle.

Nobel Prize-winning scientist Rudolph A. Marcus was able to discover the function and significance of the electron transport chain.

Otto Heinrich Warburg and Dean Burk discovered the I-quantum photosynthesis reaction that splits the CO2, activated by the respiration. [78]

In 1950, first experimental evidence for the existence of photophosphorylation in vivo was presented by Otto Kandler using intact Chlorella cells and interpreting his findings as light-dependent ATP formation. [79] In 1954, Daniel I. Arnon et al. discovered photophosphorylation in vitro in isolated chloroplasts with the help of P 32 . [80] [81]

Louis N.M. Duysens and Jan Amesz discovered that chlorophyll a will absorb one light, oxidize cytochrome f, chlorophyll a (and other pigments) will absorb another light but will reduce this same oxidized cytochrome, stating the two light reactions are in series.

Development of the concept

In 1893, Charles Reid Barnes proposed two terms, photosyntax and photosynthesis, for the biological process of synthesis of complex carbon compounds out of carbonic acid, in the presence of chlorophyll, under the influence of light. Over time, the term photosynthesis came into common usage as the term of choice. Later discovery of anoxygenic photosynthetic bacteria and photophosphorylation necessitated redefinition of the term. [82]

C3 : C4 photosynthesis research

After WWII at late 1940 at the University of California, Berkeley, the details of photosynthetic carbon metabolism were sorted out by the chemists Melvin Calvin, Andrew Benson, James Bassham and a score of students and researchers utilizing the carbon-14 isotope and paper chromatography techniques. [83] The pathway of CO2 fixation by the algae Chlorella in a fraction of a second in light resulted in a 3 carbon molecule called phosphoglyceric acid (PGA). For that original and ground-breaking work, a Nobel Prize in Chemistry was awarded to Melvin Calvin in 1961. In parallel, plant physiologists studied leaf gas exchanges using the new method of infrared gas analysis and a leaf chamber where the net photosynthetic rates ranged from 10 to 13 μmol CO2·m −2 ·s −1 , with the conclusion that all terrestrial plants having the same photosynthetic capacities that were light saturated at less than 50% of sunlight. [84] [85]

Later in 1958–1963 at Cornell University, field grown maize was reported to have much greater leaf photosynthetic rates of 40 μmol CO2·m −2 ·s −1 and was not saturated at near full sunlight. [86] [87] This higher rate in maize was almost double those observed in other species such as wheat and soybean, indicating that large differences in photosynthesis exist among higher plants. At the University of Arizona, detailed gas exchange research on more than 15 species of monocot and dicot uncovered for the first time that differences in leaf anatomy are crucial factors in differentiating photosynthetic capacities among species. [88] [89] In tropical grasses, including maize, sorghum, sugarcane, Bermuda grass and in the dicot amaranthus, leaf photosynthetic rates were around 38−40 μmol CO2·m −2 ·s −1 , and the leaves have two types of green cells, i. e. outer layer of mesophyll cells surrounding a tightly packed cholorophyllous vascular bundle sheath cells. This type of anatomy was termed Kranz anatomy in the 19th century by the botanist Gottlieb Haberlandt while studying leaf anatomy of sugarcane. [90] Plant species with the greatest photosynthetic rates and Kranz anatomy showed no apparent photorespiration, very low CO2 compensation point, high optimum temperature, high stomatal resistances and lower mesophyll resistances for gas diffusion and rates never saturated at full sun light. [91] The research at Arizona was designated Citation Classic by the ISI 1986. [89] These species was later termed C4 plants as the first stable compound of CO2 fixation in light has 4 carbon as malate and aspartate. [92] [93] [94] Other species that lack Kranz anatomy were termed C3 type such as cotton and sunflower, as the first stable carbon compound is the 3-carbon PGA. At 1000 ppm CO2 in measuring air, both the C3 and C4 plants had similar leaf photosynthetic rates around 60 μmol CO2·m −2 ·s −1 indicating the suppression of photorespiration in C3 plants. [88] [89]

There are three main factors affecting photosynthesis [ clarification needed ] and several corollary factors. The three main are: [ citation needed ]

Total photosynthesis is limited by a range of environmental factors. These include the amount of light available, the amount of leaf area a plant has to capture light (shading by other plants is a major limitation of photosynthesis), rate at which carbon dioxide can be supplied to the chloroplasts to support photosynthesis, the availability of water, and the availability of suitable temperatures for carrying out photosynthesis. [95]

Light intensity (irradiance), wavelength and temperature

The process of photosynthesis provides the main input of free energy into the biosphere, and is one of four main ways in which radiation is important for plant life. [96]

The radiation climate within plant communities is extremely variable, with both time and space.

In the early 20th century, Frederick Blackman and Gabrielle Matthaei investigated the effects of light intensity (irradiance) and temperature on the rate of carbon assimilation.

  • At constant temperature, the rate of carbon assimilation varies with irradiance, increasing as the irradiance increases, but reaching a plateau at higher irradiance.
  • At low irradiance, increasing the temperature has little influence on the rate of carbon assimilation. At constant high irradiance, the rate of carbon assimilation increases as the temperature is increased.

These two experiments illustrate several important points: First, it is known that, in general, photochemical reactions are not affected by temperature. However, these experiments clearly show that temperature affects the rate of carbon assimilation, so there must be two sets of reactions in the full process of carbon assimilation. These are the light-dependent 'photochemical' temperature-independent stage, and the light-independent, temperature-dependent stage. Second, Blackman's experiments illustrate the concept of limiting factors. Another limiting factor is the wavelength of light. Cyanobacteria, which reside several meters underwater, cannot receive the correct wavelengths required to cause photoinduced charge separation in conventional photosynthetic pigments. To combat this problem, a series of proteins with different pigments surround the reaction center. This unit is called a phycobilisome. [ clarification needed ]

Carbon dioxide levels and photorespiration

As carbon dioxide concentrations rise, the rate at which sugars are made by the light-independent reactions increases until limited by other factors. RuBisCO, the enzyme that captures carbon dioxide in the light-independent reactions, has a binding affinity for both carbon dioxide and oxygen. When the concentration of carbon dioxide is high, RuBisCO will fix carbon dioxide. However, if the carbon dioxide concentration is low, RuBisCO will bind oxygen instead of carbon dioxide. This process, called photorespiration, uses energy, but does not produce sugars.

RuBisCO oxygenase activity is disadvantageous to plants for several reasons:

  1. One product of oxygenase activity is phosphoglycolate (2 carbon) instead of 3-phosphoglycerate (3 carbon). Phosphoglycolate cannot be metabolized by the Calvin-Benson cycle and represents carbon lost from the cycle. A high oxygenase activity, therefore, drains the sugars that are required to recycle ribulose 5-bisphosphate and for the continuation of the Calvin-Benson cycle.
  2. Phosphoglycolate is quickly metabolized to glycolate that is toxic to a plant at a high concentration it inhibits photosynthesis.
  3. Salvaging glycolate is an energetically expensive process that uses the glycolate pathway, and only 75% of the carbon is returned to the Calvin-Benson cycle as 3-phosphoglycerate. The reactions also produce ammonia (NH3), which is able to diffuse out of the plant, leading to a loss of nitrogen.

The salvaging pathway for the products of RuBisCO oxygenase activity is more commonly known as photorespiration, since it is characterized by light-dependent oxygen consumption and the release of carbon dioxide.

  1. ^"photosynthesis". Online Etymology Dictionary. Archived from the original on 2013-03-07 . Retrieved 2013-05-23 .
  2. ^φῶς . Liddell, Henry George Scott, Robert A Greek–English Lexicon at the Perseus Project
  3. ^σύνθεσις . Liddell, Henry George Scott, Robert A Greek–English Lexicon at the Perseus Project
  4. ^ ab
  5. Bryant DA, Frigaard NU (Nov 2006). "Prokaryotic photosynthesis and phototrophy illuminated". Trends in Microbiology. 14 (11): 488–496. doi:10.1016/j.tim.2006.09.001. PMID16997562.
  6. ^
  7. Reece J, Urry L, Cain M, Wasserman S, Minorsky P, Jackson R (2011). Biology (International ed.). Upper Saddle River, NJ: Pearson Education. pp. 235, 244. ISBN978-0-321-73975-9 . This initial incorporation of carbon into organic compounds is known as carbon fixation.
  8. ^
  9. Olson JM (May 2006). "Photosynthesis in the Archean era". Photosynthesis Research. 88 (2): 109–117. doi:10.1007/s11120-006-9040-5. PMID16453059. S2CID20364747.
  10. ^
  11. Buick R (Aug 2008). "When did oxygenic photosynthesis evolve?". Philosophical Transactions of the Royal Society of London, Series B. 363 (1504): 2731–2743. doi:10.1098/rstb.2008.0041. PMC2606769 . PMID18468984.
  12. ^
  13. Nealson KH, Conrad PG (Dec 1999). "Life: past, present and future". Philosophical Transactions of the Royal Society of London, Series B. 354 (1392): 1923–1939. doi:10.1098/rstb.1999.0532. PMC1692713 . PMID10670014.
  14. ^
  15. Whitmarsh J, Govindjee (1999). "The photosynthetic process". In Singhal GS, Renger G, Sopory SK, Irrgang KD, Govindjee (eds.). Concepts in photobiology: photosynthesis and photomorphogenesis. Boston: Kluwer Academic Publishers. pp. 11–51. ISBN978-0-7923-5519-9 . 100 × 10 15 grams of carbon/year fixed by photosynthetic organisms, which is equivalent to 4 × 10 18 kJ/yr = 4 × 10 21 J/yr of free energy stored as reduced carbon.
  16. ^
  17. Steger U, Achterberg W, Blok K, Bode H, Frenz W, Gather C, Hanekamp G, Imboden D, Jahnke M, Kost M, Kurz R, Nutzinger HG, Ziesemer T (2005). Sustainable development and innovation in the energy sector. Berlin: Springer. p. 32. ISBN978-3-540-23103-5 . Archived from the original on 2016-09-02 . Retrieved 2016-02-21 . The average global rate of photosynthesis is 130 TW.
  18. ^
  19. "World Consumption of Primary Energy by Energy Type and Selected Country Groups, 1980–2004". Energy Information Administration. July 31, 2006. Archived from the original (XLS) on November 9, 2006 . Retrieved 2007-01-20 .
  20. ^
  21. Field CB, Behrenfeld MJ, Randerson JT, Falkowski P (Jul 1998). "Primary production of the biosphere: integrating terrestrial and oceanic components". Science. 281 (5374): 237–240. Bibcode:1998Sci. 281..237F. doi:10.1126/science.281.5374.237. PMID9657713. Archived from the original on 2018-09-25 . Retrieved 2018-04-20 .
  22. ^ abc
  23. "Photosynthesis". McGraw-Hill Encyclopedia of Science & Technology. 13. New York: McGraw-Hill. 2007. ISBN978-0-07-144143-8 .
  24. ^
  25. Whitmarsh J, Govindjee (1999). "Chapter 2: The Basic Photosynthetic Process". In Singhal GS, Renger G, Sopory SK, Irrgang KD, Govindjee (eds.). Concepts in Photobiology: Photosynthesis and Photomorphogenesis. Boston: Kluwer Academic Publishers. p. 13. ISBN978-0-7923-5519-9 .
  26. ^Anaerobic Photosynthesis, Chemical & Engineering News, 86, 33, August 18, 2008, p. 36
  27. ^
  28. Kulp TR, Hoeft SE, Asao M, Madigan MT, Hollibaugh JT, Fisher JC, Stolz JF, Culbertson CW, Miller LG, Oremland RS (Aug 2008). "Arsenic(III) fuels anoxygenic photosynthesis in hot spring biofilms from Mono Lake, California". Science. 321 (5891): 967–970. Bibcode:2008Sci. 321..967K. doi:10.1126/science.1160799. PMID18703741. S2CID39479754.
  29. ^
  30. "Scientists discover unique microbe in California's largest lake". Archived from the original on 2009-07-12 . Retrieved 2009-07-20 .
  31. ^Plants: Diversity and EvolutionArchived 2016-09-01 at the Wayback Machine, page 14, Martin Ingrouille, Bill Eddie
  32. ^
  33. Oakley T (19 December 2008). "Evolutionary Novelties: Opsins: An amazing evolutionary convergence". Archived from the original on 17 April 2019 . Retrieved 17 April 2019 .
  34. ^
  35. Tavano CL, Donohue TJ (December 2006). "Development of the bacterial photosynthetic apparatus". Current Opinion in Microbiology. 9 (6): 625–631. doi:10.1016/j.mib.2006.10.005. PMC2765710 . PMID17055774.
  36. ^ ab
  37. Mullineaux CW (1999). "The thylakoid membranes of cyanobacteria: structure, dynamics and function". Australian Journal of Plant Physiology. 26 (7): 671–677. doi:10.1071/PP99027.
  38. ^
  39. Sener MK, Olsen JD, Hunter CN, Schulten K (October 2007). "Atomic-level structural and functional model of a bacterial photosynthetic membrane vesicle". Proceedings of the National Academy of Sciences of the United States of America. 104 (40): 15723–15728. Bibcode:2007PNAS..10415723S. doi:10.1073/pnas.0706861104. PMC2000399 . PMID17895378.
  40. ^
  41. Campbell NA, Williamson B, Heyden RJ (2006). Biology Exploring Life. Upper Saddle River, New Jersey: Prentice Hall. ISBN978-0-13-250882-7 . Archived from the original on 2014-11-02 . Retrieved 2009-02-03 .
  42. ^
  43. Ziehe D, Dünschede B, Schünemann D (December 2018). "Molecular mechanism of SRP-dependent light-harvesting protein transport to the thylakoid membrane in plants". Photosynthesis Research. 138 (3): 303–313. doi:10.1007/s11120-018-0544-6. PMC6244792 . PMID29956039.
  44. ^ ab
  45. Raven PH, Evert RF, Eichhorn SE (2005). Biology of Plants (7th ed.). New York: W. H. Freeman and Company. pp. 124–127. ISBN978-0-7167-1007-3 .
  46. ^
  47. "Yachandra/Yano Group". Lawrence Berkeley National Laboratory. Archived from the original on 2019-07-22 . Retrieved 2019-07-22 .
  48. ^
  49. Pushkar Y, Yano J, Sauer K, Boussac A, Yachandra VK (February 2008). "Structural changes in the Mn4Ca cluster and the mechanism of photosynthetic water splitting". Proceedings of the National Academy of Sciences of the United States of America. 105 (6): 1879–1884. Bibcode:2008PNAS..105.1879P. doi:10.1073/pnas.0707092105. PMC2542863 . PMID18250316.
  50. ^ ab
  51. Williams BP, Johnston IG, Covshoff S, Hibberd JM (September 2013). "Phenotypic landscape inference reveals multiple evolutionary paths to C4 photosynthesis". eLife. 2: e00961. doi:10.7554/eLife.00961. PMC3786385 . PMID24082995.
  52. ^
  53. Taiz L, Geiger E (2006). Plant Physiology (4th ed.). Sinauer Associates. ISBN978-0-87893-856-8 .
  54. ^
  55. Monson RK, Sage RF (1999). "The Taxonomic Distribution of C
    4 Photosynthesis". C₄ plant biology. Boston: Academic Press. pp. 551–580. ISBN978-0-12-614440-6 .
  56. ^
  57. Dodd AN, Borland AM, Haslam RP, Griffiths H, Maxwell K (April 2002). "Crassulacean acid metabolism: plastic, fantastic". Journal of Experimental Botany. 53 (369): 569–580. doi: 10.1093/jexbot/53.369.569 . PMID11886877.
  58. ^
  59. Tooulakou, Georgia Giannopoulos, Andreas Nikolopoulos, Dimosthenis Bresta, Panagiota Dotsika, Elissavet Orkoula, Malvina G. Kontoyannis, Christos G. Fasseas, Costas Liakopoulos, Georgios Klapa, Maria I. Karabourniotis, George (August 2016). "Alarm Photosynthesis: Calcium Oxalate Crystals as an Internal CO 2 Source in Plants". Plant Physiology. 171 (4): 2577–2585. doi:10.1104/pp.16.00111. ISSN0032-0889. PMC4972262 . PMID27261065.
  60. ^
  61. Gómez-Espinoza, Olman González-Ramírez, Daniel Bresta, Panagiota Karabourniotis, George Bravo, León A. (2020-10-02). "Decomposition of Calcium Oxalate Crystals in Colobanthus quitensis under CO2 Limiting Conditions". Plants. 9 (10): 1307. doi: 10.3390/plants9101307 . ISSN2223-7747. PMC7600318 . PMID33023238.
  62. ^
  63. Badger MR, Price GD (February 2003). "CO2 concentrating mechanisms in cyanobacteria: molecular components, their diversity and evolution". Journal of Experimental Botany. 54 (383): 609–622. doi: 10.1093/jxb/erg076 . PMID12554704.
  64. ^
  65. Badger MR, Andrews JT, Whitney SM, Ludwig M, Yellowlees DC, Leggat W, Price GD (1998). "The diversity and coevolution of Rubisco, plastids, pyrenoids, and chloroplast-based CO2-concentrating mechanisms in algae". Canadian Journal of Botany. 76 (6): 1052–1071. doi:10.1139/b98-074.
  66. ^
  67. Miyamoto K. "Chapter 1 – Biological energy production". Renewable biological systems for alternative sustainable energy production (FAO Agricultural Services Bulletin – 128). Food and Agriculture Organization of the United Nations. Archived from the original on 7 September 2013 . Retrieved 4 January 2009 .
  68. ^ ab
  69. Ehrenberg, Rachel (2017-12-15). "The photosynthesis fix". Knowable Magazine. Annual Reviews . Retrieved 2018-04-03 .
  70. ^ ab
  71. Maxwell K, Johnson GN (April 2000). "Chlorophyll fluorescence – a practical guide". Journal of Experimental Botany. 51 (345): 659–668. doi: 10.1093/jexbot/51.345.659 . PMID10938857.
  72. ^
  73. Govindjee R. "What is Photosynthesis?". Biology at Illinois. Archived from the original on 27 May 2014 . Retrieved 17 April 2014 .
  74. ^ ab
  75. Rosenqvist E, van Kooten O (2006). "Chapter 2: Chlorophyll Fluorescence: A General Description and Nomenclature". In DeEll JA, Toivonen PM (eds.). Practical Applications of Chlorophyll Fluorescence in Plant Biology. Dordrecht, the Netherlands: Kluwer Academic Publishers. pp. 39–78.
  76. ^
  77. Baker NR, Oxborough K (2004). "Chapter 3: Chlorophyll fluorescence as a probe of photosynthetic productivity". In Papaqeorgiou G, Govindjee (eds.). Chlorophylla Fluorescence a Signature of Photosynthesis. Dordrecht, The Netherlands: Springer. pp. 66–79.
  78. ^
  79. Flexas J, Escalnona JM, Medrano H (January 1999). "Water stress induces different levels of photosynthesis and electron transport rate regulation in grapevines". Plant, Cell and Environment. 22 (1): 39–48. doi: 10.1046/j.1365-3040.1999.00371.x .
  80. ^
  81. Fryer MJ, Andrews JR, Oxborough K, Blowers DA, Baker NR (1998). "Relationship between CO2 assimilation, photosynthetic electron transport, and active O2 metabolism in leaves of maize in the field during periods of low temperature". Plant Physiology. 116 (2): 571–580. doi:10.1104/pp.116.2.571. PMC35114 . PMID9490760.
  82. ^
  83. 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. PMID16151873. S2CID291238.
  84. ^
  85. Genty B, Briantais J, Baker NR (1989). "The relationship between the quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence". Biochimica et Biophysica Acta (BBA) - General Subjects. 990 (1): 87–92. doi:10.1016/s0304-4165(89)80016-9.
  86. ^ ab
  87. Baker NR (2008). "Chlorophyll fluorescence: A probe of photosynthesis in vivo". Annual Review of Plant Biology. 59: 89–113. doi:10.1146/annurev.arplant.59.032607.092759. PMID18444897. S2CID31451852.
  88. ^ abc
  89. Bernacchi CJ, Portis AR, Nakano H, von Caemmerer S, Long SP (2002). "Temperature response of mesophyll conductance. Implications for the determination of Rubisco enzyme kinetics and for limitations to photosynthesis in vivo". Plant Physiology. 130 (4): 1992–1998. doi:10.1104/pp.008250. PMC166710 . PMID12481082.
  90. ^ abcd
  91. Ribas-Carbo M, Flexas J, Robinson SA, Tcherkez GG (2010). "In vivo measurement of plant respiration". University of Wollongong Research Online.
  92. ^ abcd
  93. Long SP, Bernacchi CJ (2003). "Gas exchange measurements, what can they tell us about the underlying limitations to photosynthesis? Procedures and sources of error". Journal of Experimental Botany. 54 (392): 2393–2401. doi: 10.1093/jxb/erg262 . PMID14512377.
  94. ^
  95. Bernacchi CJ, Portis A (2002). "R., Nakano H., von Caemmerer S., and Long S.P. (2002) Temperature response of nesophyll conductance. Implications for the determination of Rubisco enzyme kinetics and for limitations to photosynthesis in vivo". Plant Physiology. 130 (4): 1992–1998. doi:10.1104/pp.008250. PMC166710 . PMID12481082.
  96. ^
  97. Yin X, Struik PC (2009). "Theoretical reconsiderations when estimating the mesophyll conductanceto CO2 diffusion in leaves of C3 plants by analysis of combined gas exchange and chlorophyll fluorescence measurements". Plant, Cell and Environment. 32 (11): 1513–1524 [1524]. doi: 10.1111/j.1365-3040.2009.02016.x . PMID19558403.
  98. ^
  99. Schreiber U, Klughammer C, Kolbowski J (2012). "Assessment of wavelength-dependent parameters of photosynthetic electron transport with a new type of multi-color PAM chlorophyll fluorometer". Photosynthesis Research. 113 (1–3): 127–144. doi:10.1007/s11120-012-9758-1. PMC3430841 . PMID22729479.
  100. ^
  101. Palmer J (21 June 2013). "Plants 'seen doing quantum physics ' ". BBC News. Archived from the original on 3 October 2018 . Retrieved 21 June 2018 .
  102. ^
  103. Lloyd S (10 March 2014). "Quantum Biology: Better living through quantum mechanics". The Nature of Reality. Nova: PBS Online WGBH Boston. Archived from the original on 3 July 2017 . Retrieved 8 September 2017 .
  104. ^
  105. Hildner R, Brinks D, Nieder JB, Cogdell RJ, van Hulst NF (June 2013). "Quantum coherent energy transfer over varying pathways in single light-harvesting complexes". Science. 340 (6139): 1448–1451. Bibcode:2013Sci. 340.1448H. doi:10.1126/science.1235820. PMID23788794. S2CID25760719.
  106. ^
  107. Gale J (2009). Astrobiology of Earth: The emergence, evolution and future of life on a planet in turmoil. Oxford University Press. pp. 112–113. ISBN978-0-19-154835-2 .
  108. ^
  109. Davis K (2 October 2004). "Photosynthesis got a really early start". New Scientist. Archived from the original on 1 May 2015 . Retrieved 8 September 2017 .
  110. ^
  111. Hooper R (19 August 2006). "Revealing the dawn of photosynthesis". New Scientist. Archived from the original on 24 May 2015 . Retrieved 8 September 2017 .
  112. ^
  113. Caredona, Tanai (6 March 2018). "Early Archean origin of heterodimeric Photosystem I". Heliyon. 4 (3): e00548. doi:10.1016/j.heliyon.2018.e00548. PMC5857716 . PMID29560463. Archived from the original on 1 April 2019 . Retrieved 23 March 2018 .
  114. ^
  115. Howard V (7 March 2018). "Photosynthesis Originated A Billion Years Earlier Than We Thought, Study Shows". Astrobiology Magazine . Retrieved 23 March 2018 . [permanent dead link]
  116. ^
  117. Venn AA, Loram JE, Douglas AE (2008). "Photosynthetic symbioses in animals". Journal of Experimental Botany. 59 (5): 1069–1080. doi: 10.1093/jxb/erm328 . PMID18267943.
  118. ^
  119. Rumpho ME, Summer EJ, Manhart JR (May 2000). "Solar-powered sea slugs. Mollusc/algal chloroplast symbiosis". Plant Physiology. 123 (1): 29–38. doi:10.1104/pp.123.1.29. PMC1539252 . PMID10806222.
  120. ^
  121. Muscatine L, Greene RW (1973). Chloroplasts and algae as symbionts in molluscs. International Review of Cytology. 36. pp. 137–169. doi:10.1016/S0074-7696(08)60217-X. ISBN978-0-12-364336-0 . PMID4587388.
  122. ^
  123. Rumpho ME, Worful JM, Lee J, Kannan K, Tyler MS, Bhattacharya D, Moustafa A, Manhart JR (November 2008). "Horizontal gene transfer of the algal nuclear gene psbO to the photosynthetic sea slug Elysia chlorotica". Proceedings of the National Academy of Sciences of the United States of America. 105 (46): 17867–17871. Bibcode:2008PNAS..10517867R. doi:10.1073/pnas.0804968105. PMC2584685 . PMID19004808.
  124. ^
  125. Douglas SE (December 1998). "Plastid evolution: origins, diversity, trends". Current Opinion in Genetics & Development. 8 (6): 655–661. doi:10.1016/S0959-437X(98)80033-6. PMID9914199.
  126. ^
  127. Reyes-Prieto A, Weber AP, Bhattacharya D (2007). "The origin and establishment of the plastid in algae and plants". Annual Review of Genetics. 41: 147–168. doi:10.1146/annurev.genet.41.110306.130134. PMID17600460. S2CID8966320. [permanent dead link]
  128. ^
  129. Raven JA, Allen JF (2003). "Genomics and chloroplast evolution: what did cyanobacteria do for plants?". Genome Biology. 4 (3): 209. doi:10.1186/gb-2003-4-3-209. PMC153454 . PMID12620099.
  130. ^
  131. Allen JF (December 2017). "The CoRR hypothesis for genes in organelles". Journal of Theoretical Biology. 434: 50–57. doi: 10.1016/j.jtbi.2017.04.008 . PMID28408315.
  132. ^The endosymbiotic origin, diversification and fate of plastids - NCBI - NIH
  133. ^
  134. Tomitani A, Knoll AH, Cavanaugh CM, Ohno T (April 2006). "The evolutionary diversification of cyanobacteria: molecular-phylogenetic and paleontological perspectives". Proceedings of the National Academy of Sciences of the United States of America. 103 (14): 5442–5447. Bibcode:2006PNAS..103.5442T. doi:10.1073/pnas.0600999103. PMC1459374 . PMID16569695.
  135. ^
  136. "Cyanobacteria: Fossil Record". Archived from the original on 2010-08-24 . Retrieved 2010-08-26 .
  137. ^
  138. Smith A (2010). Plant biology. New York: Garland Science. p. 5. ISBN978-0-8153-4025-6 .
  139. ^
  140. Herrero A, Flores E (2008). The Cyanobacteria: Molecular Biology, Genomics and Evolution (1st ed.). Caister Academic Press. ISBN978-1-904455-15-8 .
  141. ^ ab
  142. Martin, Daniel Thompson, Andrew Stewart, Iain Gilbert, Edward Hope, Katrina Kawai, Grace Griffiths, Alistair (2012-09-04). "A paradigm of fragile Earth in Priestley's bell jar". Extreme Physiology & Medicine. 1 (1): 4. doi:10.1186/2046-7648-1-4. ISSN2046-7648. PMC3707099 . PMID23849304.
  143. ^
  144. Gest, Howard (2000). "Bicentenary homage to Dr Jan Ingen-Housz, MD (1730–1799), pioneer of photosynthesis research". Photosynthesis Research. 63 (2): 183–90. doi:10.1023/A:1006460024843. PMID16228428. S2CID22970505.
  145. ^Eugene Rabinowitch (1945) Photosynthesis and Related Processes via Biodiversity Heritage Library
  146. ^
  147. Walker DA (2002). " ' And whose bright presence' – an appreciation of Robert Hill and his reaction" (PDF) . Photosynthesis Research. 73 (1–3): 51–54. doi:10.1023/A:1020479620680. PMID16245102. S2CID21567780. Archived from the original (PDF) on 2008-03-09 . Retrieved 2015-08-27 .
  148. ^Otto Warburg – BiographyArchived 2010-12-15 at the Wayback Machine. (1970-08-01). Retrieved on 2011-11-03.
  149. ^
  150. Kandler O (1950). "Über die Beziehungen zwischen Phosphathaushalt und Photosynthese. I. Phosphatspiegelschwankungen bei Chlorella pyrenoidosa als Folge des Licht-Dunkel-Wechsels" [On the relationship between the phosphate metabolism and photosynthesis I. Variations in phosphate levels in Chlorella pyrenoidosa as a consequence of light-dark changes] (PDF) . Zeitschrift für Naturforschung. 5b (8): 423–437. doi:10.1515/znb-1950-0806. S2CID97588826. Archived (PDF) from the original on 2018-06-24 . Retrieved 2018-06-26 .
  151. ^
  152. Arnon DI, Whatley FR, Allen MB (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.
  153. ^
  154. Arnon DI (1956). "Phosphorus metabolism and photosynthesis". Annual Review of Plant Physiology. 7: 325–354. doi:10.1146/annurev.pp.07.060156.001545.
  155. ^
  156. Gest H (2002). "History of the word photosynthesis and evolution of its definition". Photosynthesis Research. 73 (1–3): 7–10. doi:10.1023/A:1020419417954. PMID16245098. S2CID11265932.
  157. ^
  158. Calvin M (July 1989). "Forty years of photosynthesis and related activities". Photosynthesis Research. 21 (1): 3–16. doi:10.1007/BF00047170 (inactive 31 May 2021). PMID24424488. CS1 maint: DOI inactive as of May 2021 (link)
  159. ^
  160. Verduin J (1953). "A table of photosynthesis rates under optimal, near natural conditions". Am. J. Bot. 40 (9): 675–679. doi:10.1002/j.1537-2197.1953.tb06540.x. JSTOR2439681.
  161. ^
  162. Verduin J, Whitwer EE, Cowell BC (1959). "Maximal photosynthetic rates in nature". Science. 130 (3370): 268–269. Bibcode:1959Sci. 130..268V. doi:10.1126/science.130.3370.268. PMID13668557. S2CID34122342.
  163. ^
  164. Hesketh JD, Musgrave R (1962). "Photosynthesis under field conditions. IV. Light studies with individual corn leaves". Crop Sci. 2 (4): 311–315. doi:10.2135/cropsci1962.0011183x000200040011x. S2CID83706567.
  165. ^
  166. Hesketh JD, Moss DN (1963). "Variation in the response of photosynthesis to light". Crop Sci. 3 (2): 107–110. doi:10.2135/cropsci1963.0011183X000300020002x.
  167. ^ ab
  168. El-Sharkawy, MA, Hesketh JD (1965). "Photosynthesis among species in relation to characteristics of leaf anatomy and CO2 diffusion resistances". Crop Sci. 5 (6): 517–521. doi:10.2135/cropsci1965.0011183x000500060010x.
  169. ^ abc
  170. El-Sharkawy MA, Hesketh JD (1986). "Citation Classic-Photosynthesis among species in relation to characteristics of leaf anatomy and CO2 diffusion resistances" (PDF) . Curr. Cont./Agr.Biol.Environ. 27: 14. [permanent dead link]
  171. ^
  172. Haberlandt G (1904). Physiologische Pflanzanatomie. Leipzig: Engelmann.
  173. ^
  174. El-Sharkawy MA (1965). Factors Limiting Photosynthetic Rates of Different Plant Species (Ph.D. thesis). The University of Arizona, Tucson, USA.
  175. ^
  176. Karpilov YS (1960). "The distribution of radioactvity in carbon-14 among the products of photosynthesis in maize". Proc. Kazan Agric. Inst. 14: 15–24.
  177. ^
  178. Kortschak HP, Hart CE, Burr GO (1965). "Carbon dioxide fixation in sugarcane leaves". Plant Physiol. 40 (2): 209–213. doi:10.1104/pp.40.2.209. PMC550268 . PMID16656075.
  179. ^
  180. Hatch MD, Slack CR (1966). "Photosynthesis by sugar-cane leaves. A new carboxylation reaction and the pathway of sugar formation". Biochem. J. 101 (1): 103–111. doi:10.1042/bj1010103. PMC1270070 . PMID5971771.
  181. ^
  182. Chapin FS, Matson PA, Mooney HA (2002). Principles of Terrestrial Ecosystem Ecology. New York: Springer. pp. 97–104. ISBN978-0-387-95443-1 .
  183. ^
  184. Jones HG (2014). Plants and Microclimate: a Quantitative Approach to Environmental Plant Physiology (Third ed.). Cambridge: Cambridge University Press. ISBN978-0-521-27959-8 .


  • Bidlack JE, Stern KR, Jansky S (2003). Introductory Plant Biology. New York: McGraw-Hill. ISBN978-0-07-290941-8 .
  • Blankenship RE (2014). Molecular Mechanisms of Photosynthesis (2nd ed.). John Wiley & Sons. ISBN978-1-4051-8975-0 .
  • Govindjee, Beatty JT, Gest H, Allen JF (2006). Discoveries in Photosynthesis. Advances in Photosynthesis and Respiration. 20. Berlin: Springer. ISBN978-1-4020-3323-0 .
  • Reece JB, et al. (2013). Campbell Biology. Benjamin Cummings. ISBN978-0-321-77565-8 .


  • Gupta RS, Mukhtar T, Singh B (Jun 1999). "Evolutionary relationships among photosynthetic prokaryotes (Heliobacterium chlorum, Chloroflexus aurantiacus, cyanobacteria, Chlorobium tepidum and proteobacteria): implications regarding the origin of photosynthesis". Molecular Microbiology. 32 (5): 893–906. doi:10.1046/j.1365-2958.1999.01417.x. PMID10361294. S2CID33477550.
  • Rutherford AW, 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. PMC1693113 . PMID12594932.

40 ms 3.3% 40 ms 3.3% recursiveClone 40 ms 3.3% [others] 360 ms 30.0% Number of Wikibase entities loaded: 1/400 -->

Biology - Plants and photosynthesis

Carbon dioxide, water and light are all needed for photosynthesis to take place.

Happens inside chloroplasts, which are mostly found in leaf cells.

Epidermis is thin and transparent - to allow more light to reach the palisade cells.

Thin cuticle made of wax - to protect the leaf from infection and prevent water loss without blocking out light.

Palisade cell layer at top of leaf - to absorb more light and increase the rate of photosynthesis.

Spongy layer - air spaces allow carbon dioxide to diffuse through the leaf.

The stomata control gas exchange in the leaf. Each stomata can be opened or closed, depending on how turgid its guard cells are.

In the light, the guard cells absorb water by osmosis, become turgid and the stoma opens.
In the dark, the guard cells lose water, become flaccid and the stoma closes.

Thin - gases only have to travel a short distance to reach the cells where they're needed.

Air spaces inside the leaf - lets gases like carbon dioxide and oxygen move easily between cells. Also increases the surface area for gas exchange.

The limiting factor depends of the environmental conditions.

If the concentration of carbon dioxide is increased, the rate of photosynthesis will therefore increase.

At low temperatures, the rate of photosynthesis is low because fewer molecular collisions occur per unit time between enzymes and substrates.

As you increase the temperature the number of molecular collisions increase per unit time .

The net (overall) effect depends on the time of day and the light intensity. Photosynthesis doesn't occur at night. When there is no photosynthesis, there is a net release of carbon dioxide and a net uptake of oxygen.

If there is enough light during the day, then:

Most transpiration happens at the leaves.

This evaporation creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels.

This means more water is drawn up from the roots, and so there's a constant transpiration stream of water through the plant.

If wind speed around a leaf is low, the water vapour just surrounds the leaf and doesn't move away. This means there's a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn't happen as quickly.

Hold the leaf in forceps and plunge it into the boiling water for 5 seconds. This will kill the cells, stop all chemical reactions and make the leaf permeable to alcohol and iodine solution later on.

Put the leaf at the bottom of a test-tube and cover it with ethanol.

Place the test-tube in the hot water and leave it for 5 minutes. The alcohol will boil and dissolve out the chlorophyll in the leaf.

Your leaf should be white or very pale green.

Fill the test-tube with cold water and the leaf will should float to the top.

Use forceps to spread the leaf flat in a petri dish. Use a dropping pipette cover the leaf with iodine solution for one minute.

Take the leaf to the sink and holding it on the petri dish, wash away the iodine solution with some cold water.

This shows the importance of chlorophyll in photosynthesis.

The gas syringe should be empty to start with. Sodium hydrogen-carbonate may be added to the water to make sure the plant has enough carbon dioxide.

A source of white light is placed at a specific distance from the pond-weed.

The pond-weed is left to photosynthesise for a set amount of time. As it photosynthesises, the oxygen released will collect in the empty capillary tube.

At the end of the experiment, the syringe is used to draw the gas bubble in the tube alongside a ruler and the length of the gas bubble is measured. This is proportional to the volume of oxygen produced.

The experiment is repeated again with the light source placed at different distances from the pond-weed.

The control variables are things like temperature, amount of time the pond-weed has been left to photosynthesis and the amount of carbon dioxide.

Cut a shoot underwater to prevent air from entering the xylem. Cut it at a slant to increase the surface area available for water uptake.

Assemble the potometer in water and insert the shoot underwater, so no air can enter.

Remove the apparatus from the water but keep the end of the capillary tube submerged in a beaker of water.

Check the apparatus is watertight and airtight.

Dry the leaves, allow time for the shoot to adjust and shut the tap.

Remove the end of the capillary tube from the beaker of water until one air bubble has formed, then but the end of the tube back into the water.

Record the starting position of the air bubble.

Start a stopwatch and record the distance moved by the bubble per unit time.

Watch the video: στο φως του φεγγαριού 16 21 02 2010 by www isobitis com (December 2021).