The oxygen released with water vapour as a photosynthetic by-product, provides most of the atmospheric oxygen vital to respiration in plants and animals. Animals in turn produce carbon dioxide necessary to plants. Photosynthesis can therefore be considered as the ultimate life process for nearly all plants and animals by providing the source of energy that drives their metabolic functions. Furthermore, the role photosynthesis plays in the natural environment, by absorbing atmospheric CO 2 may well be essential to mitigating the climate changing effects of atmospheric greenhouse gasses GHG.
By combining the reestablishment of plant communities with other management measures required to reduce soil loss, photosynthesis can nurture soil health by promoting an increase in soil organic matter and, thus sequestering atmospheric GHG and promoting food production through soil regeneration. Photosynthesis is the biochemical process by which plants convert CO 2 , water and sunlight generally in the presence of the green pigment chlorophyll into chemical compounds of carbohydrates, glucose, fats and proteins from which the plant derives its food.
Photosynthesis produces oxygen as waste, which is released to the atmosphere through the plant leaves termed respiration. Plants release some carbon during photosynthesis but a significant proportion is retained and stored in live woody tissue to be utilised for new cell formation and energy. When a plant dies, the absorbed carbon is locked in the slowly decomposing biomass and soil organic matter that is the remains of the dead plant. Photosynthesis also occurs in the aquatic environment.
Aquatic plants and algae use CO 2 , water and sunlight to make their own food in the same way terrestrial plants do. Unlike the terrestrial environment, however, atmospheric CO 2 dissolves in the surface waters of the ocean where photosynthesis by tiny marine plants phytoplankton process it into organic carbon.
While some of the carbon remains as dissolved gas, much of it is turned into other chemical compounds to be incorporated into marine organisms as structural calcium carbonate, a building material of shells and skeletons. When aquatic organisms die, their dead remains sink into deep water and decay to be absorbed on the sea or lake floor where it forms layers of carbon-rich sediments. The amount of atmospheric CO 2 absorbed by plants through photosynthesis is enormous.
The process is therefore critical to mitigate the effects of GHG. Plants have the ability to absorb and in turn sequester enormous amounts of carbon over the long term. Much of the excess atmospheric CO 2 is the result from the burning of fossil fuels. In it was estimated nine billion tonnes of CO 2 are annually released in to the atmosphere from fossil fuel consumption.
In plants, photosynthesis takes place in chloroplasts, which contain the chlorophyll. Chloroplasts are surrounded by a double membrane and contain a third inner membrane, called the thylakoid membrane , that forms long folds within the organelle.
In electron micrographs, thylakoid membranes look like stacks of coins, although the compartments they form are connected like a maze of chambers.
The green pigment chlorophyll is located within the thylakoid membrane, and the space between the thylakoid and the chloroplast membranes is called the stroma Figure 3, Figure 4. Chlorophyll A is the major pigment used in photosynthesis, but there are several types of chlorophyll and numerous other pigments that respond to light, including red, brown, and blue pigments. These other pigments may help channel light energy to chlorophyll A or protect the cell from photo-damage.
For example, the photosynthetic protists called dinoflagellates, which are responsible for the "red tides" that often prompt warnings against eating shellfish, contain a variety of light-sensitive pigments, including both chlorophyll and the red pigments responsible for their dramatic coloration. Figure 4: Diagram of a chloroplast inside a cell, showing thylakoid stacks Shown here is a chloroplast inside a cell, with the outer membrane OE and inner membrane IE labeled.
Other features of the cell include the nucleus N , mitochondrion M , and plasma membrane PM. At right and below are microscopic images of thylakoid stacks called grana.
Note the relationship between the granal and stromal membranes. Protein import into chloroplasts. Nature Reviews Molecular Cell Biology 5, doi Figure Detail. Photosynthesis consists of both light-dependent reactions and light-independent reactions. In plants, the so-called "light" reactions occur within the chloroplast thylakoids, where the aforementioned chlorophyll pigments reside. When light energy reaches the pigment molecules, it energizes the electrons within them, and these electrons are shunted to an electron transport chain in the thylakoid membrane.
Meanwhile, each chlorophyll molecule replaces its lost electron with an electron from water; this process essentially splits water molecules to produce oxygen Figure 5.
Figure 5: The light and dark reactions in the chloroplast The chloroplast is involved in both stages of photosynthesis. The light reactions take place in the thylakoid. There, water H 2 O is oxidized, and oxygen O 2 is released. The dark reactions then occur outside the thylakoid. The products of this reaction are sugar molecules and various other organic molecules necessary for cell function and metabolism. Note that the dark reaction takes place in the stroma the aqueous fluid surrounding the stacks of thylakoids and in the cytoplasm.
The thylakoids, intake of water H 2 O , and release of oxygen O 2 occur on the yellow side of the cell to indicate that these are involved in the light reactions. The carbon fixation reactions, which involve the intake of carbon dioxide CO 2 , NADPH, and ATP, and the production of sugars, fatty acids, and amino acids, occur on the blue side of the cell to indicate that these are dark reactions.
An arrow shows the movement of a water molecule from the outside to the thylakoid stack on the inside of the chloroplast. Another arrow shows light energy from the sun entering the chloroplast and reaching the thylakoid stack. An arrow shows the release of an oxygen molecule O 2 from the thylakoid stack to the outside of the chloroplast.
Once the light reactions have occurred, the light-independent or "dark" reactions take place in the chloroplast stroma. During this process, also known as carbon fixation, energy from the ATP and NADPH molecules generated by the light reactions drives a chemical pathway that uses the carbon in carbon dioxide from the atmosphere to build a three-carbon sugar called glyceraldehydephosphate G3P. Cells then use G3P to build a wide variety of other sugars such as glucose and organic molecules.
Many of these interconversions occur outside the chloroplast, following the transport of G3P from the stroma. The products of these reactions are then transported to other parts of the cell, including the mitochondria, where they are broken down to make more energy carrier molecules to satisfy the metabolic demands of the cell.
In plants, some sugar molecules are stored as sucrose or starch. This page appears in the following eBook. Aa Aa Aa. Photosynthetic Cells. Here is the word equation for photosynthesis:.
Photosynthesis takes place inside plant cells in small objects called chloroplasts. Chloroplasts contain a green substance called chlorophyll.
This absorbs the light energy needed to make photosynthesis happen. Plants and algae can only carry out photosynthesis in the light. The Rights Holder for media is the person or group credited. Tyson Brown, National Geographic Society. National Geographic Society.
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Text on this page is printable and can be used according to our Terms of Service. Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Plants are autotrophs, which means they produce their own food.
They use the process of photosynthesis to transform water, sunlight, and carbon dioxide into oxygen, and simple sugars that the plant uses as fuel.
These primary producers form the base of an ecosystem and fuel the next trophic levels. Without this process, life on Earth as we know it would not be possible. We depend on plants for oxygen production and food.
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