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No use, distribution or reproduction is permitted which does not comply with these terms. The carbon cycle would not be possible without photosynthesis, because this process accounts for the "building" portion of the cycle Figure 2. However, photosynthesis doesn't just drive the carbon cycle — it also creates the oxygen necessary for respiring organisms.
Interestingly, although green plants contribute much of the oxygen in the air we breathe, phytoplankton and cyanobacteria in the world's oceans are thought to produce between one-third and one-half of atmospheric oxygen on Earth.
Photosynthetic cells contain special pigments that absorb light energy. Different pigments respond to different wavelengths of visible light. Chlorophyll , the primary pigment used in photosynthesis, reflects green light and absorbs red and blue light most strongly. 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. Working with the These marine invertebrates tend to move slowly and Print Email Share.
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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Marine ecosystems contain a diverse array of living organisms and abiotic processes.
From massive marine mammals like whales to the tiny krill that form the bottom of the food chain, all life in the ocean is interconnected.
While the ocean seems vast and unending, it is, in fact, finite; as the climate continues to change, we are learning more about those limits. Explore these resources to teach students about marine organisms, their relationship with one another, and with their environment. Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar. Producers convert water, carbon dioxide, minerals, and sunlight into the organic molecules that are the foundation of all life on Earth.
A heterotroph is an organism that consumes other organisms in a food chain. Join our community of educators and receive the latest information on National Geographic's resources for you and your students.
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