How does cellulose differ from glycogen? How do vacuoles help maintain homeostasis? How do cell walls differ from cell membranes? See all questions in Plants Overview. Impact of this question views around the world. You can reuse this answer Creative Commons License. The reason phycobiliproteins absorb light of different colors is that they contain chemical molecules called bilins inside them, which give them their bright colors.
These bilins are responsible for absorbing light of one color and emitting light of another color, thus causing a change in the color of light. Advanced instruments have let us analyze the arrangement of these molecules and proteins in the cyanobacteria.
We know that phycobiliproteins are shaped like disks [ 3 ], and the disks are stacked on top of each other to form the hat-like structure. This assembly joins to the core, made of APC. This entire structure is linked to Chl, which accepts the red light emitted by APC. The arrangement of the hat-like structure has been shown in Figure 3. The change in light color from green to red takes place through a process known as fluorescence. Let us see what fluorescence is. Imagine a transparent container filled with a pink-colored liquid that, when illuminated with a flashlight, shines a bright orange!
That is exactly what CPE does Figure 4. All phycobiliproteins possess this exciting property of giving off visible light of a color different from the color of light that is shone on them. APC takes up this light-red light and changes it to a deep red light for Chl.
So, now we have the green light changed to red, which is the color of light that nature intended Chl to absorb. The entire process is a sort of a relay race, where each participant picks up where the previous one left off Figure 5. These phycobiliproteins are an important part of the tiny microscopic organisms called cyanobacteria, which carry out photosynthesis in much the same way as land plants do.
The only difference is that they use a different set of chemical molecules—cyanobacteria use phycobiliproteins while land plants use Chl.
Respiration is vital to the health of the planet, as humans, animals and all other respiring organisms need the process of plant photosynthesis and respiration to survive. Plants respire all the time, whether it is dark or light, because their cells need energy to stay alive. But they can only photosynthesize when they have light. Several elements may affect the rate of photosynthesis: carbon dioxide concentration, temperature and light intensity.
If there is insufficient carbon dioxide, a plant cannot photosynthesize, even if it has plenty of light. If it is too cold, the rate of photosynthesis will drop. If it is too hot, plants will not be able to photosynthesize. If a plant doesn't have enough light, it cannot photosynthesize very quickly, even if it has sufficient water and carbon dioxide.
B The transformations of organic to inorganic carbon through decomposition and photosynthesis continue in rivers; here, CO2 will re-exchange with the atmosphere degassing or be converted to dissolved carbonates. These carbonates do not exchange with the atmosphere and are mainly exported to the coastal ocean. Organic carbon is also exported to the ocean or stored in flood plains.
C In the coastal ocean, photosynthesis, decomposition, and re-exchanging of CO2 with the atmosphere still continue. Solid organic carbon e. Dissolved inorganic and organic carbon are also exported to the open ocean, and possibly deep-ocean waters, where they are stored for many centuries. Indeed, the fossil fuels we use to power our world today are the ancient remains of once-living organisms, and they provide a dramatic example of this cycle at work.
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.
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