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. What Is Photosynthesis?
Why Is it Important? Figure 2. Figure 3: Structure of a chloroplast. 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. What Are the Steps of Photosynthesis?
Figure 5: The light and dark reactions in the chloroplast. The chloroplast is involved in both stages of photosynthesis. Photosynthetic cells contain chlorophyll and other light-sensitive pigments that capture solar energy. In the presence of carbon dioxide, such cells are able to convert this solar energy into energy-rich organic molecules, such as glucose. These cells not only drive the global carbon cycle, but they also produce much of the oxygen present in atmosphere of the Earth.
Essentially, nonphotosynthetic cells use the products of photosynthesis to do the opposite of photosynthesis: break down glucose and release carbon dioxide. Cell Biology for Seminars, Unit 1. Topic rooms within Cell Biology Close. No topic rooms are there. Or Browse Visually. Student Voices. Creature Cast. Simply Science. Green Screen. Green Science. Bio 2. The Success Code. Why Science Matters. The Beyond. Plant ChemCast. Postcards from the Universe.
Brain Metrics. Mind Read. Eyes on Environment. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image 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. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. The process During photosynthesis, plants take in carbon dioxide CO 2 and water H 2 O from the air and soil. Chlorophyll Inside the plant cell are small organelles called chloroplasts, which store the energy of sunlight. Light-dependent reactions vs. C3 and C4 photosynthesis Not all forms of photosynthesis are created equal, however.
C3 photosynthesis. C4 photosynthesis. Calvin cycle. Part of the chloroplast where light-dependent reactions take place. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. Media If a media asset is downloadable, a download button appears in the corner of the media viewer. Text Text on this page is printable and can be used according to our Terms of Service.
Notice that the light reaction makes no sugar. This is where sugar is made. But the light reaction does produce something we use: oxygen. All the oxygen we breathe is the result of this step in photosynthesis, carried out by plants and algae which are not plants the world over. The next step takes the energy from the light reaction and applies it to a process called the Calvin cycle.
The cycle is named for Melvin Calvin, the man who discovered it. The Calvin cycle is sometimes also called the dark reaction because none of its steps require light. But it still happens during the day. This is the space inside the chloroplast but outside the thylakoid membranes. The glucose molecule goes on to bigger things. Plants also can store the energy packed in a glucose molecule within larger starch molecules.
All of these molecules are carbohydrates — chemicals containing carbon, oxygen and hydrogen. CarbOHydrate makes it easy to remember. The plant uses the bonds in these chemicals to store energy. But we use the these chemicals too. Carbohydrates are an important part of the foods we eat, particularly grains, potatoes, fruits and vegetables. With the help of an enzyme, six molecules of carbon dioxide bond to six molecules of RuBP to create six new molecules. Several intermediate steps, which require ATP, NADPH, and additional enzymes, rearrange the position of the carbon, hydrogen, and oxygen atoms in these six molecules, and when the reactions are complete, one new molecule of glucose has been constructed and five molecules of RuBP have been reconstructed.
The thousands of glucose molecules produced in this reaction are processed by the plant to produce energy in the process known as aerobic respiration, used as structural materials, or stored.
The regenerated RuBP is used to start the Calvin cycle all over again. Plants such as corn and crabgrass that have evolved in hot, dry environments, however, must overcome certain obstacles to photosynthesis. On hot days, they partially close the pores in their leaves to prevent the escape of water. With the pores only slightly open, adequate amounts of carbon dioxide cannot enter the leaf, and the Calvin cycle comes to a halt.
To get around this problem, certain hot-weather plants have developed a way to keep carbon dioxide flowing to the stroma without capturing it directly from the air.
They open their pores slightly, take in carbon dioxide, and transport it deep within the leaves. Here they stockpile it in a chemical form that releases the carbon dioxide slowly and steadily into the Calvin cycle. With this system, these plants can continue photosynthesis on hot days, even with their pores almost completely closed. A field of corn thus remains green on blistering days when neighboring plants wither, and crabgrass thrives in lawns browned by the summer sun.
Bacteria lack chloroplasts, and instead use structures called chromatophores-membranes formed by numerous foldings of the plasma membrane, the membrane surrounding the fluid, or cytoplasm, that fills the cell. The chromatophores house thylakoids similar to plant thylakoids, which in some bacteria contain chlorophyll.
For these bacteria, the process of photosynthesis is similar to that of plants, algae, and seaweed. Many of these chlorophyll-containing bacteria are abundant in oceans, lakes, and rivers, and the oxygen they release dissolves in the water and enables fish and other aquatic organisms to survive.
Certain archaebacteria, members of a group of primitive bacteria-like organisms, carry out photosynthesis in a different manner. The mud-dwelling green sulfur and purple sulfur archaebacteria use hydrogen sulfide instead of water in photosynthesis. These archaebacteria release sulfur rather than oxygen, which, along with hydrogen sulfide, imparts the rotten egg smell to mudflats.
Halobacteria, archaebacteria found in the salt flats of deserts, rely on the pigment bacteriorhodopsin instead of chlorophyll for photosynthesis. These archaebacteria do not carry out the complete process of photosynthesis; although they produce ATP in a process similar to the light-dependent reaction and use it for energy, they do not produce glucose.
0コメント