Why calvin cycle depends on light reactions

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. In plants, carbon dioxide CO 2 enters the leaves through stomata, where it diffuses over short distances through intercellular spaces until it reaches the mesophyll cells.

Once in the mesophyll cells, CO 2 diffuses into the stroma of the chloroplast, the site of light-independent reactions of photosynthesis. These reactions actually have several names associated with them.

Other names for light-independent reactions include the Calvin cycle, the Calvin-Benson cycle, and dark reactions. The most outdated name is dark reactions, which can be misleading because it implies incorrectly that the reaction only occurs at night or is independent of light, which is why most scientists and instructors no longer use it.

These energy-carrying molecules are made in the stroma where the Calvin cycle takes place. The light-independent reactions of the Calvin cycle can be organized into three basic stages: fixation, reduction, and regeneration. In the stroma, in addition to CO 2 ,two other components are present to initiate the light-independent reactions: an enzyme called ribulose bisphosphate carboxylase RuBisCO and three molecules of ribulose bisphosphate RuBP. RuBP has five atoms of carbon, flanked by two phosphates.

The Calvin Cycle : The Calvin cycle has three stages. In stage 3, RuBP, the molecule that starts the cycle, is regenerated so that the cycle can continue.

Only one carbon dioxide molecule is incorporated at a time, so the cycle must be completed three times to produce a single three-carbon GA3P molecule, and six times to produce a six-carbon glucose molecule.

This is a reduction reaction because it involves the gain of electrons by 3-PGA. Recall that a reduction is the gain of an electron by an atom or molecule. Both of these molecules return to the nearby light-dependent reactions to be reused and reenergized. At this point, only one of the G3P molecules leaves the Calvin cycle and is sent to the cytoplasm to contribute to the formation of other compounds needed by the plant.

But each turn makes two G3Ps, thus three turns make six G3Ps. One is exported while the remaining five G3P molecules remain in the cycle and are used to regenerate RuBP, which enables the system to prepare for more CO 2 to be fixed. Reactants and Products. Leaf Structures. When you select "Subscribe" you will start receiving our email newsletter. Use the links at the bottom of any email to manage the type of emails you receive or to unsubscribe.

See our privacy policy for additional details. Learn Site. Chloroplasts have a complex internal structure, and different reactions take place in different parts of the chloroplast. The light-dependent reactions convert light energy into chemical energy.

External Sources Article from Scitable that details the internal structure of chloroplasts. Get our awesome anatomy emails! About News Contact. All Rights Reserved.

User Agreement Privacy Permissions. The basic equation for photosynthesis is deceptively simple. In reality, the process takes place in many steps involving intermediate reactants and products.

Glucose, the primary energy source in cells, is made from two three-carbon GA3Ps. Basic Photosynthetic Structures In plants, photosynthesis generally takes place in leaves, which consist of several layers of cells. Visual Connection. Photosynthesis takes place in chloroplasts, which have an outer membrane and an inner membrane. Stacks of thylakoids called grana form a third membrane layer.

The Two Parts of Photosynthesis Photosynthesis takes place in two sequential stages: the light-dependent reactions and the light-independent reactions. Photosynthesis takes place in two stages: light-dependent reactions and the Calvin cycle. Link to Learning. Everyday Connection. Foods that humans consume originate from photosynthesis. Section Summary The process of photosynthesis transformed life on Earth. Visual Connection Questions Figure On a hot, dry day, the guard cells of plants close their stomata to conserve water.

Review Questions Which of the following components is not used by both plants and cyanobacteria to carry out photosynthesis? What two main products result from photosynthesis?

Thylakoids are assembled into stacks. Thylakoids exist as a maze of folded membranes. The space surrounding thylakoids is called stroma. Thylakoids contain chlorophyll. They are both end products of photosynthesis. They are both substrates for photosynthesis. They are both produced from carbon dioxide. They both store energy in chemical bonds. Critical Thinking Questions What is the overall outcome of the light reactions in photosynthesis?

Why are carnivores, such as lions, dependent on photosynthesis to survive? Because lions eat animals that eat plants. ATP-It is a energy rich compound. The light energy is stored in it. It provides the energy for the formation of energy rich chemical bonds in glucose. Finally, it changed into ADP. Finally, it oxidised into NADP. Thank You B K Mishra.