Name the major inputs and outputs of the Calvin cycle.
The Correct Answer and Explanation is:
Correct Answer:
Major inputs of the Calvin cycle:
- Carbon dioxide (CO₂)
- ATP
- NADPH
Major outputs of the Calvin cycle:
- Glucose (or more accurately, G3P – glyceraldehyde-3-phosphate)
- ADP
- NADP⁺
- Inorganic phosphate (Pi)
Explanation:
The Calvin cycle is a set of biochemical reactions that occur in the stroma of chloroplasts in photosynthetic organisms. It is also known as the light-independent or dark reactions because it does not require light directly. The Calvin cycle uses the products of the light-dependent reactions to fix carbon dioxide into organic molecules.
The main inputs to the Calvin cycle are carbon dioxide (CO₂), ATP, and NADPH. Carbon dioxide enters the plant through small openings called stomata. ATP and NADPH are energy-rich molecules produced during the light-dependent reactions of photosynthesis. They provide the energy and reducing power needed to convert carbon dioxide into sugar.
The cycle begins with the fixation of carbon dioxide by the enzyme RuBisCO, which attaches it to a five-carbon sugar called ribulose bisphosphate (RuBP). This reaction forms an unstable six-carbon compound that quickly breaks into two molecules of 3-phosphoglycerate (3-PGA). Through a series of reactions, ATP and NADPH are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P), a three-carbon sugar.
Some G3P molecules leave the cycle and can eventually be used to form glucose and other carbohydrates. The rest of the G3P molecules are used to regenerate RuBP so the cycle can continue. This regeneration step also uses ATP.
The outputs of the Calvin cycle include G3P (used to make glucose), ADP, NADP⁺, and inorganic phosphate. ADP and NADP⁺ return to the light-dependent reactions to be recharged into ATP and NADPH.
In summary, the Calvin cycle is essential for synthesizing sugars from carbon dioxide. It relies on the energy and electrons provided by ATP and NADPH and produces energy-storing carbohydrates that plants and other organisms use as fuel.
