Calvin-Benson Cycle

Definition

The Calvin-Benson Cycle, also known simply as the Calvin Cycle, is a series of biochemical reactions that occur in the chloroplasts of photosynthetic organisms, where carbon dioxide is fixed into organic molecules. This process is crucial for converting inorganic carbon into organic forms that can be utilized by living organisms, playing a key role in photosynthesis and the global carbon cycle.

5 Must Know Facts For Your Next Test

1. The Calvin-Benson Cycle occurs in three main phases: carbon fixation, reduction, and regeneration of ribulose bisphosphate (RuBP).
2. The cycle uses ATP and NADPH generated from the light-dependent reactions of photosynthesis to convert carbon dioxide into glucose.
3. The enzyme RuBisCO plays a critical role in fixing atmospheric CO2 by attaching it to RuBP, ultimately forming 3-phosphoglycerate (3-PGA).
4. For every three molecules of CO2 that enter the cycle, one molecule of glyceraldehyde-3-phosphate (G3P) is produced, which can be converted into glucose or other carbohydrates.
5. The Calvin Cycle must turn six times to produce one molecule of glucose since it takes six carbon atoms to create one glucose molecule from CO2.

Review Questions

• How does the Calvin-Benson Cycle contribute to the overall process of photosynthesis?
  • The Calvin-Benson Cycle is essential to photosynthesis as it takes the energy captured from sunlight and converts atmospheric carbon dioxide into organic compounds. This cycle relies on ATP and NADPH produced during the light-dependent reactions. By fixing carbon dioxide and transforming it into glucose and other carbohydrates, the cycle provides the energy source for plants and, ultimately, all life on Earth.
• Discuss the importance of RuBisCO in the Calvin-Benson Cycle and how its efficiency impacts photosynthesis.
  • RuBisCO is crucial for the Calvin-Benson Cycle because it catalyzes the first step of carbon fixation. Its efficiency directly affects how well plants can perform photosynthesis. If RuBisCO operates efficiently, more CO2 is fixed into organic molecules, leading to higher glucose production. Conversely, low efficiency can lead to reduced carbohydrate synthesis and lower plant productivity.
• Evaluate how changes in environmental factors such as CO2 concentration and light intensity can influence the rate of the Calvin-Benson Cycle.
  • Environmental factors like CO2 concentration and light intensity significantly affect the rate of the Calvin-Benson Cycle. Higher CO2 levels can increase the rate of carbon fixation if other conditions are favorable, enhancing plant growth and productivity. Meanwhile, increased light intensity boosts ATP and NADPH production during light reactions, providing more energy for the Calvin Cycle. However, excessive light can lead to photoinhibition, negatively impacting photosynthesis. Therefore, understanding these interactions is vital for optimizing plant health and crop yields.

Related terms

Photosynthesis: The process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose, using carbon dioxide and water.

RuBisCO: Ribulose bisphosphate carboxylase/oxygenase, an enzyme that catalyzes the first major step of carbon fixation in the Calvin-Benson Cycle.

NADPH:

Nicotinamide adenine dinucleotide phosphate, a cofactor used in anabolic reactions, providing the reducing power necessary for the synthesis of glucose in the Calvin Cycle.