Calvin Cycle

Definition

The Calvin Cycle is a series of biochemical reactions that take place in the stroma of chloroplasts in photosynthetic organisms, primarily plants. It is part of the light-independent reactions of photosynthesis, where carbon dioxide is fixed into organic molecules, ultimately producing glucose. This cycle plays a crucial role in energy conversion and carbon fixation, linking light energy captured during photosynthesis to the synthesis of carbohydrates.

5 Must Know Facts For Your Next Test

1. The Calvin Cycle occurs in three main stages: carbon fixation, reduction, and regeneration of ribulose bisphosphate (RuBP).
2. The cycle uses ATP and NADPH generated during the light-dependent reactions to convert carbon dioxide into glucose.
3. For every three molecules of carbon dioxide that enter the cycle, one molecule of glyceraldehyde-3-phosphate (G3P) is produced, which can eventually be converted into glucose.
4. The enzyme RuBisCO is critical for the first step of the Calvin Cycle and is considered one of the most abundant proteins on Earth.
5. The entire cycle must turn six times to produce one molecule of glucose, incorporating six carbon dioxide molecules into the process.

Review Questions

• Explain how the Calvin Cycle contributes to the overall process of photosynthesis and why it is considered light-independent.
  • The Calvin Cycle contributes to photosynthesis by utilizing ATP and NADPH produced in the light-dependent reactions to fix carbon dioxide into organic molecules. Although it does not require light directly, it relies on the energy carriers generated during light absorption. This process allows plants to convert atmospheric carbon into glucose, which serves as an energy source for growth and development.
• Discuss the significance of RuBisCO in the Calvin Cycle and its impact on global carbon cycling.
  • RuBisCO is significant in the Calvin Cycle as it catalyzes the initial step of carbon fixation by converting carbon dioxide and ribulose bisphosphate into 3-phosphoglycerate. Its abundance makes it a key player in global carbon cycling, influencing how efficiently plants can utilize atmospheric CO2. The enzyme's efficiency can affect plant productivity and, consequently, terrestrial ecosystems' ability to sequester carbon.
• Evaluate how variations in environmental conditions might affect the efficiency of the Calvin Cycle and subsequent plant growth.
  • Variations in environmental conditions such as temperature, light intensity, and CO2 concentration can significantly impact the efficiency of the Calvin Cycle. High temperatures may lead to increased respiration rates that outpace photosynthesis, while low CO2 levels can limit RuBisCO activity and reduce carbon fixation. Understanding these factors helps assess how climate change may influence plant growth and productivity in different ecosystems.

Related terms

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

RuBisCO: Ribulose bisphosphate carboxylase/oxygenase, an enzyme that catalyzes the first step of the Calvin Cycle by fixing carbon dioxide.

NADPH: Nicotinamide adenine dinucleotide phosphate, an electron carrier that provides the reducing power for the Calvin Cycle.