Calvin cycle

Definition

The Calvin cycle is a series of biochemical reactions that occur in the stroma of chloroplasts, where carbon dioxide is fixed into organic molecules using energy derived from ATP and NADPH, produced during the light-dependent reactions of photosynthesis. This cycle plays a crucial role in converting light energy into chemical energy in the form of glucose, which is essential for the survival and growth of plants and other photosynthetic organisms.

5 Must Know Facts For Your Next Test

1. The Calvin cycle does not directly require light; however, it relies on ATP and NADPH produced from the light-dependent reactions.
2. The cycle consists of three main phases: carbon fixation, reduction, and regeneration of RuBP.
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 Calvin cycle occurs in the stroma of chloroplasts, making it separate from the light-dependent reactions that take place in the thylakoid membranes.
5. The entire process of the Calvin cycle must turn three times to produce one molecule of G3P, requiring a total of nine ATP and six NADPH.

Review Questions

• How does the Calvin cycle utilize products from the light-dependent reactions, and what is its significance in the overall process of photosynthesis?
  • The Calvin cycle utilizes ATP and NADPH generated during the light-dependent reactions to drive the conversion of carbon dioxide into organic molecules. By harnessing this energy, the cycle synthesizes glucose and other carbohydrates necessary for plant growth and energy storage. This process is vital as it transforms solar energy captured by plants into a stable form that can be used by various organisms within the ecosystem.
• Discuss the role of RuBisCO in the Calvin cycle and explain why it is considered one of the most abundant enzymes on Earth.
  • RuBisCO is a crucial enzyme in the Calvin cycle responsible for catalyzing the reaction between carbon dioxide and ribulose bisphosphate (RuBP), initiating carbon fixation. Its abundance can be attributed to its essential function in facilitating photosynthesis across diverse plant species. Given that photosynthesis is foundational for life on Earth by providing food and oxygen, RuBisCO's widespread presence underscores its importance in global ecosystems.
• Evaluate how environmental factors such as light intensity and carbon dioxide concentration affect the efficiency of the Calvin cycle in plants.
  • The efficiency of the Calvin cycle is directly influenced by environmental conditions like light intensity and carbon dioxide concentration. Higher light intensity increases ATP and NADPH production during light-dependent reactions, leading to more efficient carbon fixation. Similarly, elevated levels of carbon dioxide enhance RuBisCO activity, boosting overall glucose production. However, extreme conditions such as high temperatures can lead to photorespiration, which decreases efficiency. Thus, understanding these dynamics helps explain how plants adapt to their environments.

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.

Light-Dependent Reactions: The initial phase of photosynthesis that captures sunlight to produce ATP and NADPH, which are used in the Calvin cycle to convert carbon dioxide into glucose.

RuBisCO: An enzyme that catalyzes the first step of the Calvin cycle by fixing carbon dioxide to ribulose bisphosphate (RuBP), playing a key role in carbon fixation.