Light-independent reactions

Definition

Light-independent reactions, also known as the Calvin Cycle, are the series of biochemical processes in photosynthesis that convert carbon dioxide and other compounds into glucose without the direct involvement of light energy. These reactions utilize ATP and NADPH produced during the light-dependent reactions to drive the fixation of carbon and ultimately synthesize carbohydrates, thus playing a crucial role in the overall process of photosynthesis.

5 Must Know Facts For Your Next Test

1. The light-independent reactions occur in the stroma of chloroplasts, where the environment is conducive for carbon fixation and synthesis of glucose.
2. Carbon dioxide enters the Calvin Cycle through a process known as carbon fixation, primarily involving the enzyme RuBisCO, which attaches CO2 to ribulose bisphosphate (RuBP).
3. ATP and NADPH generated from the light-dependent reactions are crucial for powering the Calvin Cycle and driving the synthesis of glucose from fixed carbon.
4. The end products of light-independent reactions are not limited to glucose; they also produce other carbohydrates like starch and sucrose, which serve as energy storage molecules.
5. The efficiency of light-independent reactions can be influenced by environmental factors such as temperature, light intensity, and availability of water, all affecting the overall rate of photosynthesis.

Review Questions

• How do light-independent reactions utilize products from light-dependent reactions to produce glucose?
  • Light-independent reactions use ATP and NADPH produced during the light-dependent reactions to facilitate the conversion of carbon dioxide into glucose. ATP provides the necessary energy while NADPH supplies electrons and protons needed for reducing carbon compounds. This process allows plants to synthesize glucose, which is vital for their growth and energy needs.
• Compare and contrast the roles of RuBisCO in light-independent reactions with that of chlorophyll in light-dependent reactions.
  • RuBisCO plays a critical role in light-independent reactions as it catalyzes the first step of carbon fixation by converting CO2 into organic molecules. In contrast, chlorophyll is essential for light-dependent reactions as it absorbs sunlight to generate ATP and NADPH. While RuBisCO is focused on incorporating carbon into usable forms, chlorophyll's primary function is capturing light energy to initiate photosynthesis.
• Evaluate how changes in environmental conditions can impact the efficiency of light-independent reactions and overall photosynthesis.
  • Changes in environmental conditions, such as increased temperature or decreased water availability, can significantly affect the efficiency of light-independent reactions. For instance, high temperatures can lead to increased rates of photorespiration due to excess oxygen competing with CO2 for RuBisCO's active site, reducing glucose production. Conversely, optimal conditions enable more efficient carbon fixation and enhance overall photosynthesis. Understanding these impacts is crucial for agricultural practices and managing plant growth in varying climates.

Related terms

Calvin Cycle: The Calvin Cycle is the specific set of light-independent reactions in photosynthesis that take place in the stroma of chloroplasts, where carbon fixation occurs.

RuBisCO:

RuBisCO is an enzyme that catalyzes the first major step of carbon fixation in the Calvin Cycle, helping to convert carbon dioxide into organic compounds.

NADPH:

NADPH is a reducing agent generated during the light-dependent reactions, providing electrons and protons for the reduction of carbon compounds in light-independent reactions.