Light-independent reactions

Definition

Light-independent reactions, often referred to as the Calvin Cycle, are biochemical processes that occur in the stroma of chloroplasts where carbon dioxide is fixed and converted into glucose using energy derived from ATP and NADPH produced in the light-dependent reactions. These reactions are essential for synthesizing organic compounds from inorganic carbon sources, contributing significantly to the overall process of photosynthesis.

5 Must Know Facts For Your Next Test

1. Light-independent reactions do not require light directly but rely on the products (ATP and NADPH) generated from light-dependent reactions.
2. The main enzyme involved in carbon fixation during these reactions is RuBisCO, which catalyzes the first step of the Calvin Cycle.
3. The Calvin Cycle occurs in three main stages: carbon fixation, reduction phase, and regeneration of ribulose bisphosphate (RuBP).
4. Glucose and other carbohydrates produced from light-independent reactions serve as energy sources for plants and are crucial for growth and development.
5. These reactions play a vital role in maintaining atmospheric balance by utilizing CO2 and producing organic matter.

Review Questions

• How do light-independent reactions depend on the products of light-dependent reactions in photosynthesis?
  • Light-independent reactions rely heavily on the products generated during light-dependent reactions, specifically ATP and NADPH. These two molecules provide the necessary energy and reducing power required for converting carbon dioxide into glucose through the Calvin Cycle. Without the input of ATP and NADPH from the light-dependent phase, the light-independent reactions would not be able to synthesize organic compounds efficiently.
• Discuss the significance of RuBisCO in light-independent reactions and its impact on global carbon cycling.
  • RuBisCO is the enzyme that plays a crucial role in the carbon fixation process during light-independent reactions. It catalyzes the reaction between CO2 and ribulose bisphosphate (RuBP), making it essential for incorporating atmospheric carbon into organic molecules. This process not only helps sustain plant life but also significantly impacts global carbon cycling by sequestering CO2 from the atmosphere, thus influencing climate change dynamics.
• Evaluate how disruptions in light-independent reactions can affect plant metabolism and ecosystem stability.
  • Disruptions in light-independent reactions can severely affect plant metabolism as they hinder the synthesis of glucose and other carbohydrates, essential for energy storage and growth. If plants are unable to produce these organic compounds effectively, it can lead to reduced biomass and diminished food availability for herbivores. This imbalance can cascade through ecosystems, disrupting food chains and impacting biodiversity as well as ecosystem stability, highlighting the critical role these reactions play in sustaining life on Earth.

Related terms

Calvin Cycle:

A series of biochemical reactions that take place in the stroma of chloroplasts, where carbon dioxide is fixed into organic molecules.

Carbon Fixation: The process of converting inorganic carbon (CO2) into organic compounds, primarily during the Calvin Cycle.

ATP Synthase:

An enzyme that creates ATP from ADP and inorganic phosphate, playing a critical role in energy production during photosynthesis.