The Calvin cycle and the light-dependent reactions are two distinct processes involved in photosynthesis, which occurs in plants, algae, and some bacteria. Here are the key differences between them:
Location
- Light-Dependent Reactions: These reactions occur in the thylakoid membranes of the chloroplasts.
- Calvin Cycle: This cycle takes place in the stroma of the chloroplasts.
Requirements
- Light-Dependent Reactions: These reactions require light energy, which is captured by chlorophyll and other pigments.
- Calvin Cycle: This cycle does not require light directly; it uses the products of light-dependent reactions (ATP and NADPH) to drive the synthesis of glucose.
Main Inputs
- Light-Dependent Reactions: The main inputs are light, water (H₂O), and ADP + Pi (inorganic phosphate).
- Calvin Cycle: The main inputs are carbon dioxide (CO₂), ATP, and NADPH.
Main Outputs
- Light-Dependent Reactions: The primary outputs are oxygen (O₂), ATP, and NADPH.
- Calvin Cycle: The main outputs are glucose (or other carbohydrates), ADP, and NADP⁺.
Purpose
- Light-Dependent Reactions: The purpose is to convert light energy into chemical energy in the form of ATP and NADPH while releasing oxygen as a byproduct.
- Calvin Cycle: The purpose is to synthesize organic compounds (like glucose) from carbon dioxide using the chemical energy stored in ATP and NADPH from the light-dependent reactions.
Energy Conversion
- Light-Dependent Reactions: This process involves the conversion of solar energy into chemical energy.
- Calvin Cycle: This process involves the conversion of chemical energy (from ATP and NADPH) into stable organic compounds.
In summary, while the light-dependent reactions initiate the process of photosynthesis by converting light energy into chemical energy, the Calvin cycle uses that stored energy to fix carbon dioxide and synthesize carbohydrates.
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