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Describe the overall changes in matter that occur during the light-independent reactions. What does the plant start with and what does it end with? What is the source of energy that powers this change?

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The light-independent reactions, also known as the Calvin Cycle, occur in the stroma of chloroplasts and do not directly require light to proceed, although they are closely tied to the energy produced during the light-dependent reactions.

Starting Materials: The primary inputs into the light-independent reactions are:

  1. Carbon dioxide (CO2) from the atmosphere.
  2. ATP and NADPH produced during the light-dependent reactions.

Changes in Matter: During the Calvin Cycle, carbon dioxide is assimilated and fixed into organic compounds. The cycle involves several key steps:

  1. Carbon Fixation: CO2 is captured by ribulose bisphosphate (RuBP) in a reaction catalyzed by the enzyme Rubisco, resulting in a 6-carbon intermediate that is quickly converted into two molecules of 3-phosphoglycerate (3-PGA).
  2. Reduction Phase: The 3-PGA molecules are then phosphorylated by ATP and converted into glyceraldehyde-3-phosphate (G3P) using the reducing power of NADPH. This step is where the captured energy from the light-dependent reactions is utilized.
  3. Regeneration of RuBP: Some G3P molecules go on to form glucose and other carbohydrates, while the remaining G3P is used to regenerate RuBP, allowing the cycle to continue.

Ending Materials: At the end of the Calvin Cycle, the plant can produce:

  1. Glyceraldehyde-3-phosphate (G3P), which can be further synthesized into glucose and other carbohydrates.
  2. ADP and NADP+, which are recycled back to the light-dependent reactions to be re-energized.

Energy Source: The source of energy that powers the changes during the light-independent reactions comes from ATP and NADPH, both of which are generated during the light-dependent reactions of photosynthesis. ATP provides the energy needed for the phosphorylation and conversion processes, while NADPH provides the electrons and reducing power necessary for the transformation of 3-PGA into G3P.

In summary, the overall changes in matter during the light-independent reactions involve the conversion of carbon dioxide and energy-rich molecules (ATP and NADPH) into organic molecules (like G3P and ultimately glucose), while also recycling the components needed to sustain the cycle.