Light Independent Stage

• What is the name of the cycle that occurs in the light-independent reaction?

  Calvin cycle
• Where does carbon dioxide come from before entering the Calvin cycle?

  It diffuses from the atmosphere through stomata
• Which enzyme catalyses the fixation of carbon dioxide to RuBP?

  Rubisco
• What is the first product formed when CO₂ reacts with RuBP?

  An unstable 6-carbon compound
• Why is the first product of the Calvin cycle described as unstable?

  It quickly breaks down into two GP molecules
• Describe the events in the Calvin cycle.

  1. CO₂ reacts with RuBP, catalysed by rubisco.
  2. Forms two 3-carbon molecules of GP.
  3. Reduced NADP and ATP convert GP to TP.
  4. Some TP is converted to organic substances.
  5. Some TP regenerates RuBP using ATP.
• How many carbons are in a glucose molecule?

  Six
• How many triose phosphate molecules are needed to make one glucose molecule?

  Two TP molecules
• What happens to most of the TP molecules after step 4 of the cycle?

  They are used to regenerate RuBP
• Why does the Calvin cycle need to regenerate RuBP?

  To continue accepting CO₂ for carbon fixation
• Describe the roles of ATP and reduced NADP in the light-independent reaction.

  • ATP provides energy for reducing GP to TP.
  • Reduced NADP donates hydrogen to GP to form TP.
• What is the final product of photosynthesis created in the Calvin cycle?

  Organic substances like glucose
• Where does ATP come from in the Calvin cycle?

  From the light-dependent reactions
• What will regenerate RuBP come into contact with in the stroma?

  TP molecules using ATP
• What does glycerate 3-phosphate (GP) get converted into?

  Triose phosphate (TP)
• Which molecules from the light-dependent reaction are needed for the conversion of GP to TP?

  ATP and reduced NADP
• Why does the Calvin cycle need to regenerate RuBP?

  To ensure enough RuBP for CO₂ fixation
• Describe the adaptations of the chloroplast for the Calvin cycle.

  • Stromal environment is separate from cytoplasm.
  • High concentration of enzymes and substrates in stroma.
  • Stroma bathes grana for quick diffusion of products.
• Where are the enzymes involved in the Calvin cycle found?

  In the stroma of the chloroplasts
• Why can't the Calvin cycle take place for long in the absence of light?

  It requires ATP and reduced NADP from light reactions
• What is photolysis, and what does it produce?

  Splitting of water producing protons, electrons, oxygen
• What is the role of NADP in the light-dependent reaction?

  It acts as an electron carrier
• Explain why photolysis of water is essential for the continuation of the light-dependent reaction.

  It provides electrons to replace those lost from chlorophyll
• Which photosystems are involved in the light-dependent reaction?

  Photosystem I and Photosystem II
• Name the two key energy-carrying molecules produced in the light-dependent reaction.

  ATP and reduced NADP
• What happens to NADPH after it donates its hydrogen?

  It is oxidised back to NADP
• Where does ADP go after being used in the Calvin cycle?

  It returns to the light-dependent reaction
• What is the role of ribulose bisphosphate (RuBP) in the Calvin cycle?

  It combines with CO₂ to produce GP
• How is reduced NADP from the light-dependent reaction used in the light-independent reaction?

  It reduces GP to triose phosphate
• Apart from reduced NADP, which other product of the light-dependent reaction is used in the light-independent reaction?

  ATP
• What is the significance of the light-independent reaction?

  It produces organic substances from CO₂
• What is the importance of the Calvin cycle in photosynthesis?

  It converts CO₂ into organic compounds
• How does the Calvin cycle contribute to plant growth?

  By synthesizing glucose and other organic molecules
• Why is the Calvin cycle considered light-independent?

  It does not directly require light energy
• How does the structure of chloroplasts facilitate the Calvin cycle?

  By providing a suitable environment for reactions
• What is the relationship between the light-dependent and light-independent reactions?

  Light-dependent reactions produce ATP and NADPH for the Calvin cycle
• How does the Calvin cycle ensure a continuous supply of RuBP?

  By regenerating RuBP from TP using ATP
• What is the significance of the high concentration of enzymes in the stroma?

  It facilitates efficient reactions in the Calvin cycle
• Why is the separation of the stromal environment from the cytoplasm beneficial?

  It prevents interference with Calvin cycle reactions
• How does the diffusion of products from the light-dependent reactions affect the Calvin cycle?

  It allows quick access to necessary substrates