Photosynthesis Flashcards
Outline the two main stages of photosynthesis and their locations within the chloroplast.
- Light-dependent reactions occur in the thylakoid membranes. These involve photolysis of water, production of ATP, and reduction of NADP.
- Light-independent reactions (Calvin cycle) occur in the stroma, where CO₂ is fixed into glucose using ATP and reduced NADP.
Describe the role of chlorophyll in photosynthesis.
Chlorophyll absorbs light energy, exciting electrons to a higher energy level. These high-energy electrons are transferred through the electron transport chain, driving ATP synthesis.
Explain the importance of ATP and reduced NADP in the Calvin cycle.
ATP provides the energy for the conversion of 3-phosphoglycerate (GP) to triose phosphate (TP). Reduced NADP donates hydrogen for reducing GP to TP.
What is the significance of photolysis of water during the light-dependent reactions?
Photolysis splits water molecules into oxygen, protons (H⁺), and electrons. The electrons replace those lost by chlorophyll in photosystem II, and the protons contribute to the proton gradient used to generate ATP.
Explain why the rate of photosynthesis plateaus at high light intensities.
At high light intensities, another factor (e.g., CO₂ concentration or temperature) becomes limiting, preventing further increase in the rate of photosynthesis.
Explain how artificial lighting and CO₂ enrichment increase crop yields.
Artificial lighting extends the duration of light-dependent reactions, increasing ATP and reduced NADP production. CO₂ enrichment ensures the Calvin cycle operates at maximum efficiency, producing more glucose.
Predict the effect of a herbicide that inhibits RuBisCO activity on photosynthesis.
RuBisCO catalyzes CO₂ fixation in the Calvin cycle. Inhibiting RuBisCO would stop the production of GP, halting the Calvin cycle and reducing glucose synthesis.
Suggest a method for investigating the effect of different wavelengths of light on photosynthesis.
- Use an aquatic plant like Elodea in a solution of sodium bicarbonate.
- Expose the plant to lights of different wavelengths using colored filters.
- Measure oxygen production (using a gas syringe) or the rate of bubble formation as an indicator of photosynthesis.
Explain why high temperatures affect the rate of photosynthesis.
High temperatures denature enzymes (e.g., RuBisCO) involved in the Calvin cycle, reducing CO₂ fixation. Membrane integrity of the chloroplast may also be disrupted.
Interpret data on oxygen production under different conditions.
Oxygen production is linked to the light-dependent reactions. An increase in oxygen correlates with higher rates of photolysis, while a plateau suggests a limiting factor like CO₂ or temperature.
Explain the stages of the light-dependent reaction.
- Light excites electrons in chlorophyll (photosystem II), which are transferred to an electron transport chain.
- Energy from the electrons pumps H⁺ ions into the thylakoid lumen.
- ATP is synthesized via chemiosmosis as H⁺ ions diffuse through ATP synthase.
- Electrons reach photosystem I, are re-excited, and reduce NADP to form reduced NADP.
- Water is split (photolysis) to replace lost electrons.
Describe the Calvin cycle and its role in glucose synthesis.
- CO₂ combines with ribulose bisphosphate (RuBP), catalyzed by RuBisCO, forming two GP molecules.
- GP is reduced to TP using ATP and reduced NADP.
- Some TP is used to regenerate RuBP; the rest is converted to glucose.
Discuss how limiting factors affect the rate of photosynthesis.
Light intensity provides energy for the light-dependent reactions. Low intensity reduces ATP and NADPH production. CO₂ concentration limits the Calvin cycle as RuBisCO cannot fix sufficient CO₂ at low concentrations. Temperature affects enzyme activity, particularly RuBisCO. Too high or low reduces efficiency.
Compare photosynthesis and respiration in terms of energy transfer.
Photosynthesis is anabolic, storing energy in glucose molecules, while respiration is catabolic, releasing energy from glucose. ATP is synthesized in both processes, but photosynthesis occurs in chloroplasts, whereas respiration occurs in mitochondria.
Explain how chloroplast structure relates to function.
Thylakoid membranes provide a large surface area for light absorption and electron transport. Stroma contains enzymes for the Calvin cycle. Grana increase efficiency by stacking thylakoids for light capture.
