Photosynthesis Flashcards
Q: How do plants use solar energy to fix atmospheric CO₂ into carbohydrates?
A:
Plants capture light energy in the light reactions of photosynthesis to produce ATP and NADPH, which are then used in the Calvin cycle (dark reactions) to fix CO₂ into 3-carbon sugars, eventually forming carbohydrates like glucose.
Q: What is the function of chlorophyll and carotenoids in photosynthesis?
A:
Chlorophyll absorbs light (mainly blue and red wavelengths) and transfers energy to the reaction centers in photosystems.
Carotenoids expand the range of light absorbed and protect chlorophyll from damage caused by excess light (photoprotection).
Q: What is the ‘Z’ scheme in photosynthesis?
A:
The Z scheme describes the flow of electrons through Photosystem II and Photosystem I, leading to the generation of ATP (via chemiosmosis) and NADPH, and the evolution of oxygen from water.
Q: How are ATP and NADPH made in the light reactions?
A:
ATP is made by photophosphorylation using the proton gradient created during electron transport.
NADPH is produced when electrons are transferred from Photosystem I to NADP⁺ via ferredoxin.
Q: How is oxygen evolved during photosynthesis?
A:
Oxygen is produced when water is split (photolysis) by Photosystem II, releasing electrons, protons, and O₂ as a by-product.
Q: What is the Calvin cycle and how was it discovered?
A:
The Calvin cycle (dark reactions) fixes CO₂ using RuBisCO and produces sugars using ATP and NADPH. It was discovered using radioactive carbon tracing by Melvin Calvin.`
Q: What are the basic reactions in C₃, C₄, and CAM metabolism?
A:
C₃ plants: CO₂ is fixed directly by RuBisCO in the Calvin cycle.
C₄ plants: CO₂ is first fixed into a 4-carbon compound in mesophyll cells, then released in bundle sheath cells for the Calvin cycle.
CAM plants: CO₂ is fixed at night and stored as malate, then used during the day in the Calvin cycle.
Q: What is the role of RuBisCO in photosynthesis?
A:
RuBisCO is the enzyme that fixes CO₂ by attaching it to RuBP in the first step of the Calvin cycle. It’s the most abundant enzyme on Earth and can also catalyze oxygenation, leading to photorespiration.
What do antenna pigments do?
Extend the range of light capture, especially in green
Z scheme
light hits PSII, electrons in chlorophyll get excited moves to higher energy levels, water is split to replace electrons, electrons travel down ETC through PQ cytochrome bf complex, protons pumped into thylakoid lumen, generate ATP,, light hits PSI 700, re-excited electrons, move to higher energy level, electrons paas ed to ferredoxin used to reduce NADP to NADPH
Q: What is the role of ferredoxin in photosynthesis?
A:
Ferredoxin is a small iron-sulfur protein that accepts electrons from Photosystem I and transfers them to ferredoxin–NADP⁺ reductase (FNR), helping to form NADPH for the Calvin cycle.
Explain H+/ATP synthase
when electrons move in ETC, protons are pumped into the thylakoid lumen, theres a higher conc in lumen than stroma, Protons flow back into stroma through atp synthase, using this energy to attach Pi to adp, forming ATP
Q: How does C₄ photosynthesis improve RuBisCO efficiency?
A:
C₄ photosynthesis protects RuBisCO from binding oxygen (which causes photorespiration) by initially fixing CO₂ with PEP carboxylase in mesophyll cells. The CO₂ is then concentrated and delivered to RuBisCO in bundle sheath cells, where it can work efficiently in a high-CO₂, low-O₂ environment.
Q: What is CAM photosynthesis and how does it help RuBisCO work efficiently?
A:
CAM (Crassulacean Acid Metabolism) is a water-saving form of photosynthesis where CO₂ is taken in at night and stored as organic acids. During the day, stomata stay closed, and CO₂ is released internally for RuBisCO to use in the Calvin cycle. This keeps RuBisCO active while minimizing water loss in hot, dry environments.
