Cycle 4 Flashcards by Diya Vyas

Q: What is photosynthesis?

A: The light-dependent reduction of CO₂ to carbohydrate.

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Q: Why is there very little algae growth in the ocean around the equator?

A: There are not enough nutrients, specifically iron, which is fundamental for growth.

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Q: How much CO₂ is fixed globally each year, and how is it split?

A: 100 Gt/year; half is terrestrial, and the other half is aquatic.

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Q: What type of molecules does biology primarily build on?

A: Reduced molecules like carbohydrates, fats, amino acids, and nucleotides.

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Q: What happens to CO₂ and H₂O during photosynthesis?

A: CO₂ is reduced to glucose and H₂O is oxidized to O₂

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Q: What is the balanced equation for photosynthesis?

6CO2+6H2O -> C6H12O6 + 6O2

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Q: Why is photosynthesis an endergonic reaction (+ΔG)?

A: Products like glucose have higher free energy due to their higher enthalpy and organized, solid state compared to CO₂.

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Q: What is the primary pigment in photosynthesis, and how does it work?

A: Chlorophyll absorbs light, exciting electrons to a higher energy state (e.g., P680 to P680*).

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Q: What is P680+ and why is it important?

A: It is the strongest oxidizing molecule in biology and oxidizes water to release O₂ into the atmosphere.

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Q: What are the two key products of light reactions, and their functions?

A: ATP (drives endergonic reactions) and NADPH (provides reducing power to form C-H bonds).

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Q: How is the thylakoid lumen affected under light conditions?

A: It becomes more acidic (more H⁺) due to proton pumping during electron transport.

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Q: What are the three phases of the Calvin Cycle?

1) Fixation: CO₂ is fixed to RuBP.
2) Reduction: G3P is produced using ATP and NADPH.
3) Regeneration: RuBP is regenerated for the next cycle.

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Q: How many turns of the Calvin Cycle are needed to produce one glucose?

A: Six turns (3 turns make 1 G3P, and 2 G3P form 1 glucose).

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Q: What evolutionary advantage does oxygenic photosynthesis have over anoxygenic photosynthesis?

A: The ability to use water as an electron donor, which is abundant compared to rare donors like H₂S and Fe²⁺.

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Q: What happens to PS2 under high light conditions, and how is it repaired?

A: PS2 is damaged every 20 minutes, primarily the D1 protein. Chloroplast translation synthesizes new D1 proteins to replace the damaged ones.

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❓ Do chlamydomonas (Chlamy) have mitochondria?

✅ Yes, they have both mitochondria and chloroplasts.

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❓ Why does cellular respiration drive molecules to an oxidized state?

✅ To extract energy from the molecules.

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❓ Do both heterotrophs and autotrophs perform cellular respiration?

✅ Yes, both need to drive the reaction back to extract energy.

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❓ What are the three major stages of cellular respiration?

✅ Glycolysis, Pyruvate Oxidation/Citric Acid Cycle, Oxidative Phosphorylation.

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❓ Why can’t cells use reduced carbon directly?

✅ Glucose doesn’t bind to enzymes directly; ATP is needed to drive reactions.

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❓ In what two ways is ATP made?

Substrate-level phosphorylation
Oxidative phosphorylation (produces way more ATP!)

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❓ Where does glycolysis occur?

✅ In the cytoplasm, not the mitochondria.

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❓ What is the starting and ending molecule of glycolysis?

✅ Start: Glucose (6C)
✅ End: 2 Pyruvate (3C each)

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❓ How much ATP and NADH does glycolysis produce?

✅ Net 2 ATP (via substrate-level phosphorylation), 2 NADH.

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❓ Does glycolysis require oxygen?

✅ No, glycolysis is anaerobic.

❓ How does carbon flow in glycolysis?

✅ Glucose (6C) → 2 Pyruvate (3C each)

❓ Where does pyruvate oxidation and the citric acid cycle occur?

✅ In the mitochondrial matrix.

❓ What is the starting and ending molecule of this stage?

✅ Start: Pyruvate → Acetyl-CoA ✅ End: CO₂

❓ How much ATP, NADH, and FADH₂ are produced?

✅ 2 ATP, 6 NADH, 2 FADH₂.

❓ How does carbon flow in this stage?

✅ Acetyl-CoA (2C) → CO₂

❓ Does this stage require oxygen?

✅ Indirectly (O₂ is needed for the electron transport chain to function).

❓ What is the starting and ending molecule of this stage?

✅ Start: NADH, FADH₂ ✅ End: ATP, H₂O

❓ Where does oxidative phosphorylation occur?

✅ In the inner mitochondrial membrane.

❓ How much ATP is produced?

✅ ~32-34 ATP (via ATP synthase).

❓ Does this stage require oxygen?

✅ Yes! O₂ is the final electron acceptor, forming H₂O.

❓ What happens to carbon in this stage?

✅ No carbon remains; it was all released as CO₂.

❓ What are the main compartments of the mitochondria?

Outer mitochondrial membrane Inner mitochondrial membrane Intermembrane space Matrix

❓ Where are protons pumped during cellular respiration?

✅ Into the intermembrane space.

❓ Where is ATP synthase located?

✅ In the inner mitochondrial membrane.

❓ What happens to enthalpy and entropy during respiration?

✅ Enthalpy decreases, entropy increases.

❓ Did cellular respiration evolve in bacteria?

✅ Yes, many bacteria can break down molecules to extract energy.

❓ Is cellular respiration exergonic or endergonic?

✅ Exergonic (Releases energy, ΔG is negative).

❓ Which molecule has more free energy: Glucose or CO₂?

✅ Glucose has higher free energy than CO₂.

❓ Which molecule is oxidized and which is reduced in respiration?

Glucose is oxidized to CO₂ O₂ is reduced to H₂O

❓ What is catabolism?

✅ Breaking down molecules to release energy (ex: cellular respiration).

❓ What is anabolism?

✅ Building complex molecules from simple ones (ex: photosynthesis).

❓ Which molecule is associated with catabolic pathways?

✅ NADH.

❓ Which molecule is associated with anabolic pathways?

✅ NADPH.

❓ What happens to ATP and ADP levels when oxygen is low?

ATP decreases (cells can’t make enough). ADP increases (sign of oxygen deprivation).

❓ What is biosynthesis?

✅ Anabolic process of making complex molecules from simple ones.

❓ Why does oxygen deprivation cause ATP levels to drop?

✅ Oxidative phosphorylation requires oxygen to function.

❓ At the end of oxidative phosphorylation, is there carbon left?

✅ No, all carbon has been released as CO₂.

❓ What are the key molecules in oxidative phosphorylation?

✅ NADH and FADH₂.

❓ What is the goal of oxidative phosphorylation?

✅ Convert free energy from NADH/FADH₂ into ATP.

❓ What is oxidized and what is phosphorylated?

✅ NADH/FADH₂ are oxidized, and ADP is phosphorylated.

❓ What is the actual product of the electron transport chain (ETC)?

✅ H₂O, NOT ATP.

❓ What process couples electron transport and ATP synthesis?

✅ Chemiosmosis (proton gradient powers ATP synthase).

❓ Why are protons used in the gradient? (2)

1) They create an electrochemical gradient. 2) Water is everywhere, so protons are readily available.

❓ What is the final product of the photosynthetic electron transport chain?

✅ NADPH (needed for the Calvin cycle).

❓ Why do electrons move in the ETC?

✅ NADH is easy to oxidize (donates electrons), and complexes have increasing affinity for electrons as they move down.

❓ Why is oxygen required for the ETC?

✅ Oxygen is the terminal electron acceptor (has the highest affinity for electrons).

❓ Why is iron needed in the ETC?

✅ Iron is part of redox-active cofactors that transfer electrons.

❓ What is the main function of the respiratory ETC?

✅ Proton pumping to generate ATP.

❓ What is the final product of the respiratory electron transport chain?

✅ H₂O (not needed by the cell, just a byproduct).

❓ What happens if protons bypass ATP synthase?

✅ No ATP is made, but high electron transport rates occur.

❓ What are uncoupling proteins (UCP1, 2, 3)?

✅ Proteins in the membrane that control proton flow, used for heat generation.

❓ Why do newborns and hibernating animals have high UCP expression?

✅ To generate heat instead of ATP for survival.

❓ What are uncoupling pills used for, and why are they dangerous?

✅ Used as fat burners but can be toxic.

❓ What happens when chemical uncouplers are used?

✅ They carry protons across the membrane, preventing ATP synthesis.

❓ What is the Warburg Effect?

✅ Cancer cells only use glycolysis, even when oxygen is present.

❓ What happens to pyruvate after glycolysis if oxygen is available?

✅ It enters the mitochondria for further processing.

❓ What happens to pyruvate under low oxygen conditions?

✅ It remains in the cytoplasm and undergoes fermentation.

❓ How does the cell know if there is enough oxygen?

1) Pyruvate dehydrogenase complex acts as a gatekeeper. 2) Pyruvate dehydrogenase kinase blocks pyruvate entry under low O₂.

❓ Why do cancer cells prefer glycolysis over oxidative phosphorylation? (2)

1) Glycolysis produces ATP faster (even if less efficient). 2) Tumors often have limited oxygen supply.