Photosynthesis and respiration flashcards

Photosynthesis and respiration are complementary metabolic processes central to A-Level Biology. Photosynthesis occurs in chloroplasts and converts light energy into chemical energy stored in glucose, involving the light-dependent reactions in the thylakoid membranes and the light-independent Calvin cycle in the stroma. Respiration releases energy from organic molecules as ATP, occurring in all living cells. Aerobic respiration involves glycolysis in the cytoplasm, the link reaction, Krebs cycle, and oxidative phosphorylation in the mitochondria. Anaerobic respiration produces less ATP and generates lactate in animals or ethanol and carbon dioxide in plants and yeast. Students must understand the roles of coenzymes such as NAD and FAD, the chemiosmotic synthesis of ATP, the precise locations of each stage, and how environmental factors affect the rates of both processes.

1. Card 1

   Where do the light-dependent reactions of photosynthesis take place?

   They occur on the thylakoid membranes inside the chloroplast, where chlorophyll absorbs light energy to drive photolysis and ATP synthesis.

2. Card 2

   What is the role of photolysis in the light-dependent reactions?

   Photolysis is the splitting of water using light energy, releasing electrons, protons, and oxygen gas as a by-product, replenishing electrons lost from chlorophyll.

3. Card 3

   What happens during the Calvin cycle?

   The Calvin cycle fixes CO2 onto ribulose bisphosphate using RuBisCO, producing glycerate-3-phosphate, which is reduced using ATP and NADPH to form triose phosphate.

4. Card 4

   What is the function of NAD in respiration?

   NAD is a coenzyme that accepts hydrogen atoms during oxidation reactions, becoming reduced NADH, which later donates electrons to the electron transport chain to drive ATP synthesis.

5. Card 5

   In which part of the cell does glycolysis occur?

   Glycolysis takes place in the cytoplasm, converting one glucose molecule into two pyruvate molecules with a net gain of 2 ATP and 2 reduced NAD.

6. Card 6

   What happens during the link reaction in aerobic respiration?

   Pyruvate is decarboxylated and combined with coenzyme A to form acetyl coenzyme A, releasing CO2 and reducing NAD. It occurs in the mitochondrial matrix.

7. Card 7

   What are the products of one turn of the Krebs cycle?

   One turn produces 2CO2, 3 reduced NAD, 1 reduced FAD, and 1 ATP by substrate-level phosphorylation, regenerating the 4-carbon oxaloacetate acceptor.

8. Card 8

   How does chemiosmosis produce ATP during oxidative phosphorylation?

   Electrons from reduced NAD pass along the electron transport chain, pumping protons across the inner mitochondrial membrane; their return through ATP synthase drives ATP production.

9. Card 9

   What is the difference between cyclic and non-cyclic photophosphorylation?

   Non-cyclic photophosphorylation produces ATP, NADPH, and O2 using both photosystems; cyclic photophosphorylation uses only PSI, produces only ATP, and no NADPH or O2 is made.

10. Card 10

    What products are formed during anaerobic respiration in yeast?

    Yeast carries out alcoholic fermentation, converting pyruvate into ethanol and carbon dioxide, regenerating NAD so glycolysis can continue without oxygen.

11. Card 11

    Why is the inner mitochondrial membrane important for ATP synthesis?

    Its extensive cristae increase surface area for electron transport chain proteins and ATP synthase, and it is impermeable to protons, maintaining the proton gradient needed for chemiosmosis.

12. Card 12

    How does a limiting factor affect the rate of photosynthesis?

    A limiting factor such as light intensity, CO2 concentration, or temperature restricts the rate of photosynthesis even if other conditions are optimal, as it is in shortest supply.

• Many students incorrectly state that photosynthesis and respiration are opposites that cancel each other out, when in fact both processes occur simultaneously in plant cells at all times.
• A common error is claiming that ATP is stored as an energy reserve, when in fact ATP is a short-term energy currency that is continuously synthesised and hydrolysed and cannot be stockpiled.
• Students often confuse the location of the light-dependent and light-independent reactions, placing the Calvin cycle on the thylakoid membrane rather than correctly in the stroma of the chloroplast.

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