respiration impt questions

Question 1

qn: Explain why less glucose is required to maintain cell metabolism under aerobic conditions than under anaerobic condition? [3m]

Answer 1

1. Under aerobic conditions, complete breakdown of glucose produces 38 ATP* molecules per glucose molecule as compared to 2 ATP* molecules in anaerobic respiration
2. Under aerobic conditions, link reaction* and Krebs cycle* produce NADH* that will be oxidised and hence regenerated by the electron transport chain* during oxidative phosphorylation*, generating additional ATP;
3. However, under anaerobic conditions, glycolysis only produces a net of 2 ATP molecules* for each glucose molecule oxidized and NAD+* and is only regenerated through fermentationprocesses to allow only glycolysis* to continue.

Question 2

Describe the role of oxygen in oxidative phosphorylation [3m]

Answer 2

1. Oxygen is final electron acceptor* at the end of electron transport chain*, where it will combine with electrons and protons to form water (accept: 2e─ + 2H+ + ½O2 H2O);
2. By removing electrons, oxygen re-oxidises electron transport chain so that NADH* and FADH2can continue to donate electrons to the chain, thereby allowing oxidative phosphorylation** to continue to produce ATP;
3. This allows regeneration* of NAD+* and FAD* allowing them to pick up more electrons and protons from glycolysis, link reaction and Krebs cycle* to keep them going;

Question 3

Explain how the rate of glycolysis may be regulated by PFK enzyme [3]

Answer 3

1. (low levels of ATP promote PFK activity); When ATP* levels are high, it will bind to allosteric site of PFK;
2. This alters 3-D conformation* of enzyme’s active site, such that its substrate is no longer complementary in shape and charge* to active site, and this stabilises the inactive conformation of PFK which will have a lower affinity for substrate;
3. resulting in a decrease in rate of glycolysis due to end-product inhibition;

Question 4

Describe how the proton gradient that drives ATP synthesis is produced. [2]

(note: rmb to emphasise on the impermeability of the membrane( specifically what membrane?) –> allow for accumulation of H+ )

Answer 4

1. As NADH and FADH2 transfer electrons, electrons travel down the electron transport chain*; energy released is coupled to pumping of H+ from matrix of mitochondrion into intermembrane space;

(!!!!!) 2. cristae* is impermeable to H+ causing H+ to accumulate, creating a proton gradient across cristae;

3. H+ diffuses through ATP synthase* results in ADP and Pi to ATP, via chemiosmosis*;

Question 5

Briefly describe what happens to pyruvate if yeast is deprived of oxygen [2m]

Answer 5

1. does not enter Krebs cycle*;
2. decarboxylated/ carbon dioxide released;
3. forms ethanal/acetaldehyde which forms ethanol
   ;4. NADH* donates electron to ethanal/acetaldehyde;
4. regenerate NAD+, which is fed back into glycolysis so that ATP production in glycolysis can continue;
5. process is catalysed by alcohol dehydrogenase;

Question 6

(c)Suggest two advantages to eukaryotic cells of membrane-bound organelles. [2]

Answer 6

1. Compartmentalisation - maintain optimal conditions for enzyme reactions for each organelle;
2. Increase surface area for reactions (cristae for oxidative phosphorylation / attachment ribosomes);

Question 7

d)Suggest how the structure of the ATP synthase allows it to carry out its function and to be embedded onto the membrane. [2]

Answer 7

1. ATP synthase has a specific active site* to catalyse formation of ATP / phosphorylation of ADP.
   OR
   It has a hydrophilic pore / channel (R: core) which allows protons to diffuse across the inner mitochondria membrane during chemiosmosis* for formation of ATP / phosphorylation of ADP.
2. It has hydrophobic* R-groups that are interacting with the hydrophobic* core /region of the phospholipid bilayer* of inner mitochondria membrane /cristae, to allow protein to be embedded on membrane.
3. It has hydrophilic* R-groups that interact with the hydrophilic* phosphate heads of the phospholipid bilayer.

Question 8

Describe how the energy released from the flow of electrons in Fig. 11.1 results in the formation of ATP. [3]

(graph showing energy of etc complexes along with the direction of energy flow)

Answer 8

1.Electrons passed down electron carriers in order of electronegativity releases energy which is used to pump H+ from the matrix to the intermembrane space
;2. Quote data e.g. from ETC complex 1 of free energy 190 kJ mol-1 to ETC complex 2 of free energy 130 kJ mol-1;
3. This produces a proton motive force / H+ concentration gradient, which allows H+ to diffuse through ATP synthase* back to the matrix

;4. This diffusion of H+ through ATP synthase is coupled to the phosphorylation of ADP to form ATP by ATP synthase* via chemiosmosis*;

Question 9

During the long-distance run, ATP may be generated at times using the type of respiration that normally occurs under anaerobic conditions. However, the athlete cannot use this type of respiration continuously throughout the whole period of the long-distance run.Suggest why this type of respiration cannot be used continuously by the athlete to generate ATP during the long-distance run. [2]

Answer 9

1. Under anaerobic conditions, lactic acid fermentation* occurs;
2. Lactic acid accumulates in the muscles resulting in muscle fatigue;

Question 10

Describe and explain the use of ATP in glycolysis. [3]

Answer 10

Describe what ATP is used for (2m):
1. phosphorylates glucose: glucose to glucose-6-phosphate (accept: fructose, hexose);

2. second phosphorylation: fructose-6-phosphate to fructose-1,6-bisphosphate (accept:
   hexose) ;

Explain the use of ATP (1m):

3. the process activates / increases energy of glucose;
4. prevents glucose from leaving the cell (as cells lacks transporters for G6P);
5. keep the glucose concentration low, promoting continuous transport of glucose into the cell through the plasma membrane transporters