Topic 7: Respiration

Question 1

Name two molecules needed for aerobic respiration that can move into the
mitochondria. (2)

Answer 1

• Oxygen
• Pyruvate
• Reduced NAD

Question 2

(ii) The outer mitochondrial membrane is not permeable to hydrogen ions (H+).

Explain the importance of this feature of the membrane.

Answer 2

• to stop H+ diffusing out (of mitochondrion) / into
cytoplasm (1)

• (therefore) maintaining a high concentration (of H+
) in the
intermembrane space (1)

• so {hydrogen ions / protons / H+
} can move down
{concentration / electrochemical} gradient (1)

• (by) chemiosmosis (1)

• to synthesise ATP (1)

Question 3

Describe how oxygen is involved in the production of ATP in the cristae in the mitochondria (2)

Answer 3

• Oxygen is a terminal acceptor, accepts electrons and H+ (from NADH & FADH) at the end of the electron transport chain to form H2O
• Electrons cannot be passed along the ETC if there is no oxygen to accept them

Question 4

Explain the krebs cycle in steps

Answer 4

▪︎ A series of small enzyme catalysed steps;
▪︎ 4C compound combines with Acetyle CoA to form 6C compound
▪︎ Decarboxylation releases CO2 (now 5C)
▪︎ Dehydrogenation releases 2H
▪︎ These are accepted by NAD & FAD
▪︎ Forming reduced NAD & FAD
▪︎ These go to the ETC
▪︎ ATP formed by substrate level phosphorylation
▪︎ Another CO2 removed, reforming the 4C compound to keep the cycle going

Question 5

What are the products of one cycle of the krebs cycle?

Answer 5

2x CO2
1x ATP
3x Reduced NAD
1x Reduced FAD

Question 6

Explain the role of the krebs cycle

Answer 6

• Completely oxidises pyruvate/acetyle CoA
• To release as much energy as possible
• To generate ATP by substrate level phosphorylation
• To produce reduced NAD & FAD
• Used in the ETC to produce ATP