Key Area 1.7: Essay Questions

Question 1

Give an account of respiration under the following headings:

a) Glycolysis
b) The citric acid cycle

Answer 1

a) - glycolysis is the breakdown of glucose to pyruvate
- 2 ATP molecules are used to phosphorylase intermediates in glycolysis in the energy investment phase
- 4 ATP molecules are produced in energy pay off stage
b) - if oxygen if available in aerobic conditions pyruvate progresses to the citric acid cycle
- pyruvate is broken down to an acetyl group
- acetyl group combines with coenzyme A
- acetyl coenzyme A combines with oxaloacetate to form citrate
- citric acid cycle is enzyme controlled
- ATP generated at substrate level in the citric acid cycle
- carbon dioxide is released from the citric acid cycle
- oxaloacetate is regenerated
- NAD/NADH/FAD/FADH2 transports electrons and hydrogen ions to the electron transport chain

Question 2

Give an account of the electron transport chain in respiration

Answer 2

• electron transport chain takes place in the inner membranes if the mitochondria
• electron transport chain is a collection of proteins attached to a membrane
• NADH and FADH2 release the high energy electrons to the electron transport chain on the inner mitochondrial membrane
• electrons cascade down the chain of electron acceptors, releasing their energy
• energy is used to pump hydrogen ions across the inner mitochondrial membrane
• return flow of the hydrogen ions back into the matrix drives the enzyme ATP synthase
• the synthesis of ATP from ADP + Pi
• this stage produces the most ATP
• final electron acceptor is oxygen which joins to the hydrogen ions to form water

Question 3

Give an account of respiration under the following headings:

a) The role of ATP within the cell
b) The use of alternative respiratory substrates

Answer 3

a) - ATP produced by phosphorylation acts as a source of immediate energy for cells
- made during respiration
- used up during energy requiring processes
- mass in cell remains constant
b) - substrates are used instead of glucose when it is not available
- examples starch/ glycogen/ other sugars/ fats
- glycogen is a storage carbohydrate from liver/ muscles
- glycogen used between meals
- amino acids can be released from body bulky protein
- these amino acids can be used during extreme starvation
- other sugars can enter respiratory pathways