Quiz: The Amphibolic Pathway Quiz 1
Respiration is usually introduced as a catabolic process — a demolition crew that breaks glucose down into carbon dioxide and water. Yet the very intermediates it produces are also the raw materials from which cells build fatty acids, amino acids and other essential molecules.
This quiz tests Lesson 14 of Respiration in Plants, focusing on:
- Why glucose is the favoured respiratory substrate
- How fatty acids and glycerol enter the pathway
- How amino acids enter after deamination
- Why intermediates are withdrawn for synthesis
- Why respiration is better called amphibolic rather than purely catabolic
Work carefully through each question — the reasoning behind the entry points matters as much as the facts.
Q1. Which molecule is described as the favoured substrate for respiration?
The lesson states clearly that glucose is the favoured substrate for respiration, and that all carbohydrates are usually first converted into glucose before being used.
Q2. Before carbohydrates such as starch and sucrose are used in respiration, they are usually converted into which compound?
All carbohydrates are usually first converted into glucose before they are used for respiration, so different sugars converge on a single starting point.
Q3. When substrates other than glucose are respired, which statement about their entry into the respiratory pathway is correct?
Other substrates can also be respired, but they do not enter the respiratory pathway at the first step; each enters at a different point along the route.
Q4. Before fats can be respired, they must first be broken down into which two products?
Fats would need to be broken down into glycerol and fatty acids first before their components can enter the respiratory pathway.
Q5. If fatty acids are to be respired, they are first degraded to which compound before entering the pathway?
The lesson states that fatty acids would first be degraded to acetyl CoA and then enter the respiratory pathway.
Q6. Glycerol enters the respiratory pathway after being converted into which intermediate?
Glycerol would enter the pathway after being converted to PGAL (phosphoglyceraldehyde).
Q7. Proteins are degraded by which class of enzymes before their amino acids can be used in respiration?
The lesson states that proteins would be degraded by proteases, releasing individual amino acids.
Q8. Before amino acids can enter the respiratory pathway, they must first undergo which process?
Individual amino acids enter the pathway only after deamination, and then — depending on their structure — at some stage within the Krebs cycle, or as pyruvate or acetyl CoA.
Q9. Depending on their structure, amino acids may enter the respiratory pathway at which of the following sets of points?
The lesson states that amino acids, after deamination, enter at some stage within the Krebs cycle or even as pyruvate or acetyl CoA, depending on their structure.
Q10. Why has the respiratory pathway traditionally been considered a catabolic pathway?
Since respiration involves breakdown of substrates, the respiratory process has traditionally been considered catabolic and the pathway a catabolic pathway.
Q11. When an organism needs to synthesise fatty acids, acetyl CoA is obtained by which means?
When the organism needs to synthesise fatty acids, acetyl CoA would be withdrawn from the respiratory pathway for that purpose.
Q12. Which statement best captures the relationship between the respiratory pathway and fatty acid metabolism?
Fatty acids are broken down to acetyl CoA before entering the pathway, and acetyl CoA is withdrawn from the pathway when fatty acids are synthesised — so the pathway features in both breakdown and synthesis.
Q13. During the breakdown and synthesis of proteins, what role do respiratory intermediates play?
The lesson states that during the breakdown and synthesis of protein too, respiratory intermediates form the link.
Q14. In the terminology used in the lesson, breaking down processes within the living organism are called catabolism. What is synthesis called?
Breaking down processes within the living organism are catabolism, and synthesis is anabolism.
Q15. Why is the respiratory pathway better described as amphibolic rather than as catabolic?
Because the respiratory pathway is involved in both anabolism and catabolism, it is better considered an amphibolic pathway rather than a catabolic one.