Which of the following links carbohydrate and fat metabolism?

$A-$ Breaking down processes within the living organism is anabolism and synthesis is catabolism.
$R-$ The proteins would be degraded by proteases and the individual amino acids (after deamination) depending on their structure would enter the pathway at some stage within the Kreb's cycle or even as pyruvate or acetyl $CoA$.

Why is the respiratory pathway referred to as an amphibolic pathway?

Give scientific reasons:
$(1)$ Krebs' cycle is an important process.
$(2)$ Sometimes an amphibolic pathway is seen in respiration.

Protein is used as a respiratory substrate only when:

The following figure shows an amphibolic pathway. What are $P$,$Q$,and $R$?