Biology 9700 · AS & A Level · Respiration

Respiration — practice question

Amino acids are the monomers from which proteins are made in organisms. Amino acids also carry out other roles in the body that are not related to proteins.
(a)[2]

Fig. 7.1 displays the structures of five amino acids, which differ in how many carbon atoms they contain and how these atoms are arranged. In the liver, one of these amino acids can be changed into pyruvate, and one of them can be changed into oxaloacetate. Suggest which amino acid in Fig. 7.1 would be converted most directly into: • pyruvate • oxaloacetate.

(b(i))[2]

Because the glycinergic synapse and a cholinergic synapse use different neurotransmitters and different postsynaptic receptors, describe how the glycinergic synapse shown in Fig. 7.2 differs from a cholinergic synapse.

(b(ii))[2]

When glycine binds to receptors, as shown in Fig. 7.2, an action potential is less likely to occur in the postsynaptic neurone. Suggest why the binding of glycine to receptors reduces the chance of an action potential.

(b(iii))[4]

Before an action potential can occur, neurones must maintain a resting potential. Describe how a neurone keeps a resting potential.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: conversion: pyruvate → serine

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