A-level paper 2 mistakes

Question 1

What bond is formed when two amino acids combine in a condensation reaction?
How does it form?

Answer 1

peptide CONH

COOH group loses its OH and this combines with one of the H atoms from NH2 to form a water molecule.

Question 2

Describe the structure of collagen.

Answer 2

three polypeptide chains
Helicies joined together
Held together by hydrogen bonds

Question 3

Describe the events that lead to the release of acetylcholine at a synapse.

Answer 3

An action potential arrives at a pre-synaptic knob.
Calcium channels open so calcium ions diffuse into pre-synaptic neurone.
Vesicles move to membrane.
Vesicles fuse with the pre-synaptic membrane and release acetylcholine.

Question 4

Explain the differences in the efficiency of energy transfer between trophic levels in a food chain.

Answer 4

Lots of energy is not passed onto primary consumers from producers as they have inedible parts.
Primary producers have a higher respiration rate than producers
More energy is lost from movement by primary consumers
Primary consumers lose more energy as excretion than producers.

Question 5

Explain how auxins and cytokinins control the growth of lateral buds.

Answer 5

Auxin is released from the terminal bud.
It diffuses down the stem to inhibit lateral bud growth.
Cytokinin stimulates lateral bud growth.
Is produced from the base of the shoot