june 2017- paper 3

Question 1

how does a nerve impulse cause the release of a neurotransmitter? (3)

Answer 1

• nerve impulse causes Ca2+ channels to open
• Ca2+ enter by facilitated diffusion
• causes synaptic vesicles to fuse with the synaptic cleft

Question 2

movement of myosin up actin (2)

Answer 2

• myosin head binds to actin and bends
• whatever is attached to the myosin is pulled along actin
• next myosin head binds to actin

Question 3

method of determining species richness (3)

Answer 3

• select sampling sites at random
• use a quadrat
• identify which species are present in each quadrat

Question 4

why does phosphorylation cause enzyme catalysed reactions to happen

Answer 4

raises the energy level of substrates