Topic 8: Grey Matter

Question 1

What is the role of ATP in the transmision of impulses along neurones?

Answer 1

• ATP required for sodium/potassium pumps
  (1)
• to move ions against concentration gradient
  (1)
• to maintain potential difference across axon
  membrane (1)

Question 2

(i) Explain how the myosin head could move mitochondria along the axon

Answer 2

• attaches to {myosin-binding site / actin} (1)
• splits ATP / acts as an ATPase (1)
• (myosin head) changes position (to move
  mitochondria on) (1

Question 3

Answer 3

Question 4

Answer 4

• this (mutation) leads to a different
  {primary structure (of protein) / amino
  acid sequence} (1)
• for the protein opsin (1)
• (so) a {different / misfolded} tertiary
  structure of protein / altered shape of the
  protein (1)
• (resulting in) more light of 280nm being
  absorbed (than 500nm) (1

Question 5

(b) Rod cells form synapses with bipolar neurones.
Describe how movement of sodium ions in a rod cell affects depolarisation in a
bipolar neurone.
(4)

Answer 5

• (in the dark) sodium ions moving {in
  through sodium ion channels / into the
  outer segment} (1)
• sodium ions {removed / pumped out} at
  inner segment (1)
• so rod cell depolarises (1)
• causing { neurotransmitter / glutamate }
  to be released (1)
• inhibits depolarisation in (adjacent)
  bipolar neurone (1)

Question 6

(c) Some plants only flower when the days are long and the nights are short. They are
known as long-day plants.
(i) Describe the role of the photosensitive pigment phytochrome in the flowering
of long-day plants.
(2

Answer 6

• increased red light (due to a long day / short
  night) / limited exposure to far-red light (1)
• phytochrome red converted to phytochrome
  far-red in the day / little conversion of far
  red form to red form during the (short) night
  (1)
• {accumulation / high concentration} of
  phytochrome far red stimulates flowering (1)

Question 7

(ii) Devise an investigation to find out if a species of plant is a long-day plant or a
short-day plant.
(3)

Answer 7

• grow in conditions with different periods of
  time in light (per day) / range of hours in light
  (1)
• control a relevant abiotic factor (1)
• record whether plants flower or not (1