Chapter 8.2 (eye)

Question 1

Describe how light causes a change in the voltage across the cell surface membrane of a rod cell

Answer 1

• light intensity required
• light absorbed by rhodopsin
• rhodopsin changes shape
• rhodopsin is converted to retinal and opsin
• opsin binds with cell surface membrane
• fewer sodium ions enter rod cell ( ACCEPT: decreases permeability of membrane to sodium ions,channels close)
• sodium ions pumped out of the rod cell
• hyperpolarisation occurs leading to a change in voltage

Question 2

Suggest why a change in voltage across the cell surface membrane of a rod cell may not lead to the formation of an action potential in an optic neurone

Answer 2

• not enough rhodopsin is converted/ opsin binds to membrane
• so change in voltage is insufficient
• neurotransmitter/glutamate still released from the rod cell
• depolarisation in bipolar neurone insufficient (ACCEPT: for depolarisation threshold level not achieved)
• bipolar neurone already depolarised

Question 3

Visual transduction

Answer 3

the process by which light initiates a nerve impulse.