Transport Across Cell Membranes

Question 1

Give two similarities in the movement of substances in diffusion and osmosis.

Answer 1

• passive processes
• substances move down their concentration gradient

Question 2

The cells of beetroot contain a red pigment. A student investigated the effect of
temperature on the loss of red pigment from beetroot. He put discs cut from
beetroot into tubes containing water. He maintained each tube at a different
temperature. After 25 minutes, he measured the percentage of light passing
through the water in each tube.
(a)
(b)
The student put the same volume of water in each tube.
Explain why it was important that he controlled this experimental variable.

Answer 2

• if too much water, the concentration of pigment would be lower.
• so results are comparable

Question 3

What is simple diffusion?

Answer 3

Movement of small non-polar molecules down a concentration gradient.

Question 4

What is facilitated diffusion

Answer 4

Movement of substances down a concentration gradient via protein carrier/channel

Question 5

What is osmosis?

Answer 5

Movement of molecules down a water potential gradient