2d Movement of substances into and out of cells

Question 1

Define diffusion. (3)

Answer 1

• Diffusion is the net movement of particles
• from an area of higher concentration to an area of lower concentration
• down the concentration gradient.

Question 2

What factors affect the rate of diffusion? (4)

Answer 2

• Concentration gradient
• Surface area to volume ratio
• Diffusion distance
• Temperature

Question 3

What factors increase the rate of diffusion? (4)

Answer 3

• Steep concentration gradient
• High SA:Vol ratio
• Short diffusion distance
• High temp (leading to increased kinetic energy)

Question 4

Define active transport. (4)

Answer 4

• Active transport is the net movement of particles
• from an area of lower concentration to an area of higher concentration
• against a concentration gradient
• using energy released during respiration.

Question 5

Give two examples of active transport. (2)

Answer 5

• Root hair cells absorbing mineral ions.

- Movement of glucose through the lining of the small intestine.

Question 6

Define osmosis (3)

Answer 6

• Osmosis is the net movement of water
• from an area of higher water potential to lower water potential
• through a partially permeable membrane.

Question 7

What happens to a plant cell placed in salty solution and why? (3)

Answer 7

• The plant cell shrinks/becomes flaccid.
• The cell membrane pulls away from the cell wall (plasmolysis)
• because there is a higher water potential than in the salty solution compared with the cell, so the water leaves the cell by osmosis.

Question 8

What happens to a plant cell placed in pure water and why? (3)

Answer 8

• The plant cell swells/becomes turgid.
• because there is a higher water potential in the surrounding solution compared with the inside of the cell, so water enters the cell by osmosis.
• The cell wall prevent the cell from bursting however.

Question 9

What happens to an animal cell placed in pure water and why? (3)

Answer 9

• The animal cell bursts
• because there is a higher water potential in the surrounding solution compared with the inside of the cell, so water enters the cell by osmosis.
• There is no cell wall, so the cell bursts.

Question 10

Give 3 examples of large surface area to volume ratios for quicker movement of substances. (3)

Answer 10

• Alveoli in lungs for absorption of oxygen.
• Villi in small intestine for absorption of soluble products of digestion.
• Root hair cells for absorption of mineral ions.