2020 - Biology Past Paper Corrections

Question 1

What diffuses into the mesophyll cells?

Answer 1

molecules of carbon dioxide from the air

Question 2

Explain how the human lungs are adapted for efficient gas exchange of gases by diffusion

Answer 2

• large capillary network around the alveoli
• to remove oxygenated blood quickly
• to bring carbon dioxide to the lungs quickly
• to maintain a concentration gradient

Question 3

Explain how nitrate ions in figure four are transported into the root hair cell

Answer 3

• By active transport
• Because energy is needed
• to move nitrate ions from a lower concentration (in the soil), to a higher concentration (in the root hair cell)

Question 4

What is cytokinesis?

Answer 4

Division of the cytoplasm

Question 5

What are the three stages of the cell cycle?

Answer 5

1. Interphase
2. Mitosis
3. Cytokinesis

Question 6

Describe what happens during each stage of the cell cycle

Answer 6

1. DNA is replicated and subcellular structures increase in number
2. One set of chromosomes is pulled to each end of the cell
3. Cytoplasm and cell membrane divides to form two cells

Question 7

Explain the ‘lock and key theory’ of enzyme action

Answer 7

• the enzyme binds to the substrate because they are complementary shapes
• so substrate is broken down into products
• so the shape of the enzyme is not changed

Question 8

Why does each different type of lipase act on only one specific type of lipid molecule?

Answer 8

each active site has a specific shape, so only fits one type of lipid molecule7