2017 Biology Paper 3

Question 1

What practical considerations are taken when growing yeast in the laboratory?

Answer 1

• Suitable temperature
• Use a pH buffer to maintain the optimum pH
• Stir it
• Use aseptic techniques
• Provide respiratory substrates

Question 2

What are regulatory genes?

Answer 2

Regulatory genes control the expression of other genes.

Question 3

Which bacteria turn N₂ and H⁺ into ammonia?

Answer 3

Rhizobium

Question 4

Which bacteria turn NH₄⁺ into nitrites?

Answer 4

Nitrosomonas

Question 5

Which bacteria turn nitrites into nitrates?

Answer 5

Nitrobacter

Question 6

Where are Rhizobium, Nitrosomonas, and Nitrobacter found?

Answer 6

Rhizobium is found in root nodules, whereas Nitrosomonas and Nitrobacter are found in the soil.