Use of biological resources

Question 1

Nov 2023 1B Q9
Selective breeding

Answer 1

1. Selection of bulls based on milk-producing daughters or relatives
2. Selection of cows(female) based on highest milk yield or relatives
3. Breeding of offspring with the highest yield
   4.Repetition over many generations

Question 2

Explain the role of the stirrer in the fermenter(2)
Explain the role of the water jacket in the fermenter(2)

Answer 2

i)The stirrer keeps the mixture of milk and bacteria evenly mixed, ensuring that the bacteria are spread throughout the milk. Maintain even temperature
ii) To maintain optimal temperature therefore the enzyme won’t denature

Question 3

How Lactobacillus bacteria produce yoghurt from milk?

Answer 3

Lactobacillus ferment the lactose(carbohydrate) in milk and produce lactic acid. THe lactic acid lowers the pH, which causes the milk proteins to clot（凝结）and milk to thicken.

Question 4

Milk needed to be heated at a high temperature

Answer 4

The heat will sterilised milk
The heat will kill bacteria
This prevents competition for milk