Edexcel IGCSE Biology 5.7 Fermenter microorganism growth
Practise yoghurt production by linking Lactobacillus, lactose, temperature control, anaerobic respiration and pH changes to lactic acid.
- Syllabus
- First assessment 2019
- Course
- Biology 4BI1
Exam points
- explain why milk is heated, then cooled to 40-46°C before bacteria are added
- link Lactobacillus using lactose anaerobically to lactic acid and falling pH
- interpret acidity or oxygen-level data as evidence for the rate of yoghurt production
5.7 Lactobacillus in yoghurt production question 1
[Maximum number: 5]
Yeast is a fungus used in the production of bread.
Question (a)
(a)
Yoghurt is another food that is produced using microorganisms.
[ 5 ]
Question (i)
(i)
Explain the importance of controlling the temperature in the different stages of yoghurt production.
[ 3 ]
An explanation that makes reference to three of the following:
- milk is heated at 70−95∘C/ pasteurised / eq
- to kill any microorganisms / bacteria / eq
- cooled / kept at 40−45∘C/eq(1)
- so Lactobacillus bacteria added can survive/ eq
- provide optimum temperature for enzymes / optimum temperature for respiration / optimum temperature for fermentation / eq
Question (ii)
(ii)
Explain the importance of changes in pH during yoghurt production.
[ 2 ]
An explanation that makes reference to two of the following:
- milk has a pH of 6.7 / 7 / about neutral / eq
- lactic acid produced / eq
- this makes the pH drop / become more acidic / eq
- stops other bacteria growing / preserves the yoghurt / clots milk / makes solid / eq
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