Fermentation: Yeast and Yoghurt

IGCSE Edexcel Biology
5.5-5.8 Micro-organisms in Food Production
Key Concept: Yeast and bacteria are used in fermentation to produce bread and yoghurt.

Section A: Yeast

1. State the role of yeast in bread making. [2]
2. Write the word equation for anaerobic respiration in yeast. [2]
3. Describe three conditions needed for efficient yeast fermentation. [3]

Section B: Yoghurt and Fermenters

4. State the role of Lactobacillus bacteria in yoghurt production. [2]
5. List four conditions needed in an industrial fermenter. [4]
Total marks: 13

Mark Scheme

1. Yeast ferments sugars to produce $CO_2$, which makes dough rise [2]
2. Glucose -> ethanol + carbon dioxide [2]
3. Warm temperature, sugar/nutrients, low oxygen for anaerobic conditions, correct pH (any three) [3]
4. Lactobacillus ferments sugars to lactic acid, thickening/flavouring yoghurt [2]
5. Any four: aseptic conditions, nutrients, optimum temperature, optimum pH, oxygenation, agitation [4]