Fermentation and food biotechnologyIB MYP Biology: Flashcards

Exam questions on Fermentation and food biotechnology

1. A bakery in Lisbon makes bread by mixing flour, sugar, yeast and warm water into a dough. The baker leaves the dough in a warm place for an hour. The dough doubles in size and has a slightly sweet smell of alcohol. It is then baked in a hot oven.
   Explain why the baker uses warm water, not cold water or boiling water, to mix the dough.2 marks
2. A dairy in Istanbul makes yoghurt. Milk is heated to 85 °C, cooled to 43 °C and then a small amount of live bacteria (Lactobacillus) is mixed in. The mixture is kept at 43 °C for six hours in a closed container. By the end the milk has thickened and tastes sour.
   Explain why the milk thickens and tastes sour during the six hours.2 marks
3. A student investigates how temperature affects fermentation by yeast. She mixes 5 g of yeast with 100 cm³ of glucose solution in a flask and joins the flask by a delivery tube to an upturned measuring cylinder full of water. She measures the volume of gas collected in 10 minutes. She repeats the experiment at 15 °C, 25 °C, 35 °C, 45 °C and 65 °C. The volumes of gas collected were 4 cm³, 18 cm³, 41 cm³, 30 cm³ and 0 cm³ respectively.
   State a testable hypothesis for this investigation and give a scientific reason for it.3 marks