Fermentation and food biotechnologyIB MYP Biology: Subtopic test

1. 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.

   (a)

   Which gas makes the dough rise?

   [1 mark]

   • AOxygen
   • BHydrogen
   • CCarbon dioxide
   • DNitrogen

   (b)

   What name is given to the way yeast releases energy from sugar in the dough, where little oxygen is available?

   [1 mark]

   • AAnaerobic respiration (fermentation)
   • BAerobic respiration
   • CPhotosynthesis
   • DTranspiration

   (c)

   Explain why the baker uses warm water, not cold water or boiling water, to mix the dough.

   [2 marks]

   Total for question 1: 4 marks

2. 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.

   (a)

   Why is the milk heated to 85 °C before the bacteria are added?

   [1 mark]

   • ATo make the bacteria respire faster
   • BTo change lactose into lactic acid
   • CTo remove all the oxygen from the milk
   • DTo kill unwanted microorganisms that are already in the milk

   (b)

   Which substance do the bacteria make from the lactose in milk?

   [1 mark]

   • AEthanol
   • BLactic acid
   • CMethane
   • DStarch

   (c)

   Explain why the milk thickens and tastes sour during the six hours.

   [2 marks]

   Total for question 2: 4 marks

3. 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.

   (a)

   State a testable hypothesis for this investigation and give a scientific reason for it.

   [3 marks]

   (b)

   Describe the trend in the results and suggest one improvement to the method.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A farming cooperative in Brazil is deciding how to use its land and waste. One option is to grow more sugar cane and ferment its sugar with yeast to make bioethanol, which is blended with petrol. The other option is to build a biogas digester that ferments cattle manure and crop waste to produce methane for cooking and generating electricity. Some members worry that forest might be cleared to grow more sugar cane.

   (a)

   Discuss the advantages and disadvantages of growing sugar cane to make bioethanol, and give a justified conclusion.

   [6 marks]

   (b)

   Describe how a biogas digester produces fuel and evaluate its use for a farming village.

   [6 marks]

   Total for question 4: 12 marks

End of questions