Anaerobic respiration and comparing processesIB MYP Sciences: Subtopic test

1. 1
   A sprinter in Doha runs a 400 m race at top speed. By the final 100 m her leg muscles burn and feel heavy. After she crosses the line she stands bent over, still breathing very hard for several minutes.

   (a)

   Which substance builds up in the sprinter's muscles when they respire anaerobically?

   [1 mark]

   • ALactic acid
   • BEthanol
   • CGlucose
   • DOxygen

   (b)

   Why does the sprinter keep breathing hard after the race has finished?

   [1 mark]

   • ATo make more lactic acid for the next race
   • BTo stop her muscle cells respiring
   • CTo take in extra oxygen to break down the lactic acid, repaying the oxygen debt
   • DTo replace the glucose in her blood directly

   (c)

   Explain why the sprinter's leg muscles respire anaerobically during the race.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A bakery in Istanbul makes bread by mixing flour, water, sugar and yeast into a dough. The dough is left in a warm place for an hour. It swells to about twice its size, and when it is baked the bread has a light texture full of tiny holes.

   (a)

   Yeast respires anaerobically in the dough. Which substance, as well as carbon dioxide, does it produce?

   [1 mark]

   • ALactic acid
   • BOxygen
   • CStarch
   • DEthanol

   (b)

   What is the name for the anaerobic respiration of yeast, used in baking and brewing?

   [1 mark]

   • APhotosynthesis
   • BFermentation
   • CDigestion
   • DVentilation

   (c)

   Explain why the dough swells while it is left in a warm place.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Cape Town investigates yeast. She mixes the same mass of yeast with 100 cm³ of glucose solution in four flasks. Each flask is kept at a different constant temperature in a water bath: 20 °C, 30 °C, 40 °C and 60 °C. Each flask is sealed with a bung and a delivery tube that leads into water, and she counts the bubbles of gas leaving the tube during 5 minutes. She counts 12 bubbles at 20 °C, 28 bubbles at 30 °C, 45 bubbles at 40 °C and no bubbles at 60 °C.

   (a)

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

   [3 marks]

   (b)

   Describe the trend in the results, explain the result at 60 °C and suggest one improvement to the method.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In Brazil, sugar cane is grown on huge farms. The cane plants make glucose by photosynthesis and store it as sugar in their stems. After harvest the sugar is extracted and yeast ferments it to make ethanol, which is mixed with petrol or used on its own as a car fuel called bioethanol. Supporters say bioethanol is better for the environment than petrol. Critics say that more land is being cleared to grow cane.

   (a)

   Compare photosynthesis and aerobic respiration in the cells of a sugar cane plant.

   [6 marks]

   (b)

   Discuss and evaluate the use of bioethanol made by fermentation as a fuel for cars.

   [6 marks]

   Total for question 4: 12 marks

End of questions