10 minutes maximum! Can you do it in 5?

1-3. The image is of yeast, Saccharomyces cerevisiae, which is used in the production of food, e.g. bread. A scale is shown in the botoom right corner of the image.

yeast through microscope

 Materialscientist | CC 3.0
1. Approximately how long is one yeast cell?
  • A. 1 mm
  • B. 0.1 mm
  • C. 3 mm
  • D. 3 µm
2. Yeast belongs to which kingdom?
  • A. Plants
  • B. Animals
  • C. Fungi
  • D. Protoctists
3. Which gas released by yeast helps bread to rise?
  • A. Oxygen
  • B. Carbon dioxide
  • C. Water vapour
  • D. Nitrogen
4-6: A class of students wanted to investigate the optimum temperature for yeast when making bread. The students set up the apparatus shown in the diagram. They measured the rate of fermentation at different temperatures by placing the apparatus in thermostatically controlled water baths.

graph showing crop growth

  

4. Which of the following are the correct labels for K and L?

  K L
A Liquid paraffin Yeast and glucose
B Glucose solution Yeast suspension
C Liquid paraffin Yeast suspension
D Liquid paraffin Glucose solution
5. The students used a liquid, M, to check that the gas produced was carbon dioxide.

Liquid M is..

  • A. Water
  • B. Iodine solution
  • C. Limewater
  • D. Hydrochloric acid

6. The graph shows the mean bubbles per minute at different temperatures. 

graph showing activity of yeast

 

What is the optimum temperature for the yeast?

  • A. 10 oC
  • B. 35 oC
  • C. 40 oC
  • D. 45 oC

7-10: The diagram shows an industrial fermenter that could be used to grow microorganisms in controlled conditions:

graph showing activity of yeast

YassineMrabet | CC 3.0
7. Which one of the following organisms could not be grown in this fermenter?
  • A. Bacteria
  • B. Yeast
  • C. Algae
  • D. Penicillium mould
8. The organism and nutrients are placed in the reactor tank. More nutrients can be added through the feeding pump inlet.

Select the correct combination of fermenter part with its function.

  Stirring paddles Air inlet with filter Thermal jacket
A Mix the contents of the fermenter Supplies carbon dioxide without letting in microorganisms Keeps fermenter warm
B Keeps the temperature even Supplies carbon dioxide without letting in microorganisms Keeps fermenter cool
C Mix the contents of the fermenter Supplies oxygen without letting in microorganisms Keeps fermenter at required temperature
D Make contents hotter Supplies oxygen without letting in microorganisms Keeps fermenter cool
9. Which of the following statements is incorrect?

The temperature and pH have to be monitored and regulated because ...

  • A. enzymes in micro-organisms work best in optimal conditions
  • B. heat is produced due to respiration
  • C. the contents become more acidic as more and more carbon dioxide is produced.
  • D. the contents become more acidic as more and more carbon dioxide is used up.
10. Lactobacillus bacteria are used to make yoghurt. The bacteria ferment the lactose sugar that is in milk. The product formed in lactose fermentation is
  • A. glucose
  • B. Lactose
  • C. Lactic acid
  • D. Ethanol