Experiment: Growing Yeast
Introduction:
Yeast are living single-cell organism. They are a type of fungi. In order to
reproduce yeast need sugar (glucose) and oxygen which they respire in
order to produce energy. The equation for respiration is:
In this experiment you will grow yeast by feeding them a sugar solution and exposing them to
oxygen. The yeast will convert the oxygen and sugar to carbon dioxide, water and energy. The
carbon dioxide gas forms bubbles and will make the solution expand up the test tube. Measuring the
height of the foam gives an indication of the population of yeast.
Aim:
Hypothesis:
Materials:
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1 x medium test tube
Yeast/water/sugar suspension
Pipette
Ruler
Stopwatch
Method:
1. Gather the equipment. When told to do so
pipette 5mL of yeast suspension into the test tube
2. Measure the initial height of the yeast suspension
in mm as in Figure A. Add this value at time 0
(minutes) into the data table
3. Hold the test tube firmly in your palm for 4
minutes then measure the height in mm of the
yeast suspension with foam as in Figure B. Add
the value to the data table at time 4 minutes.
4. Hold the test tube in your palm again for 4
minutes. Continue to measure and record the
height of the foam column of yeast every 4
minutes for 24 minutes and record your results
5. Organise your data into a graph using the grid
provided and answer the discussion questions
Results:
Time (mins)
Height of column (cm)
0
4
8
12
16
20
24
Discussion:
1. Explain what was causing the solution to rise up the test tube.
2. Determine whether your hypothesis was correct or incorrect. Explain why/why not.
3. Describe the pattern or trend in the graph you have drawn
4. Describe how the population of yeast changes over time when grown in a closed system
with limited resources
5. Explain what may have happened if the yeast were given more sugar.
6. What possible reasons are there for why the yeast population does not continue to grow
forever?
7. Some students performed a similar experiment but changed the temperature of the solution
the yeast were grown in. The data is displayed below.
Discuss what this data suggests about the ideal temperature to grow yeast.
8. Write a method for a yeast growing experiment where different types of sugar are used.
Conclusion: What were the major findings? Was the aim achieved? Was your hypothesis correct?