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Summary PAG 12 Respiration Rate of Yeast
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A written practical investigation on the observation of respiration in yeast and shows a clear structure and layout.
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PAG 12 – Investigation into the respiration rate of Saccharomyces cerevisiaeAim:
We want to test the effects of different substrates glucose, fructose, sucrose and lactose) on
the respiration of yeast. The way in which I will do this is by measuring the amount of
carbon dioxide released from anaerobic respiration by counting the number of bubbles
produced from each substrate.
Introduction:
Respiration is the process where organic molecules such as glucose are digested and broken
down into smaller inorganic ions such as carbon. Some of the independent variables that
can be tested during the rate of respiration are temperature and substrates. The control
variables for this investigation are: volume of yeast, volume of water added to the boiling
tube and the pH of the solution.
Hypothesis:
Glucose, a monosaccharide, should be the most efficient and have the highest rate of
respiration in yeast, as it is directly used in the glycolysis cycle and does not require any
extra energy to hydrolyse it.
Fructose, also a monosaccharide, requires isomerase enzymes to change it to glucose so it
can enter the glycolysis cycle.
Sucrose should have a lower rate of respiration in yeast than glucose and fructose, as they
are disaccharides so require an extra step to be hydrolysed to monosaccharides.
Lactose shouldn’t cause respiration in yeast, as yeast does not have the lactate enzyme and
cannot break down lactose.
Equipment list:
14g of Yeast
Measuring cylinder 50cm3
Sugar solutions
Rubber bungs with downwards delivery tube
Distilled water
Stopwatch
Thermometer
5 x boiling tubes
Sharpie
4 x beakers 250 cm3
6 x syringes 5ml
2 x Stirring rod
Kettle
Method:
1. Label each of the 4 boiling tubes with the sugar solutions with a sharpie
2. Pour water into another boiling tube and put that tube into one of the beakers as
this is what will be used to bubble the carbon dioxide through
3. Then add 14g of yeast and 140ml of warm water in a 250cm 3 glass beaker
, 4. Stir the yeast and the warm water with a glass stirring rod until all of the yeast is
dissolved.
5. Measure out 35cm3 of the yeast mixture using a 50cm3 measuring cylinder.
6. Pour the yeast mixture into each of the 4 boiling tubes splitting the mixture equally
between the tubes
7. Draw up 5ml of a sugar solution using a 5ml syringe and add it to the designated,
correctly labelled, boiling tube.
8. Stir the yeast mixture and the sugar solution with a glass stirring rod.
9. Place the boiling tube with the yeast and sugar solution mixture into one of the
beakers
10. Add one of the bungs to the top of the yeast and sugar solution mix and add another
bung to the top of the tube containing distilled water.
11. Then the delivery tube will connect to the top of the bungs of each of the boiling
tubes to connect the 2 boiling tubes, for the carbon dioxide to bubble through from
the yeast and sugar solution mixture to the distilled water.
12. Then count how many bubbles are released into the distilled water in 5 minutes.
13. Repeat steps 7 – 10 for other sugar solutions
Results table:
Number of bubbles of Carbon dioxide produced
Substrate Start 1 min 2 min 3 min 4 min 5 min
Lactose 0 4 10 17 29 43
Sucrose 0 30 50 91 130 185
Glucose 0 58 100 160 220 263
Fructose 0 26 72 134 210 259
Conclusion:
Overall, glucose respired the fastest and Lactose respired the slowest. This is because it had
the fastest rate of CO2 bubbles being produced. This means the rate of respiration was
fastest, and it had the most energy released in the same amount of time compared to the
other substrates.
References:
Source 1: Charlotte Burrows,
Katherine Faudemer, Rachel
Kordon, Christopher Lindle,
Rachael Marshall, Christopher
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