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Investigation into the respiration rate of Saccharomyces cerevisiae
A step by step guide on how to write a PAG in specific the Investigation into the respiration rate of Saccharomyces cerevisiae for OCR Biology A
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Investigation into the respiration rate of Saccharomyces cerevisiae F HaiderIntroduction:
This practical aims to investigate the effect that temperature has on CO2 production from
respiration in Saccharomyces cerevisiae (yeast). According to Arroyo-Lopez et al (2009), temperature
was found to have the greatest influence on respiration rate (followed by sugar concentration and
then pH), thus making it the most suitable variable to investigate to produce distinct results, where
volume of CO2 could be used to measure this. Changing temperature can affect rate of aerobic
respiration as the enzymes involved will have an optimum temperature as well as a temperature at
which they begin to denature (Patricia M. Schulte, 2015) However, another variable which could be
investigated would be oxygen availability. When yeast respires aerobically in the presence of oxygen,
more molecules of ATP are generated per molecule of glucose than if the yeast respires
anaerobically in oxygen deficient conditions (Hocking et al, 2015).
Aim:
To see if temperature which is one of the most important factors affecting activity of organisms also
affects yeast respiration.
Hypothesis:
Increasing the temperature of the system will increase the rate of respiration of yeast up until the
point of around 40 degrees Celsius when enzymes will start to denature
Factors that might affect yeast growth:
Temperature, Concentration of Yeast, Concentration of Oxygen, pH, Light, Time for fermentation,
Concentration of sugar
Risk assessment:
Be careful of hot water (50-60 degrees) and avoid burning + spilling water
Method:
Independent variable is the temperature which we will change in intervals of 10 degrees.
We will mix the glucose with the yeast at the start and ensure the concentration of the glucose is
controlled throughout the experiment as we will have a known concentration at the start.
We will then use mini syringes to drop the yeast-glucose solution in. The syringes submerged into
the test tube with water will contain 1cm^3 of air and 1cm^3 of yeast/glucose solution.
Ensure that the test tube contains 8/10ths water to ensure full submersion.
Once the syringe is placed leave the solution to equilibrate for a minute to the new temperature
and use the thermometer to check the temperature.
As soon as the syringes are submerged ensure a stopwatch is started to check when to start counting
bubbles.
Make a note of the number of bubbles at each temperature and write your results in a table.
Repeat 3 times at each temperature and take an average of the 3 repeats and also use a boiling tube
with 1cm^3 of water as a control (without yeast)
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