Required Practical 9 Rate of respiration in Yeast
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of aerobic and anaerobic respiration. You can test your knowledge on these below.
What is aerobic respiration?
Aerobic respiration is a metabolic process in which glucose is broken down in the presence of oxygen to release energy, producing carbon dioxide and water as by-products.
What is the balanced chemical equation for aerobic respiration?
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ ATP).
Which gas is released during anaerobic respiration in yeast?
Carbon dioxide (CO₂)
Topic Explainer Video
Check out this @JoeDoesBiology video that explains rate of respiration in yeast or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Aim of the Practical, Apparatus and Materials
Aim of the Practical
The aim of this required practical is to investigate how different conditions affect the rate of respiration in yeast. This is achieved by measuring the volume of carbon dioxide produced, which serves as an indicator of respiration rate.
Apparatus and Materials
- Boiling tubes and bungs with delivery tubes
- Gas syringe
- Stopwatch
- Water bath (to maintain constant temperature)
- Yeast suspension
- Glucose solution
- Thermometer
- Buffer solutions (if investigating pH)
- Methylene blue (if using colour change as a respiration indicator)
Independent Variables and Controlled Variables
Independent Variables You Could Investigate
- Temperature: The rate of respiration in yeast can be investigated at different temperatures, for example, 10°C, 20°C, 30°C, 40°C, and 50°C.
- Glucose concentration: Different concentrations of glucose can be used to determine how the availability of substrate affects the rate of respiration.
- Type of sugar: Different sugars such as glucose, fructose, sucrose, and maltose can be tested to compare how efficiently yeast can metabolise each one.
- pH: By using buffer solutions, the effect of pH on the rate of respiration can be investigated.
- Yeast concentration: Varying the concentration of yeast allows investigation into how enzyme availability affects the rate of respiration.
Controlled Variables to Ensure a Valid Test
- The volume and concentration of yeast suspension must be kept constant unless being investigated as the independent variable.
- The volume and concentration of glucose solution must be kept the same in all experimental conditions unless being tested.
- The time over which respiration is measured must be identical in all replicates.
- The temperature of the experiment should be maintained using a water bath if it is not the independent variable.
- All solutions should be given time to equilibrate to any changes in temperature before measurement of respiration rate starts.
How to Analyse the Results
- The volume of carbon dioxide produced should be measured over a fixed time period (e.g., every 2 minutes for 10 minutes).
- A graph should be plotted with time on the x-axis and the volume of carbon dioxide (in cm³) on the y-axis.
- The gradient of the graph represents the rate of respiration. A steeper gradient indicates a faster rate.
Methods of Measuring the Rate of Respiration
|
Method |
Description |
Advantages |
Disadvantages |
|
Gas syringe |
Carbon dioxide gas is collected in a gas syringe connected to the reaction vessel. |
Provides accurate, quantitative data on the volume of gas produced. |
Apparatus must be airtight; leaks reduce accuracy. |
|
Bubble counting method |
Carbon dioxide bubbles are counted as they emerge into a water-filled test tube or trough. |
Simple and inexpensive. |
Not very precise as bubble sizes vary. |
|
Respirometer |
Measures oxygen uptake using a manometer, often involving soda lime to absorb CO₂. |
Sensitive to small changes; good for aerobic respiration. |
Cannot measure rate of anaerobic respiration as there will be no change in gas pressure. Cannot use organisms in solution (eg yeast) as gases will dissolve in water and gas pressure will not be affected. |
|
Methylene blue indicator |
Acts as a redox indicator. Turns colourless when reduced by hydrogen produced in respiration. |
Visual indicator of respiration occurring. |
Only qualitative or semi-quantitative; not suitable for rate calculation. |
Key Modifications to Investigate Anaerobic Conditions
Excluding oxygen:
- A layer of liquid paraffin or oil can be added on top of the yeast and glucose mixture to prevent oxygen entering the solution.
-
Alternatively, use a sealed container with a one-way valve or connect it to a gas syringe to allow gas to escape while preventing oxygen entry. Time must be allowed at the start for any oxygen within the container to be used up.
The rate of anaerobic respiration could still be measured using a gas syringe. A respirometer would not be able to be used as no oxygen is being consumed. Methylene blue could not be used as there is no oxidative phosphorylation so it would not be reduced and therefore would not change colour.
Key Terms
- Aerobic respiration: The breakdown of glucose in the presence of oxygen to release energy.
- Redox indicator: A chemical that changes colour depending on its oxidation state, such as methylene blue.
- Respirometer: A device used to measure gas exchange during respiration.
No answer provided.
Exam Tips
Clearly state the purpose of a control experiment (e.g. boiled yeast shows respiration is due to living cells).
When discussing temperature, refer to enzyme denaturation and the optimum temperature for enzyme activity.
Avoid vague statements such as "rate increased" – explain why the rate changed in terms of particle collisions or enzyme activity.
No answer provided.
A student investigates the effect of temperature on the rate of respiration of glucose in yeast using a gas syringe to measure the volume of carbon dioxide produced. Describe how the student could ensure that the results are valid and reliable. (3 marks)
-
The student should keep the volume and concentration of glucose and yeast the same in all experimental conditions to ensure that only temperature is affecting the rate of respiration.
-
The student should use a water bath to maintain each temperature accurately throughout the experiment.
-
To improve reliability, the experiment should be repeated at each temperature, and the mean volume of carbon dioxide should be calculated.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!