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Year 8

Effects of Exercise on Cellular Respiration

Background information

Bromothymol blue (BMB) is a chemical indicator that changes colour as the pH of a solution changes. It is yellow in acidic solutions and blue in basic and neutral solutions. When carbon dioxide is dissolved in water, it creates carbonic acid, pH~5.7.

One of the products of Cellular Respiration is carbon dioxide. As cells produce CO2 in cellular respiration, it is carried by our blood cells to our lungs where it is exhaled. You can measure the rate your cells carry out cellular respiration by measuring how quickly you produce carbon dioxide. You will first determine your resting rate of cellular respiration, and then you will determine your rate after exercise.


1. Hypothesis: how will exercise affect the rate of cellular respiration?

2. What is the cellular respiration equation?


- Stop watch

- Drinking straw

- BMB solution

- Conical flasks

- Graduated cylinders

- Safety Goggles


- Fill the beaker with 100 mL BMB solution

- One person is the timer while the other person performs the experiment

- When the person timing says ‘Start”, the experimenter will exhale through the straw, until the timer can see a colour change ( greenish)


- Once the colour has changed Stop the clock.

- Record the time it took for the colour change.

- Empty the conical flask and re-fill it will 100 ml of BMB

- Have the experimenter do exercise for 2 minutes.

o Jumping jacks

o Push ups

o Sit ups

o Squats

o Running laps

- You should feel winded after the exercise

- Using the same straw, exhale into the solution the same way and record how long it takes for a colour change to occur.

- Record the time taken.

- Empty the conical flask and re-fill it again with 100 ml of BMB

- This time do 5 min of exercises

- Again, blow into the BMB and record the time taken to change colour.


Plot the Data on the graph bellow (7 marks)















1. Explain why there was a difference in time before and after exercise

2. Using the graph, if you did the activity for 8 minutes straight, how quick would you expect a colour change?

3. What was the: (3marks)

a. Independent variable  ________________

b. Dependant variable ________________

c. Aim ________________

4. List 3 things a cell would use energy for? (3 marks)

a. ______________

b. ______________

c. ______________

(Hint, what do all cells do)

   5. Explain why the time between individuals may vary after exercise? (3 marks)

6. If you could do the experiment again how would you change it to improve the accuracy of your results?

Total marks       /21 marks

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