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Year 8

BMB and plants

Bromothymol blue (BMB) is a chemical indicator. During a neutral pH its colour is green, when it becomes for acid it turns yellow, and when it is more alkaline it become blue.

Carbon dioxide (CO2) when combine with water (H2O) forms Carbonic acid (H2O3). This should cause a colour change in the BMB to yellow.

In this practical you will be measuring the amount of Carbon Dioxide and Oxygen produced by plants through out the day.


1. Get three test tubes

2. Label the test tube A, B and C and write your initials on them.

3. Place one small stalk of Elodea in test tubes B and C

4. Pour BMB into all the test tubes so the elodea is covered

5. Take a picture of each test tube, make sure you show the label

6. Place test tubes A and B on the bench near sun light

7. Place test tubes C in a dark area

8. Leave it over night

9. Complete questions 1 to 5

10. Come back the net morning and observe the colour

11. Take a picture of the colour change (make sure you show the labels.)



1. What is the formula for photosynthesis (1 mark)

2. What is the formula for aerobic respiration (1 mark)

3. In the experiment above what was the (3 marks):

a. Aim ______________________

b. Independent variable  ___________________

c. Dependant variable ___________________

4. What is your hypothesis ?

5. Explain the purpose of photosynthesis and why it is important to all life (3 marks)

6. What happened to the BMB in test tube A, why did this happen and what was the purpose of having this test tube? (2 marks)

7. What happened to the BMB in test tube B and explain what was happening in the test tube (2 marks)

8. What happened to the BMB in test tube C and explain why this happened (2 marks)

9. If you could change this experiment to make the results more accurate, what would you change?

Click here for a word document of the practical

Click here to make a poster of photosynthesis

       Total marks        /15