1.1. Explain how autotrophs are different from heterotrophs.

1.2. A student wanted to set up an investigation to show that photosynthesis requires carbon dioxide.

The method they followed can be seen below:

1. De-starch 2 plants of the same species and size

2. Place each plant under a bell jar (bell jars A and B)

3. Put NaHCO₃ in bell jar A with the first plant

4. Put NaOH solution in bell jar B with the second plant.

5. Place a bung with delivery tubes in the top of bell jar A and B to allow an airflow

6. Add some soda lime to the inlet tube of jar B

7. Put the apparatus in full sunlight and leave for 24 hours.

8. Observe the results of the investigation.

The set up described in points 2 to 6 can be as seen in Figure 1.

Figure 1

The independent variable in the investigation is the presence or absence of carbon dioxide.

Suggest how stages 3, 4 and 6 allow the student to test the independent variable.

1.3. Stage 1 of the method described in part (b) refers to 'de-starching' the plants.

Describe how a plant may be de-starched and explain the purpose of de-starching in stage 1.

1.4. Before the student completed the investigation described in part (b), he made the following prediction:

'The plant in bell jar B will not photosynthesize'

After the investigation was complete, the student observed the plants but noted no fundamental differences in their visible appearance.

Describe another method that the student should use to show that the plant in bell jar A had photosynthesized whereas the plant in bell jar B had not.