Integrated Science | Unit 7 | Practicals 7.5–7.7

Necessary factors for photosynthesis

Investigate water, light, carbon dioxide and chlorophyll, then test a leaf for starch.

Experiment progress

1Destarch

2Set up

3Expose

4Iodine test

3D experiment model

Drag to orbit, scroll to zoom, or use the arrow buttons.

Loading real 3D laboratory…

Drag to orbit · Scroll to zoom

Soda lime absorbs CO₂

24 HOURS IN DARKNESSExisting starch is used up or transported away

Plant sealed beneath a transparent bell jar

Destarch the plant first

Keep the plant in darkness for at least 24 hours before changing any factor.

Change one factor at a time to make a fair comparison.

1. Destarch the plant

Darkness stops photosynthesis. The plant uses or transports away its stored starch.

2. Choose the conditions

Switch off the factor you want to investigate. Keep the other factors present.

Water Light Carbon dioxide Chlorophyll

3. Allow time for photosynthesis

☀Four hours completedConditions recorded

Now remove a leaf and test it for starch.

4. Iodine test for starch

1Boil in waterSoftens

2Heat in alcoholDecolourises

3Rinse in waterSoftens

4Add iodineTests starch

Use a hot-water bath for alcohol. Alcohol is flammable and must be kept away from naked flames.