Photosynthesis practicals – starch test on leaves and hydrogencarbonate indicator
BiologyPlant PhysiologyAges 12–13
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Sign in to playTwo virtual practicals on photosynthesis and gas exchange. Destarch a plant for 48 h in the dark, light variegated leaves, foil-covered leaves and leaves sealed with soda lime, then test them for starch (boiling water, ethanol in a water bath, warm water rinse, iodine solution). Put pondweed and snails in hydrogencarbonate indicator tubes in light, dim light and dark and follow the colour (purple: low CO₂, red: as in air, yellow: high CO₂), with results tables and the conclusion each control supports.
Lesson: Photosynthesis: chlorophyll, light and carbon dioxide are needed for starch production; gas exchange in plants and animals shown with hydrogencarbonate indicator
What it shows
This virtual lab covers two classic photosynthesis practicals for ages 12–16. On the first bench students destarch a plant, set up a variegated leaf, a leaf partly covered with foil or a leaf sealed with soda lime, and test each leaf for starch step by step, learning why each step is done. On the second bench they place pondweed and snails in sealed tubes of hydrogencarbonate indicator in light, dim light and dark, watch the colour and pH change and record the results. Model: starch production and gas-exchange rates are simplified illustrative values.
How to use
On Starch test, choose an Experiment, tick or untick Destarch the plant first and set Time in the light. Press Next step (or Run all steps), then Record result. On Hydrogencarbonate indicator, choose a Set-up, set Lamp distance, click a tube to change its contents and light, then press Start and Record result.
Parameters you can change
- Starting screen Starch test, Hydrogencarbonate indicator
- Starch test experiment Variegated leaf (chlorophyll), Foil strip (light), Soda lime flask (CO₂)
- Destarch the plant first (48 h in the dark)
- Time in the light 0–12 h
- Indicator tube set-up Pondweed and snails, light – dim – dark, Pondweed at different light levels, Snails, snails + pondweed at different light levels
- Lamp distance from the tubes 10–60 cm
Questions to explore
- Why must the plant be destarched before the starch test?
- Which part of each leaf acts as the control, and what does comparing it with the test part show?
- Why does the indicator in the tube with pondweed in dim light stay red?
