Hydrogencarbonate indicator is purple when the carbon dioxide concentration is low, red when it is the same as in normal air and yellow when it is high.
A student sets up four tubes of hydrogencarbonate indicator and seals each tube with a bung. All four tubes start red.
The Table shows the tubes and the colour of the indicator after 3 hours.
Table
| Tube | Contents | Conditions | Colour after 3 hours |
|---|---|---|---|
| A | leaf | bright light | purple |
| B | leaf | dim light | red |
| C | leaf | dark | yellow |
| D | no leaf | bright light | red |
Explain the result in tube A.
The leaf in tube B is photosynthesising, but the indicator stays red.
Explain why.
Explain why the student set up tube D.
Suggest why each tube is sealed with a bung.
117 exam-style questions on OCR GCSE Biology 1.4 Photosynthesis, covering 1.4.1 Photosynthesisers as biomass producers, 1.4.2 Factors affecting the rate of photosynthesis, and 1.4.3 Limiting factors in photosynthesis. Each one has a worked solution and a mark scheme showing where the marks go.