A student set up four boiling tubes, labelled A to D, to find out which conditions are needed before seeds will germinate. Each tube held ten cress seeds re...
Question 1 Report
A student set up four boiling tubes, labelled A to D, to find out which conditions are needed before seeds will germinate. Each tube held ten cress seeds resting on a piece of cotton wool. The tubes were treated in different ways so that in each one a single condition was changed. In tube C the water was first boiled to drive out any dissolved air and then covered with a thin layer of oil. Fig. 6.1 shows how the apparatus was arranged and the table lists the conditions inside each tube, together with whether the seeds had germinated. The tubes were left in the same place for one week before the results were recorded.
| Tube | Water | Oxygen | Temperature | Germinated? |
|---|---|---|---|---|
| A | present | present | 20 °C | yes |
| B | none (dry) | present | 20 °C | no |
| C | present | none | 20 °C | no |
| D | present | present | 2 °C | no |
(a) State which tube acts as the control and give a reason for your answer. [2]
(b) State the condition being tested in tube B and the condition being tested in tube D. [2]
(c) Explain why the seeds in tube C did not germinate. [3]
(d) Name the gas released by the germinating seeds during respiration. [1]
(e) Suggest one way of making the results of this investigation more reliable. [1]
Answer Details
This is a controlled experiment on germination. A control has all conditions favourable so it shows what normal germination looks like; each other tube removes one factor to test whether it is needed.
- (a) Tube A is the control [1], because all the conditions are present/favourable, so it shows normal germination for comparison with the others [1].
- (b) Tube B (dry) tests water [1]; tube D (2 \(^{\circ}\)C) tests temperature / warmth [1].
- (c) In tube C there is no oxygen (it was boiled out and the oil stops it re-dissolving) [1]; so the seeds cannot carry out aerobic respiration [1]; and no energy is released for the processes of germination [1].
- (d) The gas released in respiration is carbon dioxide [1].
- (e) Make it more reliable by using more seeds in each tube / repeating the whole investigation and comparing the results [1].
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