2.1.5Reproduction and Inheritance
Practical: Conditions for Germination — Edexcel International GCSE Science Double Award (Modular) - Biology Unit 2 Revision Notes & Topical Questions
5 min read 6 parts Lesson 6 of 28
Section 1 of 6What seeds need and why
Germination
Water
- Water Water is absorbed so the seed swells and the seed coat splits.
- It also allows enzymes to become active so that stored food can be broken down.
Oxygen
- Oxygen The growing seed respires aerobically to release energy for growth, which needs oxygen.
Suitable temperature
- Suitable temperature Warmth raises the rate of enzyme-controlled reactions.
- If it is too cold the reactions are too slow, and if it is too hot the enzymes are damaged.
Section 2 of 6Apparatus and method
1
Label four test tubes A, B, C and D and place a layer of cotton wool in the bottom of each.
2
Put 10 cress seeds of the same type on the cotton wool in every tube.
3
Tube A: leave the cotton wool dry, so no water is available.
4
Tube B: dampen the cotton wool with water. This is the control, with water, oxygen and warmth all present.
5
Tube C: cover the seeds completely with boiled and cooled water, then add a thin layer of oil on top to stop oxygen dissolving in.
6
Tube D: dampen the cotton wool as in B, but place the tube in a fridge at about 4 °C.
7
Keep A, B and C at room temperature, around 20 °C, for 3 to 5 days, checking that B and D stay damp.
8
Count the number of seeds that have germinated in each tube.
Section 3 of 6Expected results
| Tube | Condition being tested | Factor missing | Seeds germinate? |
|---|---|---|---|
| A | Water | Water | No |
| B | Control | None | Yes |
| C | Oxygen | Oxygen (blocked by water and oil) | No |
| D | Warmth | Warmth (cold fridge) | No |
Section 4 of 6Variables and reliability
Variables
- Variables The independent variable is the condition changed from tube to tube.
- The dependent variable is the number of seeds that germinate.
- Control variables include the type and age of seed, the number of seeds, the amount of cotton wool and the time left.
Making it reliable
- Making it reliable Repeat the whole investigation several times and use plenty of seeds per tube, then calculate a mean percentage germination.
Safety and fairness
- Safety and fairness Wash hands after handling seeds and cotton wool, and keep the tubes away from the edge of the bench.
- Boil and cool the water for tube C so it holds almost no dissolved oxygen.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Germination | The start of growth of a seed into a seedling. |
| Control | A set-up with all conditions present, used for comparison. |
| Independent variable | The factor that the investigator deliberately changes. |
| Dependent variable | The factor that is measured as the outcome. |
| Aerobic respiration | Respiration using oxygen to release energy from glucose. |
| Reliable | Giving similar results when the investigation is repeated. |
Section 6 of 6Exam technique
1
Saying that seeds need light or soil to germinate. The investigation shows that water, oxygen and warmth are needed; seeds can germinate in the dark.
2
Changing more than one factor between tubes, which makes the conclusion invalid.
3
Forgetting that tube B is a control that must show germination for the experiment to be meaningful.
4
Not explaining why the oil layer is added; it prevents air from reaching the seeds.
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