Investigate the conditions for Germination

Germination is the process where a seed begins to grow into a young plant (a seedling). A dry seed is dormant — alive but resting — until the right conditions wake it up.

For germination to start, a seed needs three conditions:

1. Water — the seed takes up water, which activates enzymes and lets the stored food be used. Water also makes the seed swell so the young root and shoot can push out.
2. Oxygen — the seed needs oxygen for aerobic respiration, which releases the energy needed for growth.
3. A suitable (warm) temperature — warmth lets the enzymes work at a good rate. Too cold and the enzymes work too slowly; very hot and they would be damaged.

Light is NOT needed for germination. This often surprises students. A seed contains its own food store (for example, starch in a seed leaf), so it does not need to photosynthesise to germinate. It can sprout perfectly well in the dark — light only becomes important later, once the green shoot is above ground and needs to photosynthesise.

Exam tip. Learn the three conditions as a set — water, oxygen, warmth — and be ready to state clearly that light is not required. A very common 1-mark trap asks which factor is not needed, and the answer is light.

The standard way to investigate germination is to set up several test tubes (or boiling tubes) of cress or bean seeds, each on damp cotton wool, and remove one condition from each tube. By comparing them you can see which condition each seed was missing.

A typical set-up uses four tubes:

Tube	Set-up	Condition removed
A — Control	Damp cotton wool, at room temperature (~20 °C), with air	None (has water, oxygen, warmth)
B — No water	Dry cotton wool, room temperature, with air	Water
C — No oxygen	Cotton wool soaked in boiled (then cooled) water, covered with a layer of oil to keep air out, room temperature	Oxygen
D — No warmth	Damp cotton wool, placed in a fridge (~4 °C), with air	Warmth

How each tube removes a factor:

• Boiling the water drives out the dissolved oxygen, and the layer of oil stops more oxygen dissolving back in from the air — so tube C has no oxygen.
• The fridge keeps tube D cold, so the enzymes work far too slowly to germinate.

Making it a fair test. The whole point is to change only one variable at a time. Everything else — the type and number of seeds, the volume of water/cotton wool, the time left, and so on — must be kept the same. Only then can you be sure that any difference is caused by the one factor you removed.

The control (tube A) has all three conditions and is what you compare the others against. Without a control you could not tell whether the seeds were capable of germinating in the first place.

Leave the tubes for about one week, keeping conditions constant, then record how many seeds have germinated in each.

Exam tip. Be ready to explain why each step removes a factor — especially "boiled, cooled water + oil removes oxygen". Examiners love asking you to justify a step rather than just describe it.

After about a week, you compare the tubes. The expected results are:

Tube	Condition removed	Result
A — Control	none	seeds germinate well
B — No water	water	seeds do not germinate
C — No oxygen	oxygen	seeds do not germinate
D — No warmth	warmth	little or no germination

How to read this. When you remove a factor and germination stops (or is greatly reduced) compared with the control, that factor must be needed for germination. So:

• Tube B failing shows water is needed.
• Tube C failing shows oxygen is needed.
• Tube D failing shows a suitable (warm) temperature is needed.

Conclusion. Seeds need water, oxygen and a suitable temperature to germinate. (You could also set up a fifth tube kept in the dark with all three conditions; it would still germinate, confirming that light is not needed.)

Here is a simple diagram of the four-tube set-up and the result you expect:

Exam tip. State the conclusion in terms of the comparison with the control: "because the seeds without water/oxygen/warmth did not germinate but the control did, each of these is needed for germination". Linking back to the control is what earns the explanation marks.

Good practical answers use the language of variables:

• Independent variable — the factor you change between tubes (the condition you remove: water or oxygen or warmth).
• Dependent variable — what you measure: the number (or percentage) of seeds that germinate (or the length of the shoot/root).
• Control variables — everything you keep the same: the type and number of seeds, the amount of cotton wool, the volume of water, the time left, and (apart from the factor being tested) the temperature and air supply.

Why keep everything else the same? If two things changed at once, you would not know which one caused the difference. Changing only one variable at a time makes it a fair test.

Reliability. To make your results more reliable, use lots of seeds in each tube (say 10–20) rather than one, and repeat the whole experiment. With more seeds you can work out the percentage that germinated, which is fairer than a single yes/no result. Repeats let you check the result is consistent and not a one-off fluke.

Validity. The investigation is valid only if you really did control the other factors — for example, if tube C had no oil, oxygen could dissolve back in and your "no oxygen" tube would not truly be oxygen-free, making the result invalid.

Exam tip. If asked "how would you improve this investigation?", reliable, high-scoring answers are: use more seeds, repeat the experiment, and calculate a percentage. Saying "do it more carefully" is too vague to score.

A strong practical answer doesn't just give results — it evaluates them and suggests improvements.

Things that could go wrong and how to fix them:

• Oxygen leaking into tube C. If you forget the oil layer (or use too little), air can dissolve back into the water, so the tube is not truly oxygen-free. Fix: always add a clear layer of oil on top.
• Too few seeds. With only one or two seeds, one dud seed (already dead) ruins the result. Fix: use many seeds and work out a percentage germinated.
• The fridge changes two things at once. A fridge is cold and dark — but since light is not needed for germination, the darkness does not affect the result, so cold remains the only factor that matters. (It is still worth mentioning you have thought about this.)
• Not enough time. Different seeds germinate at different speeds. Fix: leave all tubes for the same, sufficient time (about a week).
• Mould. Damp, warm conditions can grow mould, which can be mistaken for germination or harm the seeds. Fix: use clean apparatus and the same conditions for all tubes.

Anomalies. If one seed in the control fails to germinate, treat it as an anomalous result — it was probably already dead. This is exactly why using many seeds and a percentage is better than relying on one.

Exam tip. Evaluation marks reward specific, scientific improvements. Best answers name the weakness (e.g. "oxygen could re-dissolve") and the fix ("add an oil layer"), and explain how using more seeds and repeats makes the conclusion more reliable.