A seed lands somewhere, waits, and then starts growing. Both halves of that sentence hide a genuine puzzle: why move away from a parent that is clearly thriving, and why wait at all rather than germinate immediately? Answer those two and the whole page falls into place.
📘 What you need to know
Seed dispersal distributes seeds away from the parent plant, reducing competition between offspring and parent for light, water and minerals.
Seeds are dispersed by wind or water, by animals (eaten and egested, or hooked onto fur), or by explosive pods.
Dispersal is not pollination. Pollination moves pollen from anther to stigma; dispersal moves mature seeds.
After forming, seeds enter a period of dormancy and germinate only when conditions are favourable.
Germination requires water, oxygen and warmth — and you must be able to say why each is needed.
Water is taken up by imbibition, which activates the biochemistry of the embryo and increases metabolic activity.
The radicle emerges first and grows downwards; the hypocotyl is the first structure to appear above ground.
Why disperse at all?
It looks like a bad idea. The parent plant is growing successfully in that spot, which is direct evidence that the conditions there suit the species. Dropping seeds nearby seems safer than scattering them into the unknown.
The problem is that a seedling and its parent need exactly the same things: light, water and mineral ions. Falling at the base of a mature plant means growing in its shade, in soil its roots have already stripped. So the offspring lose the competition before they start. Dispersal trades a small chance of landing somewhere unsuitable for a much better chance of not being out-competed immediately — and as a bonus, it lets the species spread into ground the parent could never reach.
Fleshy fruit is worth thinking about as a payment. The plant spends energy on sugar so that an animal will carry the seed a long way and deposit it with a supply of fertiliser.
⚠️ The one confusion to fix now
Pollination transfers pollen from an anther to a stigma. It happens before fertilisation and is about getting gametes together.
Seed dispersal distributes mature seeds away from the parent. It happens after fertilisation and is about reducing competition.
Both can involve wind, water or animals, which is exactly why they get muddled. The distinguishing question is always: what is being moved?
Dormancy: why wait?
Once a seed has formed inside the ovary of a flower, it does not germinate straight away. It enters a period of dormancy and stays inactive until conditions become favourable. Germination is the start of growth in the seed.
The reason for waiting is simple survival arithmetic. A seedling has almost no reserves and cannot survive a cold or dry spell. A dormant seed can. By staying inactive until water, oxygen and warmth are all present at once, the seed avoids committing its one-shot food store to a season it cannot finish.
The three requirements
Requirement
Why it is needed
Water
Absorbed by imbibition, it makes the seed swell so the seed coat (testa) bursts and the embryo can emerge. It also activates the enzymes so metabolic activity can increase
Oxygen
Needed for aerobic respiration, which releases the energy required for growth
Warmth
The reactions of germination are controlled by enzymes, which work slowly at low temperatures; germination improves as temperature rises, up to a point
Notice what is not on that list: light. A seed germinating underground has no light and does not need any, because it is living entirely off its own food store. Light only becomes essential once the first leaves are open and photosynthesis has to take over. Questions that offer “light” as a requirement are testing exactly this.
What actually happens
The seed is running on a fixed budget throughout stages 1 to 4. Stage 5 is the moment it stops spending and starts earning.
In more detail: a seed contains a plant embryo and a store of food reserves. That store is endosperm tissue, transferred to the embryo through early leaf structures called cotyledons. During dormancy the seed loses water, so the first thing it must do is replace it, by imbibition. Taking up water activates the biochemistry of the embryo.
The rate of respiration and protein synthesis then increases, and the embryo prepares to break out through the seed coat. The radicle is the first structure to emerge; it responds to gravity and grows downwards, forming the initial root. The first structure to appear above ground is the hypocotyl, a curved portion of the shoot found below the cotyledons, which grows upwards. As the shoot grows, the first leaves appear from the cotyledon and photosynthesis can begin. Once the root system is established, full growth follows.
Why the root comes first. Everything the seedling needs next depends on it: anchorage, water uptake and the mineral ions required to build new tissue. Sending up a shoot first would risk the whole plant on a food store that will run out before it can be replaced. It is a sequencing decision, and examiners reward you for saying so.
Worked examples
WORKED EXAMPLE
Seeds were placed in four tubes. Only the tube with damp cotton wool at 20 degrees Celsius germinated; a tube with damp cotton wool at 20 degrees Celsius covered in oil did not. Explain the result for the oil-covered tube. [2]
Identify what the oil changeswater is present, temperature is the same — only one variable is leftName it and follow the consequencethe oil layer prevents oxygen from reaching the seedswithout oxygen there is no aerobic respiration, so insufficient energy is released for growth1 mark for oxygen excluded, 1 mark for respiration and energycontrolled-variable questions want you to spot the ONE difference, then explain it
WORKED EXAMPLE
A plant produces fleshy, brightly coloured fruit. Suggest how this aids seed dispersal and state one advantage of dispersal to the plant. [3]
Ask what the colour and the flesh are forthe bright colour and flesh attract animals, which eat the fruitthe seeds pass through the gut undamaged and are egested some distance awayGive the advantage, with a named resourceseedlings do not compete with the parent plant for light, water or mineral ions3 marks: attraction and consumption, egestion away from the parent, reduced competitionnaming the resource is what turns a vague “less competition” into a scoring answer
💡 Exam tips
Never list a germination requirement without its reason. “Oxygen for aerobic respiration to release energy” is the full answer.
If a question mentions light as a possible requirement for germination, say clearly that it is not needed, because the seed lives on its stored food until leaves open.
Keep the order straight: radicle first (downwards), then the hypocotyl and shoot (upwards), then the first leaves.
For dispersal questions, always name the resource being competed for. “Reduces competition” alone is usually too vague.
In experiment questions, find the single variable that differs between tubes and build your explanation around that.
⚠️ Common mix-ups
Confusing dispersal with pollination. The commonest error on this page, precisely because both use wind, water and animals.
Saying seeds need light to germinate. They do not, and saying so suggests you have not understood the food store.
Writing that warmth is needed “to give energy”. Energy comes from respiration. Warmth is needed because enzymes work too slowly when cold.
Muddling the seed and the fruit. The ovule becomes the seed and the ovary becomes the fruit — the fruit is the packaging.
Saying the shoot appears first. The radicle emerges first; the hypocotyl is the first structure above ground, which is a different claim.
Treating dormancy as a failure to germinate. It is an active strategy for surviving until conditions are right.
Up next: Inheritance — the alleles shuffled by meiosis and combined at fertilisation finally show themselves in the offspring, and we start predicting the outcomes.
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