Plant Biology: Germination, Photosynthesis and Pollination
From a seed in the dark to a flower waiting for a bee. What a seed needs to start, what each part of a plant is for, how photosynthesis feeds nearly everything alive, and the difference between pollination and fertilisation.
Justify the choices, the way you are assessed
Free interactive practice on the decisions the assessment actually asks you to justify.
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Three things, and light is not one
A seed is a plant on pause. To restart it needs exactly three things: **water**, **oxygen** and a **suitable temperature**. Water is absorbed and the seed swells until the seed coat splits. Oxygen is needed because the seed respires to release the energy stored in it. Temperature has to be warm enough for those reactions to run, which is why sowing dates matter. **Light is not required.** A seed germinates perfectly well buried in the dark, and it has to, because it is buried. Light matters afterwards, once the first leaves are up.
What does a seed need?
Select the TWO conditions a seed must have in order to germinate.
- Water
- Oxygen
- Light
- Fertiliser
How a seed gets going
Put the stages of germination into the order they happen.
- The seed absorbs water and swells until the seed coat splits
- The radicle, the first root, emerges and grows downwards
- Root hairs develop, taking up water and minerals from the soil
- The plumule, the first shoot, grows upwards towards the surface
- The first true leaves open and the seedling begins to feed itself
Four words for a seedling
These four come up constantly in germination questions.
Roots, stems and leaves
- The root
- The stem
- The leaf
- The root hairs
- Anchors the plant and takes up water and minerals from the soil
- Supports the plant and carries water and food between the roots and the leaves
- Broad and flat to catch light, and the site of photosynthesis
- Multiply the surface area available for absorption many times over
The reaction everything depends on
Green plants make their own food. The word equation is the one to learn: **carbon dioxide + water, using light energy and chlorophyll, produces glucose + oxygen** Two things follow, and both are examinable. The glucose is the start of nearly every food chain there is, including the one that ends with us. And the oxygen is released as a by-product, which is what animals breathe. A plant is not doing this for our benefit. It is making sugar, and the oxygen is what is left over.
Fill in the reaction
In photosynthesis a plant takes in _____ through its leaves and _____ through its roots. Using light energy captured by _____, it produces _____ for food, and releases _____ as a by-product.
Why the rainforests matter
Rainforests are described as important for life on earth. What are they actually doing?
- Photosynthesising on a huge scale, so they absorb large amounts of carbon dioxide and release large amounts of oxygen
- Producing oxygen only, since carbon dioxide is dealt with by the oceans
- Making rain, which is where the name comes from
- Building deep, fertile soils that feed the world
Label the flower
Six parts of this flower are marked. Drag the right name onto each. Two of the labels are plant parts that are not found in a flower at all.
Bribery or broadcasting
A flower has one job: get its pollen onto another flower's stigma. There are two strategies, and every feature of the flower follows from which one it uses.
Which flower is wind-pollinated?
A flower has no scent, no nectar, dull green parts, and anthers dangling outside on long stalks. What can you conclude, and why?
- It is wind-pollinated: with nothing to attract an insect and its anthers hanging in the open air, it is broadcasting pollen rather than paying a courier
- It is insect-pollinated, because all flowers rely on insects
- It is a diseased flower, since healthy flowers are brightly coloured
- There is no way to tell without watching it
Pollination is not fertilisation
**"Explain the difference between pollination and fertilisation. (4 marks)"** "Pollination is the transfer of pollen from an anther to a stigma, carried by an insect or by the wind. It is a journey, and it can happen without anything else following." "Fertilisation happens afterwards and inside the flower. A pollen tube grows down through the style to an ovule in the ovary, and the male nucleus fuses with the female nucleus there. That fusion is fertilisation, and it is what produces a seed." One is delivery, the other is what happens on arrival. Using the two words as if they meant the same thing loses marks in both directions.
Match each life cycle to an example
- Annual: completes its whole life cycle within one year
- Biennial: grows in the first year, then flowers and seeds in the second
- Perennial: lives for many years, flowering more than once
- Why a farmer cares which it is
- Barley, sown and harvested in the same growing season
- The carrot, which stores food in its root over winter before running to seed
- Perennial ryegrass, cut for silage year after year from the same ley
- It decides how often the ground must be resown and when the crop can be harvested
State why bee decline matters
Build a sentence explaining the agricultural consequence of falling bee numbers.
Fewer bees than last year
A fruit grower has noticed far fewer pollinating insects on the farm and a poorer fruit set. Work through it.
- Why would fewer insects reduce the amount of fruit, specifically?
- The neighbouring farm grows only wheat and reports no such problem. Why not?
- What could the grower actually do about it on their own land?
Your turn: from seed to seed
Explain how a plant gets from a sown seed to producing seed of its own, and what it needs at each stage.
- Name the three conditions a seed needs to germinate, and say why light is not one of them
- Explain what the radicle and the plumule do, and why they appear in that order
- Give the word equation for photosynthesis and say what the plant gains from it
- Explain the difference between pollination and fertilisation