Plant Reproduction, Grade 7
Practical task 1 is called "grow a plant and observe its life cycle". It cannot reach a life cycle.
As it is set, a bean sits between two layers of wet cotton wool for two weeks. That gets you germination and a seedling, and then it stops, because a seed living on its own food reserves in a dish has nothing to root into and nothing to feed on.
A life cycle is seed, seedling, adult plant, flower, fruit, seed again. To see it you have to pot the seedling on. This page is the assessed task done properly, with the pot-on step, and a free worksheet and memo.
Where this fits in the curriculum
| Subject | Natural Sciences |
|---|---|
| Grade | 7 |
| Term | 1 |
| Strand | Life and Living |
| Topic | Sexual reproduction, Unit 1: reproduction in flowering plants |
| Status | Practical task 1, formally assessed, 20 marks |
| Marks | 20 for the task. The topic revision is 20 and covers human reproduction too. Our worksheet is 40 |
The parts of a flower
| Whorl | Parts | Job |
|---|---|---|
| Sepals | The green outer ring | Protect the bud before it opens |
| Petals | The coloured ring | Attract pollinators. Nectar glands sit at their base |
| Stamens, the male parts | Anther on a filament | The anther makes and holds the pollen |
| Pistil, the female parts | Stigma, style, ovary, ovules | Receives pollen and holds the egg cells |
One definition is worth checking before you hand out a diagram.
The style connects the OVARY to the stigma. You will find it defined as connecting the ovule to the stigma, which is wrong, and the same topic states it correctly a page later.
The ovules sit inside the ovary. The style is the stalk above the ovary that the pollen tube grows down.
Where the word comes from
An angiosperm is a plant whose seeds develop inside a fruit. The word is Greek: angeion, meaning a vessel or container, and sperma, meaning seed. Seed in a vessel.
You will see the first half given as "angus". There is no Greek word angus, and the real one is worth having, because angeion is the same root as angiogram and angioplasty, which are both about blood vessels.
A gymnosperm is the opposite: gymnos, naked, so a naked seed sitting on a cone scale rather than wrapped in a fruit. Pines and cycads.
Pollination: getting the pollen there
Pollination is the transfer of pollen from an anther to a stigma of the same species. It is not fertilisation. Fertilisation happens afterwards, inside the ovule.
| Self-pollination | Cross-pollination | |
|---|---|---|
| Pollen goes | To a stigma on the same plant | To a stigma on a different plant of the same species |
| Advantage | Works without a pollinator | More variation in the offspring |
How to tell what pollinates a flower by looking at it
| Feature | Wind-pollinated | Insect or bird pollinated |
|---|---|---|
| Petals | Small, green, or none | Large and brightly coloured |
| Scent and nectar | None | Usually both, though bird flowers often have no scent |
| Anthers | Hanging outside, loose on long filaments | Inside, where a visitor must brush past |
| Stigma | Large and feathery, to catch drifting pollen | Small and sticky |
| Pollen | Huge amounts, light and dry | Less, and often sticky or spiky |
Grasses are the wind-pollinated flower everyone can find, and the anthers dangling on threads are unmistakable once a class has been shown one.
For bird pollination, aloes and a sunbird are the South African example. Aloe flowers are red or orange, full of nectar, tough enough to take a bird's weight, and they flower in winter when there is little else about.
Fertilisation, and the bit that is done well
- A pollen grain lands on a stigma of the same species and sticks
- A pollen tube grows down through the style into the ovary
- Each pollen grain carries two male gametes down that tube
- One fuses with the egg cell to make the zygote, which becomes the embryo plant
- The other fuses with two more cells to make the endosperm, the food store the seedling lives on
That last pair of steps is double fertilisation, and it is unusual to find it correct at this level. It is worth teaching properly, because it explains where the food in a seed actually comes from: it is made at the moment of fertilisation, not stored by the parent beforehand.
| Before | Becomes |
|---|---|
| Ovule | Seed |
| Ovary | Fruit |
| Zygote | Embryo |
| Petals, stamens, style | Wither and drop off |
Seed dispersal, with a plant that rolls
| Method | How | Example |
|---|---|---|
| Wind | Wings, parachutes, or the whole plant rolling | Dandelion, jacaranda, and Brunsvigia |
| Water | Floats | The coconut fruit, which is what floats, not the seed alone |
| Animals | Eaten and passed, or hooked onto fur | Camelthorn pods, blackjacks |
| Self | The pod dries, twists and flings the seeds | Peas and beans |
Brunsvigia is the one to use. After flowering, the whole dried head snaps off and rolls across the veld like a wheel, scattering seed as it goes. It is a South African plant doing something no diagram of a dandelion can match.
Practical task 1, done so it reaches a life cycle
Run the assessed part exactly as set. Then pot it on.
Part 1: germination, which is the assessed fortnight
- Put a bean or maize seed between two layers of damp cotton wool in a Petri dish
- Spray daily so it stays damp, never soaked
- Once the shoot appears, take the top layer off
- Measure root length, shoot length and leaf number every second day for two weeks
- Draw it at least twice, and plot the measurements on a line graph
Part 2: the rest of the cycle, which the title promises
- After two weeks, pot the seedling into soil, deep enough to cover the roots
- Water it and put it in the light
- Keep it going. A bean will flower in roughly eight to ten weeks and set pods after that
- Open a pod at the end and find the new seeds. That is the cycle closed
Beans are the right plant for this because they are fast, they are big enough to watch, and a dwarf bean will flower and pod on a windowsill inside a term.
If it does not work
| Problem | Cause | Fix |
|---|---|---|
| The seed rotted and smells | Soaked, not damp. The commonest failure | Damp cotton wool, lid off or ajar, spray rather than pour |
| Nothing has happened after a week | Old seed, or too cold | Fresh seed from a packet, and somewhere warm but not hot |
| It germinated then died in week three | It ran out of food. The cotton wool feeds it nothing | That is exactly why it has to be potted on |
| Roots grew into the cotton wool and tore when moved | Left too long before potting | Pot it at two weeks, and plant the cotton wool with it |
| It grew tall, pale and floppy | Not enough light | A windowsill. Pale and leggy means it is stretching for light |
| It flowered but set no pods | No pollinator indoors | Dab the flowers with a soft brush. Beans mostly self-pollinate, but a nudge helps |
How the 40 marks are made up
| Part | Marks |
|---|---|
| The parts of a flower and their jobs | 10 |
| Pollination, and reading a flower for its pollinator | 9 |
| Fertilisation, and what becomes what | 8 |
| The germination investigation and its graph | 9 |
| Seed dispersal | 4 |
The formally assessed task is 20 marks. The topic revision is 20 and covers human reproduction as well. Our worksheet is 40 and the split above is ours.
Free worksheet and marking memo
Both free, no sign up, straight to the PDF.
- Learner worksheet, 40 marks, including the labelled flower, the pollinator table and the growth graph
- Marking memorandum, with what to accept and the five answers that look right and score nothing
Related practicals
- Human Reproduction, Grade 7. The other half of the same topic
- Biodiversity and Classification, Grade 7. Monocots and dicots, and splitting a seed to tell them apart
- The Biosphere, Grade 7. Reproduction as one of the seven life processes
- Photosynthesis and Respiration, Grade 8. How the plant feeds itself once the seed's food runs out
What you need to run it
| Item | Price | What it is for |
|---|---|---|
| Petri dish, sterile | R48,88 | One per learner. You can watch the root from underneath without disturbing it |
| Wash bottle | R36 | Better than a spray bottle for damping cotton wool without flooding it |
| Basic botany slide set of 25 | R495 | Sections through ovaries, anthers and seeds, for when the real thing is too small |
The assessed task needs a Petri dish, cotton wool and a bean. Everything else is a pot of soil and a windowsill.
We do not sell seeds, cotton wool or potting soil, and all three are cheaper at a supermarket than anywhere else.
Petri dishes are in laboratory plasticware and the slides are in microscope slides.