Flowers and Plant Life Cycles
Section: Biology | Syllabus: Cambridge Primary Stage 5 Science (0097)
Flowering and Non-flowering Plants
- Not every plant produces flowers - plants are divided into two broad groups based on how they reproduce.
- Flowering plants produce flowers that contain the structures needed for reproduction.
- Non-flowering plants include mosses, ferns and conifers
- conifers (such as pine and fir trees) produce seeds in cones instead of flowers
- ferns and mosses reproduce using spores rather than seeds
- Many trees do flower, even though the flowers may be small, green or present for only a short time each year - a flower does not have to be large or brightly coloured to count as a flower.
Parts of a Flower and Their Functions
- A flower is built from several parts, each with a specific job in reproduction.
- The male parts of a flower make up the stamen, which produces pollen
- anther - produces pollen grains
- filament - the thin stalk that holds the anther up
- The female parts of a flower make up the carpel, which receives pollen and develops into fruit
- stigma - the sticky surface that receives pollen
- style - the stalk connecting the stigma to the ovary
- ovary - contains the ovules and develops into the fruit after fertilisation
- Other parts protect the flower or attract pollinators
- petals - often brightly coloured or scented to attract pollinators
- sepals - usually green; protect the flower bud before it opens
The stamen is the male part of a flower; the carpel is the female part
| Part | Male or female | Function |
|---|---|---|
| Petal | - | Attracts pollinators with colour and scent |
| Sepal | - | Protects the flower bud |
| Anther | Male | Produces pollen |
| Filament | Male | Holds up the anther |
| Stigma | Female | Receives pollen |
| Style | Female | Connects stigma to ovary |
| Ovary | Female | Contains ovules; develops into fruit |
The Flowering Plant Life Cycle
- A flowering plant passes through the same repeating stages every generation.
The flowering plant life cycle repeats from seed back to seed
Pollination
- Pollination is the transfer of pollen from an anther to a stigma.
- Pollen can be carried between flowers by insects, other animals, wind or water.
- If pollen lands on the stigma of the same type of plant, it can lead to fertilisation and the production of seeds.
Fruit and Seed Production
- After fertilisation, the ovary develops into a fruit, and the ovules inside it develop into seeds.
- In science, a fruit is any structure that contains one or more seeds - this includes pods, nuts and grains, not just sweet, fleshy foods.
Seed Dispersal
- Seed dispersal moves seeds away from the parent plant, reducing competition for light, water and space.
- Seeds and fruits are adapted to particular dispersal methods
- wind - light seeds with wings or hairs, such as sycamore or dandelion
- water - seeds or fruits that float, such as a coconut
- animal - seeds inside tasty fruit that are eaten and pass through an animal, or fruits with hooks that cling to fur
- explosive mechanism - a dry pod that dries out and bursts open, flinging seeds away
Seeds and fruits are adapted to be dispersed by wind, water, animals or an explosive mechanism
Germination
- Germination is the process in which a new plant begins to grow from a seed.
- Seeds generally need water and an appropriate temperature to germinate.
- Soil and light are not required by every seed for germination to begin - many seeds will germinate on wet cotton wool in darkness.
- During germination, the seed absorbs water and swells; the root (radicle) usually emerges first and grows downward, followed by the shoot, which grows upward.
The root usually emerges before the shoot during germination
Worked Example: Reading a Germination TestQuestion: Ten seeds on wet cotton wool at 22 °C produce eight seedlings. Ten seeds on wet cotton wool at 4 °C produce none. What condition is supported by the evidence? [1]
Water and seed number are the same in both tests, so temperature is the variable that was changed. The warmer group germinated but the cold group did not. AnswerThe evidence supports that seeds need an appropriate warm temperature to germinate.
Common Mistakes
MistakeAll seeds need soil and light before they can germinate.
FixStage 5 evidence focuses on water and an appropriate temperature; many seeds germinate on wet cotton wool in darkness.
MistakeOnly sweet, fleshy foods count as fruits.
FixIn science, a fruit is any structure that contains one or more seeds, including pods, nuts and grains.
MistakeFlowers exist only to look attractive.
FixFlowers contain the structures a plant needs for reproduction; their colour and scent help attract pollinators.
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