3. Augiosperms
4. No, only those that are pollinated by insects
5. No, only those that have to attract insects
6. Propagation of the specis – fertilisation of the ovaries
- Angiosperms or flowering plants, especially those with brightly coloured petals, attract insects and are pollinated by them. They are also fragrant.
- The function of the flower is to ensure the fertilisation of the ovules.
- The main functions therefore are
POLLINATION and
FERTILISATION .
Activity
Assignment 1
POLLINATION
Pollination is the process by which a ripened (mature)
grain of pollen is deposited on a mature stigma of the same type of plant.
- A grain of pollen must be ripe, or it will not be able to germinate to grow into the style. The stigma also has to be ripe and receptive to the pollen to be able to develop. The pollen has to come from the same sort of plant, or crossbreeding will result. Sometimes crossbreeding is possible, and this can result in all kinds of exotic plants.
- The structure of the grains of pollen of each type of plant differs microscopically from those of all other kinds of plants. This means that a grain of pollen virtually has to fit like a key in a lock. A ripe grain of pollen will begin to germinate as soon as it has landed on an appropriate surface.
- We have mentioned the fact that two main processes have to occur, namely pollination and fertilisation. We know what pollination is and that the ultimate goal of the grain of pollen is to reach the mature ovule to fertilise it.
Assignment 2:
- Undertake an investigation to obtain information about the pollen and pistils of different kinds of plants.
- Assemble a sheet of sketches of the different kinds of pollen and pistils that you discover.
Fertilisation is the union of the special nuclear contents (gametes or germ cells) of a grain of pollen and an ovule.
- The nuclear content that is referred to comprises a special molecule that has a code or “plan” of what the new plant must be like. We refer to this as the chromatin network, which consists of the molecule known as DNA. You will learn about the exact significance of this later.
- A zygote, the beginning of the new organism or plant, develops as soon as the nuclear contents or gametes have fused.
- The process, as it occurs step by step from the moment of pollination to fertilisation, comprises the following:Assignment 3
- Design a flower of your own with the help of the following guidelines:
Own memo
Activity 3
Assignment 1
| A ripe grain of pollen is deposited on a receptive stigma |
| Germination : growing down the a pollen tube into the style |
| Entering the carpel through the micropyle |
| Travelling through the carpel to the ovule |
| Two male gametes in the pollen tube are released |
| One fuses with the ovule's female gamete |
|
FERTILISATION has occurred – a zygote is formed |
| The zygote develops into an embryo inside the seed |
| The carpel becomes the pericarp for seed distribution |
| Carpel: develops into a fruit |
| Seed bud: develops into a seed |
| Pistil: dries up and decays – see this at the bottom of an apple, for instance |
| Zygote: develops into an embryo |
- Seed formation naturally is of the greatest importance to the process of propagation, but the process of distributing the seeds, or fruit, ranks with this in importance.
OPTIONAL / FOR ENRICHMENT
- The educator could suggest a project dealing with fertilisation through which you could investigate the interesting ways and mechanisms of propagation that form part of this process.
- The David Attenborough video dealing with “The Secret Life of Plants” could be viewed as an alternative. It contains astonishing visual material.
