Although flowers vary a great deal, and actually much of their appeal lies in the apparent differences, they have a rather similar structure.
Most flowers consist of of 4 parts, (which are actually modified leaves!), in rings round the enlarged end of a stalk:
Name of parts - and collective name |
Appearance and number | Usual Function |
> sepals - calyx |
often green, may be hairy - often 3, 4, or 5 |
to protect flower in bud stage |
> petals - corolla |
often brightly coloured and marked or scented - often 3, 4, or 5 (frequently same number as sepals) |
to attract insects for pollination, and act as landing pad |
> stamens (male organs) - androecium |
like drumsticks
> anther = tip > filament = support - usually several (multiple of above number?) |
split open to produce
> pollen (contains male gametes) |
> carpel(s) (female organs) - gynaecium |
varying shape, perhaps flask-shaped
> stigma=receptive surface > style = stalk, similar to filament > ovary = usually a bulge at base of flower - often only one or a few |
to produce
> egg cell(s) (female gametes) and > support development/form seeds after fertilisation |
insect-pollinated flowers | wind-pollinated flowers | |
position of anthers and stigmas | > inside flower | > outside flower |
type of pollen | > "large", sticky | > "small", light |
A nucleus from inside the tube enters the ovule and fuses/joins with the nucleus of the egg cell. This is the point of fertilisation. The resulting cell is a zygote.
If an ovary contains several ovules, each one may be fertilised separately by a different pollen tube growing from another pollen grain.
The ovule develops into the seed, containing an embryo plant, and the covering of the ovule becomes the seed coat (testa) .
The wall of the ovary grows thicker and develops into the fruit, with a seed or seeds inside it.
Not all fruits are sweet and soft, like apples or oranges, for example, but we shall see the similarities in structure and function of all fruits, later.
What process occurs inside the fertilised egg cell to give rise to an embryo plant?
> cell division/mitosis
Growth of flowers and fruits depends on a supply of "food".
In what (chemical) form do you think this is delivered to these structures, and by what route, i.e. via which tissue?
> sugars > phloem
What do you think happens to the petals after pollination and fertilisation?
> usually fall off
What is honey mostly composed of?
> nectar - sugars produced by flowers to attract pollinating insects
Why do you think bee-keepers were provided with extra sugar rations during the war? (Answer is not "to keep them sweet"!)
> keeping population of bees in order to ensure pollination
Why do hay fever sufferers worry about the weather in summer?
> more grass pollen is released under some conditions
Look at the flowers provided, using a hand lens or binocular microscope if necessary.
It is a good idea to place the flower on a tile or petri dish.
Remove the various parts, using a needle or scalpel (CARE!).
Count up and describe the component parts, and put the numbers into the table below, along with the name of the flower. Draw them if you can.
Plant name | Number and description (colour, etc) of : | ||||
sepals | petals | stamens | carpels including stigma, style, and ovary |
ovules | |
1) |
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2) |
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3) |
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etc |