Read the passage below. Use the information in the passage and your own knowledge
to answer the questions that follow.
How plants breed
Asexual reproduction in animals is rare but it is commonly used in plants. Plants
often use asexual reproduction when the conditions are favourable. They use sexual
reproduction when environmental conditions are changing. The ability to alter the
method of reproduction enables plants to increase their chance of survival.
5 Flowers are the sexual reproductive organs of plants. Most plants have flowers
with male and female sex organs. These flowers have stamens and carpels, and are
described as bisexual. A unisexual flower is one in which only the stamens or the
carpels are present. Dioecy is the condition of having unisexual flowers on different
plants. Dioecy may have evolved to ensure that these plants can only reproduce by
10 outbreeding.
Outbreeding involves producing offspring by the fusion of gametes from two
different plants. It is the most common method of reproduction among most plants.
In outbreeding, pollen is transferred from the anther of a flower on one plant to the
stigma in a flower on a different plant.
15 Some other plants produce both types of gamete and are self-fertilising. This method
of reproduction is known as inbreeding.
Pollination, or the transfer of pollen to a stigma, is an important part of both
inbreeding and outbreeding. Pollinators, such as insects, birds or bats, first need
to be attracted to a flower and then provided with a reason to return or to go to
20 another flower of the same species. Generally, animals are attracted to a flower by a
smell or by the colour and shape of the flower. Smells may be faint, sweet, musky or
unpleasant. Flowers offer rewards to pollinators, including pollen, nectar or fats
and oils.
Some flowers have evolved different structures or forms that prevent self-pollination
25 and so prevent inbreeding. One example is the primrose. This flower exists in two
forms, pin-eyed and thrum-eyed.
The lengths of stamens and styles in these flowers are adapted for pollination by
different pollinators, or different body parts of the same pollinator. Pollen from
a pin-eyed flower will rub off on the stigma of a thrum-eyed flower. Pollen from a
30 thrum-eyed flower will rub off on the stigma of a pin-eyed flower.
Asexual reproduction is commonly used in plants (line 1).
Give an example of a method of asexual reproduction used by a plant.
(1)
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