Reproduction in plants
How are new plants formed? New plants can grow in several ways: from seeds (sexual reproduction) or by producing things such as bulbs or tubers (asexual reproduction).
Structure of a flowering plant There are four main organs of a flowering plant : The flower - contains the reproductive organs. The leaves — these use light energy, carbon dioxide and water to make food by photosynthesis.
The stem — this provides support and a transport system for water and minerals to the leaves and flowers. It also transports food from the leaves to the roots and flowers. The roots — these anchor the plant to the ground and absorb water and minerals.
Sexual reproduction Flowers contain a plant’s reproductive organs. Most plants contain both male and female parts. Some plants have only male sex organs while others contain only female sex organs. The organs may even be separate on the same plant e.g. hazel.
Sexual reproduction needs special sex cells called gametes. The advantage of sexual reproduction is that it leads to genetic variation. If a species is varied it is more likely to be able to adapt to any changes in its surroundings.
In a flowering plant the flower develops on the receptacle. The buds of the flower are protected by sepals. Sepals are small leaves. The petals of many flowers are brightly coloured which attracts insects. These petals are often highly scented. Inside the flower there are pin-like structures called stamens.
The top of the stamen produces pollen cells, which contain the male sex cells. The club-like structure is the stigma. In the base of the stigma is the ovary. The ovary contains ovules. Each ovule contains a female sex cell. The carpel is made up of the stigma, style and ovary. When the tip of the stigma is sticky it indicates that the carpel is ripe and ready to receive grains of pollen.
Flowers differ in external colour, size and shape Flowers differ in external colour, size and shape. However they all have a similar internal structure. Some have carpels with one ovule, others have rows of ovules.
Pollination Pollination is the transfer of pollen from anthers to stigmas. This must occur before a male sex cell can fuse with a female sex cell. There are a number of ways pollination can happen. Self-pollination is when pollen is transferred from an anther to the stigma of the same flower or of another flower on the same plant.
Cross-pollination is when pollen is transferred from a flower on on€ plant to flowers on a different plant of the same species. There are different ways that this can happen. Wind pollination happens as wind blows pollen from anthers of one plant to the stigmas of others. Plants that are wind pollinated are not usually brightly coloured, for example grasses. They do, however, have long filaments with anthers that hang down in the wind. They produce millions of pollen grains. The pollen is very light: some grains even have small air sacs to help them stay in the air longer.
Insect pollination happens when insects like bees carry pollen on their bodies as they move from flower to flower. The insects are attracted to the plants because the plants produce a sugary liquid called nectar which the insects like. The flowers of plants that are insectpollinated tend to be brightly coloured, which makes it easy for the insects to find them. The pollen of these types of plant have large pollen grains and is a good food supply for the insects. Some pollen grains have spikes, which stick to the hair of insects.