Download Reproduction in plants - Barbados SDA Secondary School

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. 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.