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ANGIOSPERMS
Angiosperms are plants that have their
seeds enclosed in an ovule inside their flower.
About 80% of the plants we see and know
are angiosperms. The other type of plant is a
gymnosperm and instead of having their seeds
in flowers, their seeds are exposed, such as the
cones of a pine tree. Gymnosperms have no flowers.
Angiosperms have flowers that have male parts and
female parts. This allows them to be able to reproduce
sexually, as we will learn about later.
The Outer Parts of an Angiosperm Flower
There is a huge variety of angiosperms with very different looking flowers but all
flowers have these structures:
The peduncle is the stalk or stem that attaches the flower to the plant.
The receptacle is the top part of the stalk where all the flower parts attach to on the
peduncle.
The sepals are the small green leaves that protect a new flower bud.
The petals are the colourful parts that attract pollinators such and bees, birds and
butterflies.
DID YOU KNOW?
A gamete or sex cell is a special cell like an egg or sperm cell (reproductive cells).
Every cell in your body has DNA (deoxyribonucleic acid) that contains your
genetic code.
Gametes also contain DNA but only half a set of DNA.
When a male gamete and a female gamete join or fuse together, the half of the
female DNA joins with the half of the male DNA to make a new set of DNA which
will become the DNA of the baby.
© e-classroom 2015 www.e-classroom.co.za
GRADE 7
Grade 7 Term 1: Natural Science and Technology: Sexual Reproduction in Angiosperms
Sexual reproduction in Angiosperms
GRADE 7
The male structures include the stamen (anther and filament) and the pollen grains
which contain the male sex cells.
The stamen is made of the anther which rests on top of the filament. The anther
makes pollen. Each pollen grain contains two male sex cells or male gametes.
The Female Parts of the Angiosperm Flower
The female structures include the pistil (stigma, style and ovary) and the ovule
which contains the female sex cells.
The pistil is made of the stigma which rests on top of the style. The style is
attached to the ovary. Inside the ovary there is an ovule or ovules, depending on
the plant, and inside the ovule are the female sex cells or female gametes.
ACTIVITY
Fill in the missing labels in the diagram below. Colour the male parts blue
and the female parts pink.
ANGIOSPERM FLOWERS
Cross section of typical flower
stamen
© e-classroom 2015 pistil
www.e-classroom.co.za
Grade 7 Term 1: Natural Science and Technology: Sexual Reproduction in Angiosperms
The Male Parts of the Angiosperm Flower
GRADE 7
In order for a seed to form, a male gamete must fuse, or join, with a female gamete.
This is the process of FERTILISATION.
In order for fertilisation to take place, the male gamete has to get to the female
gamete in the female part of the flower. This is the process of POLLINATION.
1. Pollination
Stamens are the male part of a flower and produce pollen in sacclike structures
called anthers. The anther (of the male part of the flower) produces pollen.
The pollen grains each contain two male gametes and rest on top of the anther.
The pollen not only needs to move away from the anther, but it needs to be
transferred to the stigma (female part) of another flower. The plant needs help to do
this. Here are some ways that plants receive help in transferring their pollen.
a) Zinnia and butterfly
b) Hibiscus and hummingbird
c) Saguaro cactus and bat
POLLINATION BY ANIMALS
These animals are called pollinators. They could be insects (like bees and
butterflies) or birds (like sunbirds).
The plant is adapted to attract the pollinators to its flowers. Plants use their
colourful petals, strong aroma (smell) and sweet nectar to attract insects and birds.
Pollinators come to the flower to drink its sweet nectar. As they sit on the inside of
the flower (insects) or put their face into the flower (birds), pollen grains brush off the
anthers onto them. The pollinator moves from one flower to another. As they reach
a new flower some of the pollen from previous flowers rubs off onto the stigma and
the pollinator picks up new pollen.
© e-classroom 2015 www.e-classroom.co.za
Grade 7 Term 1: Natural Science and Technology: Sexual Reproduction in Angiosperms
POLLINATION AND FERTILISATION
GRADE 7
Plants that use wind and water don’t need the adaptations
that will attract pollinators (big colourful flowers with
a sweet smell and tasty nectar) but they have other
adaptations that help them become pollinated more easily.
Plants using water and wind to help them become
pollinated need the following adaptations:
•They have many anthers with lots of pollen on them,
which hang out of the flowers so that pollen can be
swept away easily.
•Each plant has lots of flowers so the chances of
pollination are greater – more flowers mean more
chance of pollination.
•
Pollen grains are not sticky like in other flowers, rather they are smooth and
dry, light and small so they can be carried easily by the wind and water.
•
Stigmas are much bigger and look feathery which make it easier for them to
“catch” the pollen grains.
Plants using the water to help them with pollination must live in the water (they are
aquatic plants). The pollen is released and floats on top of the water. The stigmas of
another plant must be close to the surface of the water so that they can catch the
pollen as it floats by.
Why is pollination important for us?
Most of our food comes from plants or from animals that eat plants. Plants need to
reproduce so that there can be enough to supply the demand of providing food.
Every piece of fruit or vegetable consumed, including wheat, comes from
plants. These are only available to us because they have been able to reproduce.
Reproduction can happen if pollination happens. We need to preserve our
pollinators so that we can preserve our food crops.
2. Fertilisation
Pollination is the transfer of pollen from one plant to another. What happens next is
what makes it possible for a plant to produce seeds.
Once the pollen grain has landed on the stigma, it releases chemicals that make a
pollen tube from the top of the stigma to the ovary. Then the male gametes travel
from inside the pollen grain down the tube and into the ovary. Inside the ovary,
the pollen tube goes into the ovule which contains the embryo sac which has the
female gametes in it.
© e-classroom 2015 www.e-classroom.co.za
Grade 7 Term 1: Natural Science and Technology: Sexual Reproduction in Angiosperms
POLLINATION BY WIND AND WATER
The other male gamete fuses with the two other female gametes inside the embryo
sac and this forms the endosperm. The endosperm becomes the food that will
keep the growing seed alive.
This process is called double fertilisation because fertilisation happens twice in the
plant. Once fertilisation has happened, no other male gametes can enter the ovule
or embryo sac.
After this, the ovary begins to swell and enlarge to form a fruit. Inside the ovule in
the ovary, the zygote grows to form a seed.
Double Fertilisation
pollen
grain
stigma
style
ovary
two sperm
nuclei
pollen
tube
One sperm
fertilises the
central cell (3n)
One sperm
fertilises the
egg cell (2n)
tube
nucleus
central
cell (2n)
ovule
egg
nucleus
ACTIVITY
Draw a flow diagram to show each step in the process of fertilisation of a plant.
© e-classroom 2015 www.e-classroom.co.za
GRADE 7
Grade 7 Term 1: Natural Science and Technology: Sexual Reproduction in Angiosperms
One of the male gametes fuses with one of the female gametes (the egg) inside the
embryo sac and this forms the zygote. This zygote will grow into the seed of the
plant. Remember that the male gamete contains half of the DNA of the male plant
and the female gamete contains half of the DNA of the female plant. When they
fuse, the DNA combines so that the zygote has a new set of DNA.
GRADE 7
There are many different types of fruit and each have different types of seeds in
them. The reason a plant makes seeds and fruit is so that these can be spread
(dispersed) to new places so the seed can germinate and grow into a new plant.
Plants use a variety of ways to spread or disperse their seeds.
Gravity
Fruit falls off the tree or plant and into the ground where is can start to germinate
or grow. The fruit may also roll further away from the tree if it is on a hill.
Explosive force
Some plants have seeds that burst open when it is ready and
the seeds shoot out of the pod and away from the parent
plant. Some plants need to be burned to activate this force.
Wind
Seeds dispersed by the wind need to be lightweight and have
parts adapted to being carried by the wind
(eg. Feathery-parts or wings).
Water
Plants that live in or near the water often use the water to
disperse their seeds. Seeds float in the water to a different
place where they land on the ground and germinate.
Animals - externally
Seeds with sticky or spiky parts stick to an animal’s hair and are
carried to a new area where they, drop off and grow in a new place.
Animals - internally
Animals eat the fruit and carry the seeds to a new place.
Seeds have a tough outer covering that prevents them
from being digested. When they pass out of the animal,
they grow in a new place.
© e-classroom 2015 www.e-classroom.co.za
Grade 7 Term 1: Natural Science and Technology: Sexual Reproduction in Angiosperms
SEED DISPERSAL
GRADE 7
ACTIVITY
Fill in the missing labels in the diagram below. Colour in the male parts in
blue and the female parts in pink.
ANGIOSPERM FLOWERS
Cross section of typical flower
pistil
stamen
petal (corolla)
stamen
pistil
sepal (calyx)
anther
receptacle
stigma
style
filament
peduncle
© e-classroom 2015 ovary
(with seeds)
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Grade 7 Term 1: Natural Science and Technology: Sexual Reproduction in Angiosperms
Answer sheet