Transcript Natural Science 2. Secondary Education

UNIT
4
The reproduction function
SEXUAL REPRODUCTION IN
PLANTS
Natural Science 2. Secondary Education
UNIT
4
Classifying plants
PLANTS
are classified as
SEEDLESS
PLANTS
PLANTS WITH
SEEDS
which can be
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GYMNOSPERMS
Natural Science 2. Secondary Education
ANGIOSPERMS
UNIT
4
Classifying plants
Seedless plants
• They do not have flowers, and they produce neither fruits nor
seeds.
• Reproduction occurs through the alternation of generations and
they disperse via spores.
• Two common examples are mosses and ferns.
Moss
Natural Science 2. Secondary Education
Fern
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UNIT
4
Classifying plants
Gymnosperms
• Their flowers are not particularly attractive and they almost always
form structures called cones, often with separate genders.
• Instead of producing fruit, the female cones mature into developed
cones which contain seeds.
• Some examples of gymnosperms are pine trees, firs and junipers.
Female cone
Seed
Male cone
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Natural Science 2. Secondary Education
UNIT
4
Classifying plants
Angiosperms
• Their flowers are generally attractive. They produce fruit, which contain
seeds.
•There are many different angiosperms, from small grasses to large
trees.
Seed
Flower with
androecium
(stamen) and
gynoecium
(pistil)
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Natural Science 2. Secondary Education
UNIT
4
Parts of a typical flower
Corrola
Petal
Stamen
Gynoecium
or pistil
Androecium
Sepal
Calyx
Natural Science 2. Secondary Education
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gynoecium to find out more
UNIT
4
Parts of a typical flower
The androecium
• It is made up of stamens. Each stamen has:
• A filament to support the anther.
• An anther, where pollen grains develop. Male gametes form
inside these grains.
Anther
Pollen
grains
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Natural Science 2. Secondary Education
Filament
UNIT
4
Parts of a typical flower
The gynoecium
• This is the female reproductive organ. It is shaped like a bottle.
• It has three parts:
• Ovary: the widest part, which contains the female gametes.
• Style: the long part.
• Stigma: the tip.
Stigma
Style
Ovary
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Natural Science 2. Secondary Education
Female
gamete
UNIT
Fertilisation
4
Pollen grain
2
When the pollen
grain reaches the
flower’s stigma it
forms a pollen tube,
which grows along
the style until it
reaches the ovary.
1
Pollination
occurs.
Pollen tube
3
Female
gamete
Male
gametes
Natural Science. Secondary Education, Year 2
Male gametes travel
down the pollen tube to
the ovary and
fertilisation takes place.
UNIT
4
Seed and fruit formation
The zygote and ovary develop into the seed and fruit
2 The walls of the ovary
1
thicken. The zygote
develops into a seed.
The flower withers
and the corolla and
the stamen fall away.
The zygote begins to
develop.
3
Natural Science 2. Secondary Education
The fruit that
envelops the seed is
formed.
UNIT
4
Seed and fruit formation
Parts of the seed
Endosperm: a
nutritious substance
that feeds the
embryo
Cotyledons: small
leaves that store
nutrients.
Embryo
Hypocotyl
Radicle
Seedcoat:
it envelops and
protects the seed.
Natural Science 2. Secondary Education
UNIT
4
Germination
Germination
1
The buried seed, in
proper conditions,
begins to absorb
water. The embryo
starts its development,
using the nutrient
supplies in the
endosperm.
2 The seed coat breaks
and a root and stem
start to grow, the
stem towards the
surface and the root
away from the
surface.
Natural Science 2. Secondary Education
3
When the stem breaks the
surface, the cotyledons
develop into leaves and
begin to carry out
photosynthesis. This is how
the new plant will get
nutrients, which will help it
grow and develop.