Download NOTES SEXUAL REPRODUCTION IN PLANTS f

IGCSE
Biology
8.2 Sexual reproduction in plants
Identify and draw, using a hand lens if necessary, the sepals,
petals, stamens, anthers, carpels, ovaries, and stigmas of
one, locally available, dicotyledonous flower.
Parts of a flower
Use a hand lens to identify and describe the anthers and
stigmas of one, locally available, named, wind-pollinated
flower.
Examine pollen grains under a light microscope or in
photomicrographs.
pollen grains under a light microscope
pollen grains under a scanning electron microscope
light microscope
Apply your understanding of the flowers you have studied to
unfamiliar flowers.
Define pollination as the transfer of pollen grains from the male
parts of the plant ( anther ) to the female part of the
plant ( stigma ).
Name the agents of pollination.
wind – wind can carry pollen from flower to flower.
animals – insects, birds, bats, others
birds tend to be attracted to
red colored flowers
Compare the different structural adaptations of insectpollinated and wind-pollinated flowers.
insect-pollinated flowers – have:
large, colorful, scented petals to attract pollinators
large, sticky pollen so that pollen can be carried from one flower to another
a supply of nectar to reward/attract the pollinators
anthers and stigma inside the flower
insect-pollinated flowers
wind-pollinated flowers – examples – grasses, stinging nettle, beech tree.
wind-pollinated flowers do not have large, scented petals, nor do they have
nectar as they do not need to attract insects or birds
wind-pollinated flowers do have:
anthers that hang outside the flower to catch the wind
very large amounts of small, light pollen grains that can be easily carried
by the wind
spreading, feathery stigmas top catch the airborne pollen grains
grass flowers
grass flowers
grass flower
( enlarged many times )
birch tree flower
birch tree flower releasing pollen
Wind pollinated
flower
Insect pollinated flower
Very small petals
Large colored petals
No scent
Scented
No nectar
Nectar
Many smooth pollen
grains
Rough pollen that easily sticks to insects
Large anthers hang
outside flower
Anthers and stigma found inside the flower petals so
that visiting insects are touched
Investigate and state the environmental conditions that affect
the germination of seeds: requirement for water and
oxygen, and suitable temperature.
When a seed reaches a suitable environment, the embryo within the seed
germinates.
Germination occurs if conditions such as amounts of oxygen and moisture and
a suitable temperature are right.
Each type of seed has unique growth requirements.
Water is needed for chemical reactions ( cell metabolism ) and to break the
seed coat.
Oxygen is needed for respiration to provide the rapidly growing embryo with
energy.
A suitable temperature is required for enzymes to work properly.
Investigate and describe the structure of a non-endospermic
seed in terms of the embryo ( radicle, plumule, and
cotyledons ) and testa by the fruit.
Seed plant embryos have regions that develop into definite structures during
germination.
The embryo is attached to one or two cotyledons, or seed leaves.
Plants such as beans are dicots and have two cotyledons ( embryonic leaves )
per seed.
Corn, a monocot, has one per seed.
In monocot seeds, most food is stored as starch as endosperm tissue.
In many dicot seeds, the cotyledons absorb food from the endosperm as the
seed matures.
In either case, food stored in seeds provides a source of energy during early
development.
dicot seed
monocot seed
cotyledons – the other one is in
the other half of the peanut
plumule – can’t be seen here
hypocotyl
radicle
Examine a dicot seed such as a peanut.
The embryo consists of:
the plumule ( embryonic terminal bud )
the hypocotyl ( embryonic stem )
the radicle ( embryonic root )
Most of the seed is the pair of cotyledons ( embryonic leaves ).
The seeds of dicots break in half between the cotyledons.
The dark seed coat ( testa ) is the old covering of the ovule.
In dicots the nutrients of the endosperm ( starch ) are transferred into the
cotyledons, and the endosperm is not seen.
The epicotyl is a part of the embryo that gives rise to the shoot (stems &
leaves ).
State that seed and fruit dispersal by wind and by animals
provides a means of colonizing new areas.
A plant may produce many seeds.
If all of the seeds were to fall to the ground and grow around the mother
plant there would be hundreds of plants growing in the same place.
All of these plants would be competing for water, sunlight and nutrients,
and so many would die.
Overcrowding is prevented by seed dispersal.
Describe, using named examples, seed and fruit dispersal by
wind and animals.
Some seeds have wings or feather-like structures that can carry them in
the wind far away from the mother plant.
Some plants have fruits that simply drop to the ground. Animals may
come and carry the fruit away to eat. After eating the fruit the seed is
left behind to germinate and grow into a plant far away from the mother
plant.
Some plants have fruits with hooks on them.
The hook will stick to the fur of animals that pass by and may be carried
far away from the mother plant.
Some plants are capable of shooting their seeds through the air.