Sexual reproduction in plants - IGCSECoordinatedScience-Dnl

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Sexual reproduction in plants
A flower is a leafy shoot
containing the sexual organs of
a flowering plant.
It is adapted for sexual
reproduction.
It is a modified terminal bud
typically composed of four sets
of modified leaves.
Insect-pollinated flower
Floral structures
Diagram of an insect-pollinated flower
Petal
Stigma
Anther
Filament
Style
Ovary
Ovule
Nectar
Sepal
Wind-pollinated flower
Diagram of a wind-pollinated flower
Bract
Anther
Filament
Ovary
Stigma
Functions of parts of the flower
 sepals
 petals
 Protects the flower during the bud stage
 Attracts insect pollinators by colour and
 Anthers
scent
 produce and release pollen grains
 filament
 positions the anther for effective pickup
 Stigma
 style
 ovaries
of pollen by the pollinating agent
 collects the pollen from the pollinating
agent
 positions the stigma for pollen collection
 site of fertilisation, protects the
developing seeds, aids in seed dispersal
.
. . . thinking
of you!
 In a form of a table,
compare the
different structural
adaptations of
insect-pollinated
and wind-pollinated
flowers.
[6]
structural adaptations of insect-pollinated
and wind-pollinated flowers
Insect-pollinated flowers
 Petals large & brightly
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coloured to attract insects
Stigma located inside the
flower where the insects have
to brush past it
Anthers inside the flower
where the insects have to
brush past them
Stigma usually small & sticky
so that pollen grains can
attach from insect body
Flower often strongly scented
Large sticky or spiky pollen
grains which stick to insects
Wind-pollinated flowers
 Petals small or absent, if





present, not brightly coloured
Stigma exposed to catch
pollen grains blowing in the
wind
Anthers exposed outside the
flower so that wind can easily
blow the pollen grains away
Stigma large & feathery to
catch pollen grains blowing
in the wind
Flowers have no scent
Light & smooth pollen that
can be blown in the wind
Pollination
 the transfer
of pollen
grains from
the male part
of the plant
(anther of
stamen) to
the female
part of the
plant
(stigma).
Agents of pollination
 . . . the means that
moves the pollen
grains from the
anther to the
stigma.
 Agents of
pollination include:
wind; insects; birds;
water & rodents.
Photomicrograph of pollen grains:
Note the spikes that attach pollen grains to insect’s body.
What happens after pollination?
 pollen grains germinates








forming pollen tube
the pollen tube grows down
style digesting the style tissue
the e pollen tube enters ovule
through micropyle
male nucleus moves into ovule
male nucleus (male gamete)
fuses with the ovum or egg cell
(female gamete) i.e.
fertilisation occurs
ovule becomes seed
ovule wall becomes seed coat or
testa
ovary becomes fruit
stigma and the style weathers
and dry up
Seed and fruit dispersal
 This is spread of seeds &
fruits some distance away
from the parent plant
 Dispersal allow seeds to
spread out to colonise new
areas so that the new plants
do not compete with parent
plant for light, water and
mineral salts
 means of seeds & fruits are:
 animals
 wind
 water
 self dispersal
Seed and fruit dispersal by Wind
 Wind dispersed seeds
Sycamore seed
Dandelion seeds
such as sycamore &
dandelion:
 are light so that they can
easily be blown by wind
 have wing –like outgrowth
or feathery hair
projections which increase
the surface area so that the
seeds can ‘float’ in air for
some time so they are
carried over long distance
from the parent plant
Seed and fruit dispersal by Animals
 Animal dispersed seeds
includes: tomato & burr grass.
 Tomato fruits:
 they are fleshy (succulent),
brightly coloured & scented
to attract animals
 Have tough seed coat to
protect the seeds from being
digested in the animals' gut
 Burr grass:
 Are covered with stiff, hooked
spines which catch onto the
animals’ fur to be carried long
distance before dropping off
Advantages of seed dispersal
 There is less
competition, with
parent plant & among
seedlings for same
resources such as;
light, water , nutrients
& space
 Dispersal allow plants
to colonise new areas
since plants are
stationary i.e. don’t
move from place to
place
External structure of a Seed
Internal structure of a Seed
plumule
radicle
micropyle
cotyledon
testa (seed coat)
 Testa; protects the
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
embryo from physical
damage & attack from
pathogens
Micropyle; a hole in the
testa that allow water &
oxygen to enter into the
seed
Cotyledons; stores
nutrients (starch, protein
& lipids) required during
germination
Plumule; grows into
shoot after germination
Radicle; grows into root
after germination
Conditions for seed germination
 Seed germination is the
process in which a plant
emerges from a seed & begins
grow
 Conditions needed for seeds
germination are:
 Suitable temperature; for
enzymes to work effectively
 Oxygen; for aerobic respiration
to provide energy to growing
embryo
 Water; for chemical reactions
to occur in solution, dissolve
nutrients for transportation,
activate enzymes & soak testa
Design & carry
out an
experiment to
investigate the
conditions
necessary for
germination of
mung bean
seeds.
I am willing to
answer questions
on sexual
reproduction in
plants.
Thank you folks!
You are such a
wonderful group
of students.

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