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Sexual Reproduction in Plants - Coggle Diagram
Sexual Reproduction in Plants
(a) Generalized structure of flower and comparing wind to insect pollinated
Wind pollinated flower
small or no petals
no scent
no nectaries
high pollen production
pendular stamens
pollen small light and smooth
large groups
simple structure
Insect pollinated
large bright petals
scented
nectaries present
relatively low pollen production
stamens inclosed so insect brushed past
pollen large and spiny
stigma small and sticky
single or small groups
complex structural modification
development of pollen
tapetum provides nutrients and regulatory molecules during the development of pollen cell wall as it is tough and resistant to chemicals
diploid mother pollen cells undergo meiosis - 4 haploid cells become pollen grains
each haploid cell nucleus goes through mitosis - 2 nuclei - generative and tube nucleus
generative produces 2 male nuclei by mitosis
pollen cell wall cannot be penetrated by UV so can occur at high altitudes w/o risk of mutation
when mature the outer layer of the anther dries out and dehiscence releases the pollen grains
every developing pollen grain develops a thick protective wall - 2 layers
the outer exine layer which is in a shape specific to certain species - pits in surface facilitate gaseous exchange
the inner intine layer is thinner and less porous
Development of ovules
ovules produced within the ovary of the flower
Female gametes formed by meiosis in the embryo sac
inside the nucellus
ovule contains mass of cells called the nucellus surrounded by two protective integuments
ovule carried on a short stalk called the funicle
once cell in the nucellus enlarges and becomes the megaspore mother cell (2n)
ovule formation
production of the female gamete takes place in the embryo sac in the ovule
cell division occurs
methods of pollination
pollination is the transfer of pollen from anthers to mature stigmas of the same species
if pollination occurs between two plants of different genetic makeup then cross pollination occurs
if transfer takes place between genetically identical then self pollination has occured
self pollination
type 1 - occurs within the same flower - pollen from the anther is tranferred to the stigma of the same flower
type 2 - occurs between 2 of the same flower on the same plant - pollen from the anther is transferred to the stigma of the same plant but different flower
less genetic variation
chances of evolution reduced
pure plant maintained
less chance of failed pollination
cross pollination
genetic variation
lower chance of pollination
purity of plant is reduced
Double Fertilisation + development of a seed
pollen grain lands on stigma and absorbs water
if pollen grain is compatible then pollen tube will germinate
pollen tube grows down the style under the control of the pollen tube nucleus which codes the hydrolase enzyme
the hydrolase enzyme digest a way through the style to the tube
pollen tube
Mitochondria
site of ATP synthesis for production of enzymes and other substances required for growth
RER
enzymes are proteins. proteins are made by ribosomes and transported through the RER
Golgi bodies
to golgi bodies where enzymes are processed and packaged into vesicles
vesicles
enzyme is carried in vesicles to the cell membrane for exocytosis
vacuole
vacuoles expand as they fill with cell sap and push nuclei down pollen tube
Double (process)
pollen lands on stigma absorbs water - if compatible pollen tube will germinate
pollen tube grows down through style under to the control of the pollen tube where codes for the production of hydrolase enzyme - digest a way through style to pollen tube
during this the generative nucleus (n) divides by mitosis to form 2 male gametes (n)
growth of tube - positive chemotrophic response. pollen tube grows towards chemicals secreted by embryo sac
tube grows through gap in the integuments (micropyle)and into the embryo sac
once entered the embryo sac the tube disintergrates
one male gamete fuses with the female gamete to produce diploid zygote (2n). the second male gamete fuses with the twopolar nuclei to form triploid primary endosperm nucleus (3n)
after fertilisation, the antipodal and synergids do nothing
Development of fruit and seed
following fertilisation - the diploid zygote divides by mitosis
Forming the diploid embryo which then differentiates into a young shoot (plumule)
young root (the radicle)
one or two seed leaves (cotyledons)
the triploid endosperm tissue divides by mitosis
this forms endosperm tissue which forms the food source for the growing embryo
in dicotylendons (eg broad beans) the endosperm is quickly absorbed and stored in two cotyledons
in some species (monocotyledons) (eg maize) the endosperm remains and only one cotyledon is present
comparing maize and broad bean
both have
plumule
testa
radicle
cotyledon
maize has
1 cotyledon
funicle
testa and pericarp fused
endosperm
broad bean has
hilum (scar of funicle)
micropyle
cotyledon 2
testa
