Pollination = the transfer of
pollen from the anther of one
flower to the stigma of another
of the same species
= when pollination occurs between
the anther and stigma of the same
flower/plant
results
in:
little genetic variation
increased risk of harmful recessive alleles
coming together
preservation of successful genomes
Inbreeding
Cross-pollination
= pollination of different
flowers/plants of the same species
results in:
greater genetic variation
reduced chance of harmful recessive
alleles coming together
Outbreeding
Ensuring cross-pollination:
Stamen and stigma ripen at different times
Protandry = stamen ripens
before the stigmas
Anther located below stigma,
reducing risk of pollen falling on it
Some plants have seperate male and female flowers/plants
Some plants have genetic incompatibility
pollen cannot germinate of
stigma of same plant
Double fertilisation
Fertilisation = fusion of the male
gamete with the female gamete,
producing a diploid zygote
1. when pollen grain lands on stigma
of another plant it germinates,
producing a pollen tube
2. growth of tube controlled by
pollen tube nucleus, also
producing hydrolases e.g.
celluloses + proteases
3. hydrolyses digest a path through style
towards micropyle and into embryo sac,
guided by chemical attractants e.g. GABA
4. tube nucleus disintegrates, two male
gametes enter ovule
5. one male nucleus fuses with haploid
female nucleus (oosphere), forming zygote
6. second male nucleus fuses with diploid
polar nucleus, forming triploid nucleus,
which develops into endosperm, which will
provide nutrition for developing embryo
Development of fruit and seed
fruit = a structure developing from
the ovary wall, containing one or
more seeds
seed = structure developed from
a fertilised ovule, containing an
embryo and food store enclosed
within a testa
1. diploid zygote divides by
mitosis, forming embryo
2. triploid endosperm
nucleus develops into food
store