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Plant Reproduction Research
Background:
Angiosperm - a flowering plant
Male reproductive organ – stamen
Produces pollen grains

Female reproductive organ – carpel
Produces ovules

Role of Petals – Bright colours, scents and nectar attract insects for
pollination
Pollen grains are adapted for protection during transfer from the male to
female reproductive organs, they have a tough resistant wall to prevent it
from drying out
...

Wing-pollinated flowers – the anthers hang outside the flower so that the
wind can blow away the small, smooth and light pollen
...


Structures of Gametes:
Male Stamen:

Female Carpel:

A long filament
supports the
anthers which
produce pollen
grains
...


The filament
contains
vascular tissue
and transports
food materials
necessary for
the production
of pollen
...


The anther is usually made up of four pollen sacs
arranged in two pairs, side by side
...


The ovary bears a
stalk-like structure
at its apex, called the
style
...


Development of the Pollen Grain:

A pollen grain consists of a sculptured
outer wall (exine), an inner wall (intine) and
two nuclei – the generative nucleus and the
pollen tube nucleus
...

Inside the pollen grain, the haploid nucleus undergoes mitosis to produce
two nuclei, a generative nucleus and a tube nucleus
...

When the pollen grain is mature, the outer layers of the anthers dry out and
tensions are set up in lateral grooves
...


Development of Ovules:
Ovules develop within the ovary
...

The megaspore mother cell divides by mitosis into a tetrad of haploid
megaspores
...

This megaspore undergoes three meiotic divisions that result in a haploid
embryo sac
...

The ovary is protected by
...


Pollination:
Self-pollination The pollen from the anthers of a flower needs only to be transferred to the
stigma of the same flower, or another flower of the same plant
...

Advantages - can preserve good genomes that may be suited to a specific
environment
...
There is also a
greater chance of two undesirable recessive alleles being brought together at
fertilisation
...

Advantages - increased variation has greater evolutionary significance, as it
is more likely to lead to advantageous genomes
...
These
include the stamen and stigma ripening at different times, being at different
levels within the flower, or there may be separate male and female flowers
...
Pollination is only the bringing together of the gametes
...




The pollen tube grows down the style, secreting enzymes and gaining
nutrients from the digested products
...




The tube grows between the integumentary, the micropyle, and passes
into the embryo sac
...

The tip of the tube bursts open releasing the male gametes into the
embryo sac and the two male nuclei enter
...
The other gamete fuses with both polar nuclei to form a
triploid endosperm nucleus
...


Development of the seed and fruit:
The seed develops from the fertilised ovule, and contains an embryonic plant
and food store
...

A triploid endosperm nucleus develops into a food store to provide reserves
for the developing embryo
...

The ovule becomes the seed, the ovary becomes the fruit
...
They have food stores for transportation
...
They can become dormant, until the conditions are favourable for
germination
...

Water – needed for the mobilisation of enzymes, vacuolation of cells
and for transport
...


The process of Germination –



Water is taken up rapidly by the seed in the initial stages, causing the
tissues to swell as well as mobilising the enzymes
...




The seed coat ruptures as the radicle pushes its way through first
...




The enzyme, amylase, hydrolyses starch into maltose; proteases
convert proteins to amino acids
...




The plumule grows upward to develop into the shoot
...




Food reserves in the seed are insoluble and so cannot be transported
in the seedling
...




If the seed has been planted at the right depth, when the plumule
emerges it unfurls and begins to photosynthesise
...




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