Thursday 30 April 2020
Describe what happens in a flower from the time of pollination up to the time of seed and fruit development
After pollination, the pollen grain absorbs nutrients from the stigma;
and develops a pollen tube; it grows down the style to the embryosac; taking
along the male nuclei; the tube nuclei initiates and maintains pollen tube
growth; while the generative nucleus divides by mitosis; to form two male
gamete nuclei; which follow behind the tube nucleus as the pollen tube grows
down the style; pollen tube enters the ovule through the micropyle; its tip
bursts open; while the tube nucleus disintegrates; one of the male gamete
nucleus fuses with the egg cell nucleus/oosphere/megaspore; to form the zygote;
while the other fuses with the two polar nuclei; to form a triploid nucleus;
called the primary endosperm nucleus; after fertilization, the zygote undergoes
repeated mitotic divisions; to form an embryo consisting of the plumule,
radicle and seed leaves/cotyledons; primary endosperm nucleus divide
repeatedly, become separated by membranes; to form an (semi-fluid nutritive)
endosperm; ovary walls change into the pericarp; ovary changes/develops into a
fruit; while ovules lose water and become seeds; the integuments; change into
seed coats/testa; style/filaments/petals/sepals wither and fall off (or may
persist);
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