Full notes of sexual reproduction in plants including flower structure, gamete development, self-pollination, cross-pollination, double fertilisation, development of the fruit and seed, germination of the broad bean and the effect of gibberelin.
Large, colourful petals, scent & nectar Small, green & inconspicuous, no
Scent, petals usually absent
Anthers within flower Anthers hanging outside flower so
wind con blow pollen away
Stigma within flower Large feathery stigmas hang outside
providing Large S.A. for pollen grains
Small quantities of Sticky, large pollen Large quantities of smooth, Small &
light pollen
, Pollination = the transfer of pollen from the on anther of one flower to the mature stigma of mother flower
of the some species.
Cross-pollination:
• by insects - insects e.g. bees enter flower to obtain rector, the others brush against its legs & thorax leaving
sticky pollen which is the brushed against stigma of mother flower that it enters
• by wind - wind blows away small, smooth & light pollen from hanging anther, hanging feathery stigma of
another flower catches pollen due to large S.A.
Gamete development
Development of the male gamete:
• in pollen sacs of the anther, diploid pollen mother cells undergo meiosis, each forming a tetrad four haploid cells
becoming four pollen grains.
• the layer surrounding the pollen sacs, the tapetum, provides nutrients to developing pollen grains, had a role in
formation of pollen cell wall which is tough & resistant to desication (so pollen grains transferred without drying
out)
• the haploid nucleus within the pollen grain undergoes mitosis producing a generative & pollen tube nucleus
• the generative nucleus further produces 2 male nuclei by mitosis.
• as the outer layers of the other mature & day out, causing tension in lateral grooves, the anther opens releasing
pollen grains - dehisence
Transverse section of anther
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