Gametogenesis in plants and fertilisation in plants Flashcards
Two phases of life cycles
Sporophyte generation is diploid ,produces spores by meiosis
Gametophyte generation results in haploid gametes
Can exist as separate plants or in flowering one
Flower structure in terms of phases
Main body diploid sporophyte that we see
Haploid gametophytes contents of anther and ovary produced by meiosis of spore mother cells
Anthers
Meisosis occurs .
Vast number of pollen grains that carry the male gametes
each contains four pollen sacs large numbers of microspore mother cells
Microspore mother cells
Diploid divide by meisosis to form haploid microspores (gametophyte generation )
Microgametes
microspores by mitosis with one cell enveloping another to form pollen grain containing to haploid nucleases
Two haploid nucleases
tube nucleus = produce pollen tube penetrates through stigma style and ovary and into the ovule
generative nucleus=fuses with nuclear of ovule to form a new individual
Formation of pollen grain
See book pg.138 figure C
Ovary of plant
Meiosis results in relative small number of ova contained within ovules inside the ovary .Number of ovule varies
Ovule is attached to the wall of ovary by a pad of special tissue called the placenta
embryo sac
complex structure of integuments (coverings) forms around tissue known as nucellus .In centre of embryo sac forms gametophyte generation
Diploid megaspore mother cells
divide by meiosis to four haploid megaspores three of which are degenerate leaving one to develop
megaspore under goes three mitotic divisions result in embryo sac containing an egg cell (megagamete) two polar nuclei and various other cells some which degenerate
Megagametogenesis
see pg.138 fig 3
How pollinated
flowers can attracted other organisms such as insects birds or mammals to transfer pollen from plant to another (pollination)
wind
External fertilisation
outside body ,female and male gametes shed into the environment meet and fuse.common in aquatic as vulnerable the gametes to drying .a matter of chance .synchronisation can be done through environmental cues e.g.temp change and day length
Internal fertilisation
transfer of male gametes directly to the female make fertilisation more likely .some male produce packages of sperm for female to pick up others direct -makes sure ova and sperm in moist environment and are as close together as possible -maxmises chance
Fertilisation in plants 1
Male gamete in pollen and female embedded deep in the tissue of the ovary.
Pollen grain lands on surface of the stigma on the flower
molecules on surface of pollen grain and stigma interact
if recognise same species pollen grain begins to grow or germinate (often must be from different plant to prevent self fertilisation that decrease variety)
can be pollen grains from same plant may start to germinate but are unable to penetrate the carpel.
Pollen tube 2
begins to grow out of the tube cell of pollen grain through the stigma into the style
tip of pollen tube contains hydrolytic enzymes to digest style so pollen tube can make way down
digested tissue acts as a nutrients source for pollen tube as grows
generative cell containing generative nucleas travels down it nucleas divides by mitosis to form two male nuclei
pollen tube and ovary 3
grows through ovary to reach an ovule and eventually passes through micropyle of the ovule
growth fast due to rapid elongation
two male nuclei passed not ovule
flowering plants undergo double fertilisation
one male fuses with two polar nuclei to form endosperm nucleus which is triploid provides embryo plant with food when begins to germinate
other male male nucleas fuses with egg to form diploid zygote see fig c pg.142
polyspermy
fertilisation of an egg by more than one sperm
generations explained
The gametophyte generation begins with a spore produced by meiosis. The spore is haploid, and all the cells derived from it (by mitosis) are also haploid. In due course, this multicellular structure produces gametes — by mitosis — and sexual reproduction then produces the diploid sporophyte generation.
The sporophyte generation thus starts with a zygote. Its cells contain the diploid number of chromosomes. Eventually, though, certain cells will undergo meiosis, forming spores and starting a new gametophyte generation.
