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Fertilisation in humans.
For sexual reproduction to be successful the two gametes must be fused.
The sperm swims towards the egg cell. as it does the acrosome region becomes
mature and is able to release enzymes which will later penetrate the ovum.
The ovum is surrounded by a protective jelly like layer ( zona pellucida) and
follicle cells. Once the sperm makes contact with the zona pellucida, the
acrosome reaction takes place.
This is where the digestive enzymes are released from the acrosome of the
sperm, these enzymes pour out of the open acrosome and begin to digest the
zona pellucida and the follicle cells.
The sperm moves though the zona pellucida, as the sperm head fuses with the
cell membrane of the egg cell, the cortical reaction is triggered this is when the
egg cell releases contents of vesicles called cortical granules into the space
between the cell membrane and the zona pellucida.
The chemicals from the cortical granules thicken the zona pellucida making it
impenetrable to other sperms this ensures only one sperm fertilises the egg.
Sperms nucleus enters the egg cell and the tail region is discarded.…read more

Slide 2

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The nucleus of the sperm fuses with the nucleus
of the egg cell.
The two sets of haploids (23 chromosomes )
combine and make a new unique individual
with total 46 chromosomes.
Acrosome reaction cortical reaction…read more

Slide 3

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Fertilisation in plants
Double fertilisation occurs in flowering plants.
A pollen grain ( contains male gametes) lands on the stigma during pollination,
the grain absorbs water and splits open.
a pollen tube grows out of the pollen grain down the style and there are three
nuclei in the pollen tube
ones is tube nucleus at the tubes tip
The other two are male gamete nuclei.
The tube nucleus makes enzymes that digest the surrounding making its way
though for the pollen tube.
When the tube gets to the ovary it grows though the micropyle and into the
embryo sac within the ovule.
The tube nucleus disintegrates ; the pollen tube bursts releasing the male
One male gamete nucleus fuses with the egg nucleus and makes a zygote,
divides by mitosis and becomes embryo of the seed.
The second male gamete nucleus fuses with the 2 other female nuclei, this
divides to become endosperm ( food storage for mature seeds )
Double fertilisation has occurred AND THIS ONLY HAPPENS IN FLOWERING
PLANTS.…read more

Slide 4

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Totipotent cells
· potential to give rise to any and all human
cells, such as brain, liver, blood or heart cells.
· It can even give rise to an entire functional
· The first few cell divisions in embryonic
development produce more totipotent cells.
· After four days of embryonic cell division, the
cells begin to specialize into pluripotent stem
cells…read more


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