beginning of cells


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  • Created by: callum
  • Created on: 31-03-12 14:46

gametes- mammalian gametes

in mammals the sperm and ovum (egg) cells are the gametes (sex cells)

gametes are adapted for their roles in sexual reproduction . The ovum is a large cell incapable of independent movement . It is wafted along one of the oviducts from the ovary to the uterus by ciliated cells lining the tubes and by muscular contraction by the tubes. The cytoplasm of the ovum contains proteins and lipid food reserves for a developing embryo . surrounding the cell is a jelly like coating called the zona pellucida.

the sperm cell is much smaller than the ovum and can move. The sperm tail has a long tail powered by energy released by mitochondria . Sperm which enter the vagina during intercourse swim through the uterus, their movement assisted by muscle contractions of the uterus walls.  if intercouse happens during ovulation the sperm may meet the ovum in the oviduct. The sperm are attracted to the ovum by chemicals released by it. The acrosome in the head of the sperm released digestive enzymes which break down the zona pellucida to penatrate the ovum.

once the sperm fuses with and penatrates the membrane surrounding the egg, the ovum releases chemicals to thicken the zona pellucida which prevents anymore sperm reaching the ovum.
the spermsnucleus that enters the egg fuses with the ovum nucleus to create a ferilised egg.

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how a fertilised egg is formed.

1. sperm reaches the ovum

2.  chemicals released from the cells surronding the ovum triggerring the acrosome reaction.

3.  the acrosome swells, fusing with the sperm cell surface membrane.

4. digestive enzymes in the

5. the enzymes digest through the follicle cells and the jelly like layer surrounding the ovum

6. the sperm fuses with the ovum membrane

7. the sperm nucleus enters the ovum

8. enymes released from lysosomes in the ovum thicken the zona pellucida preventing entry from other sperm

9. nuclei of the ovum and sperm fuse

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plant gametes

The male part of the plant is called the stamen, made up of the anther attached to the stalk known as a filament .

Inside the anther cells divide to produce pollen grains, which contain the mae gamete nuclei.

inside the female ovary one or more ovules devlopwhich contain the female gametes , the ova.

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gamete cells are unusual

all 'normal' induviduals wihtin a species will have the same number of chromosomes in each cell.

humal cells contain 46 chromosomes made up of 22 homologous pairs and one pair of sex chromosomes.

the main difference between gametes and other cells are the amount of chromosomes they contain. ( gametes have half the number of chromosomes - one from each homologous pair )

gametes containe 23 chormosomes meaning when they fuse the full 46 is restored.

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