Fertilisation

Question 1

When does fertilisation occur?

Answer 1

Fertilisation occurs when a single sperm penetrates an egg cell

Question 2

The several stages of fertilisation

Answer 2

1. Capacitation
2. Acrosome reaction
3. Fusion of sperm
4. Cortical reaction
5. Fusion of nuclei

Question 3

Capacitation

Answer 3

The surface of the sperm undergoes functional changes while in the female reproductive tract that allow it to fertilise the egg cell. The sperms cholesterol coat is dissolved which improves motility, and the acrosome cap is destabilised.

Question 4

The acrosome reaction

Answer 4

Enzymes from the acrosome are released and digest a pathway through the follicle cells and zone pellucida surrounding the secondary oocyte. The action of many sperm are required for just on to enter the egg cell.

Question 5

Fusion of membranes

Answer 5

The membranes of the sperm and egg fuse, and the nucleus of the sperm enters the egg cytoplasm which causes a sudden membrane depolarisation that acts as a fast block to further sperm entry. This also triggers the completion of meiosis II in the egg cell and induces the next stage of the fertilisation process

Question 6

The cortical reaction

Answer 6

Cortical granules in the egg cytoplasm released their content into the space between the plasma me,brand and the Vitelli never layer. Substances released from the granules raise and harden the Vitelli next layer to form a fast (permanent) block to further sperm

Question 7

Fusion of Nuclei

Answer 7

The membranes of both gametes disappear so that the chromosomes can fuse together, returning to a diploid state. The diploid fertilised egg is now referred to as a zygote.

Question 8

Cleavage and Morula

Answer 8

The rapid cell division takes place immediately after fertilisation (cleavage), increasing the number of cells, but not the size of the zygote. The first cleavage is completed after 36 hours, and each succeeding division takes less time.
After three days, successive cleavages have produced a soiled mass of cells called a morula, which is still about the same size as the original zygote.

Question 9

Blastocyst and implantation

Answer 9

After several days in the uterus, the morula it develops into the blastocyst.

Question 10

HCG

1. Released from?

Answer 10

1. Corpus