Component 2.3 - Fertilisation and Implantation

Question 1

What is capacitation?

Answer 1

Spermatids can only fertilise a secondary oocyte after a process called capacitation has taken place.

Removal of cholesterol and glycoproteins from the cell membrane in front of the acrosome. Membrane becomes more fluid and it’s permeability is increased .

Question 2

What is the acrosome reaction?

Answer 2

Acrosome reaction releases proteases which digest the cells of the corona radiata.

On contact with the zona pellucida the acrosome membrane ruptures and releases hydrolase enzymes which digest the zone pellucida

Question 3

How does the sperm enter ?

Answer 3

The cell membrane of the secondary oocyte and the sperm fuse and the head (genetic material) of the sperm cell enters the secondary oocyte

Question 4

What is the cortical reaction?

Answer 4

Cortical reaction in which cortical granules fuse with the cell membrane and their contents modify the zone pellucida to form the fertilisation membrane and prevents polyspermy

Question 5

What happens after the sperm head enters and the cortical reaction has taken place?

Answer 5

It stimulates the completion of meiosis II to continue forming the ovum and the second polar body.

The nuclei of the sperm and ovum fuse to form a zygotic nucleus

Question 6

What happens after the zygote is formed?

Answer 6

1) Undergoes repeated mitotic divisions, called cleavage, to form a ball of cells called the blastocyst
2) Moves to the uterus where trophoblastic villi which are protrusions from trophoblast cells penetrate the endometrium

Question 7

How are trophoblastic villi adapted to their function?

Answer 7

They increase the surface area for the absorption of nutrients from the endometrium

Question 8

What is implantation?

Answer 8

The sinking of the blastocyst into the endometrium