3.3.2 - Fertilisation In Mammals

Question 1

What Is Fertilisation?

Answer 1

The fusion of the nuclei from a male gamete and a female gamete

Question 2

Describe The Process That Occurs Before Fertilisation
(4 Points)

Answer 2

~ Semen is ejaculated high up into the vagina of a female, near the cervix.

~ Sperm cells follow a chemical trail released by the egg cell and travel up through the cervix and uterus, to reach the oviduct.

~ Oviduct is where the egg cell is located.

~ Once the sperm cell meets the egg cell in the oviduct, fertilisation can occur.

Question 3

Describe The Process Of Fertilisation
(6 Points)

Answer 3

~ Sperm cell swims towards the egg cell in the oviduct.

~ (Acrosome Reaction) Acrosome releases digestive enzymes, that digest a path through the zona pellucida allowing the sperm to pass through the egg cell membrane.

~ (Cortical Reaction Pt.1) Egg cell immediately then releases contents of vesicles called cortical granules into the space between the egg cell membrane and the zona pellucida.

~ (Cortical Reaction Pt.2) Chemicals from the cortical granules make the zona pellucida rapidly thicken and harden, making it impenetrable to other sperm ensuring only one sperm cell can fertilise the egg cell.

~ Only the sperm nucleus enters the egg cell, its tail is discarded.

~ The nucleus of the sperm cell fuses with the nucleus of the egg cell, forming a zygote.

Question 4

Describe The Acrosome Reaction

Answer 4

Acrosome releases digestive enzymes, that digest a path through the zona pellucida allowing the sperm to pass through the egg cell membrane.

Question 5

Describe The Cortical Reaction
(2 Points)

Answer 5

~ Egg cell immediately then releases contents of vesicles called cortical granules into the space between the egg cell membrane and the zona pellucida.

~ Chemicals from the cortical granules make the zona pellucida rapidly thicken and harden, making it impenetrable to other sperm ensuring only one sperm cell can fertilise the egg cell.

Question 6

Describe What Happens After The Process Of Fertilisation
(3 Points)

Answer 6

~ Zygote divides by mitosis, forming 2 new cells.

~ These cells continue to divide like this until an embryo is formed after a few days.

~ Cell division continues and eventually many of the new cells produced become specialised to perform a particular function and form all the body tissues of the offspring.