2.4 Sexual reproduction in mammals

Question 1

Define spermatogenesis

Answer 1

• The formation of spermatozoa from a primodial germ cell

Question 2

Define Oogenesis

Answer 2

• The formation of the ova via a primodial germ cell

Question 3

Where does spermatogenesis take place in mammals

Answer 3

Testes

Question 4

Where does oogenesis occur in mammals

Answer 4

Foetus

Question 5

Explain the process of spermatogenesis

Answer 5

• Diploid primordial germ cell divides several times to form diploid spermatogonium
• Spermatogonium then divides again by mitosis to form primary spermatocytes
• Primary spermatocytes then divide by meiosis to form haploid secondary spermatocytes
• Secondary spermatocytes go under second meiotic division to form 4 daughter haploid spermatids
• These then mature to form spermatazoa

Question 6

Describe the process of oogenesis

Answer 6

• Diploid primordial germ cell divides by mitosis to form primary oogonia
• Primary oogonia then divide again by meiosis to form primary oocyte and a polar body
• Second meiotic division takes place after fertilisation occurs which causes the formation of an ovum and another polar body via meiosis
• Polar bodies die and degenerate as ovum develops and grows

Question 7

When does the production of sperm start in males and when does the production of ova in females start?

Answer 7

• Males , after they reach puberty
• Females, before they are born in the foetus

Question 8

Describe how the products of oogenesis and spermatogenesis differ

Answer 8

• Ova are larger cells which require more materials than spermatozoa
• Spermatozoa contain acrosome, ova does not
• Spermatozoa has flagellum, ova does not
• Oogenesis produces polar bodies, spermatogenesis does not

Question 9

Describe the process of fertilisation

Answer 9

• Many sperm cluster around the oocyte
• Enzymes are released from the acrosome and digest the inner follicle cells and zona pellucida
• The head of one sperm cells fuses with the cell membrane ( tail is left behind)
• Sperm head absorbs water and bursts releasing the chromosomes to fuse with the ovum and create a gamete

Question 10

Why cant only one sperm cell digest the follicle cells and zona pellucida

Answer 10

• Insufficient enzymes

Question 11

What are cortical granules ?

Answer 11

• Secretory vesicles found underneath the egg cell underneath the cell membrane, they contain protease enzymes

Question 12

Describe how polyspermy is prevented

Answer 12

• Sperm cell fuses with egg cell membrane
• Cortical cells move towards the egg cell membrane and fuses with the egg cell membrane
• Exocytosis of the cortical granules happen and the enzymes the contain move into the jelly layer of the cell
• Protease cause the egg cell membrane to harden and thicken forming a fertilisation membrane
• Ion channels in the cell membrane open and close to change charge across cell membrane.

Question 13

Describe how ion channels change to prevent polyspermy

Answer 13

• Ion channels change by opening and closing changing the charge in the egg cell to positive which blocks entry to the sperm to all other sperm

Question 14

Describe the stage of cleavage

Answer 14

Special type of mitosis where there is no interphase.

Question 15

What is known as totipotency?

Answer 15

The potential to form all known cell types in an organism

Question 16

What is meant by pluripotency

Answer 16

Potential to form most types of cells in an organism `