Fertilisation in animals

Question 1

What do sperm cells meet once they arrive in oviduct?

Answer 1

An undeveloped ovum, secondary oocyte

Question 2

Once sperm cells cluster around the ovum what happens?

Answer 2

Acrosome reaction is triggered, enzymes are released to digest ovum’s defences.

Question 3

What happens when one sperm penetrates the weakened barrier and touches surface of oocyte?

Answer 3

Oocyte undergoes second meiotic division, producing haploid egg nucleus to fuse with haploid male nucleus

Question 4

Once sperm head of sperm is inside ovum what happens?

Answer 4

It absorbs water, swells and releases its chromosomes forming a diploid zygote

Question 5

How are other sperms prevented from entering egg after fertilisation?

Answer 5

-Ion channels in cell membrane open and close, there is a charge so blocks entry of other sperm
- Cortical granules move towards cell membrane and release their contents which hardens membrane, cortical reaction

Question 6

First phase of embryo development:

Answer 6

The zygote undergoes special type of mitosis, divides repeatedly without interphase

Question 7

What is the blastocyst?

Answer 7

Small mass of undifferentiated cells after 4 days of embryo development

Question 8

Where is the blastocyst implanted?

Answer 8

In the uterus wall

Question 9

What does the outer layer and inner layer of blastocyst form?

Answer 9

Outer layer: Placenta
Inner layer: Pluripotent embryonic stem cells

Question 10

Which organelle is only inherited from mothers?

Answer 10

Mitochondria as it never leaves sperm during fertilisation