Unit 2- Sexual Reproduction In Mammals

Question 1

Features of a male gametes:

Answer 1

Small
Motile/mobile
Produced in large numbers

Question 2

Features of female gametes

Answer 2

Large
Contain food stores
Produced in small numbers

Question 3

What is a hermaphrodite?

Answer 3

When an organism in a species can produce both male and female gametes

Question 4

Structure of a sperm

Answer 4

Acrosome at front
Nucleus in head
Mitochondria packed mid piece
Flagellum (tail)

Question 5

Structure of an egg gamete

Answer 5

Central nucleus 
Surrounded by cytoplasm
Polar body at one side
Membrane cover
Zone pellucida (jelly coat) around the membrane
Follicle cells on the zone pellucida

Question 6

Summary of spermatogenesis:

Answer 6

Primordial germ cells —mitosis—> spermatogonia — growth—> primary spermatocyctes — meiosis—> spermatozoa

Question 7

What is the advantage of unequal cell division to produce a secondary oocyte?

Answer 7

The ovum contains all the nutrients in the cytoplasm to nourish the embryo after fertilisation

Question 8

When does spermatogenesis and oogenesis first begin?

Answer 8

Spermatogenesis: after puberty
Oogenesis: as a foetus the primordial germ cells begin to divide

Question 9

Summary of oogenesis:

Answer 9

Primordial germ cell —mitosis—> oogonia —growth—> primary oocytes —meiosis 1 each month —> secondary oocyte + polar body

Question 10

When does meiosis 2 occur of the secondary oocyte?

Answer 10

After fertilisation

Question 11

What is the cortical reaction?

Answer 11

The entry of the first sperm into the egg triggers cortical granules to fuse with the cell membrane releasing enzymes that cause cross links in the zone pellucida to form, preventing entry of another sperm

Question 12

Fertilisation all 6 steps:

Answer 12

1- sperm uses flagella to swim through follicle cells
2- sperm releases hydrolytic enzymes from acrosome by exocytosis, digesting the zone pellucida
3- the first sperm reaches the ovum cell membrane, the 2 membranes fuse, so the sperm nucleus enters the egg cytoplasm
4- entry of sperm nucleus triggers cortical reaction
5- egg completes meiosis 2
6- DNA of both nuclei is replicated, both the nuclear envelopes disperse and the cell becomes a zygote

Question 13

What’s it called when multiple sperm enter the egg?

Answer 13

Polyspermy

Question 14

What enzymes are involved in fertilisation?

Answer 14

Hydrolytic enzymes found in sperm cell acrosome which digest zone pellucida

Question 15

How does the sperm nucleus enter egg cytoplasm?

Answer 15

Exocytosis

Question 16

Where does fertilisation occur?

Answer 16

Near the top of the oviduct

Question 17

How does the zygote move down the oviduct?

Answer 17

Beating cilia

Question 18

What is cleavage division?

Answer 18

A special form of division with a short interphase and no growth phase

Question 19

What occurs in the first 3 days after fertilisation?

Answer 19

Mitosis of zygote (cleavage division)

Question 20

What happens 4 days after fertilisation?

Answer 20

The zygote has divided 3 times, 8 cells, and has arrived at the uterus

Question 21

When does implantation occur?

Answer 21

8 days after fertilisation

Question 22

What is implantation?

Answer 22

When the blastocyst (128 cell complex) embeds itself into the lining of the uterus

Question 23

What happens in the first 9 days after fertilisation?

Answer 23

1-3) zygote divides repeatedly by cleavage
4) the 8 cell ball reaches the uterus
5) now 128 cells named blastocyst
8-9) blastocyst implants itself into uterus lining