Gametogenesis

Question 1

What is gametogenesis?

Answer 1

Process which forms gametes

Question 2

What happens to the special cells (primordial germ cells)?

Answer 2

In the sex organs they divide by mitosis, grow, then meiosis 1 and 2, then they differentiate into sex cells.

Question 3

Spermatogenesis explained
4 points:

Answer 3

.Two mitotic divisions of a germ cell, primary spermatocyte produced
.Primary spermatocyte undergoes division by meiosis 1
.Secondary spermatocyte divides by meiosis 2
.Differentiation of spermatids occurs to produce 4 sperm cells

Question 4

Oogenesis explained
4 points:

Answer 4

.Two mitotic divisions to produce primary oocyte
.Primary oocyte undergoes division by meiosis 1
.Secondary oocyte undergoes division by meiosis 2
.By the end 3 polar bodies and only 1 ovum is produced

Question 5

Why is only 1 ovum produced?

Answer 5

The fertilised egg should have enough cytoplasm, if oogenesis produced 4 equal cells like spermatogenesis, each egg would be too small for an embryo.

Question 6

4 adaptations of egg cell

Answer 6

.Most of cytoplasm contains food to nourish growing embryo
.Follicle cells that form a protective coating
.Jelly like glycoprotein bilayer (zona pellucida), that forms impenetrable barrier after fertilisation
.Cortical granules located near the cell membrane control fertilisation

Question 7

3 adaptations of sperm cell

Answer 7

.Flagellum to swim towards the egg cell
.Many mitochondria that provide energy to move flagellum
.Acrosome that contains digestive enzymes to break down the zona pellucida

Question 8

Gametogenesis for female gamete in plants:

Answer 8

.Diploid mega-spore in ovule divides by meiosis to produce 4 mega-spore cells.
.One of mega-spores undergoes mitosis 3 times to produce a embryo sac with 8 haploid nuclei (other 3 mega spores disintegrate).

Question 9

What do anthers contain?

Answer 9

4 pollen sacs with large numbers of diploid ,mother cells which divide by meiosis to form 4 microspores

Question 10

What’s formed when microspores divide by mitosis?

Answer 10

Large tube cell and generative cell.
Generative cell engulfed by tube cell to form pollen grain with 2 genetically identical haploid nuclei.

Question 11

What happens firstly for formation of egg cells in plants?

Answer 11

Diploid mother cell undergoes meiosis to produce 4 haploid megaspores

Question 12

Megaspore undergoes 3 mitotic divisions to produce embryo sac containing what?

Answer 12

-Egg cell (mega gamete)
-2 Polar nuclei
-2 synergids
-Antipodal cells

Question 13

What do synergids and antipodals do?

Answer 13

Synergids: Guide pollen tube
Antipodals: Supply nutrition to egg