Topic 11.4 Reproduction

Question 1

Gametogenesis

Answer 1

The process by which diploid precursor cells undergo meiotic division to become haploid gametes (sex cells).

Question 2

Process of Gametogenesis

Answer 2

Occurs in the gonad and involves the following steps:

Multiple mitotic divisions and cell growth of precursor germ cells.

Two meiotic divisions (meiosis I and II) to produce haploid daughter cells.

Differentiation of the haploid daughter cells to produce functional gametes.

Question 3

Spermatogenesis

Answer 3

Spermatogenesis describes the production of spermatozoa (sperm) in the seminiferous tubules of the testes.

Question 4

Oogenesis

Answer 4

Oogenesis describes the production of female gametes (ova) within the ovaries (and, to a lesser extent, the oviduct).

Question 5

How many cells are produced in spermatogenesis and oogenesis?

Answer 5

Four functional gametes for spermatogenesis and one functional gamete plus 2-3 polar bodies

Question 6

Size of cells produced

Answer 6

In spermatogenesis, the cells that are formed following differentiation are all of equal size with equal amounts of cytoplasm.

In oogenesis, one daughter cell (the ovum) retains all of the cytoplasm, while the other daughter cells form polar bodies. The polar bodies remain trapped within the surrounding layer of follicle cells until they eventually degenerate.

Question 7

Timing of the processes

Answer 7

Spermatogenesis begins during puberty and continues until death.

Oogenesis:
It begins before birth (prenatally) with the formation of a fixed number of primary oocytes (~40,000).

It continues with the onset of puberty according to a monthly menstrual cycle.

It ends when hormonal changes prevent the further continuance of the menstrual cycle (menopause).

Question 8

Seminiferous Tubule

Answer 8

The testes are composed of seminiferous tubules which produce sperm.

Question 9

Ovary

Answer 9

The ovary contains follicles in various stages of development. These follicles will develop over the course of a menstrual cycle and hence will not always be apparent upon inspection.

Question 10

Sperm

Answer 10

A typical human spermatozoa can be divided into three sections – head, mid-piece and tail.

Question 11

Structure of Sperm

Answer 11

The head region contains three structures – a haploid nucleus, an acrosome cap and paired centrioles.

The mid-piece contains high numbers of mitochondria which provide the energy (ATP) needed for the tail to move.

The tail (flagellum) is composed of a microtubule structure called the axoneme, which bends to facilitate movement.

Question 12

Egg

Answer 12

A typical egg cell is surrounded by two distinct layers – the zone pellucida (jelly coat) and corona radiata.

Question 13

Internal Fertilisation

Answer 13

Internal fertilization involves the fusion of gametes (egg and sperm) inside of the body of a parent.

Question 14

Key processes of human fertilization

Answer 14

Capacitation – biochemical changes which occur post ejaculation to improve sperm motility.

Acrosome reaction – the release of hydrolytic enzymes which softens the zona pellucida (jelly coat).

Cortical reaction – hardening of the jelly coat post fertilization to prevent potential polyspermy.

Question 15

Capacitation

Answer 15

Capacitation occurs after ejaculation, when chemicals released by the uterus dissolve the sperm’s cholesterol coat.

Question 16

Acrosome Reaction

Answer 16

When the sperm reaches an egg, the acrosome reaction allows the sperm to break through the surrounding jelly coat.

Question 17

Cortical Reaction

Answer 17

The cortical reaction occurs once a sperm has successfully penetrated an egg in order to prevent polyspermy.

Question 18

Placenta

Answer 18

The placenta functions as the life support system for the foetus, serving two key functions:

It facilitates the exchange of materials between the mother and foetus.

It secretes hormones to maintain the pregnancy after the corpus luteum has degenerated.

Question 19

Positive Feedback in Child Birth

Answer 19

Positive feedback involves a response that reinforces the change detected (it functions to amplify the change)

In the case of childbirth, fetal growth eventually causes stretching of the uterine walls, which is detected by stretch receptors.

This triggers the release of hormones (oxytocin) that induce uterine muscles to contract, further reducing space in the womb.

This causes more stretching and hence more contraction until the origin stimulus (the foetus) is removed (i.e. birth).