Reproductive System in Vertebrates – SS2 Biology Lesson Note (Second Term)

The reproductive system is the group of organs that produces gametes and brings them together so that a zygote can form and grow into a new organism.

Behavioural objectives

By the end of the lesson, students should be able to:

1. name the parts of the male and female reproductive systems in mammals;
2. state the function of each part of the male and female reproductive systems;
3. define a gamete;
4. describe the structure of a sperm and state the function of each part;
5. describe the structure of an ovum;
6. state the differences between a sperm and an ovum.

What is the reproductive system?

The reproductive system is the set of organs that makes gametes and enables sexual reproduction.

• Gametes: specialised male and female reproductive cells made by most multicellular animals and plants.
• Zygote: the single cell formed when a male gamete and a female gamete unite.
• Development: the zygote divides again and again to form a new organism.
• Male reproductive system: produces sperms and delivers them to the female.
• Female reproductive system: produces eggs, receives sperms and nourishes the developing young.

What are the parts and functions of the male reproductive system in mammals?

The male reproductive system has nine main parts: testis, seminiferous tubules, epididymis, vas deferens, seminal vesicle, prostate gland, Cowper’s gland, urethra and penis.

Why are the testes outside the body?

• Temperature: the scrotal sacs keep the testes cooler than the body.
• Sperm production: sperms develop best at this lower temperature.

What is seminal fluid?

Seminal fluid is the liquid, made by the seminal vesicles, prostate gland and Cowper’s gland, in which sperms leave the body.

• Energy: it contains fructose, which the sperms use for energy.
• Medium: it carries the sperms and helps them swim.
• Protection: it raises the acidic pH of the female reproductive medium, which protects the sperms.

What are the parts and functions of the female reproductive system in mammals?

The female reproductive system has seven main parts: ovaries, oviduct, uterus, vagina, cervix, vulva and clitoris.

What is fertilisation?

Fertilisation is the fusion of the nucleus of a sperm with the nucleus of an ovum to form a zygote.

1. Sperms are deposited in the vagina during intercourse.
2. The sperms swim through the cervix and uterus into the oviduct.
3. Enzymes from the acrosome dissolve the membranes around the ovum.
4. One sperm enters the ovum.
5. The sperm nucleus fuses with the ovum nucleus to form the zygote.
6. The zygote divides as it moves to the uterus, where the embryo implants and develops.

What are the structures of mammalian gametes?

What is a gamete?

A gamete is a mature sexual reproductive cell with a single set of unpaired chromosomes (haploid).

• Types: male gamete (sperm) and female gamete (ovum).
• Where formed: in the gonads (testis or ovaries).
• Process: gametogenesis.

What is a sperm?

A sperm (spermatozoon) is the male gamete, made in the testis by spermatogenesis.

• Size: microscopic, about 0.05 mm (0.005 cm) long.
• Shape: unicellular, smaller and more elongated than the egg.

A sperm has a head, a middle piece and a tail. Its four main parts are:

• Acrosome: at the upper part of the head, contains lytic enzymes that dissolve egg membranes so the sperm can enter during fertilisation.
• Nucleus: in the head, contains the genetic material (DNA, deoxyribonucleic acid), which fuses with the nucleus of the ovum.
• Middle piece: contains mitochondria that release the energy the sperm uses to swim towards the egg.
• Flagellum: the long whip-like tail that propels the sperm.

What is an ovum?

An ovum (egg) is the female gamete, made in the ovary by oogenesis.

• Size: larger than the sperm, about 0.1 mm in diameter.

Each ovum is made up of the following parts:

• Cytoplasm: the living material that fills the cell.
• Central nucleus: contains the chromosomes that carry the genes.
• Granules and yolk droplets: food for the embryo at the early stage of development.
• Plasma membrane: surrounds the cytoplasm.
• Vitelline membrane and jelly coat: the outer layers, the jelly coat being made of glycoprotein.

• Note: the nuclei of the sperm and ovum carry the genes that pass characters from parents to offspring.

What are the differences between a sperm and an ovum?

A sperm is the small, motile male gamete with a tail. An ovum is the large, non-motile female gamete with stored food.

Evaluation

1. Why are the testes found in scrotal sacs outside the body?
2. State the functions of the seminal fluid and name two glands that secrete part of it.
3. Where does fertilisation take place in the female reproductive system?
4. List the four parts of a spermatozoon and state the function of the acrosome.
5. Name three components of an ovum.

Assignment

1. Draw a table that compares the testis and the ovary. Include where each is found, the gamete each produces, the hormones each produces and one other function of each.