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

The reproductive system is the group of organs that produces male and female gametes and brings them together so that a zygote can form and develop into a new organism. In vertebrates such as mammals, it is divided into the male reproductive system and the female reproductive system.

Behavioural objectives

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

• name the parts of the male and female reproductive systems in mammals;
• state the function of each part of the male and female reproductive systems;
• define a gamete;
• describe the structure of a sperm and state the function of each part;
• describe the structure of an ovum.

What is the reproductive system?

Most multicellular animals and plants undergo a complex form of sexual reproduction in which specially differentiated male and female reproductive cells (gametes) unite to form a single cell, known as a zygote. The zygote later undergoes successive divisions to form a new organism. The process takes place with the help of the system known as the reproductive system. This system can be divided into:

• the male reproductive system and
• the female reproductive system.

Structures and functions of the male reproductive system in mammals

Structures and functions of the female reproductive system in mammals

Structure of mammalian gametes

What is a gamete?

A gamete is a mature sexual reproductive cell having a single set of unpaired chromosomes. It can be a male or female gamete. Gametes are formed in the gonads (testis or ovaries) through a process called gametogenesis.

Male gamete: the sperm

The male gamete is called a sperm (spermatozoon). It is produced in the male gonads (testis) by a process called spermatogenesis. It is microscopic and unicellular. It is usually smaller and more elongated than the egg, about 0.05 mm (0.005 cm) long.

A spermatozoon consists of the following parts:

1. Acrosome: It is found at the upper part of the head and contains lytic enzymes used to dissolve egg membranes to enhance penetration during fertilisation.
2. Middle piece: It contains mitochondria for the generation of energy used by the sperm for swimming towards the egg.
3. Flagellum: The long whip-like tail for propelling the sperm cell.
4. Nucleus: It is found in the head of the sperm cell and contains genetic material (DNA, deoxyribonucleic acid), which fuses with the nucleus of the ovum at fertilisation.

Female gamete: the ovum

The female gamete is called an egg (ovum). It is produced in the female gonad (ovary) by a process called oogenesis. It is larger than the sperm, about 0.1 mm in diameter.

Each ovum is made up of the following:

1. Cytoplasm
2. A central nucleus: It contains the chromosomes which carry the genes.
3. Granules and yolk droplets: A source of nourishment for the embryo at the early stage of development.
4. Plasma membrane: It surrounds the cytoplasm.
5. Outer vitelline membrane and jelly coat of glycoprotein.

Note: The nuclei of the sperm and ovum contain chromosomes, which carry the genes responsible for the transmission of characters from parents to offspring.

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. State three functions of the testis and three functions of the ovaries.
2. Give two differences between a sperm and an ovum.
3. Describe the function of the uterus and the cervix.