Introduction

• The process by which mature individuals produce offspring.
• Reproduction is an essential characteristic of all living organisms.
• There are two types of reproduction: sexual and asexual

Sexual reproduction involves the fusion of male and female gametes to form a zygote. The fusion of the nuclei of male and female gametes is known as fertilization. Asexual reproduction does not involve gametes, instead parts of a mature organism may develop to new individuals.

Importance of reproduction

1. Procreation - reproduction sustains the species so that it does not become extinct.
2. Quality improvement- it allows for the mixing of genetic materials leading to variation among individuals in a species. This is seen in sexual reproduction. The variations form basis of adaptability in their habitats.

CELL DIVISION

Cell division starts with division of nucleus i.e. the chromosome then the cytoplasm. In unicellular organisms the cell divides into two separate daughter cells while in multicellular ones the cell divides into two and continues to divide in the same way.

Chromosomes

• In the nucleus are a number of thread-like structures called chromosomes. Each cell has fixed number of chromosomes.
• Each chromosome is made up of two parallel strands called chromatids each pair of chromatid is connected atone point by a structure called centromere.
• Chromosomes are present in the nucleus all the time, but only become visible when viewed under a microscope during cell division.
• Chromosomes occur in pairs in the body cells and each pair has a characteristic length. The member of each pair is called a homologous chromosome. This means that they look alike in appearance although their genetic composition may be different.
• Along the length of the chromosomes is a series of structures called genes. They are too small to be seen even under a powerful microscope. Genes determine the characteristics of the cell and its progeny.
• Genes are made up of a protein chemical substance called DNA (Deoxyribonucleic acid) which contain coded information of instructions that dictate the characteristics of the offspring.

The sequence of events leading to cell division in plants and animals is basically the same.

There are two types of cell division namely mitosis and meiosis.