Advance Biology Reproduction Form Six Full Notes Njige
REPRODUCTION
Definition:
Reproduction is the biological process by which new organisms of the same
species are produced from existing ones.
Importance
of reproduction
• It is an
important process for the existence of all living things.
• It is a
process which leads to an increase in the number of individuals of a species in
a given population.
• Sexual
reproduction introduces genetic variation through the mixing of genetic
material from two parents.
•
Reproduction is central to the process of evolution. Genetic variation
resulting from reproduction provides the raw material upon which natural
selection acts, driving evolutionary changes over time.
Types
of reproduction
There are two main
types of reproduction: sexual and asexual.
(a) Sexual reproduction Involves the fusion of gametes
(sperm and egg) from two parents to produce offspring with genetic diversity.
It occurs in most animals and plants.
Sexual reproduction involves the following
steps:
•
Gametogenesis: production of gametes through meiosis, which halves the number
of chromosomes.
• Fertilization: Where a sperm cell fertilizes
an egg cell, forming a zygote with a complete set of chromosomes.
• Development of the zygote into an embryo and
eventually into a new organism.
•
Gestation and birth: Once fully developed, the offspring is born through the
process of labor.
(b) Asexual reproduction Involves the production of
offspring from a single parent without the involvement of gametes.
There are
several forms of asexual reproduction:
• Binary
fission: Where an organism divides into two identical organisms. E.g bacteria
• Budding:
Where a new organism grows from an outgrowth or bud on the parent organism. E.g
yeast
•
Fragmentation: Where a parent organism breaks into fragments, and each fragment
develops into a new organism. E.g tapeworm
•
Parthenogenesis: Where an egg develops into an embryo without fertilization by
a sperm. E.g Banana. • Vegetative propagation: New individuals develop from
specialized vegetative structures of the parent plant, such as stems, roots, or
leaves. Examples include runners in strawberries, tubers in potatoes, and bulbs
in onions.
