Sexual and Asexual Reproduction
•Reproduction is a production of a new generation of
individuals (offspring) from pre existing ones
•The importance of reproduction is to ensure the
continuity or perpetuation of the species.
•There are two types of reproduction, namely sexual
•This is a rapid method of increasing the number of
•The new individuals are formed from one parent
and they are genetically identical to each other and
to the parent.
•There are five major types of asexual reproduction:
a. Binary fission
c. Spore formation
d. Vegetative reproduction
•Binary fission is seen in bacteria, Amoeba and
•The unicellular organism divides into two equal
parts (daughter cells)
Binary fission in Amoeba
•Budding is seen in yeast and Hydra.
•The parent produces an outgrowth or bud which
detaches to become a new individual.
Budding in yeast
•Spore formation is seen in
bacteria, fungi, mosses and
•Spores are formed in spore –
bearing structures called
•Spores are generally very
small and light, which helps
them to be dispersed by wind
•Each spore can develop into a
Spore formation in
pin mold (Mucor)
•This type of asexual reproduction is seen in many
•Part of a plant (root, stem, leaf or bud) detaches and
grows into a new plant.
•A slender shoot that arises in the axil
of a leaf and grows horizontally on
the surface of the grounds.
•The runner bears root and becomes
independent before the parent plant
Runner of grass
•A bulb has a short stem and fleshy
leaves containing food (mainly sugar)
•It is surrounded by brown scaly leaves.
•New shoots arise from buds in the axils
of the fleshy leaves.
•A horizontally growing underground
stem which stores food.
•It produces lateral buds, some of which
develop into shoots.
•When the old rhizome dies, the new
shoots become independent plants.
Rhizome of ginger
•A short, vertical, underground
stem swollen with food
•It is protected by scaly leaves.
•Buds are located at the axils of
•Cocoyam, water chestnut
Corm of cocoyam
•The swollen ends of
•New shoots sprout out from
axilary buds or “eyes”
Tuber of potato
•Rejuvenation refers to the replacement of parts of an
organism that are lost due to injury.
•Rejuvenation is a form of asexual reproduction if it
results in two or more individuals in which there was
only one before.
•Animals such as sponges, flatworms and starfish are
capable of rejuvenating complete organisms from parts
of their bodies.
•If a sponge is chopped into hundred parts, a hundred
new sponges are generated. A starfish cut into half
gives two starfish.
Rejuvenation in Planarian (a flatworm)
•Rejuvenation is common in plants. It is called
vegetative propagation. Whole plants can be grown
from cuttings and grafts.
•Sexual reproduction is the production of offspring by
the fusion of specialized sex cells or gametes.
•The male gamete (sperm) fuses with the female gamete
(ovum or egg) by a process known as fertilization. This
results in the formation of a zygote. The zygote develops
into a new individual.
•There are two types of fertilization, internal and
•The internal fertilization, the sperm are deposited in
the female reproductive tract and fertilization occurs
within the body of the female. The zygote develops
internally and live individuals are born. Internal
fertilization occurs in insect, reptiles, birds and
•The external fertilization, which is limited almost
entirely to aquatic organisms, sperms and eggs are
shed into the water in great numbers simultaneously.
Only a small number of eggs are fertilized by the
sperms. External fertilization occurs in most fish,
amphibians and aquatic plants.
Advantages of internal fertilization over
•The eggs have a better chance of being fertilized by the
sperms. Thus, there is less wastage of gametes.
•The developing young receives nourishments from the
female parent before the birth.
Comparison between sexual and
Asexual reproduction Sexual reproduction
•Involves the production of a new generation of
individuals of the same species.
•One Number of parents
•No Gametes involved •Yes, two types:
Genetic make–up of
parents and they
Offspring •Produces fewer
Rapid form of
Speed of reproduction •Less rapid from