REPRODUCTION
Definition: Reproduction is the process through which living organisms give rise to new offspring of their
species.
All living organisms strive to live forever, but this is not possible as they each have only a certain
lifespan. Therefore, they must continue to produce offspring to continue the existence of the species.
There are two types of reproduction: Sexual Reproduction and Asexual Reproduction.
(a) Sexual Reproduction
The production of new living organisms by combining genetic information from two individuals of
different types (sexes). In most higher organisms, one sex (male) produces a small motile gamete
(sperm) which travels to fuse with a larger stationary gamete (ovum) produced by the other (female).
The fusion of these sex cells is called fertilization. In sexual reproduction, there is variation in the
offspring.
(b) Asexual Reproduction
It involves only one individual, which divides into 2 or more parts. Each part then develops into a new
individual. e.g. budding in yeast, spore formation in bread mould:
Characteristics of Sexual Reproduction
1. It is a slow method of increasing the population of living species of plants and animals.
2. It takes place in plants and higher animals like mammals. 2 parents are involved which produce the 2
gametes (1 male, 1 female)
3. There is fertilization (fusion of gametes) It is less prolific (few offsprings result).
4. There is variation of offspring, they differ from each other and from their parents.
Types of Sexual Reproduction
1) Conjugation: This form of reproduction is common in lower organisms like the spirogyra where
filaments called conjugants are involved. They both lie side-by-side and exchange their cellular content.
One acts as the male (+), and the other, female (-)
2) Mating: This occurs in higher animals where the male copulates with the female, resulting to internal
or external fertilization.
External fertilization: This occurs when both gametes are released into the surrounding medium and
fusion takes place externally. It is common in amphibians and fishes
. 1
,Internal fertilization: Takes place when ejaculated sperms fertilize the egg released and retained within
the female's reproductive system. This is common in insects, reptiles, birds and mammals.
Types of Asexual Reproduction
1) Fission: This is the simplest form of asexual reproduction in which the parent cell divides into two
identical daughter cells having the same number of chromosomes. This type of reproduction is common
in bacteria, and protozoa. When two identical daughter cells are produced, it is known as binary fission.
In unſavourable conditions, the nucleus of the parent cell can divide repeatedly, followed by division
into many daughter cells. This is multiple fission e.g. plasmodium, bacteriophage.
2) Spore Formation/ sporulation: Spore mother cells or sporangia produce spores by meiosis, which are
discharged from the parent by wind. Each spore has a nucleus. The spores are produced in large
numbers. This is common in tungi (mushroom- Agaricus campestris, penicillium Penicillium notatum,
bread mould- Rhizopus nigricans. mucor -Mucor mucedo etc.)
3) Budding: A kind of asexual reproduction in which a new individual is produced as an outgrowth (bud)
of the parent and later released as an independent, identical copy of the parent. It later grows to
maturity and continues the budding process. eg. yeast.
4) Fragmentation: A common type of reproduction where pieces of the growing filament simply break
away and continue to grow independently from the 'parent' filament, e.g algae (spirogyra)
5) Regeneration: The ability of many animals to grow and replace their lost parts. e.g. An earthworm is
able to regenerate a new tail if cut at any point after the first 40 segments. A starfish can regenerate
from a cut starfish arm. A lizard can regenerate a tail.
6) Vegetative Propagation: Occurs when a new bud grows from the stem of a plant which eventually
separates to grow up to form a new Individual. Through this way. several plants can be produced from a
single parent plant.
Two types exist; Natural and artificial vegetative propagation.
i) Natural vegetative propagation occurs in many flowering plants by leaves, underground stems
such as corms, rhizomes, bulbs and tubers or by suckers, runners creepers etc.
* Rhizomes -Ginger, Corms- cocoyam, runners- grass, tubers - Irish potato, suckers -plantain and banana,
Bulbs- onion and garlics
ii) Artificial propagation occurs when gardeners produce plants with desired qualities. Examples include
grafting, cutting, layering.
7) Cloning: An artificial modern method of asexual reproduction where an organism or group of
organisms can reproduce from a single cell of an animal or plant or from a tissue fragment of the
organism. This is known as tissue culture. Clones are genetically identical organisms.
. 2
,8) Parthenogenesis
-the development of an organism from an unfertilized egg/gamete or sex cell
-the parent is always diploid and the gametes are produced by mitosis or meiosis -some animals,
including aphids, brine shrimp, bees, and some species of fish, frogs, and lizards
reproduce asexually through parthenogenesis -two types: diploid parthenogenesis, in which the gamete
is produced by mitosis and therefore the offspring are also diploid
-haploid parthenogenesis, in which the gametes are produced by meiosis, giving rise to haploid eggs.
which may develop directly into haploid offspring e.g. honey bee
9) Parthenocarpy, development of fruit without fertilization. The fruit resembles a normally produced
fruit but is seedless. Varieties of the pineapple, banana, cucumber, grape, orange, grapefruit,
persimmon, and breadfruit exemplify naturally occurring parthenocarpy.
10) Cloning as a methods of asexual reproduction in humans
- cloning is the process of creating an exact copy of a single gene, cell, or organism e.g. sheep,
cattle .The copies produced through cloning have identical genetic makeup and are known as clones e.g
Identical twins resulting from one fertilized egg
Advantages of Sexual Reproduction
1. It leads to genetic variation in offsprings as new characteristics are acquired from the different
parents.
2. Variated offsprings better adapt to environmental changes.
3. There is the survival of the fittest in the prevailing condition.
4. There is a high degree of parental care in some animals protecting the offsprings from environmental
hazards and feeding them till they can fend for themselves.
Disadvantages of Sexual Reproduction
1. It is slow
2. It depends on the chance of 2 gametes to meet for fertilization to occur.
3. In plants, fertilization will not occur when agents of pollination are lacking. 4. Not all the eggs are
fertilized in cases of external fertilization as in amphibians and fishes.
Advantages of Asexual Reproduction
. 3
, 1. Parental characteristics are transmitted from parents to offsprings creating resemblances.
2. Many offspring are produced at a time thus a faster means of reproduction.
3. It doesn't depend on external factors like pollinators (wind, insects, birds), water.
4. Temporal nourishment is obtained from the parent especially during unfavourable conditions and
gestation.
5. The species can continue existing even if only one individual is left.
Disadvantages of Asexual Reproduction
1. There is overcrowding of species due to the large number of offsprings produced. Therefore there is a
high competition for food.
2. Reduction in strength and vigour in succeeding generation.
Comparism between sexual and asexual reproduction.
DIFFERENCES
Sexual Asexual
Sexual Reproduction in Flowering Plants
. 4
Definition: Reproduction is the process through which living organisms give rise to new offspring of their
species.
All living organisms strive to live forever, but this is not possible as they each have only a certain
lifespan. Therefore, they must continue to produce offspring to continue the existence of the species.
There are two types of reproduction: Sexual Reproduction and Asexual Reproduction.
(a) Sexual Reproduction
The production of new living organisms by combining genetic information from two individuals of
different types (sexes). In most higher organisms, one sex (male) produces a small motile gamete
(sperm) which travels to fuse with a larger stationary gamete (ovum) produced by the other (female).
The fusion of these sex cells is called fertilization. In sexual reproduction, there is variation in the
offspring.
(b) Asexual Reproduction
It involves only one individual, which divides into 2 or more parts. Each part then develops into a new
individual. e.g. budding in yeast, spore formation in bread mould:
Characteristics of Sexual Reproduction
1. It is a slow method of increasing the population of living species of plants and animals.
2. It takes place in plants and higher animals like mammals. 2 parents are involved which produce the 2
gametes (1 male, 1 female)
3. There is fertilization (fusion of gametes) It is less prolific (few offsprings result).
4. There is variation of offspring, they differ from each other and from their parents.
Types of Sexual Reproduction
1) Conjugation: This form of reproduction is common in lower organisms like the spirogyra where
filaments called conjugants are involved. They both lie side-by-side and exchange their cellular content.
One acts as the male (+), and the other, female (-)
2) Mating: This occurs in higher animals where the male copulates with the female, resulting to internal
or external fertilization.
External fertilization: This occurs when both gametes are released into the surrounding medium and
fusion takes place externally. It is common in amphibians and fishes
. 1
,Internal fertilization: Takes place when ejaculated sperms fertilize the egg released and retained within
the female's reproductive system. This is common in insects, reptiles, birds and mammals.
Types of Asexual Reproduction
1) Fission: This is the simplest form of asexual reproduction in which the parent cell divides into two
identical daughter cells having the same number of chromosomes. This type of reproduction is common
in bacteria, and protozoa. When two identical daughter cells are produced, it is known as binary fission.
In unſavourable conditions, the nucleus of the parent cell can divide repeatedly, followed by division
into many daughter cells. This is multiple fission e.g. plasmodium, bacteriophage.
2) Spore Formation/ sporulation: Spore mother cells or sporangia produce spores by meiosis, which are
discharged from the parent by wind. Each spore has a nucleus. The spores are produced in large
numbers. This is common in tungi (mushroom- Agaricus campestris, penicillium Penicillium notatum,
bread mould- Rhizopus nigricans. mucor -Mucor mucedo etc.)
3) Budding: A kind of asexual reproduction in which a new individual is produced as an outgrowth (bud)
of the parent and later released as an independent, identical copy of the parent. It later grows to
maturity and continues the budding process. eg. yeast.
4) Fragmentation: A common type of reproduction where pieces of the growing filament simply break
away and continue to grow independently from the 'parent' filament, e.g algae (spirogyra)
5) Regeneration: The ability of many animals to grow and replace their lost parts. e.g. An earthworm is
able to regenerate a new tail if cut at any point after the first 40 segments. A starfish can regenerate
from a cut starfish arm. A lizard can regenerate a tail.
6) Vegetative Propagation: Occurs when a new bud grows from the stem of a plant which eventually
separates to grow up to form a new Individual. Through this way. several plants can be produced from a
single parent plant.
Two types exist; Natural and artificial vegetative propagation.
i) Natural vegetative propagation occurs in many flowering plants by leaves, underground stems
such as corms, rhizomes, bulbs and tubers or by suckers, runners creepers etc.
* Rhizomes -Ginger, Corms- cocoyam, runners- grass, tubers - Irish potato, suckers -plantain and banana,
Bulbs- onion and garlics
ii) Artificial propagation occurs when gardeners produce plants with desired qualities. Examples include
grafting, cutting, layering.
7) Cloning: An artificial modern method of asexual reproduction where an organism or group of
organisms can reproduce from a single cell of an animal or plant or from a tissue fragment of the
organism. This is known as tissue culture. Clones are genetically identical organisms.
. 2
,8) Parthenogenesis
-the development of an organism from an unfertilized egg/gamete or sex cell
-the parent is always diploid and the gametes are produced by mitosis or meiosis -some animals,
including aphids, brine shrimp, bees, and some species of fish, frogs, and lizards
reproduce asexually through parthenogenesis -two types: diploid parthenogenesis, in which the gamete
is produced by mitosis and therefore the offspring are also diploid
-haploid parthenogenesis, in which the gametes are produced by meiosis, giving rise to haploid eggs.
which may develop directly into haploid offspring e.g. honey bee
9) Parthenocarpy, development of fruit without fertilization. The fruit resembles a normally produced
fruit but is seedless. Varieties of the pineapple, banana, cucumber, grape, orange, grapefruit,
persimmon, and breadfruit exemplify naturally occurring parthenocarpy.
10) Cloning as a methods of asexual reproduction in humans
- cloning is the process of creating an exact copy of a single gene, cell, or organism e.g. sheep,
cattle .The copies produced through cloning have identical genetic makeup and are known as clones e.g
Identical twins resulting from one fertilized egg
Advantages of Sexual Reproduction
1. It leads to genetic variation in offsprings as new characteristics are acquired from the different
parents.
2. Variated offsprings better adapt to environmental changes.
3. There is the survival of the fittest in the prevailing condition.
4. There is a high degree of parental care in some animals protecting the offsprings from environmental
hazards and feeding them till they can fend for themselves.
Disadvantages of Sexual Reproduction
1. It is slow
2. It depends on the chance of 2 gametes to meet for fertilization to occur.
3. In plants, fertilization will not occur when agents of pollination are lacking. 4. Not all the eggs are
fertilized in cases of external fertilization as in amphibians and fishes.
Advantages of Asexual Reproduction
. 3
, 1. Parental characteristics are transmitted from parents to offsprings creating resemblances.
2. Many offspring are produced at a time thus a faster means of reproduction.
3. It doesn't depend on external factors like pollinators (wind, insects, birds), water.
4. Temporal nourishment is obtained from the parent especially during unfavourable conditions and
gestation.
5. The species can continue existing even if only one individual is left.
Disadvantages of Asexual Reproduction
1. There is overcrowding of species due to the large number of offsprings produced. Therefore there is a
high competition for food.
2. Reduction in strength and vigour in succeeding generation.
Comparism between sexual and asexual reproduction.
DIFFERENCES
Sexual Asexual
Sexual Reproduction in Flowering Plants
. 4
