Written by Edidiong Ibiam Ndon M a Nigerian writer

1. GENERAL REPRODUCTION
BY
DR. OBIAGERI FLORENCE AJAH

2. Objectives
By the end of this class, students will be able to:
Define reproduction
Differentiate between sexual and asexual
reproduction
Identify various types of reproduction that occur
in different organisms
Understand the processes that are involved in
human reproduction

3. Reproduction
• Reproduction is a biological process by which an
organism reproduces an offspring that is
biologically similar to the organism or generates
individuals of the same species.
• Reproduction is the main feature of life on earth
that ensures that there is continuity and
sustainability of species

4. Types of Reproduction
• Two types of reproduction exists; they are
dependent on the number of individuals that
are involved in the process
• Asexual Reproduction – involves one individual
• Sexual Reproduction – involves two individuals

5. Asexual Reproduction
• Asexual reproduction is the type of reproduction
where only a single organism gives rise to new
individual(s)
• It does not involve the fusion of gametes, therefore,
the offsprings produced are genetically identical to
the parent .
• These offsprings are sometimes called clones
because they have exact copies of their parents cell
and chromosomes
• The organisms produced by asexual reproduction are
less diverse in nature. This type of reproduction is
seen widely in unicellular organisms

6. Binary Fission
• Binary Fission occurs in
single-celled organisms
• It involves 4 processes:
genetic material
duplication, cell growth, cell
division, and independence
• The nucleus divides, the cell
increases in size to
accommodate the divided
nucleus, the cell membrane
divides to form 2 daughter
cells that will separate to
become independent
organisms that are capable
of growing and continuing
the cycle of life.

7. Fragmentation
• Fragmentation is a form of
asexual reproduction where a
parent organism splits into
fragments or several parts
that eventually grows into a
complete new organism
• Fragmentation involves 3
processes: breakage,
regeneration, and
independence
• The breakage can occur as a
result of accident or of natural
cause

8. Budding
• Budding is a form of asexual
reproduction where an offspring
develops from an outgrowth or
bud on a parent organism
• It involves 3 processes: bud
formation, development, and
separation.
• A bud develops form the parent
organism, it keeps increasing in
size while still attached to the
parent, it matures and detaches
itself from its parents and
becomes independent to
continue the cycle of life

9. Sporogenesis
• The mushroom has a network of
filaments called mycelium, which
acts as the root. Specialized
structures on the mycelium
produce microspores.
• These spores are released into the
atmosphere and dispersed by
wind, animals and water.
• If these spores fall on suitable soil
with enough moisture, it produces
hypha which later develop and
branch into mycelium; this will
eventually develop to become new
mushroom.

10. Parthonogenesis
• This is the type of asexual
reproduction where egg develop
into an embryo without fertilization.
• It involves 4 processes: egg
activation, embryo development and
offspring formation
• An unfertilized egg, undergo a
process called egg activation, where
the egg is triggered to develop as if it
was fertilized. The genetic material
inside this egg duplicates and divides
to form new cells as a result of
mitotic cell division. The embryo
continues to grow and develop until
it becomes a new individual capable
of continuing the cycle of life.

11. Advantages of Asexual Reproduction
• Asexual reproduction encourages massive population
growth
• It brings about continuity of life and encourages
resilience in organism
• It prevents extinction
• It helps in the conservation of energy
• It helps to reduce unnecessary intraspecific rivalry
Disadvantage:
• A major disadvantage of asexual reproduction is lack of
genetic diversity which makes it easy for these
organisms to be susceptible to disease outbreak

12. Assignment
• Read and identify organisms that undergo different
types of asexual reproduction that we talked about
• Read up other forms of asexual reproduction that we
did not talk about
• Know how the processes of their reproduction occur
• Understand the complexities of these organisms:
* Can they be identified as plant or animal or do they
have
the characteristics of both plant and animal
* Know if they have the ability to reproduce both
sexually
and asexually

13. Reproduction in Higher Plants
• Plants have the ability to reproduce both sexually and
asexually.
• The main mode of asexual reproduction in plant is called
vegetative propagation (reproduction from the stems,
roots and leaves of plants); which can occur naturally or
be induced by humans
• Natural mode of vegetative propagation can occur by
the rise of an offspring from the root, leaf and the bud.
• Human-induced vegetative propagation includes
grafting, budding, layering, cutting, marcotting and
micropropagation. Human-induced propagation must be
done under aseptic conditions to avoid contamination

14. Budding
• This is a procedure where a
bud (scion) from a parent
plant with desired
vegetative feature is
attached to another plant
(rootstock) with desired
quality; this results in the
formation of a new plant
that has the desired
characteristics of the two
plants

15. Marcotting
• Marcotting is also
known as air layering;
it entails the induction
of root on a branch in
the mother plant
before detaching the
rooted branch, and
planting it directly in
the soil to grow as an
independent plant.

16. Cutting
• Cutting is a technique where
a section of a plant (stem,
leaf, or root) is cut off the
mother plant and placed in a
moist, nutrient-rich
environment to encourage
root formation. Once roots
develop, the cutting can be
transplanted into the soil
where it will continue to
grow into a new plant.

17. Layering
• Layering entails bending a
stem of a mother plant to
the soil, and pegging it
down to the soil; it stays
buried until it starts rooting
and developing new
vegetative parts before it is
finally cut off the mother
plant.

18. Grafting
• This is similar to budding;
the difference here is that a
stem (scion) is joined to
another stem containing
root (rootstock).
• This procedure helps to
combine two desirable
qualities in two different
plants into one plant

19. Micropropagation
• Micropropagation is also known
as tissue culture; it takes plant
propagation to the microscopic
level! This procedure gives rise to
test tube plants!
• It involves the selection of healthy
plant tissue in an aseptic laboratory
environment and growing them in
nutrient media (essential minerals,
sugar, plant hormones) to make
them totipotent (to develop shoot
and then, roots) and have the
ability to grow into new plantlet.
• These plantlets will thereafter be
transplanted to the soil to continue
the cycle of life.

20. Assignment
• Which of these vegetative propagation
techniques excites you the most? Why?
• Try any one of them and document your
experiences

21. Sexual Reproduction in Angisoperm
• The flower is the main organ of sexual reproduction
in flowering plants.
• A typical flower has four main parts, or whorls: the
calyx, corolla, androecium, and gynoecium.
• The green, leafy structure at the outermost whorl of
the flower is called sepals; collectively they are called
the calyx, and they help to protect the unopened
bud.
• The second whorl is the petals, usually brightly
colored, and collectively called the corolla. The
number of sepals and petals varies depending on
whether the plant is a monocot or dicot. Together,
the calyx and corolla are known as the perianth.
• The third whorl contains the male reproductive
structures called the androecium. The androecium
has stamens with anthers that contain the
microsporangia which houses the pollen grains.
• The female part, the gynoecium is the most delicate
part of the flower. The carpel is the individual unit of
the gynoecium and has a stigma, style, and ovary.

22. Gametogenesis
Male Gametophyte (Pollen Grain)
• The pollen grain are birthed within
the anther, located in the stamen.
• The microspore mother cells
undergo meiosis to produce
haploid microspores which
eventually matures into pollen
grains. The development of pollen
grains takes place in a structure
called the microsporangium.
• At maturity, the anther wall splits
open, and releases the pollen
grains into the air.
• As this pollen falls on stigma of a
flower, fertilization eventually takes
place
Female Gametophyte (Embryo Sac)
• The embryo sac develops within
the ovule; originating from a single
diploid cell called the megaspore
mother cell. This mother cell will
undergo meiosis to produce four
haploid megaspores.
• Through several mitotic division,
only one megaspore will survive ,
and mature into an embryo sac
• This embryo sac awaits fertilization
by pollen grain to initiate the
development of an embryo

23. The Flower
• A flower that has all four whorls present, is called a complete
flower.
• Flower with any of the four parts missing, is called an
incomplete flower.
• Flower that contain both an androecium and a gynoecium is
called a perfect or bisexual flower.
• There are two types of incomplete flowers: staminate flowers
- contain only an androecium; carpellate flowers – contain
only a gynoecium
• When both male and female flowers are borne on the same
plant, the plant is described as a monoecious plant
• When male and female flowers borne on separate plants, the
plant is described as a dioecious plant.

24. Assignment
• Research and list 3 flowers each that can be
described as:
* Complete
* Incomplete
* Perfect
* Staminate
* Carpellate
• List out 5 plants that are:
* Monoecious
* Dioecious

25. Floral Arrangement Based on the Position of Ovary
• Flowers can be classified based on the
orientation of the ovary in relation to other
floral parts
• Based on this, we have 3 floral arrangements:
* Hypogynous flower
* Epigynoius flower
* Perigynous flower

26. Hypogynous Flower
These flowers are
described as having
asuperior ovary because
the ovary is located
above the attachment of
other floral parts such as
the sepals, petals, and
stamens.

27. Perigynous flower
These flowers are
described as having a
half-inferior ovary
because the ovary is
located almost at the
same level as the other
floral parts. The ovary is
partially submerged
within the floral tube
formed by the fused bases
of the sepals, petals, and
stamens

28. Epigynous Flower
These flowers are described
as having an inferior ovary,
because the ovary is
situated below the
attachment of other floral
parts. The receptacle fuses
around the ovary, making it
appear as if the sepals,
petals, and stamens arise
directly from the top of the
ovary.

29. Processes of Sexual Reproduction in Angiosperm
• Sexual reproduction in flowering plants takes place in the flower
when fertilization occurs; the production of a new organism
occurs when there is a fusion of the male (pollen) and the female
(ovule) gametes.
• This fusion results in the formation of a zygote and an endosperm
nucleus, which grow into seeds and fruits respectively.
• The transfer of pollen grains from the anther to the stigma is called
pollination
• After pollination, the pollen tube grows through the style to ensure
that the pollen grain is deposited inside the ovule; this is called
germination
• After successful fertilization, the ovule forms the seeds while the
ovary forms the fruit
• A few plants produce seeds without fertilization and the process is
called apomixis. Here, the ovule or the ovary gives rise to new seeds.

30. Fertilization in Plants
• Plant fertilization is the fusion of the male gametes (pollen) with
the female gametes (ovum) to form a diploid zygote.
• It is a physicochemical process that occurs after pollination . The
complete series of this process takes place in the zygote to develop
into a seed.
• During fertilization, pollen grains containing the male gametes
(sperm cells), is transferred from the anther (pollen sac) of the
stamen (male reproductive organ) to the stigma (receptive surface)
of the carpel (female reproductive organ) in the flower.
• This transfer can happen through wind, insects or animals, and the
final product will be the formation of the embryo in a seed.

31. Stages of Fertilization
• For fertilization to be effective, these 4 steps be
completed:
* Pollination
* Germination of Pollen
* Penetration of the Ovule
* Fusion of Gametes
* Formation of Zygote
* Formation of Endosperm

32. Pollination
• Pollination is the transfer of pollen grains from the
anther to the stigma of a flower.
• These pollen grains can be dispersed into the air,
and carried by wind, water, or wildlife (both insects
and animals) to reach the female gamete.
• The pollen is deposited on a plant's stigma, which is
part of the pistil (the elongated part of a flower
extending from the ovary).
• There are 2 types of pollination
* Self-pollination
* Cross-pollination

33. Self-pollination
• When the pollen is transferred from the anther to the
stigma of the same plant, it is known as self-pollination.
• Hermaphrodite or monoecious plants are the best
examples of this pollination. It can further be divided into:
• Autogamy- A type of self-pollination where pollen grain is
directly transferred from the anther to the stigma of the
same flower. This often occurs before the flower even
opens, ensuring self-fertilization.
• Geitonogamy is a type of self-pollination where pollen is
transferred from the anther of one flower to the stigma of
another flower on the same plant.

34. Assignment
• Give 3 advantages and 3 disadvantages of:
* Autogamy
* Geitonogamy
• List 3 plants that exhibit :
* Autogamy
* Geitonogamy

35. Cross-pollination
• Cross-pollination involves the transfer of pollen grains from the
anther of a flower in one plant to the stigma of a flower in another
plant of the same species.
• Here, the agents of pollination are birds, insects, water, wind, and
animals.
• There are five different types of cross-pollination; they are classified
based on the agent of pollination involved. They are:
* Hydrophilous
* Anemophilous
* Zoophilous
* Entomophilous
* Ornithophilous

36. Types of Cross-pollination
• Hydrophilous flowers: Water is the medium of pollen transfer in this type
of flower. This type of pollination is rare and occurs in aquatic plants. Their
pollen grains are buoyant and designed to float on water; their flowers are
usually small.
• Anemophilous flowers: Wind is the medium of pollen transfer in this type
of flower. This type of flower are often small, inconspicuous, and have
lightweight pollen grains than can easily be dispersed by wind.
• Zoophilous flowers: Animals like insects, birds, and mammals are the
agents of pollination. These animals are attracted to flowers by their vibrant
colors, sweet scents, and nectar. As they move from flower to flower in
search of nectar, they distribute transfer pollen grains that are attached to
their bodies, thereby, facilitating cross-pollination.
• Entomophilic flowers: Insects are strictly the agents of pollination in these
flowers.
• Ornithophilous flowers: This is a rare form of pollination where pollination
is done strictly by birds.

37. Assignment
• What are the advantages and disadvantages of:
* Self-pollination
* Cross-pollination

38. Fertilization Processes
Germination
• After pollination, the pollen
tubes begin growing, or
germinating, toward the
ovary
• The pollen grain germinates
and grows into the style by
creating the pathway for the
pollen grain to move down
to the ovary.
Penetration of the Ovule
• The pollen tube penetrates the
ovule, which contains the
female gametes.
• The pollen tube opens into the
ovule through the micropyle
and bursts into the embryo sac.
• This initiates the fusion of the
gametes.

39. Types of Fertilization Based on Pollen tube Entry
• Fertilization must occur for zygote to be
formed; pollen deposited at the style must
travel down the ovule in other to fertilize the
egg present in the embryo sac.
• The route of entry of the pollen into the ovule
gave rise to 3 types of fertilization namely:
* Porogamy
* Chalazogamy
* Mesogamy

40. Porogamy
• This is the most common
type of fertilization. The
pollen tube enters the ovule
through the micropyle, a
small opening at the apex of
the ovule.
• The micropyle provides
structural guidance and
chemical signals to direct the
pollen tube towards the
embryo sac.

41. Chalazogamy
• Chalazogamy occurs in
plants where the ovule is
physically constrained or
where the micropyle is
obstructed.
• The pollen tube penetrates
the ovule through the
chalaza (the basal part of the
ovule in plants, where
nucleus and integuments
join.) or through the region
opposite the micropyle.

42. Mesogamy
• In mesogamy, the pollen
tube penetrates the ovule
through the integument
(outermost layers of the
ovule enveloping the
embryo sac).

43. Formation of Zygote
• The male nucleus unites with the
nucleus of an egg inside the ovule
forming a diploid zygote, which
later swells up and develops into a
fruit.
• After fertilization, the cells of the
zygote will undergo cellular
division, this turns the zygote into
an embryo, or developing plant.
• The embryo is stored in a seed
capsule, where it remains dormant
until environmental conditions
support its development into a
new plant.

44. Double Fertilization
• Double fertilization is a phenomenon
that is characteristic of angiosperm
where both the egg and the polar
nuclei in the embryonic sac get
fertilized.
• Two pollen grains enter the embryo
sac, one pollen grain fertilizes the egg
cell, forming a zygote (2n) while the
other pollen grain fuses with the two
polar nuclei, forming a triploid cell (3n).
• The first fertilization is the normal
fertilization that gives rise to a zygote
while the second fertilization develops
into an endosperm, a nutrient-rich
tissue that nourishes the developing
embryo.

45. Sexual Reproduction in Animal
• Sexual reproduction involves the fusion of the male gamete
(sperm) and female gamete (ovum) to produce a zygote that is
genetically and physically similar to its parents
• The zygote inherits a mix of genetic information from both
parents, leading to genetic diversity.
• Gametogenesis is the formation of the gametes: the production
of sperm in the testes is achieved through a process called
spermatogenesis while oogenesis is the process that produces
eggs in the ovaries.
• After gametogenesis, there must be mating which will bring
these two gametes together through a process called
fertilization
• Without fertilization, sexual reproduction will not be complete.

46. Fertilization
• The fusion of the gametes produces a zygote;
the zygote goes through series of cellular
division to form an embryo in a process known
as embryogenesis .
• A single drop of semen contains millions of
sperms. A single sperm fuses with the ova
during fertilization.
• The nuclei of the egg and the sperm fuse
together to form a single nucleus. Thus, a
zygote is formed.

47. Types of Fertilization
• Internal Fertilization is when the fusion of
the male and female gametes takes place
inside the female reproductive tract.
• External Fertilization is when the fusion of the
male sperm fertilizes the egg of the female
outside the female’s body

48. Types of Internal Fertilization
• Oviparity – Eggs are laid and developed outside the body
of the female, the fertilized eggs are laid outside, where
they receive nourishment from the yolk. Most fish,
amphibians and some reptiles are oviparous
• Ovoviviparity – Eggs are developed inside the body of the
female but they rely on their own yoke for nourishment
The eggs are then laid right before they hatch.
• Viviparity – The offsprings are born directly instead of
hatching from the eggs. They receive nutrition from the
mother.

49. Assignment
• List five animals that exhibit:
* Viviparity
* Oviparity
* Ovoviviparity
• What are the evolutionary advantages and
disadvantages of internal fertilization

50. External fertilization
• External fertilization takes place outside the female;
this type of fertilization is peculiar to aquatic animals,
where the fusion of sperm and eggs occurs in the
surrounding water body.
• Most of this fertilization takes place during the process
called spawning; where many species release large
quantities of gametes (eggs and sperm) into the water
then, rely on chance, environmental currents and
water temperature to fertilize their eggs
• Spawn is the eggs and sperm released or deposited
into water by aquatic animals

51. Viviparous and Oviparous Fertilization Comparison

52. Reproduction in Human
• Sexual reproduction in humans
involves the fusion of a haploid
sperm and a haploid ova to form a
diploid zygote, which received half of
its DNA from the father and the
other half from the mother.
• The male reproductive organs
comprise of a pair of testes,
epididymis, scrotum, vas deferens,
sperm ducts, and a penis.
• The sperms are produced in the
seminiferous tubules within the
testes. The sperms are very small in
size with a head, a middle piece, and
a tail.
• The sperm is mobile and moves fast

53. Male Reproductive System
• Testes (testicles): This is the primary
gonad, 2 in number, located in a bag of
skin called scrotum which lies outside
the pelvic cavity.
• The testes play 2 essential functions:
- Sperm Production: Sperm cells are
produced in the seminiferous tubules
within the testes.
- Testosterone Production: Leydig cells
produce testosterone, the hormone
responsible for male sexual
development and characteristics.
• Epididymis: Is attached to each
testicles; it receives sperm cells from
the testicles, houses them, giving them
room to mature
• Vas Deferens: Carries sperm from the
epididymis to the ejaculatory ducts
• Accessory Glands: Contribute fluids to
the semen, providing nourishment and
protection to the sperm
• Prostate Gland: Secretes an alkaline
fluid that aids sperm survival in the
acidic female reproductive tract.
• Urethra: Provides the pathway for the
seminal fluid and urine in males. It is
longer in males and shorter in females.
• Bulbourethral Glands (Cowper's
Glands): Produce a clear fluid that
lubricates the urethra and may
neutralize acidity.
• Penis: The external male organ
involved in sexual intercourse and
urination

54. Male Reproductive System
• The testes drive the whole
process of the male reproductive
system because it produces the
sperm cells (spermatozoa) and
the male sex hormones called
androgens.
• The other genital organs are
primarily responsible for the are
transportation of the
spermatozoa from the testes to
the exterior: this allow their
maturation on the way, and to
provide certain secretions that
help form the semen

55. Female Reproductive System
• The female reproductive
organs comprise of a pair of
ovaries, oviducts, uterus, cervix
and vagina.
• The eggs (ova) are produced by
the ovaries. A mature egg is
released into the oviduct
(fallopian tube) every month.
• The development of the foetus
takes place in the uterus.
• The foetus is expelled from the
cervix.

56. Female Reproductive System
• Ovaries: The ovaries are the primary
gonad, 2 in number located above the
2 sides of the uterus; situated around
the pelvic region.
• The ovaries play 2 essential functions:
-Egg production: The egg/ova is produced
by the ovaries; the ovaries release at
least one egg every month.
-Hormone production: The ovaries
produce a hormone called oestrogen
and progesterone which regulate the
female sexual development and
physiological characteristics.
• Fallopian tubes: Also called the
oviducts, are tubes that arise from the
ovaries and end at the uterine fundus.
They carry the eggs produced by the
ovaries into the uterus.
• Uterus: It is a large muscular organ
that is present in the pelvic cavity. The
uterus is the region of action during
the menstrual cycle, fertilization and
the development of the fetus.
• Cervix: Is a circular muscle ring that is
present towards the lower end of the
uterus that dilates at the time of
delivery of the baby.
• Vagina: Is a muscular tube-like
structure that is present at the lower
end of the cervix and leads towards
the outside of the female body. The
vagina functions as the pathway for
the penis to enter the female body and
deposit the sperms which then swim
their way to the uterus to fertilize the
female egg.

57. Ovulation
• The ovaries drive the process of the female
reproductive system.
• Ovulation is the process of the release of egg(s)
from either or both of the ovaries. The egg is
formed under the influence of both female sex
hormones estrogen and progesterone, in a
process called Oogenesis.
• Ovulation mostly takes place around the 14th day
within a female monthly cycle.
• As the egg(s) are produced and carried away by
the fallopian tubes into the uterus; the ovaries
produce corpus luteum (a mass of cells that
temporary forms in an ovary every month). It
produces the hormone progesterone during early
pregnancy but disappears if fertilization does not
occur. It also produces the hormone
progesterone during early pregnancy. The role of
the corpus luteum depends on whether or not
fertilization occurs.

58. The Menstrual Cycle
• If fertilization occurs, the corpus
luteum stays and no shedding of the
uterine lining occurs because the
uterus prepares for the implantation of
the foetus
• If fertilization does not occur, the
corpus luteum disintegrates after 14
days and the progesterone levels
drops.
• This causes disintegration of the
uterine lining which results in the flow
of the menses or menstruation or the
monthly cycle.
• Menstruation is the monthly
discharge of blood and mucosal tissue
from the inner lining of the uterus
through the vagina of a non-pregnant
woman from puberty to menopause.
The menstrual cycle is characterized by
the rise and fall of the sex hormones.
• A normal menstrual cycle is between
21 and 35 days, and the bleeding lasts
between three to seven days.

59. Male Gender Differentiation
• The gestation period of humans is 9
months but, the gender of a child is
determined at the time of
fertilization.
• The difference between a male and a
female can be genetically determined
by the chromosomes that each
possesses in the nuclei of the cells.
• Series of physiological changes occur
once the genetic gender is
determined
• There is usually no clear indication of
the gender of an embryo during the
first eight weeks of its life within the
uterus.
• The gender can be determined during
the 15th – 20th week of the pregnancy
through an ultra sound scan.
• Starting around the eighth week after
conception in genetically male (XY)
embryos, there is a gene called SRY on
the Y chromosome
• The SRY gene is crucial in initiating male
gender determination by triggering
undifferentiated gonadal tissue to
transform into testes
• Testes is responsible for secreting
testosterone which triggers other
changes in the developing embryo,
causing it to develop a complete
male reproductive system
• Without a Y chromosome, an embryo
will develop ovaries, that will
produce estrogen

60. Female Gender Differentiation
• Estrogen results in the formation of
the other organs of a female
reproductive system.
• Female embryos therefore, have the
(XX) chromosomes
• Male and female reproductive
systems are different at birth, but
they are immature and are incapable
of producing gametes or sex
hormones.
• From puberty to adulthood,
hormones from the hypothalamus
and pituitary gland stimulate the
testes or ovaries to start producing
sex hormones.
• The sex hormones
are testosterone for the males
and estrogen and progesterone
for the females
• Sex hormones lead to the
growth and maturation of the
reproductive organs, rapid body
growth, and the development
of secondary sex characteristics,
such as body and facial hair,
breasts, deeper voices in males,
broader hips in females and so
on.

61. Phases of Fertilization in Human
• Sexual reproduction consists of a set of events
which are divided into three phases:
* Pre-fertilization
* Fertilization
* Post-fertilization.

62. Pre-Fertilization
• This phase involves all the events that occur before
fertilization takes place.
* Gamete formation (gametogenesis)
* Transfer of gamete
• Gametes are sex cells, and are haploid (23
chromosomes) in nature and are distinct in male
(sperm) and female (ova)
• The female gamete is immobile while the male
gamete is mobile with the help of the flagellum; this
helps it to move and get transferred for fertilization.

63. Fertilization
• This is the fusion of the gametes formed during the pre-
fertilization phase. This phase is sacrosanct if sexual
reproduction is to take place.
• This fusion, results in the formation of a zygote, in a
process called syngamy or fertilization.

64. Post-Fertilization
• This phases entails the developmental activities that occur
after fertilization and implantation .
• These activities include the continuous cellular division,
development and differentiation that occur. This phase
stretches to 9 months gestational period in human.

65. Importance of Reproduction
• Living things are wonderful. Wars, poverty, natural
disasters, murders, hunting, etc., happen and exist
in the world. But it is still estimated that the earth is
the home to around 10 million species.
• One dies, another is born. It never ends and is a
cycle of life that will continue as far as the earth
remains. The secret is within us, it is reproduction in
organisms. It helps organisms to continue the
perpetuation of their species.