HOW DO ORGANISMS REPRODUCE

Sources
http://www.tooter4kids.com/Frogs/life_cy
cle_of_frogs.htm
http://ecs.lewisham.gov.uk/youthspace/c
a/Lorraine/frog_life_cycle.htm

Sources
http://classroom.jc-schools.net/sci-
units/frog-cycle.ppt
http://encarta.msn.com/encyclopedia_76
1552464/Frog_(animal).html
Images provided by Google Image
Search.

Reproduction
 Reproduction is one of the ubiquitous
properties of life.
 Evolution is inextricably linked to reproduction.
 Two modes of reproduction are recognized:
 Asexual
 Sexual

Asexual vs. Sexual Reproduction
Asexual reproduction – the production
of offspring whose genes all come from
one parent without the fusion of egg and
sperm.
Usually diploid eggs are produced by
mitosis which then develop directly.

Asexual vs. Sexual Reproduction
 Sexual reproduction –
the production of
offspring by the fusion of
haploid gametes (eggs
& sperm) from two
parents to form a diploid
zygote (fertilized egg).
 Dioecious
 Gametes arise by
meiosis.
 Genetic variability is
increased by the random
combinations of genes
from the parents.

Asexual Reproduction
 Bacteria and
many protozoa
can reproduce by
binary fission –
separating into
two or more
individuals
approximately the
same size.

 Budding is a form of
asexual reproduction
where new
individuals form as
offshoots of a parent.
 The offspring may
separate or remain
attached to form
colonies.

Freshwater sponges release specialized
groups of cells called gemmules that
can grow into new individuals.

Fragmentation results when an
organism’s body is broken into several
pieces and each piece grows into a new
organism.
Regeneration – the regrowth of lost body
parts.

 Fragmentation
occurs in some
sponges, cnidarians,
polychaete annelids,
tunicates.
 Sea stars can
regenerate lost limbs,
but only species in
the genus Linckia can
form new individuals
from broken arms.

Asexual Reproduction - Advantages
 Animals living far from
members of their own species
can reproduce without having
to search for a mate.
 Numerous offspring quickly –
ideal for colonizing a new
area.
 Advantageous in a stable,
favorable environment
because it reproduces a
successful genotype precisely.

Sexual Reproduction
 Generally involves two parents.
 Special germ cells unite to form a zygote.
Sexual reproduction recombines parental
characters.
 A richer, more diversified population results.
 In haploid asexual organisms mutations are
expressed and selected quickly.
 In sexual reproduction a normal gene on the
homologous chromosome may mask a gene
mutation.

Sexual Reproduction
 Why do so many animals reproduce sexually
rather than asexually?
 The costs of sexual reproduction are greater
than asexual methods:
 More complicated.
 Requires more time.
 Uses more energy.
 The cost of meiosis to the female is passage of
only half of her genes to offspring.
 Production of males reduces resources for females
that could produce eggs.

Sexual Reproduction
 However:
 Sexual organisms produce more novel genotypes
to survive in times of environmental change.
 In crowded habitats, selection is intense and
diversity prevents extinction.
 On a geological time scale sexual lineages with
less variation are prone to extinction.
 Many invertebrates with both sexual and asexual
modes enjoy the advantages of both.

Reproduction is the
process by which
living organisms
produce new
individuals similar to
themselves.

Reproduction
ensured
continuity of
life on earth.

Reproduction -
A bridge to
hereditary
transmission.

It involves continuation of
characters from the parents to
daughter cells by
Copying of DNA (Deoxyribose
Nucleic Acid) molecules present
in the
chromosomes of the cell.

Copying of DNAs is also not a
foolproof exercise, even
minute changes bring
about Variation in the blue
print of the offsprings.

The useful variations are
retained while the harmful one
does not go beyond.

Actually variations help the
species to withstand drastic
environmental
changes, thus save the species
from becoming extinct and
promotes its
survival for a longer time.

This inbuilt tendency of
variation is the "fuel" for
Evolution.

Both
Parents
involved
A single
parent is
involved

Gametes
are
formed
Gametes
not
formed

Progeny is Identical
to parent
eg. Fission in
Amoeba
Progeny is only
genetically
similar to the
parent.

In this method, a
single individual
(parent) is capable
of producing
offspring.

As a result, the
offspring are identical
to one another and are
exact copies of their
parent. They are
termed as clones.

Asexual reproduction is
common among single-
celled organisms and
those with simple
organizations like
Protists and Monerans.

The cell
division itself is
the mode of
reproduction.

is extremely useful as a
mean of rapid
multiplication.
It is common in lower
plants and animals.

Fission Budding
Regeneration
Spore
formation
Fragmentation

Fission; splits into
many cells-multiple
Fission
the parent cell
divides/splits into
two daughter cell-
Binary

In this process, a cell
divides into two halves
and each rapidly grows
into an adult (e.g.,
Amoeba, Paramecium).

The production of a new organism without the fusion of two nuclei. The
new organism develops FROM the cells of a single parent and has
identical characteristics as the parent. This is very rapid and many
offspring are produced.
Cell division consists of two processes:
1. Nuclear Division
• This is called Mitosis or mitotic cell division
• There is an exact duplication of a set of chromosomes creating
two identical sets.
2. Cytoplasmic Division
• This occurs during or after mitosis resulting in the formation of
two daughter cells, each containing an identical set of
chromosomes.
What is a chromosome? A thick threadlike structure that
contains genetic information in the form of DNA.

A Chromosome is a double strand of chromatid
joined in the center by a centromere.

Mitosis
In Animals
•Prophase
•Metaphase
•Anaphase
•Telophase

Interphase
•Not really a part of Mitosis (it
happens before)
•Lasts from the end of one cell
division to the beginning of the
next.
•Known as the “resting period”
Prophase
•Single stranded chromosome replicates into
a double-stranded chromosome
•Double stranded chromosomes are joined by
centromeres.
•Centrioles migrate to opposite ends (poles)
of the cell forming spindle fibers.

Metaphase
•The double stranded chromosomes line up in the
middle of each cell
Anaphase (think apart)
•The double stranded chromosomes break at
the centromere and divide into single-
stranded daughter chromosomes
•The daughter chromosomes then move
apart to opposite poles with the aid of spindle
fibers.
Telophase
•Last stage of mitosis
•Begins when chromosomes reach the poles
•A nuclear membrane forms around each daughter cell
•Cytokinesis divides the cell into two cells and the
cytoplasm pinches in and identical two cells are made.

Mitosis in plants
Plant cell division and
animal cell division differ
in two ways:
1. Plants do not have centrioles
2. Plants have a rigid cell wall
which prevents the cell
membrane from pinching in.
Instead, a cell plate forms
which divides the plant cell in
half.

Types of Asexual Reproduction
•Binary Fission
•Budding
•Spore Formation
•Regeneration
•Vegetative Propagation
(Binary Fission of Amoeba)
Binary Fission
•Parent divides into two
equal parts.
•The two daughter cells are
equal in size and grow to
normal size.
•Examples are Amoeba
and Paramecium

Recall Protista characteristics
 Contains single-celled and simple multi-
cellular organisms
 They are eukaryotic – they have a
membrane-enclosed nucleus and membrane
enclosed organelles
 Some feed by taking in organic substances,
others can photosynthesise.

Examples include:
 Amoeba – moves by means of pseudopods and
is well known as a representative unicellular
organism.
 Algae – a large and diverse group of plant like
organisms ranging from unicellular to
multicellular forms
 Paramecium – consist of a single cell yet are
visible to the naked eye

Amoeba
 Consists of a single cell
 It is a consumer. It feeds on small plants,
animals and bacteria
 It lives in freshwater ponds (most likely to be
found on the mud at the bottom)

Cytoplasm
Ectoplasm
Endoplasm
Nucleus
Pseudopod
Contractile Vacuole
Food Vacuole
Fat Droplets
Waste products
Structure of Amoeba
Cell membrane

Structure of Amoeba
 Cell membrane –
semi-permeable
 Cytoplasm divided up
into
 Endoplasm
 Ectoplasm

Endoplasm and ectoplasm
• The endoplasm is
fluid-like. It has a
grainy appearance
due to the presence
of food vacuoles and
waste materials
• Ectoplasm can
become soft in places
to allow the
development of
pseudopodia
EndoplasmEctoplasm

Development of Pseudopod
 Pseudopods are
referred to as ‘false
feet’ as they are
produced at any
point on the body
and have no fixed
position
 Pseudopodia extend
in the direction
Amoeba wishes to
move

Development of Pseudopod
 Pseudopods develop
when the ectoplasm
softens and moves
forward and the
endoplasm moves in to
replace it
 Amoeba uses
pseudopodia to engulf
its prey

Endoplasm and ectoplasm
Before After

Food vacuoles
• Amoeba feeds by
surrounding its prey
with pseudopodia and
secreting digestive
enzymes into the
vacuole created
• Food can then be
stored within the
vacuole.
Food vacuole

The Contractile Vacuole
High
sugar/salt
concentration
Low sugar/salt
concentration
Amoeba’s
cytoplasm is more
concentrated than
the surrounding
fresh water

As a result water
constantly rushes in
by osmosis
High
sugar/salt
concentration
Low sugar/salt
concentration

In order to deal with
this uptake of water
Amoeba forms a
contractile vacuole
Excess water
enters the
contractile vacuole

The contractile
vacuole swells with
water and moves to
the edge of the
cell…

Where it bursts
and expels the
water…

The cycle is then
repeated

Contractile vacuole
 The contractile vacuole is said to be responsible
for osmo-regulation
 Without it the Amoeba would expand and burst

Reproduction
Asexual
reproduction in
amoeba takes
place by Binary
Fission.
The amoeba cell
divides by mitosis
to form two
amoeba cells.

A new organism is
produced as an outgrowth
of the parent body part.

In this process, the division is
unequal and small buds are
produced that remain attached
initially to the parent cell,
which eventually get separated
and mature into new organisms
(e.g. Yeast).

Budding
•The Parent cell divides into two unequal parts.
•Yeast (unicellular)
Two daughter cells are produced and one is larger than the
other.
•Hydra (multicellular)
The daughter is a multicellular outgrowth of the parent, which bud
separates from the parent.
(Yeast budding)
(Hydra budding)

Spores are small, bulb like
structure develops at the top of
the erect hyphae of the fungus
plant, released into the air and
germinate , into new individuals
after landing into food or soil.

It is the accidental
process when the broken
pieces of an organism
(fragments) grows into a
complete organism.

Sporulation
•Many single celled reproductive cells are
released into to environment
•Under the right temperatures and
moisture conditions these can develop
into new individuals.
•Examples are bread mold and
mushrooms.
Regeneration
•This is the development of a new organism from
part of the original.
•It can also mean the replacement of a body part.
•A new starfish can develop from part of the parent.
•A lobster can grow a new claw if one it torn off.
•An earthworm can re-grow if one tip is cut off.
•A salamander can also re-grow limbs
(blueberry)
(salamander)

When the simple animals like Hydra Planaria
develop a new individual from their broken
older part it is known as regeneration. It is
carried out by specialised cells which grow
large numbers of cells.

A mode of reproduction in
which part like the stem,
root, leaves develop into
new plant under favourable
conditions.

Vegetative Propagation
•The growing of new plants form parts of other plants.
•Examples include:
Propagation Organism
cuttings (stem, leaf, root) geranium
bulbs onion, tulip
tubers potato
runners strawberry
grafting (joining of two parts) seedless orange or watermelon
(any different version of a fruit)

1. Plants can bear flowers, fruits earlier than
those produced from seeds.
2. Growing Banana, orange, rose, jasmine that
have lost the capacity to produce seeds.
3. Genetical similarity is maintained in the
plants. eg. Sugarcane, rose, grapes by layering
or grafting.
Benefits

When reproduction takes
place as a result of fusion
between two gamets, one
from each parent, it is
called sexual
reproduction.

This process of
fusion between two
gamets is called
fertilization.

The formation of gamets involves
exchange of chromosomal (genetic)
fragments between homologous
chromosomes causing genetic
recombination which leads to
variation.

It occurs mostly in flowering
plants. In fact flowers are the
reproductive organ of plants.

Both male and
female
reproductive part
i.e., stamen &
carpel present.
Eg. Hibiscus,
mustard
Either male or
female
reproductive
part is present.
Eg. Papaya,
Watermelon

The transfer of pollen from
the anther of one flower to
stigma of the same flower, or
another flower in the same
plant, or another flower in a
different plant is
called pollination.
Therefore, pollination is of
two types- self and cross
pollination.
Self pollination: It occurs in bisexual
flowers. It is of two types:

It occurs within
the same flower.
Pollen from the
anther is
transferred to
stigma of the
same flower.
It occurs between
two flowers of the
same plant. Pollen
from the anther
of one flower is
transferred to
stigma of another
flower in the same
plant.

The Parts of a Flower
• Most flowers have
four parts:
• sepals,
• petals,
• stamens,
• carpels.

A typical flower
consists of four main
whorls namely calyx
(sepals), Corolla
(Petals), Androecium
(Stamens) and
Gynoecium (Carpels).

The parts of a flower
• Sepals protect the
bud until it opens.
• Petals attract
insects.
• Stamens make
pollen.
• Carpels grow into
fruits which
contain the seeds.

Stamen (male)
• Anther: pollen
grains grow in the
anther.
• When the grains
are fully grown, the
anther splits open.

Pistil (female)
• Stigma
• Style
• Carpel (ovary)
• Ovules (eggs)

Pollination
• Flowering plants
use the wind,
insects, bats, birds
and mammals to
transfer pollen
from the male
(stamen) part of
the flower to the
female (stigma)
part of the flower.

Pollination
• A flower is
pollinated when a
pollen grain lands
on its stigma.
• Each carpel grows
into a fruit which
contains the seeds.

Fertilisation
• Pollen grains germinate
on the stigma, growing
down the style to
reach an ovule.
• Fertilised ovules
develop into seeds.
• The carpel enlarges to
form the flesh of the
fruit and to protect
the ovary.

Wind pollination
• Some flowers, such as
grasses, do not have
brightly coloured
petals and nectar to
attract insects.
• They do have stamens
and carpels.
• These flowers are
pollinated by the wind.

Seed dispersal
Seeds are dispersed
in many different
ways:
• Wind
• Explosion
• Water
• Animals
• Birds
• Scatter

How birds and animals help
seed dispersal
• Some seeds are
hidden in the
ground as a winter
store.
• Some fruits have
hooks on them and
cling to fur or
clothes.

How birds and animals help
seed dispersal
• Birds and animals
eat the fruits and
excrete the seeds
away from the
parent plant.

Humans use a
Sexual Mode of
reproduction.

It needs sexual maturation which
includes creation of the germ cells
ie, egg
(ova) in the female and sperm in the
male partener & this period of sexual
maturation is called Puberty.

Human beings
have a well
developed male
and female
reproductive
system.

Humans, like other organisms, pass
certain characteristics of themselves to
the next generation through their genes,
the special carriers of human traits. The
genes parents pass along to their
children are what make children similar
to others in their family, but they are
also what make each child unique. These
genes come from the father's sperm and
the mother's egg, which are produced by
the male and female reproductive
systems.

Most species have two sexes: male
and female. Each sex has its own
unique reproductive system. They
are different in shape and
structure, but both are specifically
designed to produce, nourish, and
transport either the egg or sperm.

Unlike the female, whose sex organs are located entirely
within the pelvis, the male has reproductive organs,
or genitals, that are both inside and outside the pelvis.
The male genitals include:
•the testicles
•the duct system, which is made up of the epididymis and
the vas deferens
•the accessory glands, which include the seminal vesicles
and prostate gland
•the penis

In a guy who's reached sexual maturity,
the two testicles, or testes, produce and
store millions of tiny sperm cells. The
testicles are oval-shaped and grow to be
about 2 inches (5 centimeters) in length
and 1 inch (3 centimeters) in diameter. The
testicles are also part of the endocrine
system because they produce hormones,
including testosterone

Testosterone is a major part of puberty in
guys, and as a guy makes his way through
puberty, his testicles produce more and
more of it. Testosterone is the hormone
that causes guys to develop deeper voices,
bigger muscles, and body and facial hair,
and it also stimulates the production of
sperm.

The formation of
male germ cell
(sperms) takes place
in the testes (male
reproducture organ)

Actually a pair of testes
are located inside scrotum
situated outside the
abdominal cavity. It is
meant to keep relatively a
low temperature needed
for the production of
sperms by testes.

Moreover testes release a
male sex hormone called
testosterone whose
function is to:

Regulate the production
of sperm
Brings about changes in
appearance seen in boys
at the time of puberty.

The male reproductive system
consists of portions which
produce the germ-cells and
other portions that deliver the
germ-cells to the site of
fertilisation.

The formation of germ-cells or
sperms takes place in the
testes. These are located
outside the abdominal cavity in
scrotum because sperm
formation requires a lower
temperature than the normal
body temperature.

The sperms formed are
delivered through the vas
deferens which unites with a
tube coming from the urinary
bladder. The urethra thus
forms a common passage for
both the sperms and urine.

Along the path of the vas deferens, glands
like the prostate and the seminal vesicles
add their secretions so that the sperms are
now in a fluid which makes their transport
easier and this fluid also provides nutrition.
The sperms are tiny bodies that consist of
mainly genetic material and a long tail that
helps them to move towards the female
germ-cell.

The female germ cells or
eggs are made in the
ovaries, a pair of which is
located in both side of
abdomen.

When a girl is born, the
ovaries already contain
thousands of immature
eggs.

At the puberty, some of
these Eggs start
maturing. One egg is
produced every
month by one of the
ovaries.

The Egg is carried from the
ovary to the womb through a
fallopian tube. These
two fallopian tube unite into
an elastic bag like structure
known as Uterus.

The Uterus
opens into the
vagina through
the cervix.

Fertilization
occurs in the
fallopian tube of
female genital
tract.

When the male ejaculates during intercourse, semen is
deposited into the female's vagina. From the vagina the
sperm make their way up through the cervix and move
through the uterus with help from uterine contractions.
If a mature egg is in one of the female's fallopian tubes,
a single sperm may penetrate it, and fertilization,
or conception, occurs.

This fertilized egg is now called a zygote and
contains 46 chromosomes — half from the egg
and half from the sperm. The genetic material
from the male and female has combined so that a
new individual can be created. The zygote divides
again and again as it grows in the female's uterus,
maturing over the course of the pregnancy into
an embryo, a fetus, and finally a newborn baby.
Actually uterus is richly supplied with blood to
nourish the growing embryo.

The Embryo gets nutrition from the
mother's blood with the help of a special
tissue called PLACENTA. It provides a
large surface area for glucose and oxygen
to pass from the mother to the embryo.
Similarly the wastes from developing
embryo are removed to mother's blood
through placenta.

The child is born as a result of rhythmic
contractions of the muscles in the uterus.
after Nine months (36 weeks) of
development inside mother's womb.
It is also called
Gestation Period.

If the egg is not fertilised, it lives for about one
day. Since the ovary releases one egg every
month, the uterus also prepares itself every
month to receive a fertilised egg. Thus its lining
becomes thick and spongy.
This would be required for nourishing the embryo
if fertilisation had taken place. Now, however,
this lining is not needed any longer. So, the lining
slowly breaks and comes out through the vagina
as blood and mucous.

This cycle takes place
roughly every month or at
a regular interval of 28
days. This process is
called MENSTRUATION.
It usually lasts for about
two to eight days.

The sexual cycle in a woman
continues upto the age of 45 to
50 years. After that the ovary do
not release egg. This stage is
called Menopause. It a also
marks the end of menstruation in
the woman.

Reproductive Health means a
total well-being in all aspects
of reproductive, ie., physical
emotional, social and
behavioural.

It is the avoidance of
pregnancy. It can be
achieved by
Contraception

To prevent union
of sperm & egg.
Use of condoms,
Diaphragm &
cervical caps.

Also called sterilization in
Vasectomy, the vas
deferens of male is blocked
to prevent sperm transfer.
Also called sterilization in
Vasectomy, the vas
deferens of male is blocked
to prevent sperm transfer.
In Tubectomy, the
fallopian tube of female
is blocked to prevent
egg to reach uterus.
In Tubectomy, the
fallopian tube of female
is blocked to prevent
egg to reach uterus.
Copper-T or loop is
placed in uterus to
prevent pregancy.
Copper-T or loop is
placed in uterus to
prevent pregancy.

Oral contraceptive (OCs) -
drugs commonly need to be
taken orally as pills,
changes the hormonal
balance to check the egg
release in females. OCs
cause side effect.
Oral contraceptive (OCs) -
drugs commonly need to be
taken orally as pills,
changes the hormonal
balance to check the egg
release in females. OCs
cause side effect.

Healthy society needs a
balanced sex ratio that can be
achieved by educating the
people to avoid malpractices like
female foeticide & pre-natal sex
determination.

Sexually transmitted diseases
(STDs) are infectious
diseases that spread from
person to person through
intimate contact. STDs can
affect guys and girls of all
ages and backgrounds who are
having sex — it doesn't
matter if they're rich or
poor.

Unfortunately, STDs
(sometimes also called STIs
for "sexually transmitted
infections") have become
common among teens. Because
teens are more at risk for
getting some STDs, it's
important to learn what you can
do to protect yourself.

STDs are more than just an
embarrassment. They're a serious
health problem. If untreated, some
STDs can cause permanent damage,
such as infertility (the inability to
have a baby) and even death (in the
case of HIV/AIDS).

How STDs Spread
One reason STDs spread is because people
think they can only be infected if they
have sexual intercourse. That's wrong. A
person can get some STDs, like herpes or
genital warts, through skin-to-skin contact
with an infected area or sore.

Another myth about STDs is that you
can't get them if you have oral sex.
That's also wrong because the viruses
or bacteria that cause STDs can enter
the body through tiny cuts or tears in
the mouth and anus, as well as the
genitals.

Some of the things that increase a person's
chances of getting an STD are:
Sexual activity at a young age. The younger a person starts having
sex, the greater his or her chances of becoming infected with an STD.
Lots of sex partners. People who have sexual contact — not
just intercourse, but any form of intimate activity — with many
different partners are more at risk than those who stay with the
same partner.
Unprotected sex. Latex condoms are the only form of birth control
that reduce your risk of getting an STD, and must be used every time.
Spermicides, diaphragms, and other birth control methods may help
prevent pregnancy, but they don't protect a person against STDs.

Human Reproductive System
If it wasn't for me
You wouldn't be
I've kept population through many
a day
So the human race will stay
by Joey F.

The reproductive system is the system
that allows for the continuation of the
human species
This system is different in males and
females

The role of the male’s reproductive
system is to manufacture sperm and
then to deliver them to the female’s
reproductive tract where fertilization
may occur

The role of the female’s reproductive system is
basically the same except that it goes further if
the sperm meets an egg.
If fertilization occurs the female reproductive
system is designed to nurture and care for the cell
that will soon grow into a baby

• The sperm is produced in the male testis and then
travels through a series of ducts to reach the
body exterior
• The eggs are produced in the ovary of a female.
When a egg is to be expelled or ovulated a “blister
forms on the exterior of the ovary. When the
“blister” bursts the egg may be collected by the ends
of the fallopian tubes and travels through the fallopian
tubes where it can be fertilized by a single sperm

• If an egg is fertilized it travels down into the uterus
where it embeds in the wall of the uterus.
• There it divides rapidly and the cells begin to
specialize into the different organs of a pregnancy.
Some of the cells form the amniotic sac while some
form the placenta and the umbilical cord.
• Only a small number of these cells will eventually form
the fetus

The scrotum and penis are the
male genitalia. The male
gonads, called testis, are
tightly coiled tubes surrounded
by tissue. Sperms develop in
these tubes. The male gonads
are located outside of the body
since sperm productions can only
occur at about two degrees
Celsius lower than normal body
temperature. After the sperm
are produced they mature and
are stored in the epididymis.

male reproductive system
The male reproductive
system also contains
three glands that add
secretions to the
semen.
seminal vesicles
prostate gland
bulbourethral
glands

seminal vesicles
Sixty percent of semen is secreted by the seminal
vesicles. They lie behind and below the bladder
and empty directly into the ejaculatory duct. The
fluid secreted is clear and thick. It contains
mucus, amino acids, and fructose. The fructose
provides energy for the sperm.

prostate gland and bulbourethral
glands
• The prostate gland surrounds the beginning of the
urethra in which it secretes its products. Prostatic
fluid is milky, thin, and alkaline in order to balance the
acidity of any urine remaining in the urethra and the
acidity of vaginal fluids
• Bulbourethral glands lie along the urethra below the
prostate. Although their specific function is still
unknown, they do secrete a viscous fluid before
ejaculation

male reproductive system
Three layers of spongy tissue
comprise the human penis.
When sexually aroused, this
tissue fills with blood from the
arteries, while the veins are
sealed. This produces an
erection.
The shaft of the penis is covered
in relatively thick skin. The
head, or glans penis, is covered
with thinner skin. This results
in extra sensitivity in the glans
penis area.

Ovaries, the female gonads,
are located below the
digestive system in the
abdominal cavity. Inside
each ovary are many
follicles which consist of a
single egg cell and one or
more layers of follicle cells.
Follicle cells protect and
nourish the egg cells. A
woman is born with about
400,000 follicles and cannot
produce more.

Ovulation is the process in
which an egg is expelled from
a follicle. The egg is expelled
directly into the abdominal
cavity and is picked up by the
fallopian tubes. Inside the
fallopian tubes are cilia which
sweep the egg toward the
uterus. At the neck of the
uterus is the cervix followed
by the vagina which has very
thin walls, much thinner than
those of the uterus.

Human Reproduction
Before fertilization can occur,
the sperm must reach the
egg. Each egg is only viable
for 12 to 48 hours and some
sperm can survive for as long
as 72 hours, but most can only
retain their fertilizing power
for 12 to 48 hours. Therefore
in order to produce offspring,
sex must occur no more than
72 hours before ovulation or
no later than 24 hours after.

Human Reproduction
• The moment of ejaculation, millions of sperm are
released into the female’s reproductive tract.
Many are able to swim up through the vagina
towards the cervix. Many are killed by the
acidity of the vaginal fluids. Here thousands of
sperm are killed by phagocytes which recognize
them as “non-self.” Of the millions of sperm
that are ejaculated, only a few thousand are
able to reach the egg.

Human Reproduction
• Should sperm reach the egg, they cannot
immediately fertilize it. As time must pass for
their membranes to become capacitated, or
weakened. This is facilitated by the cervical
mucus, and in the following 6-8 hours the sperm
are gradually capacitated.
• After capacitation has occurred, the acrosomal
reaction follows. This reaction releases enzymes in
the area surrounding the egg therefore weakening
the intracellural cement that surrounds the egg.
Once weakened a single sperm is allowed to
penetrate the egg and fertilize it.

HOW DO ORGANISMS REPRODUCE

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