Reproduction of Living
Organisms
• Life on Earth has existed for 4 billion years.
Reproduction has made the continuation of
life possible.
• Organisms can reproduce either sexually or
asexually.
• In this unit, you will learn about plant &
animal reproduction, reproductive organs &
the stages of development of various
organisms.
Asexual & Sexual Reproduction
• Successful reproduction ensures the survival
of a species (through evolution).
• There are many different forms of
reproduction (each species has its own unique
method) but there are 2 basic ways of making
more organisms: asexual & sexual
reproduction.
Asexual Reproduction
• Requires the involvement of only one living
organism.
• It does not depend on the presence of male
and female parts.
• It produces offspring that are identical to their
parent (share the same genetic material, &
same physical & behavioral characteristics).
• The species continues to evolve (change) by
genetic mutation.
Examples of Asexual Reproduction:
• Fission, budding, vegetative propagation,
sporulation, fragmentation.
Sponge Budding
Fern Spores
Strawberry with
Runner
Planaria Fragmenting
Bacterial Fission
Sexual Reproduction
• Requires the involvement of a male & female
parent.
• Although offspring share many similarities
with their parents, they each possess a unique
genetic makeup consisting of a combination of
genes from both parents.
Reproduction in Animals
• Animals are classified into 2 groups –
invertebrates (no backbones, 97% of animals)
& vertebrates (have backbones).
• Invertebrates reproduce either asexually or
sexually.
• Vertebrates mostly reproduce sexually.
Asexual Reproduction in Animals
• A single organism can produce one or many
identical individuals.
• Ex: sponges & hydra reproduce by budding.
Individuals produce buds that develop directly
on the parent. When these individuals reach
maturity, they may break off & become
independent.
Reproduction in Sponges & Hydras
• When sponge buds remain attached to the
parent, it leads to the formation of sponge
colonies.
Sexual Reproduction in Animals
• Most vertebrates reproduce this way.
• Male animals produce male gametes or
spermatozoa.
• Female animals produce female gametes or
ova.
• Spermatozoa & ova each contain half the
genetic material of the future offspring.
Steps of Vertebrate Reproduction
1. A male gamete fuses with a female gamete.
2. Fusion produces an initial cell called a zygote
that contains complete genetic material.
3. The zygote divides & transforms into an
embryo consisting of many cells.
4. The embryo develops into a small animal.
5. When it becomes an adult, it produces
gametes & is capable of reproduction.
Cycle of Sexual Reproduction in
Animals
Sexual Reproduction
• To be successful, the following criteria must be
met:
– Male & female gametes must be at the same
place at the same time.
– The zygote must obtain nutrients & protection to
survive, get warmth & moisture needed for its
development.
Mating
• During mating, 2 individuals of an animal
species unite to combine their gametes &
achieve fertilization.
• Many animals have only 1 mating period each
year, usually when environmental conditions
are ideal for the development of their
offspring.
– Ex: Many Que. mammals mate in fall, embryos
develop in winter, & young are born in spring
when climate & food supply are favorable.
– Ex: Birds mate in spring & their young hatch a few
weeks later.
Fertilization
• Occurs when a spermatozoon & ovum of a
single species combine.
• Must take place in a moist environment so
that sperm can move, & egg membrane is
supple enough for sperm to penetrate (the
cells will die if they dry out).
Types of Fertilization
• 2 main types in animals:
1. External = gametes combine outside the bodies
of both parents.
• Ex: Common in aquatic animals like fish, sea
anemones, frogs
2. Internal = spermatozoa enter the female &
migrate toward the ovum or ova.
•
Ex: Most land animals like reptiles, mammals
Examples of External Fertilization
Examples of Internal Fertilization
Oviparous Creatures
• Oviparous = creatures that lay eggs.
• Most reptiles, birds, amphibians, fish & insects are
oviparous.
• The egg contains all the necessary nutrients for the
development of the embryo.
• When development is complete, the young animal
hatches from its shell.
• In reptiles, fish & amphibians, as soon as the young
emerge from their shells they are able to find their
own food & defend themselves against predators. Birds
are different in that they care for their young.
Viviparous Creatures
• Viviparous = the fertilized ovum completely
develops inside the mother’s body.
• All mammals are viviparous, except the duckbilled platypus & spiny anteater.
• Male mammals have penises that are used to
deposit semen inside the female.
• The female’s body is where the zygote obtains
nutrients and protection it needs to develop.
After birth, females produce milk to feed the
offspring.
Ovoviviparous Creatures
• Ovoviviparous = females keep their eggs inside
their bodies until they hatch.
• The incubation period occurs inside the
female’s body, & the young are born live.
• Certain species of snake are ovoviviparous.
Rattle snake
giving birth
Hermaphrodites
• Hermaphrodites = animals equipped with
both male & female reproductive organs.
• They produce both male & female gametes,
but must exchange semen in order to
reproduce.
• They reproduce by internal fertilization.
• Worms & snails are hermaphrodites.
Reproduction In Worms
• When 2 worms mate, they each inject their semen
into the genital opening of the other. Each worm
then lays fertilized eggs. Two individuals can
therefore produce eggs after only 1 act of mating.
Reproduction In Humans
• All mammals, including humans, begin life as a
tiny, fertilized egg. Over weeks & months, it
transforms into a collection of tissues &
organs that make up a baby.
The Human Reproductive System
• It is similar to that of sexually reproducing
plants & animals: It produces & combines
male & female gametes.
• It occurs by internal fertilization.
• It all begins with sex hormones (messengers)
that travel through the blood stream & tell the
testicles (in boys) & ovaries (in girls) when to
begin producing gametes.
Puberty
• Is a stage of sexual development in which a
series of hormonally triggered changes
prepares the human body for reproduction.
• The majority of girls & boys start to feel these
changes at the beginning or during
adolescence.
Puberty
• At puberty the pituitary gland starts to release
sex hormones.
– In males, the main hormone is testosterone.
– In females, the 2 main hormones are progesterone &
estrogen.
• These hormones travel in the blood stream until
they reach the testes or ovaries, where they send
a signal to produce spermatozoa or ova,
respectively.
• During each menstrual cycle an ovum is released
by the ovaries.
Other changes During Puberty
• Puberty leads to several physical changes,
including:
– Pubic hair & other body hair begins to grow
– Girls start developing breasts
– In boys, changes in the larynx cause their voices
to become deeper
Male Reproductive Organs
Male Reproductive Organs
Male Reproductive Organs
Reproductive organ
Purpose
Scrotum
Pouch that contains the testicles. Holds testicles away from
body because sperm production requires temperatures
below body temperature.
Testicles
Contain the seminiferous tubules.
Seminiferous tubules
Produce an average of 400 million male gametes per day.
Epididymis
The sperm produced are stored in this small, elongated
organ lying above the testicles.
Vas deferens
The sperm enter the vas deferens before being released
outside the body during ejaculation.
Prostrate & seminal
vesicles
They produce semen, the fluid that contains sperm. Semen
helps the sperm move & is rich in sugar to provide energy
for swimming into the woman’s vagina after ejaculation.
Male Reproductive Organs
Reproductive organ
Purpose
Urethra
Semen flows through this tube during ejaculation. Urethra
also carries urine from the bladder outside the body.
Cowper’s gland
Cowper’s gland releases a fluid into the urethra, which
neutralizes the acidity caused by any remaining traces of
urine that could threaten the survival of sperm.
Female Reproductive Organs
Follicles inside
Female Reproductive Organs
Reproductive Organ
Purpose
Ovaries
A woman has 2 ovaries. They take turns releasing 1 ovum
every 28 days. This is called ovulation.
Follicles
They are located in the ovaries. Each follicle contains a single
ovum & brings it to full maturity.
Fallopian Tubes
The ovum released by the follicle travels through the
fallopian tube to reach the uterus. An ovum survives
between 24-48 hours in the fallopian tube, where it can be
fertilized.
Uterus
A hollow, pear-shaped organ where the zygote develops if
the ovum is fertilized by a sperm.
Vagina
The passage into which the penis penetrates to release its
sperm. The baby also leaves the uterus through the vagina
during birth.
The Menstrual Cycle
• The menstrual cycle causes changes to the
reproductive organs.
• It lasts about 28 days.
• One ovum reaches maturity during every
cycle.
• The body reacts as though the ovum is about
to be fertilized & an embryo about to develop.
• The lining of the uterus thickens to help the
zygote implant & begin its development.
Menstrual Cycle
• Body temperature changes throughout the
cycle: it increases during ovulation.
Menstrual Cycle
• If the ovum is not fertilized after a few days, it
is expelled from the body along with the cells
that lined the uterus. This process is called
menstruation or a woman’s period.
When Can a Woman Become
Pregnant?
There Are Several Ways to Tell When a
Woman is Fertile
• Calendar, temperature, or mucus method:
Problems
Pregnancy
• When male gametes (sperm) are deposited
into a woman’s vagina, they swim towards the
uterus, then the fallopian tubes.
• Of the several million sperm released, only a
few thousand will reach the ovum. Only 1 of
these will succeed in fertilizing the ovum.
Pregnancy
• After fertilization, the zygote moves from the
fallopian tube to the uterus. On its way it
undergoes a series of cell divisions.
• By the time it begins to implant in the uterus
wall, it may be a clump of about 16 cells & is a
fluid-filled ball. It contains a group of cells known
as the embryoblast.
• The external cells of the zygote will form the
placenta & the embryoblast will become the
embryo.
Embryo & Placenta
• Between the 10th & 14th days, 2 important
tissues are formed:
1. The amnion – develops into the amniotic sac,
containing the embryo & amniotic fluid. This
fluid protects the embryo from shock.
2. The second tissue gives rise to the placenta - an
organ that carries nutrients & oxygen from the
mother to the fetus through the umbilical cord.
The umbilical cord also carries wastes away from
the fetus.
Pregnancy
• During initial cell division, embryonic cells are
almost identical, but during the 2nd week, the
cells begin to differentiate.
• They form the gastrula, which consists of 3 layers:
1. the ectoderm - will form skin & nervous system
2. the mesoderm - will form kidneys, skeleton,
muscles, blood vessels & glands
3. the endoderm – will form lungs & walls of digestive
system
From Embryo to Fetus
• The heart begins to beat at around 3 weeks,
even though there is not yet any blood for it
to pump!
• By the end of the 4th week the embryo has
grown to 500X its initial size.
• Gestation = the period of development before
birth. It lasts 38-40 weeks.
Gestation
• Can be divided into 3 trimesters, each about
13 weeks or 3 months.
First Trimester (Weeks 1-13)
• For 1st 8 weeks, baby is referred to as an embryo.
From end of 8th week & onward, it is called a
fetus.
• Week 4: About 1 cm long. Brain, heart, limbs,
eyes & spinal column begin to form.
• Week 8: About 3 cm long. First bone cells are
produced. Fetus has arms & legs, but no fingers
or toes yet.
• Week 12: 8-10 cm long. Main organs begin to
sprout: liver, stomach, brain, heart. Sex of fetus
can be determined. Fetus can move.
Second Trimester (Week 14-26)
• Week 16: About 16 cm long. Skeleton begins to form.
Fingers & toes become differentiated & nails start to
grow. Genital organs are formed. Brain develops
quickly & nervous system begins to work. Most organs
are present but not fully developed.
• Week 20: About 25-30 cm long. Hairs begins to grow
on head. Buds of permanent teeth appear beneath
milk teeth. Can hear sounds from outside womb. Can
suck thumb. Can use digestive system by swallowing a
little amniotic fluid.
Second Trimester
• Week 24: 27-35 cm long. Lungs have just
formed but cannot breath. Has fingerprints.
Jumps when it hears a sudden noise.
Third Trimester (Week 27-40)
• There is rapid growth of the fetus, especially the
brain.
• The mother must eat a healthy diet so the fetus
receives the nutrients it requires.
• Week 28: About 38 cm long. Immune system
develops. Bones begin to harden. Can open its
eyes.
• Week 32: About 42 cm long & grows 1cm/week.
Lungs & brain continue to develop. Settles into
head-down position in preparation for birth.
Third Trimester
• Week 36: About 50 cm long. Fetus can
distinguish between light & dark. Recognizes
its mother’s voice. Nails & hair continue to
grow. Often gets hiccups.
Birth
• After the 38th to 40th week, the baby is ready
to make its way into the world.
• The birth signal to expel the fetus is sent by
the pituitary gland in the form of a hormone
called oxytocin. It stimulates contractions of
the uterus. This is the start of labor.
Is it a boy or a girl?
• Depends on which sex chromosomes it has: X or Y.
• XX = girl; XY = boy
• The sex of the unborn child is decided at fertilization, & it’s
the father’s sperm cell that is decisive.
• Every egg that a woman produces is female because it
contains only an X chromosome.
• In a man, only ½ the sperm cells carry an X while the other
½ carry a Y.
• If an X sperm fertilizes the egg, it results in 2 X
chromosomes, so it will be a girl.
• If a Y sperm fertilizes the egg, it results in an XY, so it will be
a boy.
Pregnancy Videos
• First Trimester: http://www.babycenter.com/2_insidepregnancy-weeks-1-to-9_10302602.bc
• http://www.babycenter.com/2_inside-pregnancyweeks-10-to-14_10308108.bc
• Second Trimester:
http://www.babycenter.com/2_inside-pregnancyweeks-15-to-20_10308111.bc
• http://www.babycenter.com/2_inside-pregnancyweeks-21-to-27_10312242.bc
• Third trimester: http://www.babycenter.com/2_insidepregnancy-weeks-28-to-37_3658874.bc
• http://www.youtube.com/watch?v=vj9Ck8qBh8k
Risks During Pregnancy
• Everything that the mother eats, drinks & breathes
during the pregnancy can end up in the fetus via the
umbilical cord. Hence, it is important that she avoid
hazardous substances such as cigarette smoke, alcohol
& drugs.
• These can interfere with the normal development of
the fetus, causing such problems as low birth weight,
physical defects, mental illness or developmental
delays.
– Ex: Fetal alcohol syndrome
• The fetus is especially sensitive to these
substances during the first trimester.
Fetal Alcohol Syndrome
Genetic Disorders
• Genetic disorders sometimes occur, either due
to inheritance of defective genes, or due to
mutations.
• Ex: Down Syndrome or Trisomy 21 results
when a baby is born with an extra
chromosome # 21.
Twins & Multiples
• Identical = single fertilized egg splits in two
• Fraternal = 2 eggs fertilized by 2 sperm
• Conjoined = identical twins in which fusion
occurs (a fertilized egg completely separates, but
stem cells (which search for similar cells) find likestem cells on the other twin and fuse the twins
together)
• Multiples = often fertility drugs stimulate release
of multiple eggs which become fertilized
Twins
Family Planning
• Humans are the only organisms who can
control certain aspects of their reproduction –
like birth control.
Reproduction In Plants
• Plants can reproduce both sexually &
asexually.
Asexual Reproduction in Plants
• Occurs when plants reproduce from a part of
themselves, such as a root, stem, or leaf.
– Ex: Duckweed: multiplies by growing new fronds
which detach when mature to form new plants.
– Strawberries: stems (runners) arch over, reach the
ground & begin to take root, forming a new plant.
Sexual Reproduction In Plants
• 3 Forms in the Plant Kingdom:
1. Reproduction by flowers – produce seeds
•
•
Also known as angiosperms (enclosed seeds - in a pod ,
shell or pulp)
All flowering plants
2. Reproduction by cones – produce seeds
•
•
Also known as gymnosperms (naked seeds - protected
only by a seed coat)
All conifer trees
3. Reproduction by spores – produce spores
•
Ex: ferns, algae & mosses
Reproduction in Flowering Plants
• Over ½ of all known plant species belong to
angiosperm family.
• Some produce large flowers, others tiny flowers
(ex: grasses & trees).
• All flowers contain the reproductive organs of the
plant.
• Some plants only have the male reproductive
organs (stamens), others only have the female
reproductive organs (pistils). Often, plants have
both.
• Male Organ = Stamen
– Anther = part of the stamen where pollen is
produced & stored
– Pollen grains = cases that contain male gametes
(spermatozoa)
– Filament = long, thin stalk that supports the
anther
• Female Organ = Pistil
– Stigma = sticky surface of pistil captures pollen
grains
– Style = long, thin stalk that supports the stigma
– Ovary = Swollen base of the pistil that contains
female gametes (ovules)
– Ovules = female gametes
Pollination & Fertilization
• Pollen grains are produced by anthers.
• They must land on the stigma of the pistil in
order to fertilize the flower so it can produce
seeds. This is called pollination.
• Self-pollination occurs when pollen is
transferred to the pistil of the same flower.
• For most angiosperms, pollen is carried to the
pistil of a different flower. This is called crosspollination.
• The wind & insects are important agents of
cross-pollination.
Pollination Leads to Fertilization
• During fertilization, the male & female
gametes combine. The fused gametes are
called a zygote.
Seed Development
• The formation of the zygote is the first stage
of seed development.
• This first cell divides many times to form more
cells that eventually become specialized.
– Some play a role in embryo development.
– Some become food storage cells called
cotyledons.
– Others form a protective envelope called the seed
coat.
Seeds
• It contains everything it needs to produce a
new plant.
• It carries a small, immature plant called an
embryo.
• It has food reserves in the cotyledon.
• It has a protective covering called the seed
coat.
Cotyledon
Envelope
Future Leaf
Future Stem
Future Root
Seed Dispersal
• Fruit are the primary means of seed dispersal
in flowering plants.
• There are 5 main agents of seed dispersal:
1.
2.
3.
4.
Animals
Water
Wind
The plant itself (some “shoot” their seeds out of
seed pods)
5. Humans
Seed Dispersal
• It is important that seeds be dispersed far
from the parent plant to avoid competition for
light, nutrients & water.
Reproduction in Conifers
• Gymnosperms reproduce by means of cones,
not flowers.
• Male cones contain male gametes, female
cones contain female gametes.
• Seeds develop in the female cones once the
ovules have been fertilized.
• Some conifer species produce male & female
cones on different trees, but most species
produce both types on the same tree.
Reproduction in Spore-Producing
Plants
• Spores are cells that contain complete genetic
material. A spore can therefore transform into
a young plant without fertilization.
• Male spores develop into plants that produce
spermatozoa & female spores develop into
plants that produce ovules.
• Examples are mosses, ferns & liverworts.
Sexual Reproduction in Moss
Sexual Reproduction in Ferns