Reproduction of plants and simple animals

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Prepared by
Rajeev G. Bayan
REPRODUCTION OF
PLANTS AND
ANIMALS

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OVERVIEW
REPRODUCTION is a process by
which new individuals are produced.
It ensures that, as old individuals
die, new ones are born to take their
place to continue life of the species.
Organisms reproduce themselves,
either by asexual or sexual means.

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OVERVIEW
In asexual reproduction, organisms produce
offspring without forming sex cells. Thus, the
offspring are genetically the same or show no
variation.
Sexual reproduction, on the other hand, involves
the production of sex cells and their fusion
during fertilization.
Sexual reproduction results in variation due to
genetic recombination.
The offspring are never exactly like any one of
the parents, but a combination of the characters
or both.

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Topics to Discuss
Cell Division
Asexual Reproduction in Plants and Other
Organisms
Sexual Reproduction in Flowering Plants
Sexual Reproduction in Some Animals

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Cell Division: Chromosomes
▪ Multicellular organisms have two
types based on function and
chromosome number: (a) vegetative,
somatic or body cells; and (b)
reproductive cells.
▪ Body cells are diploid – they have two
sets of chromosomes represented by
the symbol 2N.
▪ Reproductive cells are haploid; they
have only one set of chromosomes
represented by the symbol N.

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▪ One distinctive characteristic of a
species is a constant chromosome in
each cell.
▪ In a diploid cell, each kind of
chromosome is represented by a pair;
the two identical chromosomes are
described as homologous.
▪ A human female has 23 pairs of
homologous chromosomes, of which
22 pairs are body chromosomes and
the 23rd a pair of sex chromosomes
(symbol: XX)

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▪ A human male has 23 pairs of
chromosomes, of which 22 pairs are
homologous while the 23rd pair is
made up of two different sex
chromosomes, an X and a Y
chromosome (symbol: XY).
▪ When the cell contains more than two
sets of chromosomes, the
phenomenon is known as polyploidy.
▪ Polyploidy organisms usually have
larger body sizes, larger flowers or
larger fruits.

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Cell Division: Mitosis and Meiosis
▪ Cells divide for growth, repair and
reproduction.
▪ Cell division involves the division
of nucleus (mitosis) and the
division in the cytoplasm
(cytokinesis).
▪ There are two types of nuclear
division: Mitosis and Meiosis

z Cell Division: Mitosis
▪ Mitosis consists of a single division,
at the end of which, two daughter
cells are formed.
▪ Mitosis maintains the chromosome
number from the parent cell to the
daughter cell.
▪ Multicellular organisms go through
mitosis to grow and repair damaged
tissues, while unicellular organisms
use it as a form of asexual
reproduction.

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Cell Division: Interphase
INTERPHASE is the stage between two
successive cell divisions.
It has three stages:
Gap 1 (G1) phase is the period when
the cell increases its size in
preparation for cell division. RNA and
proteins including enzymes needed for
making DNA are synthesized.
Synthesis (S) phase is the period
during which DNA is synthesized and
chromosomes are replicated. Each
strand of the double stranded
chromosome produced is called a
sister chromatid.
Gap 2 (G2) phase is the period when
the cell continues to synthesize RNA
and proteins and increase in size.

z Cell Division: Gap 0
Although DNA synthesis is confined to
a narrow window at S phase, the
synthesis of organelles occurs
throughout interphase
Thus, before cell division, the cells
grow into their characteristic adult
size.
After cell division, the cells may go
though G1 to prepare to the next
division.
Or they may go into an arrested,
quiescent stage known as G0 state to
differentiate.
Some cells, such as nerve cells and
blood cells, remain in G0 all their lives.

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Cell Division: Stages of Mitosis
Prophase is when chromosomes coil up into rod –
shaped structures, nucleoli and nuclear membrane
disappear, and spindle fibers are formed.

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Metaphase involves the alignment of double – stranded
chromosomes at the equatorial plate, with the kinetochores
attaching the chromosomes to the spindle fibers.

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Anaphase begins with the division of the centromeres
and ends with the migration of single – stranded
chromosomes to the poles.

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Telophase is also known as ‘reverse prophase’ since it involves
uncoiling of chromosomes, reappearance of the nucleoli and
nuclear membrane, and the disappearance of the spindle fibers.

z Cell Division: Cytokinesis
Cytokinesis in plant cells involves the formation of cell plate that
eventually develops into the cell wall and the middle lamella.
Cytoplasmic division in animal cells occurs with the formation of a
cleavage furrow.

z Cell Division: Meiosis
▪ Meiosis consists of two successive
cell divisions ( Meiosis I and
meiosis II), at the end of which
four daughter cells are formed.
▪ Meiosis reduces the chromosome
number of the daughter cells to
half that of the parent cell.
▪ Sexually reproducing organisms
undergo meiosis to produce
haploid gametes in preparation for
reproduction.

z Mitosis vs. Meiosis
Property MITOSIS MEIOSIS
DNA Replication Occurs during interphase before
mitosis begins.
Occurs during interphase before
meiosis I begins.
Number of divisions One, including prophase,
metaphase, anaphase and
telophase.
Two, each including prophase,
metaphase, anaphase and telophase.
Synapsis of homologous
chromosomes
Does not occur. Occurs during Prophase I along with
crossing over between nonsister
chromatids; resulting chiasmata
hold pairs together due to sister
chromatid cohesion.
Number of daughter cells
and genetic comparisons
Two, each diploid (2n) and
genetically identical to the parent
cell.
Four, each haploid (n), containing
half as many chromosomes as the
parent cell. And from each other.
Role in the animal body Enables multicellular adult to
arise from zygote; produces cells
for growth, repair and in some
species, asexual reproduction.
Produces gametes; reduces number
of chromosomes by half and
introduces genetic variability
among the gametes.

z Reproduction of Plants,
Protists and Simple
Animals
▪ Living things can perpetuate their species
through reproduction.
▪ There are two main types of reproduction:
1. Asexual Reproduction
2. Sexual Reproduction

z Asexual Reproduction
In asexual reproduction, the offspring is not a
product chance combination of genes derived
from two different parent gametes.
The offspring is genetically identical with its
single parent.
In other words, asexual reproduction results
in the formation of clones.

Asexual reproduction is common among
plants and protists and less among animals.
It allows formation of numerous offspring in
a short time.
This is most advantageous for the
perpetuation of the species in a stable,
favorable environment.

There are different types of Asexual
Reproduction:
1. Budding
2. Spore Formation
3. Fission
4. Fragmentation
5. Regeneration
6. Vegetative Reproduction

z Asexual Reproduction:
Budding
The figure shows how buds
occur in Hydra and Yeasts.
‘Buds’ or outgrowths from
the parent cell/ body grow
into new individuals.
The buds may separate from
their parent or remain
attached to form extensive
colonies.

Spore Formation
Bread molds, mosses and
ferns reproduce by spore
formation.
Spores are haploid
reproductive cells that can
germinate into new
individuals without
fertilization.

Fission
Single – celled organisms
like bacteria and some
protozoans, generally
reproduce by fission.
Take a look at the figure. It
can either be longitudinal
fission or transverse
fission.

Fragmentation
In this asexual type of
reproduction, the parent body
breaks up into several pieces.
The pieces or ‘fragments’
develop into new organisms.
Fragmentation is a common
method of reproduction among
plants and in many sponges and
flatworms in the animal
kingdom.

Regeneration
Similar to fragmentation is the reproductive
method, called regeneration.
In the figure, when a sea star is cut into
pieces such that each arm has a portion of
the central disk, each piece grows the rest of
the central disk and the other arms.
The growth of lost body parts of an animal is
also called regeneration.
Examples are the lost tail of a lizard or a lost
arm of the brittle star.
Each of the two cases does not form new
individual, thus, they are not examples of
reproduction.

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Asexual Reproduction:
Vegetative Reproduction of Plants
Propagating plants from leaves,
stems and roots is known as
vegetative reproduction.
This is possible due to the active
division of parenchyma cells in
the leaves and of meristematic
cells in the stems and roots.
Actively dividing cells in these
plant parts are differentiated
into various kinds of specialized
cells.

z Sexual Reproduction in
Flowering Plants
Sexual reproduction is the process by which
individuals give rise to new individuals through
fertilization, which involves fusion of gametes.
In plants, a flower is a visible sign that the plant is
ready to reproduce by sexual means.
A fruit is an unmistakable proof that the plant has
reproduced sexually.
A seed is an indication that a new life has begun.
Hence, sexual reproduction in plants involves the
production of flowers, and the development of their
fruits and seeds.

Flowering Plants
How do plants know when to flower?
Plants flower according to season.
One of the most important factors that change with
the season is photoperiod, which refers to the
proportion of the length of day to the length of the
night in a 24 – hour period.
Plants are classified according to their photoperiod
requirements for flowering.
The critical day length used as reference in temperate
regions is 8.5 hours.

Flowering Plants
The following are the types of plants and
their photoperiod requirements:
1. Long – day plants can flower only when
the days are longer than the critical.
2. Short – day plants can flower only when
the days are shorter than the critical.
3. Day – neutral plants flower at any season
during the year.

Flowering Plants
Flowers of flowering plants are structurally designed
for sexual reproduction:
1. Stamen, which represents the male sexual
reproductive organ, is basically made up of
filaments and anthers, from which the male
gametophyte, called the pollen grain, develops.
2. Pistil, which represents the female sexual
reproductive organ, is composed of stigma, style
and ovary, from which the female gametophyte,
called the embryo sac, develops.

Flowering Plants
These reproductive organs are often found arranged
together in a specialized structure, which is the flower.
The flower is composed of four sets of organs, namely the:
1. Calyx consisting of a whorl of sepals;
2. Corolla made up of series of petals;
3. Androecium composed of all stamens in the flower;
and
4. Gynoecium referring to the collection of pistils in the
flower.
Although the stamens and pistils assume their roles in
sexual reproduction, the other parts help protect the
reproductive parts and facilitate the reproductive process.

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Stages of Sexual Reproduction
of Flowering Plants
The following are the stages of
Sexual Reproduction in Plants:
1. Megasporogenesis
2. Microsporogenesis
3. Pollination
4. Pollen germination
5. Double fertilization
6. Fruit development
7. Seed germination

z Megasporogenesis
Megasporogenesis leads to the formation of the female
gametophyte, the embryo sac, which contains the egg.
Megasporogenesis occurs in the ovule inside the
ovary.
The ovule consists of central mass called nucellus and
the two outer layers of cells called the integuments.
The integuments do not completely surround the
nucellus.
The ovule has a tiny opening called microphyte which
leads to the nucellus.
As the ovule becomes larger, one of the cells of the
nucellus differentiates into a reproductive cell called
megasphore mother cell.

z Megasporogenesis
The megaspore mother cell is diploid.
It undergoes meiosis, forming four haploid
cells called megaspores.
The three megaspores disintegrate, leaving
only one functional megaspore.
The functional megaspore undergoes mitosis
three times, giving rise to 8 nuclei in seven
cells: 3 antipodals, 2 synergids, 1 egg and 1
central cell with 2 polar nuclei. The 7 – celled
structure is called the embryo sac.

z Microsporogenesis
Microsporogenesis forms the male
gametophyte, the pollen grain.
Viewed at cross section, an anther has four
lobes.
Each lobe contains many cells that
differentiate into reproductive calls called
microspore mother cells.

z Pollination
After the formation of
embryo sacs and pollen
grains, sexual reproduction
in flowering plants has a
very long way to go.
The pollen grains will have
to reach the pistil of the
flower of the same species
through a process called
POLLINATION.

z Pollination
The transfer of the pollen
grains from the anther to
the stigma of the flower in
the same plant is known as
self – pollination.
The transfer of pollen
grains from the anther to
the stigma of the flower of
the same species in a
different plant is known as
cross-pollination.

z Pollination
How do pollen grains reach
the pistils?
Among the most agents of
nature that transfers pollen
grains are the following:
(1) Insects such as bees,
butterflies, moths,
beetles and flies;
(2) Birds;
(3) Bat; and
(4) Wind.

z Pollination
Wind – pollination flowers, on the other
hand, usually have the following
characteristics:
(a) Most of them do not have petals.
Their stamens and stigmas are
exposed to the wind;
(b) The stigma is feathery or sticky;
pollen grains stick to it easily; and
(c) They produce great numbers of
very tiny pollen grains that are
scattered far and wide by the wind.
Corn, rice, and other grasses are wind –
pollinated.

z Pollen Germination
What happens after the pollen
has landed on the stigma of the
flower?
The pollen grain absorbs liquid
(water with dissolved sugar)
from the stigma and germinates.
The generative cell divides by
mitosis, producing two sperm
cells.
Since the sperm cells are naked
(with cell membrane but without
cell wall), they are now called
sperm nuclei.

The tube cell (or tube
nucleus) guides the
growth of a long
cylindrical extension of
the pollen called pollen
tube.
The pollen tube lengthens
until it reaches the
micropyle of the ovule.

What happens after the
pollen tube reaches the
ovule?
The sperm nuclei travel
down the tube.
As the wall at the tip of
the pollen tube breaks,
the sperm nuclei are
discharged into the
embryo sac.

z Double Fertilization
One haploid sperm (N) fertilizes the
haploid egg (N), forming the diploid (2N)
zygote.
The other sperm (1N) fertilizes the
central egg (2N) containing 2 polar
nuclei, forming the triploid endosperm
(3N).
Since there are two fertilization events,
the process is called double fertilization.

z Double Fertilization
The zygote undergoes a series of mitotic
divisions, producing a mass of
undifferentiated cells called embryo.
The endosperm cell divides, producing a
nutritive tissue that will nourish the
developing embryo.
A seed coat, which will protect the
embryo, develops from the ovule’s
integuments.

z Fruit and Seed Development
After fertilization, the two major changes
are:
▪ The ovary develops into a fruit; and
▪ The embryo becomes a seed.
As the embryo and the endosperm grow,
so do the ovule and the entire ovary.

The fertilized ovule develops into a seed
and the ovary develops into a seed and
the ovary develops into a fruit.
Since the seed comes from the ovule, all
seed parts also comes from ovule parts
also comes from ovule parts.
Since the fruit is a fertilized ovary, then all
fruit parts come from the parts of the
ovary.

The ff. summarizes the development of
the ovary parts:
▪ The embryo undergoes partial
differentiation to produce one or two
cotyledons, an epicotyl or hypocotyl.
▪ The fruit is composed of two parts,
the pericarp or fruit wall and one or
many endosperm and embryo. The
embryo contains cotyledon, the
epicotyl and the hypocotyl.
▪ As the fruit ripens and the seed
matures, the other parts of the flower
dry up.

z Seed Germination
Seeds of plants ay fall to the ground or may
be carried by animals to other places.
If the conditions are favorable, the seed
germinates.
The seed coat ruptures as the seed absorbs
water.
The hypocotyl of the embryo grows towards
the soil and develops into the primary root
of the plant.
The epicotyl grows towards the light and
develops into the shoot, made up of stems
and leaves.
The seedling grows into a mature plant and
eventually flowers. And the cycle repeats.

zSexual Reproduction in Some
Animals
The ff. are among the ‘facts of life’ that we
have learned in grade school:
1. Every organism is born and, after some
time, dies. The individuals of some species
live longer than others.
2. Reproduction makes it possible for a
species to continue life on Earth.
3. Species reproduce in different ways

zReproduction in Earthworms
The Earthworm is unique because it
produces both eggs and sperm.
Animals with both male and female
organs are said to be
hermaphroditic.
The reproductive system of the
Earthworm consists the ff.:
1. FEMALE ORGANS – 2 ovaries, 2
oviducts, 2 pairs of sperm receiving
sacs or seminal receptacles.
2. MALE ORGANS – 2 sperm –
storage sacs or seminal vesicles, 2
pairs of testes, 2 vas deferens

To mate (or copulate), two
worms join their anterior
portions along their ventral
surfaces, with their
anterior ends pointing to
opposite directions.
Each worm discharges
sperm into the sperm –
receiving sacs of the other.
Then the two separates.

The clitellum of each worm secretes a slime of
mucous ring.
By contracting slowly, the worm gradually
pushes the clitellum towards its anterior end,
then it discharges eggs in the oviducts.
The sperm passes from its storage towards
the seminal receptacles of the other.
Eventually, the clitellum is pushed over the
anterior end of the worm and drops to the
ground, which is now called, the cocoon.
It is in the cocoon that fertilization takes
place and the development of the embryo.
The young earthworms come out from the
cocoon about three months.

z Reproduction in Frogs
In the female frog, two ovaries
produce many eggs.
It has two oviducts with a
ciliated, funnel – shaped
opening.
The movement of the cilia
creates a current in the fluid
inside the body cavity; the
current sweeps the eggs into the
oviducts.
As they pass through the
oviduct, the eggs become coated
with a jelly – like material.

z Reproduction in Frogs
During mating, the male frog
clutches the female from the back.
The pressure helps the female expel
the eggs into the water outside.
The male frog discharges sperm
over them.
The water causes the jelly – like
material surrounding the eggs to
swell, becoming something like well
– beaten egg white where
fertilization of the eggs as well as
development of the embryos take
place.
Soon, tiny tadpoles emerge from its
frothy nest.

z References
Rabago, L., Joaquin, C., et. al., Functional
Biology Modular Approach, Vibal
Publishing House Inc., 2004
Reece, J., Urry, L., et. al., Campbell Biology
Volume 1, Pearson Education, Inc., 2011
Solomon, E., Berg, L., Martin, D., Biology,
Seventh Edition, Brooks/Cole, Thomson
Learning Asia, 2006

Reproduction of plants and simple animals

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