Transcript Class - Educast

BIOLOGY FOR CLASS IX
Class IX
Chapter #15
Reproduction
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Types Of Reproduction
Asexual Reproduction In Plants
Vegetative Propagation Of Flowering Plants
Advantages And Disadvantages Of Vegetative Propagation
Uses Of Artificial Propagation By Cutting, Grafting And
Cloning
Sexual Reproduction In Flowering Plants
Life Cycle Of A Flowering Plant(Angiosperm)
Importance Of Pollination To Agriculture
Dispersal Of Seeds And Fruits
Seeds And Its Germination
Reproduction And Development In Animals
Reproduction And Development In Frog
Reproduction
The process by which plants and animals give rise to
offspring and which fundamentally consists of the
segregation of a portion of the parental body by a sexual or
an asexual process and its subsequent growth and
differentiation into a new individual.
Asexual reproduction
A form of reproduction that does not
involve meiosis, ploidy reduction or fertilization, and
the offspring is a clone of the parent organism;because
of no exchange of genetic material.
vegetative reproduction
A form of asexual reproduction in plants, in which
multicellular structures become detached from
theparent plant and develop into new individuals that
aregenetically identical to the parent plant. For exam
ple,liverworts and mosses.
Bulbs
Bulbs, such as daffodils, form lateral buds
from the base of the mother bulb, which
produce new smaller bulbs or bulbels in
subsequent years.
Rhizomes
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Rhizomes are root-like stems that grow horizontally
under the ground. New roots and shoots form at the
nodes with shoots growing upwards to form new
plantlets. Lateral buds grow out to form new rhizomes.
Examples include iris and root ginger.
Stolons
Stolons or runners are horizontal stems that
grow above the ground, for example,
strawberries. Tiny plantlets form along the
stolon, and roots form where they touch the
ground. When the connection with the parent
plant breaks, the new plant becomes
independent.
Tubers
Tubers are swollen portions of an underground
stem that store food so a plant can
lie dormant over the winter, for example,
potatoes. Axillary buds, commonly known as
‘eyes’, form over the surface of the tuber and
produce shoots that grow into a new plant the
following year.
Advantages of Vegetative
 The offsprings are genetically identical and therefore
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advantageous traits can be preserved.
Only one parent is required which eliminates the need for
special mechanisms such as pollination, etc.
It is faster. For example, bacteria can multiply every 20 minutes.
This helps the organisms to increase in number at a rapid rate
that balances the loss in number due to various causes.
Many plants are able to tide over unfavourable conditions. This
is because of the presence of organs of asexual reproduction like
the tubers, corm, bulbs, etc.
Vegetative propagation is especially beneficial to the
agriculturists and horticulturists. They can raise crops like
bananas, sugarcane, potato, etc that do not produce viable
seeds. The seedless varieties of fruits are also a result of
vegetative propagation.
The modern technique of tissue culture can be used to grow
virus-free plants.
Disadvantages of Vegetative Propagation
The plants gradually lose their vigour as
there is no genetic variation.
Since many plants are produced, it results in
overcrowding and lack of nutrients.
Uses Of Artificial Propagation By Cutting, Grafting And
Cloning
 Cutting
 Cutting involves removing a piece of the parent plant -
stem, root or leaf, and planting it in a suitable medium. At
first roots are produced and then the shoot with the leaves.
If a stem is taken, it must contain the nodal region. In some
cases, rooting hormone may be required to initiate root
formation.For example:
 Stem cutting is commonly done for rose, sugarcane,
banana, geranium, etc.,
 Root cutting is done for dahlia
 Leaf cuttings are used for African violets.
Layering
Layering is the method of ind5ucing certain
branches of the parent plant to produce roots
by bending and pegging them to the ground
around the parent plant leaving the tips
exposed. Once the roots develop the branch is
then cut off from the parent body.
The branch that produces the roots is called
the layer. It is a natural method in plants such
as black raspberries. However, it is induced in
plants like Jasminum, Rhododendron,
strawberries, Magnolia, etc.
Grafting
It is the transfer of a part of one plant to the
stump of another plant. The part taken from a
plant is a portion of the stem with many buds.
This portion is called scion and is selected for
the quality of its fruit. The stump to which the
scion is attached is called the stock. Stock is
selected for qualities such as disease
resistance and hardiness.
The cut ends of both the scion and stock are shaped
such that they complement each other and their
cambial tissues are close to each other. The two cut ends
are brought together and covered with grafting wax.
After some time, the tissues of the scion and the stock
become continuous. The plant bears flowers and fruits
characteristic of the scion.It is commonly practised on
apple trees and on such plants which either do not
produce viable seeds or the seeds which have a lot of
variation.
Budding or Bud Grafting
 It is a variation of the grafting method explained above. In
this method, the scion is a bud along with some bark. A
'T'-shaped cut is made on the stock into which the scion is
inserted and bound with a tape.
 Three Stages of Bud Grafting - Method of Cleft Grafting
 The bud, once fixed, gives rise to new branches. For
example, bud grafting is done on roses, plums, peaches,
pears, citrus, etc.
Sexual Reproduction in flowering plants
The structure of a flower
Petals: Brightly coloured structures used to attract insects by
their bright colour and scent.
 Sepals: Green leaves around the outside of the flower. Sepals
are usually smaller than the petals,. Used to protect the flower
while it is still in bud.
 Stamens: Male part of the flower. Consist of two parts:
the filament (a thin stalk) and the anther ( a swelling at the top
of the stalk). Pollen, which contains the male gamete, is formed
on the anther.(Anther + filament = stamen)
 Carpel: Female part of the flower. Contains the ovary, stigma
and style. The ovules, which contain the female gamete, are
found in the ovary.(Stigma + style + ovary = carpel)
Angiosperm Life Cycle
The Stages of the Flower Life Cycle
The plant life cycle starts when a seed falls on the ground.
There are many different kinds of plant life, but the
flowering plants, or angiosperms, are the most advanced
and widespread due to their amazing ability to attract
pollinators and spread seeds. Flowers are more than
beautiful objects to look at or decorate with; they serve a
very Important purpose in the reproduction of plants. The
major stages of the flower life cycle are the seed,
germination, growth, reproduction, pollination, and seed
spreading stages.
Seed Stage
The plant life cycle starts with a seed; every seed holds a
miniature plant called the embryo. There are two types of
flowering plant seeds: dicots and monocots. An example of a
dicot is a bean seed. It has two parts called cotyledons in
addition to the embryo. The cotyledons store food for the
plant. Cotyledons are also the first leaves that a plant hasthey emerge from the ground during germination. Monocots
have only one cotyledon-the corn seed is an example. Both
kinds of seeds have the beginnings of a root system as well.
The hard outside of the seed is called the seed coat and it
protects the embryo. Some seeds are capable of growing even
after many years if they are kept cool and dry.
Seed Stage
Germination
When a seed falls on the ground, it needs warmth and water in order
to germinate; some seeds also need light. Dicots have seed coats
that soften with moisture. After being planted in the soil for a few
days, the seed absorbs water and swells until the seed coat splits.
Monocots have harder seed coats that do not split, but stay in one
piece. The stem, called the hypocotyl, pushes through the soil along
with the ,or seed leaves; this is called germination, or sprouting. The
tiny root pushes down and grows, looking for water and nutrients.
Soon the cotyledons fall off and the firsttrue leaves
emerge. It is important that the seed is planted in
the right place at the right time in order for it to
germinate. Some seeds need to go through a fire in
order to sprout, such as prairie grasses. Some need to
go through the stomachs ofanimals, or be scraped.
Different seedhave different needs!
Growth
In order to complete the flower life cycle stage of growth, plants
have to produce their own food. This process is called
photosynthesis. As soon as the leaves emerge, they start the
process of photosynthesis. Plants contain chloroplasts in the
leaves which convert the energy from sunlight, carbon dioxide,
and water into sugars, which they use as food. The plants store the
sugars in the roots and stem. The root system continues to
develop, anchoring the plant into the ground and growing root
hairs which help the plant to better absorb water and nutrients.
The stem grows longer towards the sun and transports water and
food between the roots and leaves. Sugars and starches are
changed into energy used to make new plant growth. New leaves
grow from the top of thestem, or meristem. After a while, flower
buds develop. Some plants flower within days while it takes others
months or even years.
Reproduction
The female part of the flower is called the pistil and it has four
parts-- the stigma, style, ovary, and ovules. The male part of the
flower is called the stamen and it consists of the long filament
and the anther, where pollen is made. In the center of the flower,
there is a long slender tube that ends in a rounded oval. The tube
is called the style. On the top of the style is the stigma-its job is
to catch pollen. It may be sticky, hairy, or shaped in a way that
helps it to better trap pollen. Sometimes several stamens
surround the pistil. Once the pollen is trapped it travels down
the style to the rounded part at the end, called the ovary, where
eggs are waiting to be fertilized. The fertilized eggs become seeds
in this stage of the flower life cycle. In fruit producing plants, the
ovary ripens and becomes fruit.
Pollination
 Some flowers have only male parts, and some have only female
parts. In others, the male and female structures are far apart.
These plants depend on insects, birds, animals, wind, water, or
other pollinators to carry pollen from the male flowers or male
parts to the female flowers or female parts. Without
pollinators, there would be no seeds or new plants in these
plant species. . Even flowers that can self-pollinate benefit
from being fertilized by pollen from a different plant, which is
called cross pollination, because cross pollination results in
stronger plants.
 Brightly colored petals, strong smell, nectar, and
pollen attract pollinators. Flowers are specially
adapted to attract their specific pollinators. For
example, the corpse flower smells like rotting flesh
in order to attract flies. Pollen sticks to the legs
and wings of insects that go from flower to flower
for nectar and pollen, which they use as a food.
Pollen sticks to the fur of animals and even to the
clothes of humans. Wind blows pollen which
lands on other flowers.
Spreading Seeds
 Seed spreading, or dispersal, is the final stage of the
flower life cycle. Seeds are spread in many ways. Some,
like dandelion seeds, are scattered by the wind. Others
rely on animals-an example of this is the cockleburs
that get stuck in the fur of animals and hitchhike to
new locations. Water lilies depend on water to spread
their seeds. Humans spread many seeds intentionally
by planting gardens. Once the seeds fall to the ground,
the plant life cycle starts all over again.
Importance Of Pollination To Agriculture
 Pollinators are vital to creating and maintaining the
habitats and ecosystems that many animals rely on for
food and shelter. Worldwide, over half the diet of fats
and oils comes from crops pollinated by animals. They
facilitate the reproduction in 90% of the world’s
flowering plants.
 Pollinators are vital to creating and maintaining the
habitats and ecosystems that many animals rely on for
food and shelter. Worldwide, over half the diet of fats
and oils comes from crops pollinated by animals. They
facilitate the reproduction in 90% of the world’s
flowering plants.
 Foods and beverages produced with the help of
pollinators include: apples, bananas, blueberries,
chocolate, coffee, melons, peaches, potatoes,
pumpkins, vanilla, almonds, and tequila. (Imagine a
world without some of these things!)
 In the United States, pollination by honeybees and
other insects produces $40 billion worth of products
annually!
Fruit and seed dispersal
 Poricidal fruit
Triodanis perfoliata(clasping Venus' looking-glass)
When ripe, pores in the side of the fruit open, allowing
the tiny seeds to shake out.
Winged fruit
Acer rubrum (red maple) - Maple fruits are winged, two seeded
samaras. They spin like helicopters as they fall from the
tree, providing a longer time for dispersal by wind.
"Parachutes"
Carduus nutans (nodding plumeless thistle) - The dry,
one-seeded fruits are carried on the wind by plumose
"parachutes".
Fleshy fruits
The seeds of many plants are dispersed after passing
through the digestive system of animals that have
eaten the fleshy fruits.
Diospyros virginiana (persimmon) - The sweet fruits
are enjoyed by many animals including humans
Reproduction And Development In
Animals
 Animals reproductive by asexual and sexual
methods:
• Asexual is the production of offspring with genes
all from one individual, without the fusion of
gametes.
• Sexual involves formation of gametes and
fertilization, genetic variation
 sexual reproduction, which is when two parents
produce offspring with unique combinations of genes
from both parents. Some multicellular animals, like
corals, use both asexual and sexual reproduction,
while others, like mammals, only reproduce sexually.
A sexual reproduction
Budding in Hydra
Gemmules in Sponges
Starfish Regeneration
PARTHENOGENESIS
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parthenogenesis, like reproduction without the need of male
gametes, there are costs, such as a decrease in genetic variation.
In the intricate eusocial organization of honeybees, there are three
social classes –queen bee, worker bees and drone bees. The queen
bee, as the name entails, holds the superior position in the colony.
The queen bee lays all the eggs in the colony, being the only bee with
a set of completely developed ovaries and having life-long fertility
(Back Yard Beekeepers Association n.d.). After only one mating
flight were the queen mates with a couple male drone bees, she
stores the sperm to later fertilizes some of the eggs. The eggs that get
fertilized develop into female worker bees and the eggs that develop
without fertilization produce male drone bees. Due to the high
maintenance of both the colony and its products, i.e. honey, most of
the bees in a hive are female worker bees. These worker bees carry on
a magnitude of different tasks, not including reproduction, which is
reserved only for the queen. The male drone bees are reserved for
mating with the queen bee.
Queen
Worker (female)
Drone (male)
Binary Fission
 Binary Fission
 Binary fission involves mitosis only and hence the resultant
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individuals are genetically identical to each other and to the
parent.It is the simplest and most common method of asexual
reproduction. The whole parental body acts as the reproductive
unit. The nucleus of the unicellular parent organism divides into
two. This is followed by the division of the cytoplasm and 2
daughter cells of almost equal size are formed. The daughter cells
grow in size and then divide again.
Examples: Seen in euglena, amoeba, paramoecium.Based on the
plane of cytoplasmic division binary fission is of 3 types, namely:
a) Simple binary fission
b) Transverse binary fission
c) Longitudinal binary fission
Simple binary fission
 When the cytoplasmic division passes through any
plane, the fission is called simple binary
fission.Example: Amoeba
b) Transverse binary fission
 When the plane of cytoplasmic division coincides with
the transverse axis of the individual, the fission is
called transverse binary fission.Example:
Paramoecium, Planaria
Longitudinal binary fission
 When the plane of cytoplasmic division coincides with
the longitudinal axis of the individual, the fission is
called longitudinal binary fission.Example: Euglena
Multiple Fission
 In some organismsthe nucleus of the parent divides into
many daughter nuclei by repeated divisions (amitosis). This
is followed by the division of the cytoplasm into several
parts with each part enclosing one nucleus. So a number of
daughter cells are formed from a single parent at the same
time. This kind of fission is known as multiple
fission.Example: Seen in Plasmodium (malarial parasite)
where it is known as schizogony or sporulation, amoeba.
BUDDING
 During the process of bud formation or budding an outgrowth or
bud appears on the parent body. The bud may be unicellular as in
some protozoans (suctoria) or multicellular as in certain lower
metazoans like, Sycon (sponge), Hydra (Goelenterate), Planaria
(flatworm), Syllis (annelid) etc.
 One or more such buds may be produced from a single parent
body. The bud, which is much smaller than the parent develops to
its full size either after detachment from the parent or prior to
detachment being attached to its parent body. Budding may be
external or exogenous as in Hydra or internal or endogenous as in
Acinata.
 In Hydra the external bud develops as a conical outgrowth
from the body wall by the accumulation of intcrsitial cells.
The bud gradually develops tentacles around the mouth,
coelenteron and later separated lion) its parent by
developing a constriction at its base.
 When the body of Hydra or Planaria is cut into several
fragments, each fragment develops into a new individual.
This process is known as fragmentation. Regeneration is a
process by which organisms develop or regenerate their lost
or worn-out parts. Regeneration is highly developed in lower
animals like protozoans, sponges, coelenterates, planarians,
echinoderms etc.
Regeneration
 Many animals can regenerate—that is, regrow
or grow new parts of their bodies to replace
those that have been damaged. Here are a few
of these amazing creatures.
 Lizards who lose all or part of their tails can
grow new ones. This is a good escape
technique. A lost tail will continue to wiggle,
which might distract the predator and give the
lizard a chance to escape. Most lizards will
have regrown their tail within nine months.
 Planarians are flat worms. If cut
into pieces, each piece can grow
into a new worm.
 Sharks continually replace lost teeth. A shark may grow
24,000 teeth in a lifetime.
 Spiders can regrow missing legs or parts of legs.
 Sponges can be divided. In that case, the cells of
the sponge will regrow and combine exactly as
before.
 Starfish that lose arms can grow new ones;
sometimes an entire animal can grow from a single
lost arm
Sexual Reproduction:
 Sexual reproduction is commonly found in the complex,
multicellular organisms. It involves the union of male and female
sex cells or gametes to form the zygote which grow into a new
individual. Two different sexes (male and female) take part in the
process. The testes in male produce male gametes or sperms and
the ovaries in female produce female gametes or ova.
 Both these sex organs may be present in the same body. Such
animals are known as bisexual or hermaphrodite animals, e.g.
earthworm. Formation of sperms and ova involves meiosis or
reduction division during which haploid gametes are formed
from the diploid cells. Gametes vary in shapes and sizes in
different animals.
 Fusion of male and female gamete is known as fertilization.
During fertilization a haploid (n), motile male gamete or sperm
fuses with a non- motile, haploid (n) female gamete or ovum to
form a diploid (2n) zygote which gives rise to a new individual
Advantages of Sexual Reproduction:
 1. The offspring’s produced due to sexual reproduction
adapt themselves successfully to the changing
environmental conditions.
 2. Formation of gametes by meiosis and their fusion
during fertilization produce reshuffling of genes and
variation in the offspring’s. Variations in the offspring’s
help them in natural selection and evolution.
Disadvantages of Sexual Reproduction
 Since two parents of opposite sexes are needed i.e.,
biparental reproduction (except hermaphrodite forms)
it is not as easy or as frequent as asexual or uni
parental reproduction.
major differences between asexual and
sexual reproduction
 Asexual reproduction
 sexual reproduction
1. It occurs in lower 1. It occurs almost in all
invertebrates and lower types of animals and mostly
chordates and plants in higher plants.
with
simple
organisations.
2. It is always uni-parental.
2. It is usually bi-parental.
3. Gametes are not formed.
3. Gametes
formed.
are
always
4. No fertilization.
5. It involves only mitosis.
4. Fertilization takes place.
5. It involves both meiosis
and mitosis.
6.
Daughter
organisms
6. Daughter organisms are
genetically identical to the genetically differ from the
parents.
parent.
7. Multiplication is not as
7. Multiplication occurs
rapid
as
in
asexual
rapidly.
reproduction.
8. Since there are variations,
8. Since there is no variation,
so it does not contribute to so it contributes to evolution
of the species.
evolution of the species.
Frog Embryology
 The Egg
 The frog egg is a huge cell; its volume is over 1.6 million times
larger than a normal frog cell. During embryonic
development, the egg will be converted into a tadpole
containing millions of cells but containing the same volume
of material.
 The upper hemisphere of the egg - the animal pole - is dark.
 The lower hemisphere - the vegetal pole - is light.
 When deposited in the water and ready for fertilization, the
haploid egg is at metaphase of meiosis II.
Fertilization
 Entrance
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of the sperm initiates a sequence of
events:Meiosis II is completed the cytoplasm of the egg
rotates about 30 degrees relative to the poles
In some amphibians (including Xenopus), this is revealed
by the appearance of a light-colored band, the gray
crescent.
The gray crescent forms opposite the point where the
sperm entered.
It foretells the future pattern of the animal: its dorsal (D)
and ventral (V) surfaces; its anterior (A) and posterior (P);
its left and right sides.
The haploid sperm and egg nuclei fuse to form
the diploid zygote nucleus.
Cleavage
 The zygote nucleus undergoes a series of mitoses, with the
resulting daughter nuclei becoming partitioned off,
by cytokinesis, in separate, and ever-smaller, cells. Thefirst
cleavage occurs shortly after the zygote nucleus forms.A
furrow appears that runs longitudinally through the poles
of the egg, passing through the point at which the sperm
entered and bisecting the gray crescent.
 This divides the egg into two halves forming the 2-cell
stage
 The second cleavage forms the 4-cell stage. The cleavage
furrow again runs through the poles but at right angles to
the first furrow.
 The furrow in the third cleavage runs horizontally but in a
plane closer to the animal than to the vegetal pole. It
produces the 8-cell stage.
 The next few cleavages also proceed in synchrony, producing
a 16-cell and then a 32-cell embryo.However, as cleavage
continues, the cells in the animal pole begin dividing more
rapidly than those in the vegetal pole and thus become
smaller and more numerous.
 By the next day, continued cleavage has produced a hollow
ball of thousands of cells called the blastula. A fluid-filled
cavity, the blastocoel, forms within it.
 During this entire process there has been no growth of
the embryo. In fact, because the cells of the blastula
are so small, the blastula looks just like the original
egg to the unaided eye.
 there has been no transcription and translation of
zygote genes. All of the activities up to now have been
run by gene products (mRNA and proteins) deposited
by the mother when she formed the egg.
Gastrulation
 The start of gastrulation is marked by the pushing inward
("invagination") of cells in the region of the embryo once
occupied by the middle of the gray crescent. This
produces:an opening (the blastopore) that will be the future
anus
 a cluster of cells that develops into the Spemann
organizer (named after one of the German embryologists
who discovered its remarkable inductive properties).
Summary
 As gastrulation continues, three distinct "germ
layers" are formed:ectoderm
 mesoderm
 endoderm
 Each of which will have special roles to play in
building the complete animal. Some of these are listed
in the table.
 A single-celled zygote will undergo multiple rounds of cleavage,
or cell division, in order to produced a ball of cells, called a blastula,
with a fluid-filled cavity in its center, called a blastocoel.
 In animals with little yolk in the egg, the zygote
undergoes holoblastic cleavage, in which the entire zygote is cleaved
repeatedly; in animals with a lot of yolk in the egg, the zygote
undergoes meroblastic cleavage, in which only part of the zygote is
cleaved.
 The blastula eventually organizes itself into two layers: the inner cell
mass (which will become the embryo) and the outer layer
or trophoblast (which will become the placenta); the structure is
now called a blastocyst.
 During gastrulation, the blastula folds in on itself to form three
germ layers, the ectoderm, the mesoderm, and the endoderm, that
will give rise to the internal structures of the organism.
 gastrulationthe stage of embryo development at
which a gastrula is formed from the blastula by the
inward migration of cells
 Blastomere any cell that results from division of a
fertilized egg
 Meroblasticundergoing only partial cleavage
 trophoblast
 the membrane of cells that forms the wall of a blastocyst
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during early pregnancy, providing nutrients to the embryo
and later developing into part of the placenta
blastula
a 6-32-celled hollow structure that is formed after a zygote
undergoes cell division
inner cell mass
a mass of cells within a primordial embryo that will
eventually develop into the distinct form of a fetus in most
eutherian mammals
holoblastic
cleaving, and separating into separate blastomeres
 Neurulation is the development of the nervous
system in the vertebrates, at the thickened area above
the notochord in ectoderms.
METAMORPHOSIS:
The Lifecycle of a Frog
Metamorphosis is the change of shape during an animal’s
life. During metamorphosis the tadpole will develop back
legs first, then front legs. Around 6 weeks of life the mouth
starts to widen. Sometime around 10 weeks the froglet’s, as
it is now called, eyes start to swell out and the tail begins to
shrink and eventually disappear. When the lungs finish
developing the froglet makes it’s way onto the land.
 Frog eggs floating in a pond: these clusters of floating
eggs are called "egg masses".
 Frogs lay up to 4,000 eggs at one time!
 Tadpoles hatch from the eggs and live in the pond.
 The tadpoles turn into Froglets. The body shrinks
and legs form.
 The Froglet's tail shrinks, the lungs develop and the
back legs grow and then we have a Frog.