Chapter 1.Reproduction in organisemPresentation Transcript
Reproduction in organism.
• The period of birth to natural death of an
organism is called life span. No individual is
immortal except unicellular organism. Because
it continue its life in progeny by fission.
Approximate life span of some
The continuity of life on earth is achieved by the
process of reproduction.
• Reproduction: It is a biological process in which
an organism gives rice to young ones or
• Reproduction enables the continuity of species
generation after generation.
• Types of reproduction:
• Asexual reproduction: It is the reproduction by
single parent with out formation of gametes.
• Sexual reproduction: It is the reproduction in
which two parents of opposite sex involves with
the formation and fusion of gametes.
• The offspring developed by asexual reproduction
are exact copy of heir parents. They are
genetically identical. Hence they are termed as
• Asexual reproduction is common in unicellular
organism. In plants and in animals having simple
• Binary fission: The single cell organism of
kingdom Monera and Protista reproduce by
simple cell division called binary fission. The cell
divides in to two half. Each half develops in to
new an adult.
Binary fission in amoeba.
• Zoospores: These are
motile asexual spores
of algae, fungi. They
use flagellum for
• Bud: In yeast the cell
division is unequal and
small buds are produced.
Initially these are attached
to parent cells. Later
separates and develops
into new individual.
• In hydra small outgrowth
• Conidia: These are
the asexual spores of
fungus generated by
• Ex: penicillium.
• In phylum
develops on special
• Gemmules: These are
the internal buds of
fresh water sponges.
temp, freezing, lac of
• Asexual reproduction in plants is termed as
• Naturally it occurs by
6. Bulb etc.
• Runner or stolon: It is
slender stem that grows
horizontally to ground.
Naturally it cut off and
separated develops in to
• Ex: strawberry.
• Rhizome: It is the
• If a rhizome is separated
into pieces, each piece
may be able to give rise
to a new plant.
• Ex: Ginger. canna
• Suckers: It is a basal
shoot, root sprout,
adventitious shoot. It
grows from a bud at
the base of a tree or
shrub or from its
• Ex: Cherry. Apple.
• Tuber: Tubers modified
plant structures that are
enlarged to store
• These are short,
• It bears minute scale
leaves with a bud. It has
the ability for developing
into a new plant.
• Ex: potato
• Offset: Offset is a
plant that asexually
produced on the
• Ex: water hyacinth.
• Bulb: A bulb is a
short stem with
fleshy leaves or
• Ex: Onion, Garlic
• Terror of Bengal:
• Aquatic plant
( Eichhornia) is
terror of Bengal. It
introduced in India
and shape of leaf.
• It rapidly reproduced by
offset in short period. It
drains Oxygen from
water that leads to
death of fishes. Hence it
considered as water
• It involves the formation of male and female
gametes in same individual ( bisexual) or
different individual (unisexual) of opposite
• All organism reaches the stage of growth and
maturity before they reproduce sexually.
• Juvenile phase: In animals , the period of
growth to attain maturity is called juvenile
phase. In plants is called vegetative phase.
• In angiosperms end of vegetative phase
completes as soon as they start flowering.
• Senescent phase: The end of reproductive phase
is called senescent phase or old age. After this
individual dies up.
flowering in plants:
• In annual and biannual plants, flowering is once
or twice in a year. In these plants vegetative,
reproduction and senescent phase are clearly
Ex: Rice, wheat, marigold etc.
• In some plants flowering occurs several times in
• In some plants flowering occurs only once in a life
time. After that plats dies up.
• Ex: bamboo flowering
after 50 to 100 years.
• Kuranji ( strobilanthus
once in 12 years.
Reproductive cycles in animals.
• Reproduction in animals is seasonal. Birds lay
eggs only in specific season.
• The placental animals exhibits reproductive
cycle that leads to change in ovaries and
• Oestrus cycle:
• It is the reproductive cycle of non primates
animals like cow. dogs, rats, tigers etc.
• These animals are reproductively active only
in specific season. Hence these are called
• Menstrual cycle: it is the reproductive cycle of
primates like monkeys, apes and human these
are reproductively active through out their
• Hence these are called continues breeders.
• Events in sexual reproduction:
• 1. pre fertilization event: It involves the
gametogenesis and gamete transfer.
• 2. post fertilization event: It involves the formation
of zygote and embryogenesis.
• Gametogenesis: It is the process of formation of
male and female haploid gametes.
• Homogametes or isogametes: These
morphologically similar male and female gametes.
• Heterogametes: These morphologically different
male and female gametes.
• Anthrozoid or sperm: male gamete.
• Egg or ovum: female gamete.
Sexuality in organisms.
• Homothallic or monoecious: It is the bisexual
condition in fungi, and plant. In this both male
and female reproductive structure are present
in single individual.
• Heterothelic or diecious: It is the unisexual
condition in plants. In this male and female
reproductive parts are found in different
• Male flower – staminate bears only stamens.
• Female flower – pistillate bears only pistils.
• Ex for monoecious plants:
• Ex for diecious plants:
papaya. date palm.
• Sexuality in animals:
• Hermaphrodite or
• Animals having both
male and female
• Ex: Tape worm. Earth
worm. Sponges, leach
• Unisexual animals: Animals having only male
or female reproductive organ. Cockroach.
Insects. Birds. Fishes. Amphibians. Mammals.
• Haploid organism: The individual having only
one set of chromosomes in somatic cells.
• Monera. Fungi, algae, bryophytes has haploid
• Diploid organism: The individual having two set
of chromosomes in somatic cells.
• Pteridophytes. Gymnosperms. Angiosperms
and most of animals.
• In diploid organisms the gamete forms by
meiosis. At the end of meiosis haploid gametes
Transfer of gametes.
• In majority of organisms male gametes are
motile. Female gametes are non-motile. In few
fungus and algae both male and female
gametes are motile.
• In algae, bryophytes and pteridophytes male
gametes moves in water to reach female
• The large number of male gamete are fails to
reach female gamete. To compensate this loss,
male gametes are produces several thousand
times to female gamete.
• In bisexual self fertilizing plants pollen grains
are easily transferred to stigma.
• In unisexual and cross fertilizing plants
pollination occurs by media like air, insects, bird
• Fertilization or syngamy: It is the process of
fusion of male and female gametes that result in
the formation of zygote.
• Parthenogenisis: It is the development of new
individual with out fertilization.
• Ex: honey bee. Some lizards. Turkey bird etc.
• The seed less fruits are parthenocarpic fruits.
• External fertilization: In this fusion of male
and female gamete occurs outside the body in
• Ex: aquatic organism like algae, fishes.
• The dis advantages of external fertilization:
1. Organism produces large number of gametes.
2. The predators destroys eggs and offsprings.
3. The survivality rate of offspring to adult is
• Internal fertilization: In this fusion of male
and female gamete occurs inside the female
• Ex: Seed plants ( gymnosperms and
angiosperms). Terrestrial animals.
• Zygote: The fusion of haploid male and female
gamete result in the formation of diploid
• In fungi and algae the zygote formed has thick
cell wall. It helps to resists the unfavorable
• In haplontic ( algae like
volvex, spirogyra, chlamydomanas) zygote
divides by meiosis toform haploid spores.
These spores develops into haploid
• In diplontic plant (Gymnosperms and
angiosperms) zygote undergoes mitosis to
develops into diploid dominant sporophyte.
• In haplo diplontic ( Bryophytes and
pteridophytes) zygote undergoes mitosis to
develops into diploid sporophyte.
• Embryogenesis: It is the process of
development of embryo from zygote. The
zygote undergoes division and differentiation
• Oviparous (egg laying animals): The reptiles
and birds lay egg in safe environment. After
incubation young one hatches out.
• In oviparous embryogenesis takes place
outside the body.
• Viviparous ( animals that gives birth to young
one): most of mammals except prototheria (
egg laying mammal) are viviparous. These are
placental animals. In these embryogenesis
takes place inside the female body.
• Because of proper embryo care and protection
the chance of survivality of young one are
more in viviparous than oviparous.
• Post fertilization
changes in flower.
• After zygote
formation, the sepals,
petals and stamens of
flower falls off.
• In some plants like
tomato, brinjal sepals
persist with fruit.
• The zygote develops
• The ovule develops
• The ovary develops
into fruit (pericarp).
Sexual reproduction in flowering
• The reproductive
structures of flower
are androecium and
• The male
consists of whorl of
• Stamen: It has slender stalk
called filament. At the tip it
contains a bilobed structure
• Generally anthers are bilobed
that contains two theca
(dithecous) separated by
• The T.S of anther consists of
four sided microsporangia two
in each lobe.
• Microsporangia develops in to
pollen sac. Inside this pollen
grains are present.
Structure of microsporangia.
• Microsporangium is
surrounded by 4 layers.
1. Epidermis: outer single layer
of protective cells.
2. endothecium: It is a single
layer of cells has the character
of dehiscence. It helps to
release pollen. The
dehiscence character is due
to their hygroscopic nature.
3. Middle layers: It is formed by
3 to 4 layers of cells.
4. Tepetum: It is the inner most
layer of microsporangia. It
provides nutrition to
• Microsporengiogenesis: It is the process of
formation of microspores from pollen mother
cells by meiotic cell division.
• The microspores formed are cluster of 4 cells
called microspore tetrad.
• As the anther matures, it dehydrates. The
microspores dissociate and develops into
• pollen grains are spherical in
shape. It has two layers. Outer
called exine and inner intine.
• The exine is made up of an
organic compound sporopollenin.
• It is very hard and resistance
organic compound.no one
enzyme known to be degrade this
one. The exine has a prominent
pore called germ pore.
• As the pollen grain matures it contains two
cells a bigger vegetative cell and smaller
• The generative cell divides mitotically in to two
• The gynoecium is the
female reproductive part
of the flower.
• It consist of pistil.
• monocarpellary :
Gynoecium consists of
Gynoecium consists more
than one pistil.
• Syncarpous: Gynoecium
with fused pistil.
• Apocarpous: Gynoecium
with free pistil.
• Each pistil has three
parts - the stigma, style
• Stigma: Stigma is the tip
of pistil that serves as a
landing platform for
• Style: The style is the
elongated slender part
beneath the stigma.
• Ovary: Ovary is the basal
bulged part of the pistil.
• The cavity present
Inside the ovary is
called ovarian cavity
• The megasporangia
ovules arises from the
• The number of ovules
in an ovary may be one
(wheat, paddy, mango)
or many (papaya, water
Megasporangium (Ovule) :
• The ovule is a small
to the placenta
with stalk called
• The body of the
ovule fuses with
funicle in the
• Each ovule has one
or two protective
encircle the ovule
except at the tip.
• the small opening
present at tip called
• Opposite to the
micropylar end the
chalaza is present.
• It represents the
basal part of the
• The integument
Encloses a mass of
cells called the
• These cells have
• The embryo sac
located in the
• An ovule
generally has a
single embryo sac
formed from a
• The process of formation
of megaspores from the
megaspore mother cell is
• Ovules generally
differentiate a single
megaspore mother cell
(MMC) in the micropylar
region of the nucellus.
• The MMC undergoes
• The majority of flowering plants, one of the megaspores
is functional while the other three degenerate.
• Only the functional megaspore develops into the female
• Note- the nucellus is diploid.
• MMC is diploid,
• the functional haploid
• female gametophyte is haploid.
• The nucleus of the functional megaspore divides
mitotically to form two nuclei.
• These two moves to the opposite poles, forming the
2-nucleate embryo sac.
• Two more sequential mitotic nuclear divisions result
in the formation 8-nucleate stages of the embryo
• One nucleus from
each pole comes
to center of
embryo sac. They
fuse together to
• The three nuclei
at the chalazal
• The three nuclei at
the micropylar end
organise in to egg
• They are identified in
to two synergids and
an egg between
• The angiosperm
embryo sac, at
maturity, though 8nucleate has 7-celled
• Transfer of pollen grains to
the stigma of a pistil is
• Autogamy: Transfer of
pollen grains from the
anther to the stigma of the
same flower is called
• In these flower anthers and
the stigma lie close to each
other. So that selfpollination can occur
• chasmogamous flowers
• Some plants produces
two types of flowers. Ex:
Viola (common pansy),
Oxalis, and Commelina
• Flowers with exposed
anthers and stigma are
• Flowers which do not
open are called
• chasmogamous flowers and Cleistogamous
• Geitonogamy – Transfer
of pollen grains from the
anther to the stigma of
the different flower of
the same plant is called
• genetically it is similar to
autogamy because the
pollen grains come from
the same plant.
• Xenogamy: Transfer of
pollen grains from anther to
the stigma of a different
plant of same species.
• Agents of Pollination :
Plants use two abiotic (wind
and water) and one biotic
(animals) agents to achieve
• Majority of plants use biotic
agents for pollination. Only
a small proportion of plants
use abiotic agents
• Anemophily: The
pollination occurred by
the effect of wind as an
agent is called
• Hydrophily: The
pollination occurred by
the effect of water as an
agent in hydrophytes is
• Zoophily: The pollination
occurred by the effect of
animals as an agent is
• On the bases of different
types of animals involved it
is once again classified into,
• Entamophily: The
pollination occurred by the
effect of insects as an
agent is called
• Ornithophily: The
pollination occurred by the
effect of birds as an agent
is called ornithophily.
• Chirapterophily: The
pollination occurred by the
effect of bats as an agent is
• Anemophily: It is the
pollination by wind.
Small flowers are
• These plants
amount of pollen
• Ex: grasses, rice,
bamboo, sugar cane.
• The anemophilous
flowers are small and
• They are odourless and
never produce nectar.
• Pollen grains are very
small, dry and light.
• Stigmas are hairy and
branched to trap pollen
grains floating in air.
• Hydrophily: It is the pollination by water. Very
few aquatic plants undergoes hydrophily.
• When the pollination occurs below the water
level is called hypohydrogamic. It seen in
plants like Ceratophyllum, Hydrilla.
• When the pollination occurs at the water level
is called epihydrogamic. It seen in plants like
• In other aquatic plants like water hyacinth
(eichhornia), water lily flower emerges out of
water and pollination occurs by wind or
• In vallisneria, the sub-merged aquatic plant, the
male flowers opens at the water surface.
• The released pollen grains floats on water
• The pedicel of female flower elongates till it
reaches the water surface to contact with pollen
• Zoophily: It is the pollination by animals like insects,
bees, wasp, birds, bats etc.
• Majority of plants are pollinated by insects.
• The entamophilous flowers has some characteristic
• The flowers are fragrant and omits odour. Ex
• The flowers are colour full to attract insects.
• The nectar gland produces nectar to feed visiting
• The pollen grains are sticky or spiny. It helps to attach
the body of visiting insects.
• To catch pollen grains the stigma becomes sticky.
• Yucca plant is pollinated by moth.
The moth and yucca cannot
complete their life without each
• The moth bores a hole in ovary to
lay its eggs. Then it collects pollen
grains from several flowers and
pushes in the hallow end of
• After fertilization and seed
development, the larvae of moth
feed on developing seeds.
• The unconsumed seeds dispersed
to propagation. Thus moth cannot
survive without moth and yucca
cannot reproduce sexually
• Inbreeding: The fertilization occurs within the
single plant is called inbreeding
• majority of plants are bisexual. The autogamy
(self fertilization) and geitonogamy results in
• The major disadvantage of self fertilization is,
the progeny gets weak and causes decreased
fitness in population. It is called inbreeding
• To avoid this plants developed many device
that discourage self fertilization.
• Outbreeding: The fertilization occurs between
two different plants of same species is called
• The xenogamy ( cros- pollination) results in
• The plants achieved out breeding by many
• unisexuality: The unisexual flowers are produced
in same plant or different plant.
• In monoecious plants with unisexual flowers, like
maize, cucurbita, castor it avoids autogamy.
• In dioecious plants like papaya, mulberry, it
results in xenogamy.
• Self-sterility or
incompatability: In this pollen
of the flower has no fertilizing
effect on stigma of the same
• Ex: Passiflora, potato.
• Dichogamy: In this male and
female sex organ matures at
• Ex: china rose, lady’s finger,
jasmine. Custard apple.
• Herkogamy: The anther and
stigma are placed at different
position so that pollens unable
to reach stigma of same flower.
• Pollinating the pollen grains of one flower to the
other flower of different plants of same species is
called artificial hybridization.
• It is one of the major approach of crop
• In this method desired pollen grains are used for
• The stigma is protected from contamination with
other pollen grains. It is achieved by
emasculation and bagging.
• Emasculation: It is the
flower bud before it
• Bagging: It is the
with butter paper to
with other pollens.
Pollen pistil interaction
• It is the ability of pistil to recognize the pollen
of same species. It undergo post pollination
event that leads to fertilization.
• If wrong pollen grain (other species) is landed
on stigma, pistil rejects by preventing pollen
• The acceptance and rejection is mediated by
the chemical component of pollen grain
interacting with pistil.
• The fertilization in angiosperms is termed as double
fertilization and triple fusion.
• As the pollen grains matures usually contains one vegetative
cell and two generative cell that developed into male gamete.
• In some plants pollen grain sheds as two cell condition. In
this, generative cell divides into two male gamete as pollen
• As the pollen
grain lands on
stigma, it starts to
• The pollen tube
out of germ pore.
• It grows through
the tissue of
stigma, style and
• The entry of pollen tube in to ovule is from different place
is identified into,
1. Porogamy: It is the entry of pollen tube through
2. Chalazogamy: It is the entry of pollen tube through
3. Misogamy: It is the entry of pollen tube through
integument or funicle.
• As pollen tube enters the ovule, the tip
ruptures inside the embryo sac releasing two
• One of the male gamete fuses with egg and forms
• The another male gamete fuses with diploid
secondary nucleus to form triploid endosperm.
• The fusion of two polar nuclei (to form
secondary diploid nucleus) and male gamete
is termed as triple fusion.
• The two fusions as zygote formation and
triple fusion is termed as double fertilization.
• Post-fertilization events.
• It is the events that takes place after double
fertilization. It includes,
1. Endosperm development.
2. Embryo development.
3. Maturation of ovule into seed.
4. Maturation of ovary into fruit.
• The endosperm cell formed by triple fusion under
goes repeated mitotic cell division to form
triploid endosperm tissue. It provides nutrition to
the developing embryo.
• Three different types of endosperms are
• Nuclear endosperm: In this endosperm cell
nucleus undergoes free nuclear division. All these
nuclei are pushed to the periphery forming
• The cytokinesis results in the formation of
• Ex: coconut. The vacuole is filled with fluid.
• Cellular endosperm: In this endosperm
cellular division undergoes cytokinesis. Ex:
• Helobial endosperm: In first endosperm cell
division two unequal cells forms. One cell
undergoes cellular division and other under
goes free nuclear division. Ex : monocots.
• In pea, groundnut, beans endosperm is
completely consumed by developing embryo.
• In some seeds like groundnut, castor
endosperm persists mature seeds.
• In Dicot: The zygote
divides transversely in
to upper suspensor
cell present at
micropyle region and
lower embryonal cell
present at chalazal
• The suspensor cell
divides and forms 7 –
10 cells called
• The upper cell of
and attaches to the
• The embryonal cell
divides eight cells. The
lower four cells
develops in to plumule
and two cotyledon.
• The above four cells
near the suspensor
develops in to
hypocotyl and radicle.
• The fully developed embryo of dicotyledons has an
embryonal axis that differentiated into plumule,
two cotyledons and radicle.
• The lower end of radicle (root tip) is covered with
• In the beginning embryo is globular. When two
cotyledons differentiates it forms heart shaped.
• In monocots: The zygote divides transversely in to
upper suspensor cell present at micropyle region and
lower embryonal cell present at chalazal region.
• The embryonal cell divides into globular embryo. It
forms a massive cotyledon and plumule. Plumule
covers by coleoptile.
• The single cotyledon is called scutellum.
• At lower end of embroynal axis radicle develops. It is
covered by a sheath called coleorhiza.
• Seed: It is the final product of
sexual reproduction. It is the
• Seed consists of seed coat,
cotyledon and embryonal axis.
• The cotyledons are swollen due to storage of reserve food.
• The seeds are albuminous or non-albuminous.
• In albuminous seed endosperm is not completely used up
by embryo. Ex: wheat, maize, castor, sunflower.
• In some seeds like black pepper the nucellus also present.
The residual persistant nucellus is called perisperm.
• In non albuminous seed endosperm is completely used up
by embryo. Ex: Pea. Ground nut.
• The integument of ovule develops into seed coat.
• The micropyle remains as a pore in the seed coat.
It facilitate the entry of oxygen and water in to
seed during germination.
• Seeds dry up by loosing water. The embryo enters
the stage of inactivity called dormancy. As the
favorable condition available it starts germination.
• The wall of ovary develops into fruit wall called
pericarp. It surrounds the seed.
• In apple, strawberry the thalamus develops into
fruit wall. Hence these are called false fruit.
• The fruits developed from unfertilized ovary are
called parthenocarpic fruits. These are seedless
• Apomixis: The seed developed without
fertilization of ovule is called apomixes.
• The fruits developed from unfertilized ovule are
called apomictic fruits.
• The progeny of hybrid segregate their
characters and not maintains hybrid character
generation after generation. Hence the formers
should buy hybrid seeds every year. It makes
• The apomixes is done in hybrid plants to avoid
the segregation of characters. The formers can
use hybrid seeds to raise new crop every year.
• Polyembryony: The presence of more than
one embryo in seed is called polyembryony.
Ex: citrus fruit seeds.