REPRODUCTION IN ORGANISMS
Reproduction is a biological process of formation of new offsprings from pre- existing organisms.Reproduction becomes a vital process without which species couldnot survive for long
It ensures continuity of species generation after generations as older individual undergoes senescence and ultimately die.
Life span - The period from birth to the natural death of an organism is called life span
Life span of organisms varies from few day (Butterfly-1to 2 weeks) to thousands of year (Banyan tree)
Types of Reproduction
(i)ASEXUAL REPRODUCTON
(ii)SEXUAL REPRODUCTION
When the offspring is produced by single parents with or without the involvement of gamete
formation, the reproduction is called asexual reproduction.
When two parents (opposite sex) participates in reproduction process and also involves the
fusion of male and female gametes, it is called sexual reproduction.
Asexual Reproduction
1. Usually followed by organisms with relatively simpler organizations.
2. Off springs produced by single parent.
3. With/without involvement of gamete formation.
4. Off springs produced are genetically and morphologically similar to each other and to the parents also i.e. they are clones.
In Protista and Monera, the parent cells divides into two to give rise to new individuals
Thus, in these organisms cell division is the modes of reproduction itself.
Binary fission- in this method of asexual reproduction, a cell divides into two halves andrapidly grows into an adult
.Ex- amoeba,paramecium.
Budding small buds are produced that remain attached initially with parents and get
separated on maturation. Ex. Yeast.
Bud
Fungi and simple plants like algae reproduce through special reproductive structures like
zoospores (motile structure), conidia (penicillium), buds (hydra) and gemmules (sponges).
In plants, vegetative reproduction occurs by vegetative propagules like runner, rhizome,
sucker, tuber, offset and bulb.
Vegetative part
Example
Dahia, Asparogus, Dalbergia. guava and tapioca
WATER HYACINTH (Terror of Bengal)
One of the most invasive weeds
Grows wherever there is standing water
Drains oxygen from water- leads to death of fishes and aquatic life
Introduced in India because of its pretty flowers & shape of leaves
Vegetative propagation occurs at phenomenal rate
Asexual reproduction is the most common method of reproduction in organisms having
simpler body like in algae and fungi but during unfavorable condition they shift to sexual reproduction .
SEXUAL REPRODUCTION:
Involves formation of male and female gamete by two individuals of opposite sex.
Offspring produced by fusion of male and female gametes are not identical to each other or to the parents.
All sexually reproducing organisms share a similar pattern of reproduction.
In sexual reproduction, fusion of male and female gametes results in offspring that are not
identical to parents.
DIFFERENT PHASES IN SEXUAL REPRODUCTION:
a. Juvenile phase- The period between birth and sexual maturity is called juvenile phase. In
plants it is known as vegetative phase.The end of juvenile/vegetative phase marks the
beginning of the reproductive phase.
b. Reproductive phase
Some plants show flowering in particular season and some other flowers in all seasons.
Some other plants like bamboo species flowers once in life time (after 50-100 years),
Strobilanthus kunthiana (neelakuranji), fowers once in 12 years.
The female placental animals exhibit cyclic change in activities ovaries and accessary
glands as well as hormone during the reproductive phase.
Menstrual cycle
It occurs in monkeys, apes and human beings.
Cycle consists of 3 phases-menstrual, proliferative and secretory phase.
Blood flows in the last few days of the cycle. The broken endometrium is passed out during
menstruation.
Female does not permit copulation during menstrual phase of the cycle.
Oestrous cycle
It occurs in non primates like cow, sheep, rat, deer, dog, tiger etc.
It consists of a short period of oestrous or heat. it is 12-24 hours in cow followed by
anoestrous or passive period.
Blood does not flow in this cycle. The broken endometrium is reabsorbed.
Female permits copulation only during oestrous period.
Both in plants and animals, hormones are responsible for the transition between different
phases of life cycle. Interaction between hormones and environmental factors regulate the
reproductive processes.
C. Senescent phase-
It is the end of reproductive phase.
Old age ultimately leads to death
Events in Sexual Reproduction: Pre-fertilisation, Fertilisation, Post-fertilisation
Pre-fertilisation- all the events prior to fusion of gametes are included in it. It includes
gametogenesis and gamete transfer
a. Gametogenesis is the process of formation of male and female gametes. Gametes are
haploid cells which may be similar or dissimilar in structure. In algae, both gametes are
similar in structure called homogametes isogametes). In higher organism that reproduces
sexually, two morphologically distinct gametes are formed called heterogametes, male
gametes are called antherozoid or sperm and female gametes are called ovum or egg.
Isogametes. heterogametes
In fungi and plants, homothallic and monoecious terms are used to denote the bisexual
condition and heterothallic and dioecious are used for unisexual condition. In flowering
plants, the unisexual male flower is staminate, i.e., bearing stamens, while the female is
pistillate or bearing pistils.
In animals, species which possess both male and female reproductive organs in same
individual are called bisexual or hermaphrodites (earthworm, sponges, tapeworm etc.) and
both having either male or female reproductive organs are called unisexual (cockroach,
human).
Gametes are always haploid( having half set of chromosome ), although organisms may be
haploid and diploid. Diploid organisms form gametes by meiotic di'vision. The organisms
belonging to algae, fungi, and bryophytes have haploid plant body and pteridophytes,
gymnosperms, angiosperms and most of animals are diploid (having double set of
chromosome )
In diploid organisms, gamete mother cell (meiocyte) undergoes meiosis in which one set of
chromosome is present in gametes.
b. Gamete Transfer - in majority of organisms, male gametes are motile and females
gametes are non-motile, except in fungi and algae in which both gametes are motile.
In simple plants like algae, fungi, bryophytes and pteridophytes water is the medium
through which male and female gametes moves. The number of male gametes are much
more than number of female gametes as most of male gametes fail to reach the female
gametes.
In higher plants pollen grains are carrier of male gametes and ovule has eggs. Pollen grains
must be transferred from anther to stigma to facilitate fertilisation. The transfer of pollen
grains from anther to stigma is called pollination. Pollination may be self (anther to stigma
of same flower) or cross (anther to stigma of different flower).
Pollen grains germinate on stigma to produce pollen tube that delivers the male gametes
near the ovule.
c. Fertilisation - The fusion of male and female gamete is called fertilization or syngamy.
It results in the formation of diploid zygote.
The process of development of new organisms without fertilisation of female gametes is
called parthenogenesis. For example honey bee, rotifers, and lizards
individual are called bisexual or hermaphrodites (earthworm, sponges, tapeworm etc.) and
both having either male or female reproductive organs are called unisexual (cockroach,
human).
Gametes are always haploid( having half set of chromosome ), although organisms could also be
haploid and diploid. Diploid organisms form gametes by meiotic di'vision. The organisms
belonging to algae, fungi, and bryophytes have haploid plant body and pteridophytes,
gymnosperms, angiosperms and most of animals are diploid (having double set of
chromosome )
In diploid organisms, gamete cell (meiocyte) undergoes meiosis during which one set of
chromosome is present in gametes.
b. Gamete Transfer - in majority of organisms, male gametes are motile and females
gametes are non-motile, except in fungi and algae during which both gametes are motile.
In simple plants like algae, fungi, bryophytes and pteridophytes water is that the medium
through which male and feminine gametes moves. the amount of male gametes are much
more than number of female gametes as most of male gametes fail to achieve the feminine
gametes.
In higher plants pollen grains are carrier of male gametes and ovule has eggs. Pollen grains
must be transferred from anther to stigma to facilitate fertilisation. The transfer of pollen
grains from anther to stigma is named pollination. Pollination could also be self (anther to stigma
of same flower) or cross (anther to stigma of various flower).
Pollen grains germinate on stigma to provide plant part that delivers the male gametes
near the ovule.
c. Fertilisation - The fusion of male and feminine gamete is named fertilization or syngamy.
It leads to the formation of diploid zygote.
The process of development of latest organisms without fertilisation of female gametes is
called parthenogenesis. for instance honey bee, rotifers, and lizards
both having either male or female reproductive organs are called unisexual (cockroach,
human).
Gametes are always haploid( having half set of chromosome ), although organisms may be
haploid and diploid. Diploid organisms form gametes by meiotic di'vision. The organisms
belonging to algae, fungi, and bryophytes have haploid plant body and pteridophytes,
gymnosperms, angiosperms and most of animals are diploid (having double set of
chromosome )
In diploid organisms, gamete mother cell (meiocyte) undergoes meiosis in which one set of
chromosome is present in gametes.
b. Gamete Transfer - in majority of organisms, male gametes are motile and females
gametes are non-motile, except in fungi and algae in which both gametes are motile.
In simple plants like algae, fungi, bryophytes and pteridophytes water is the medium
through which male and female gametes moves. The number of male gametes are much
more than number of female gametes as most of male gametes fail to reach the female
gametes.
In higher plants pollen grains are carrier of male gametes and ovule has eggs. Pollen grains
must be transferred from anther to stigma to facilitate fertilisation. The transfer of pollen
grains from anther to stigma is called pollination. Pollination may be self (anther to stigma
of same flower) or cross (anther to stigma of different flower).
Pollen grains germinate on stigma to produce pollen tube that delivers the male gametes
near the ovule.
c. Fertilisation - The fusion of male and female gamete is called fertilization or syngamy.
It results in the formation of diploid zygote.
The process of development of new organisms without fertilisation of female gametes is
called parthenogenesis. For example honey bee, rotifers, and lizards
individual are called bisexual or hermaphrodites (earthworm, sponges, tapeworm etc.) and
both having either male or female reproductive organs are called unisexual (cockroach,
human).
Gametes are always haploid( having half set of chromosome ), although organisms could also be
haploid and diploid. Diploid organisms form gametes by meiotic di'vision. The organisms
belonging to algae, fungi, and bryophytes have haploid plant body and pteridophytes,
gymnosperms, angiosperms and most of animals are diploid (having double set of
chromosome )
In diploid organisms, gamete cell (meiocyte) undergoes meiosis during which one set of
chromosome is present in gametes.
b. Gamete Transfer - in majority of organisms, male gametes are motile and females
gametes are non-motile, except in fungi and algae during which both gametes are motile.
In simple plants like algae, fungi, bryophytes and pteridophytes water is that the medium
through which male and feminine gametes moves. the amount of male gametes are much
more than number of female gametes as most of male gametes fail to achieve the feminine
gametes.
In higher plants pollen grains are carrier of male gametes and ovule has eggs. Pollen grains
must be transferred from anther to stigma to facilitate fertilisation. The transfer of pollen
grains from anther to stigma is named pollination. Pollination could also be self (anther to stigma
of same flower) or cross (anther to stigma of various flower).
Pollen grains germinate on stigma to provide plant part that delivers the male gametes
near the ovule.
c. Fertilisation - The fusion of male and feminine gamete is named fertilization or syngamy.
It leads to the formation of diploid zygote.
The process of development of latest organisms without fertilisation of female gametes is
called parthenogenesis. for instance honey bee, rotifers, and lizards
d. Post Fertilisation Events- events within the reproduction after formation of zygote.
Zygote is that the vital link that ensures continuity of species between organisms of 1
generation and therefore the next. Every sexually reproducing organism, including people in general
begin life as one cell-the zygote
In the organisms, having external fertilisation, zygote is made in external medium (water)
and those having internal fertilisation zygote is made inside the body of female.
In algae and fungi, zygote develops a thick wall proof against desiccation and damage. This
germinates after a period of rest.
In the organisms having haplontic life cycle, zygote divides to create haploid spores that
germinate to create haploid individual.
Embryogenesis - the method of development of embryo from the zygote. During this, zygote
undergoes mitotie division and cell differentiation. biological process increase the amount and
cell differentiation help in formation of recent group of cells and organs.
Oviparous
Viviparous
Development of zygote takes place outside the
body of organisms and lay fertilized of
unfertilized eggs.
Development of zygote takes place inside
the body of organisms and produces
young ones.
EX- Human, dog, horse etc.
Ex-Reptiles and birds.
In flowering plants, zygote is made inside the ovule. After fertilisation, sepals, petals and
stamens of flower fall off. The zygote develops into embryo and ovules into seeds. The ovary
develops into fruits which develop a thick wall called pericarp, protective in function.
After dispersal, seeds germinate under favorable condition to provide new plants.
stamens of flower fall off. The zygote develops into embryo and ovules into seeds. The ovary
develops into fruits which develop a thick wall called pericarp, protective in function.
After dispersal, seeds germinate under favorable condition to provide new plants.
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