1
UNIT - I
Reproduction
in Organisms
CHAPTER
Paramecium are capable of both sexual and
Chapter Outline asexual reproduction.
1.1. Modes of reproduction
1.2. Asexual reproduction in continuation of species and introduces
1.3. Sexual reproduction variations in organisms, which are essential
for adaptation and evolution of their
own kind.
Learning Objectives
1.1. Modes of reproduction
➢ Learns the modes of asexual All modes of reproduction have some
reproduction in organisms. basic features such as synthesis of RNA and
proteins, replication of DNA, cell division and
➢ Understands the growth, formation of reproductive units and
significance of asexual their fertilization to form new individuals.
reproduction.
Organisms exhibit two major modes of
➢ Comprehends the reproduction namely asexual and sexual
different modes of reproduction. Reproduction by a single parent
sexual reproduction. without the involvement of gamete formation
is asexual reproduction and the offspring
➢ Realizes the significance and produced are genetically identical. Asexual
advantage of sexual reproduction and reproduction is usually by amitotic or mitotic
its role in evolution. division of the somatic (body) cells, hence
is also known as somatogenic or blastogenic
reproduction. When two parents participate
L iving organisms show a life cycle in the reproductive process involving two
involving birth, growth, development, types of gametes (ova and sperm), it is called
maturation, reproduction and death. sexual reproduction.
Reproduction is the fundamental feature of
all living organisms. It is a biological process 1.2. Asexual reproduction
by which organisms produce their young Asexual reproduction is wide spread
ones. The young ones grow and mature to among different organisms. It is common in
repeat the process. Thus reproduction results members of Protista, Bacteria, Archaea and
1
TN_GOVT_XII_Zoology_chapter1.indd 1 25-02-2019 18:17:54
, in multicellular organisms with relatively i) Simple irregular binary fission
simple organisation. The offsprings show ii) Transverse binary fission
“uniparental inheritance” without any genetic
iii) Longitudinal binary fission
variation. The different modes of asexual
iv) Oblique binary fission
reproduction seen in animals are fission,
sporulation, budding, gemmule formation, Simple binary fission is seen in Amoeba
fragmentation and regeneration. like irregular shaped organisms (Fig. 1.1),
where the plane of division is hard to observe.
Fission is the division of the parent The contractile vacuoles cease to function
body into two or more identical daughter and disappear. The nucleoli disintegrate and
individuals. Four types of fission are seen in the nucleus divides mitotically. The cell then
animals. They are binary fission, multiple constricts in the middle, so the cytoplasm
fission, sporulation and strobilation. divides and forms two daughter cells.
In binary fission, the parent In transverse binary fission, the plane of
organism divides into two halves and the division runs along the transverse axis of
each half forms a daughter individual. the individual. e.g. Paramecium and Planaria.
The nucleus divides first amitotically or In Paramecium (Fig. 1.2) the macronucleus
mitotically (karyokinesis), followed by the divides by amitosis and the micronucleus
Simple irregular Binary Fission in Amoeba
division of the cytoplasm (cytokinesis). divides by mitosis.
The resultant offsprings are genetically In longitudinal binary fission, the nucleus
Nuclear
identical to the parent. Depending on theContractile
vacuole and the cytoplasm divides membrane
in the longitudinal
plane of fission, binary fission is of the axis of the organism (Fig 1.3). In flagellates, the
Nucleus
following types Hyaline area flagellum is retained usually by one daughter cell.
Chromosomes
Simple irregular Binary Fission in Amoeba Contractile
vacuole
Nuclear
Contractile
membrane
vacuole
Nucleus
Hyaline area
Chromosomes
Contractile
vacuole Daughter amoebae
Fig. 1.1 Irregular simple binary fission in Amoeba
Macronucleus
New oral
groove
forming
Micronucleus Oral groove
disappearing
Daughter
Daughter amoebae paramecia
New
contractile
vacuoles
Macronucleus Micronucleus New
dividing dividing oral groove
amitotically mitotically forming
A B C D E
Fig. 1.2 Transverse binary fission in Paramecium
Reproduction in Organisms 2
TN_GOVT_XII_Zoology_chapter1.indd 2 25-02-2019 18:17:55
UNIT - I
Reproduction
in Organisms
CHAPTER
Paramecium are capable of both sexual and
Chapter Outline asexual reproduction.
1.1. Modes of reproduction
1.2. Asexual reproduction in continuation of species and introduces
1.3. Sexual reproduction variations in organisms, which are essential
for adaptation and evolution of their
own kind.
Learning Objectives
1.1. Modes of reproduction
➢ Learns the modes of asexual All modes of reproduction have some
reproduction in organisms. basic features such as synthesis of RNA and
proteins, replication of DNA, cell division and
➢ Understands the growth, formation of reproductive units and
significance of asexual their fertilization to form new individuals.
reproduction.
Organisms exhibit two major modes of
➢ Comprehends the reproduction namely asexual and sexual
different modes of reproduction. Reproduction by a single parent
sexual reproduction. without the involvement of gamete formation
is asexual reproduction and the offspring
➢ Realizes the significance and produced are genetically identical. Asexual
advantage of sexual reproduction and reproduction is usually by amitotic or mitotic
its role in evolution. division of the somatic (body) cells, hence
is also known as somatogenic or blastogenic
reproduction. When two parents participate
L iving organisms show a life cycle in the reproductive process involving two
involving birth, growth, development, types of gametes (ova and sperm), it is called
maturation, reproduction and death. sexual reproduction.
Reproduction is the fundamental feature of
all living organisms. It is a biological process 1.2. Asexual reproduction
by which organisms produce their young Asexual reproduction is wide spread
ones. The young ones grow and mature to among different organisms. It is common in
repeat the process. Thus reproduction results members of Protista, Bacteria, Archaea and
1
TN_GOVT_XII_Zoology_chapter1.indd 1 25-02-2019 18:17:54
, in multicellular organisms with relatively i) Simple irregular binary fission
simple organisation. The offsprings show ii) Transverse binary fission
“uniparental inheritance” without any genetic
iii) Longitudinal binary fission
variation. The different modes of asexual
iv) Oblique binary fission
reproduction seen in animals are fission,
sporulation, budding, gemmule formation, Simple binary fission is seen in Amoeba
fragmentation and regeneration. like irregular shaped organisms (Fig. 1.1),
where the plane of division is hard to observe.
Fission is the division of the parent The contractile vacuoles cease to function
body into two or more identical daughter and disappear. The nucleoli disintegrate and
individuals. Four types of fission are seen in the nucleus divides mitotically. The cell then
animals. They are binary fission, multiple constricts in the middle, so the cytoplasm
fission, sporulation and strobilation. divides and forms two daughter cells.
In binary fission, the parent In transverse binary fission, the plane of
organism divides into two halves and the division runs along the transverse axis of
each half forms a daughter individual. the individual. e.g. Paramecium and Planaria.
The nucleus divides first amitotically or In Paramecium (Fig. 1.2) the macronucleus
mitotically (karyokinesis), followed by the divides by amitosis and the micronucleus
Simple irregular Binary Fission in Amoeba
division of the cytoplasm (cytokinesis). divides by mitosis.
The resultant offsprings are genetically In longitudinal binary fission, the nucleus
Nuclear
identical to the parent. Depending on theContractile
vacuole and the cytoplasm divides membrane
in the longitudinal
plane of fission, binary fission is of the axis of the organism (Fig 1.3). In flagellates, the
Nucleus
following types Hyaline area flagellum is retained usually by one daughter cell.
Chromosomes
Simple irregular Binary Fission in Amoeba Contractile
vacuole
Nuclear
Contractile
membrane
vacuole
Nucleus
Hyaline area
Chromosomes
Contractile
vacuole Daughter amoebae
Fig. 1.1 Irregular simple binary fission in Amoeba
Macronucleus
New oral
groove
forming
Micronucleus Oral groove
disappearing
Daughter
Daughter amoebae paramecia
New
contractile
vacuoles
Macronucleus Micronucleus New
dividing dividing oral groove
amitotically mitotically forming
A B C D E
Fig. 1.2 Transverse binary fission in Paramecium
Reproduction in Organisms 2
TN_GOVT_XII_Zoology_chapter1.indd 2 25-02-2019 18:17:55
