A. If both A and R are true and R is correct explanation for A

A - Chromosomes
B - Nucleoli
C - Nucleus
D - Longitudinal furrow
E - Nuclear constriction
F - Daughter Euglena

The different modes of asexual reproduction seen in animals are fission, sporulation, budding, gemmule formation, fragmentation and regeneration.

Budding and Regeneration.

Juvenile phase I Vegetative phase, reproductive phasel maturity phase, Senescent phase.

(i) On the basis of time, breeding animals are of two types: seasonal breeders and continuous breeders.
(ii) Seasonal breeders reproduce at particular period of the year such as frogs, lizards, most birds, deers etc.,
Continuous breeders continue to breed throughout their sexual maturity. E.g. honey bees, poultry, rabbit etc.

conjugation is the temporary union of the two individuals of the same species. During their union both individuals, called the conjugants exchange certain amount of nuclear material (DNA) and then get separated. E.g. Paramecium

In syngamy, the fusion of two haploid gametes takes place to produce a diploid zygote.

It is a type of regeneration. In morphallaxis the whole body grows from a small fragment. E.g. Hydra. 

syngamy	fertilization
It is the fusion of two haploid gametes to form a diploid zygote	It is the act (or) process of rendering fertile zygote as the result of Fertilization

 

juvenile phase	reproductive phase
lt is also known as young and Vegetative Phase	It is also known as Maturity adult Phase
lt is the period of growth between the birth of the individual upto reproductive maturitiy.	The organisms reproduce and their offsprings reach maturity period

 

In monocellular organs cell division is itself a mode of reproduction. (e.g:) Bacteria, Euglena and Amoeba.

Isogamy. Eg: Monocystis

Charles Bonnet discovered the process of parthenogenesis.
Abraham Trembley was the first to study the concept of Regeneration in the Hydra.

	Asexual Reproduction	Sexual Reproduction
a	Involves only one parent	Involves two parents (male & female)
b	Only mitotic cell division takes place	Both mitosis & meiosis takes place
c	Offsprings are genetically identical to the parent.	Offsprings genetically differ from the parents.
d	Gametes are not produced	Gametes are produced

(a) Autogamy
(b) Exogamy
(c) Hologamy
(d) Paedogamy
(e) Merogamy
(f) Isogamy
(g) Anisogamy
(h) Conjugation

When buds are formed on the outer surface of the parent body, it is known as exogenous budding e.g. Hydra. In Hydra when food is plenty, the ectoderm cells increase and form a small elevation on the body surface. Ectoderm and endoderm are pushed out to form the bud. The bud contains an interior lumen in continuation with the parent's gastrovascular cavity. The bud enlarges, develops a mouth and a circle of tentacles at its free end. When fully grown, the bud constricts at the base and finally separates from the parent body and leads an independent life.

(i)  In Ovoviviparous animals, the embryo develops inside the egg and remains in the mother's body until they are ready to hatch.
(ii) This method of reproduction is similar to Viviparity but the embryos have no placental connection with the mother and receive their nourishment from the egg yolk. Ovoviviparity is seen in fishes like shark.

(i) It is a mode of asexual reproduction in sponges.
(ii) Internal buds called gemmules are formed which is a hard ball, consisting of an internal mass of food laden archaeocytes.
(iii) During unfavourable conditions, the sponge disintegrates, but the gemmule withstands adverse conditions.
(Iv) The gemmules hatch during favourable conditions.

(i) Reproduction by a single parent without the involvement of gamete formation is asexual reproduction and the offspring produced are genetically identical. (uniparental inheritance)
(ii) Asexual reproduction is usually by amitotic or mitotic division of the somatic (body) cells, hence is also known as somatogenic or blastogenic reproduction. Eg. members of Protista, Bacteria.

Oviparous animals lay eggs outside their body. These eggs are exposed to various environmental conditions and may be eaten by predators also. They face lot of risks until the young ones hatche. But the offsprings of viviparous animals are more safe and protected in the maternal womb until they are born.

1. In unicellular organism there is no special structure for reproduction.
2. In binary fission the entire parent body constitute the reproductive unit and disappears when its division into two daughter unicellular cell is completed.
3. These two daughter cells function as two new individuals.
4. There is no remains of parent body cell and parent cannot be said to have died.
5. In fact after binary fission parent continues living as two daughter individual.
Hence, the unicellular organisms which undergo binary fission are called immortal (no natural death).

1. Sexual reproduction is considered to be a better mode of reproduction because it creates a hybrid that has more vigor than the parents.
2. It also creates the variation in off springs making its survival better.
3. The fact that most of the eukaryotes reproduce sexually in evidence of its evolutionary success.
4. In many animals, it is actually the only mode of reproduction.

(a) Hologamy: In Hologamy, the adult individuals do not produce gametes, but they themselves act as gametes and fuse to form new individuals.
E.g: Trichonympha
(b) Isogamy: Fusion of morphologically & physiologically similar gametes.
E.g: Monocystis
(c) Anisogamy: Fusion of morphologically & physiologically dissimilar gametes.
Eg: Vertebrates.
(d) Merogamy: Fusion of small-sized morphologically different gametes (microgametes)
(e) Paedogamy: Fusion of young individuals produced immediately after the mitotic division of adult parent cell.

Regeneration is regrowth in the injured region. Regeneration was first studied in Hydra by Abraham Trembley in 1740. Regeneration is of two types, morphallaxis, and epimorphosis. In morphallaxis, the whole body grows from a small fragment e.g. Hydra and Planaria. When Hydra is accidentally cut into several pieces, each piece can regenerate the lost parts and develop into a whole new individual. The parts usually retain their original polarity, with oral ends, by developing tentacles .and aboral ends, by producing basal discs. Epimorphosis is the replacement of lost body parts. It is of two types, namely reparative and restorative regeneration. In reparative regeneration, only certain damaged tissue can be regenerated, whereas in restorative regeneration severed body parts can develop. e.g. starfish, the tail of wall lizard.

In binary fission, the parent organism divides into two halves and each half forms a daughter individual. The nucleus divides first amitotically or mitotically (karyokinesis), followed by the division of the cytoplasm (cytokinesis). The resultant offsprings are genetically identical to the parent. Depending on the plane of fission, binary fission is of the following types
(i) Simple irregular binary fission
(ii) Transverse binary fission
(iii) Longitudinal binary fission
(iv) Oblique binary fission
(i) Simple irregular binary fission is seen in Amoeba like irregular shaped organisms, where the plane of division is hard to observe. The contractile vacuoles cease to function and disappear. The nucleoli disintegrate and the nucleus divides mitotically. The cell then constricts in the middle, so the cytoplasm divides and forms two daughter cells.

(ii) In Transverse binary fission, the plane of the division runs along the transverse axis of the individual. E.g. Paramecium and Planaria. In Paramecium the macronucleus divides by amitosis and the micronucleus divides by mitosis.

(iii) In Longitudinal binary fission the nucleus and the cytoplasm divides in the longitudinal axis of the organism. In flagellates, the flagellum is retained usually by one daughter cell. The basal granule is divided into two and the new basal granule forms a flagellum in the other daughter individual. E.g. Vorticella and Euglena.
(iv) In Oblique binary fission the plane of division is oblique. It is seen in dinoflagellates. E.g. Ceratium.

(i) Development of an egg into a complete individual without fertilization is known as parthenogenesis.
(ii) It was first discovered by Charles Bonnet in 1745. Parthenogenesis is of two main types namely, natural Parthenogenesis and artificial Parthenogenesis.
(iii) In certain animals, parthenogenesis occurs regularly, constantly and naturally in their life cycle and is known as natural parthenogenesis.
Natural parthenogenesis are of different types:
a) Arrhenotoky: In this type only males are produced by parthenogenesis. E.g: honey bees
b) Thelytoky: In this type of parthenogenesis only females are produced by parthenogenesis E.g. Solenobia
c) Amphitoky: In this type parthenogenetic egg may develop into individuals of any sex. E.g: Aphis.
(iv) Natural parthenogenesis may be of two types, viz., complete and incomplete. Complete parthenogenesis is the only form of reproduction in certain animals and there is no biparental sexual reproduction. These are no male organisms and so, such individuals are represented by females only.
(v) Incomplete parthenogenesis is found in some animals in which both sexual reproduction and parthenogenesis occurs.
E.g. In honeybees; fertilized eggs (zygotes) develop into queen and workers, whereas unfertilized eggs develop into drones (male).
(vi) In paedogenetic parthenogenesis (paedogenesis) the larvae produce a new generation of larvae by parthenogenesis.
(vii) It occurs in the sporocysts and Redia larvae of liver fluke. It is also seen in the larvae of some insects. E.g. Gall fly.
(viii) In artifical parthenogenesis, the unfertilized egg (ovum) is induced to develop into a complete individual by physical or chemical stimuli. E.g. Annelid and seaurchin eggs.

(a) 

Binary Fission in Amoeba	Multiple fission in Plasmodium
lt results in the production of two individuals from a single parent.	It results in the production of several individuals
lt occurs under favourable conditions	It occurs both under favourable and unfavourable conditions
Nucleus of the parent cell divides only once to form two daughter nuclei	Nucleus of the parent cell undergoes repeated divisions to form a number of daughter nuclei
Cytoplasm divides after nuclear division	Cytoplasm does not divide after each nuclear division but divides during favourable condition
No part of parent body is left unused (e,g: Amoeba)	A part of the body (covering and residuai cytoplasm) is left unused. (e,g: Paramecium)

(b) Budding in yeast and budding in hydra

Budding in Yeast	Budding in Hydra
During budding the cell wall of the parent cell bulges out in the form of an out growth as bud	During budding the ectoderm cells increase and form a small elevation on the body surface as bud.
The parent nucleus divides into two daughter nuclei one of which migrates into bud.	Ectoderm and endoderm are pushed out to form the bud. The bud contains an interior lumen in continuation with parent's gastro vascular cavity (coelenteron)
As the bud enlarges and is fully formed, it is separated from the parentcell and grows into mature yeast. Sometimes a bud may produce another bud over it which is still attached to parent cell forming a false mycelium (or) pseudomycelium	The bud enlarges, develops a mouth and a circle of tentacles at its free end. When fully grown, the bud constricts at the base and finally separates from the parent body and leads an independent life

(c) Regeneration is regrowth in the injured region

Regeneration in Lizard	Regeneration in Planaria
This type of regeneration comes under epimorphosis type.	This type of regeneration comes under morphallaxis type
Several body parts can develop.	When the body is cut into several pieces, each piece can regenerate the lost parts and develops into a whole individual