STD 12 BIOLOGY HELPFUL FOR NEET/ GSET/NET EXAMINATION PREPARATION TYPES OF REPRODUCTION IN PLANTS AND ANIMALS

1. STD- 12
BIOLOGY
CHAPTER – 1
Reproduction in Organisms
SANJAY SIDDHAPARA
92750 27350

2. Reproduction is a process in which an organism gives rise to young ones
(offspring) similar to itself.
It is a biological process through which living organism produce offspring’s
similar to them.
It ensures the continuity of the species, generation after generation.
The period from birth to the natural death of an organism represents its life span.
No individual is immortal, except unicellular organisms.
There is no natural death in unicellular organisms.
Life spans of a few organisms are given below.
Reproduction

3. Organism Lifespan
Elephant 50-70 years
Parrot 140 years
Crocodile 60 years
Dog 22 years
Horse 40-50 years
Butterfly 1-2 weeks
Fruit fly 2 weeks
Crow 15 years
Tortoise 100-150 years
Cow 22 years
Rose plant 5-7 years
Banana tree 25 years
Rice plant 3-4 month
Banyan tree 200 years

4. TYPES OF REPRODUCTION
• Based on the number of participants, reproduction is of two
types:
• 1. Asexual reproduction
• 2. Sexual reproduction

5. 1. Asexual Reproduction
 It is the production of offspring by a single parent.
 It does not involve the fusion of male and female gametes.
 The offspring produced are identical to one another and to their parent. Such morphologically
and genetically similar individuals are known as clone.
 Asexual reproduction is found in unicellular organisms, and in simple plants and animals.
Advantages of asexual reproduction
 Asexual reproduction is advantageous to certain animals that remain in one particular place
like Hydra, Planaria and animals that are unable to look for mates.
 It also produces numerous offspring without costing the parent a great amount of energy or
time.
Disadvantages of asexual reproduction:
 Asexual reproduction lacks genetic variation. All the organisms that reproduce asexually are
genetically identical and therefore share the same weaknesses.
 If the stable environments changes, the consequences could be deadly to all of the individuals.

6. Types of asexual reproduction
(i) Fission: In this, the parent cell divides into two or more
individuals. E.g. Protists and Monerans.
Fission is of two types:
(a) Binary fission: In this process, the cell divides into
halves, and each half develops into an adult. E.g.,
Amoeba, Paramecium.
(b) Multiple fission: It is the division of parent cell into
many individuals. E.g. Plasmodium, Amoeba.

7. (ii) Budding:
• Budding involves the formation of new
individual from the bulging of parent body.
• In this, the cell divides unequally to form
buds, which remain attached to the parent
body but later detach and develop into a
mature individual.
• E.g. Hydra, Sponge, Yeast, etc.

8. (iii) Other asexual reproductive structures:
(a) Zoo spores: The new protoplasts acquire characters of mother cell and
transformed into motile spores.
(b) Conidia : These are non-motile, exogenous spores found in chains.
E.g. Penicillium, Mucor.
(c) Gemmules : internal budding in sponge
E.g. Sycon, .

9. Zoospore
The new protoplasts acquire characters of
mother cell and transformed into motile
spores.
• Theparent cell wall breaks and zoospores are
liberated in water. They enlarge and behave
as an adult individuals.
• Biflagellate zoospore (e.g. Chlamydomonas),
• quadriflagellate (e.g. Ulothrix),
• Multiflagellate (e.g. Oedogonium).
• Uninucleate (e.g., Ulothrix),
• multinucleate called synzoospores (e.g.
Vaucheria).

10. Conidia spores
 These are non-motile spores produced by
special hyphal branches that constrict at
the tips calledconidiophores.
 They are most common asexual spores
produced by fungi. The conidiophores
maybe branched or unbranched.
 In Penicillium conidiophore may show
branching and over these branches there
is formation of flask shaped structures
called sterigmata (phialides).
 Each sterigmata produces/cuts a chain
of conidia.
 Conidiophores are capable of producing
conidia singly (e.g., Phytophthora) or in
chains (e.g., Aspergillus and Penicillium).

11.  It is method of multiplication in which a somatic part of the plant detaches from the body of the
mother and develops into a new independent plant under suitable environmental conditions.
 The detachable somatic part involved in vegetative propagation is called vegetative propagule.
 Large number of clones are produced in a short duration and the purity, resistance, good qualities
of the variety are preserved.
Natural Vegetative Propagation
• Seen commonly among seeded plants.
• The formation of new plants is brought about by means of adventitious buds that are normally
found in the vegetative organs like roots, stem and leaves.
• Vegetative reproduction is a type of asexual reproduction as it does not involve two parents as
well as sex cells.
• These vegetative organs can be further divided as follows:
1. Stem
i. Underground stem ii. Subaerial stem iii. Aerial stem iv. Bulbils
2. Leaves
3. Root
Vegetative Propagation

12. 1. Vegetative Propagation by Stems
a. Underground stem: It is non-green, food storing, perennating structure present
below the surface of the soil. It is of several types like tuber, rhizome and bulb.
i. Tuber: It is terminal portion of underground stem branch which is swollen on account of
accumulation of food. They possess buds over their nodes. The buds sprout to produce new
plantlets, when a stem tuber or a part of it having a node is placed in the soil.
These kind of crops are grown by tubers and not by seeds. E.g. Potato.

22. Sweet potato and Asparagus

29. 2. Sexual Reproduction
Sexual reproduction involves formation of the male and female gametes, either by the same
individual or by different individuals of the opposite sex.
• It is an elaborate, complex and slow process as compared to asexual reproduction.
• It results in offspring that are not identical to the parents or amongst themselves. So sexual
reproduction give rise to diversity among living organisms.
• Higher organisms have resorted to sexual reproduction inspite of its complexity. It is because
sexual reproduction helps in introducing new variations in offspring through the combination of
the DNA from two different organisms.
• These variations allow the individual to cope with various environmental conditions and thus,
make the organisms better suited for the environment.
• Variations also lead to the evolution of better organisms and therefore, provide better chances
of survival.

30. Different phases in sexual reproduction
• All living organisms pass through three stages:
(I)Juvenile phase: It is the period of growth of an individual organism after its birth
and before it reaches its reproductive maturity. It is known as vegetative phase in plants.
(II) Reproductive phase: It is the phase when an individual organism reproduces
sexually.
(III) Senescent phase: It is the period when an organism grows old and loses the ability
to reproduce.

31. Reproductive phase in Plants
• Reproductive phase: It is the phase when an individual organism reproduces sexually.
• It is easily seen in higher plants.
• In higher plants, the flowering indicates the end of vegetative phase and the beginning
of reproductive phase.
• Some plants flower seasonally and some throughout the year.
• Annual and biennial plants show clear cut vegetative reproductive and senescent phases,
but in perennial species it is very difficult to identify these phases.
• Few plants exhibit unusual flowering phenomenon E.g.:
Bamboo species flower only once in their lifetime (after 50-100 years); produce large
number of fruits and die.
Strobilanthus Kunthiana flowers once in 12 years.

32. Reproductive phase in Animals
• In animals, juvenile phase is followed by morphological and physiological changes prior to
active reproductive behaviour.
• In animals, sexual reproduction is usually seasonal.
• Birds living in nature lay eggs only seasonally. However, birds in captivity (e.g., poultry) can be
made to lay eggs throughout the year.
• In placental mammals, there is occurrence of cyclical changes in the activities of ovaries and
accessory ducts as well as hormones.
• In non-primate mammals like cows, sheep, rat, deer, dog, tiger, etc., these cyclical changes
during reproduction is called oestrus cycle.
• In primate mammals like monkey, apes and humans, these cycles are called menstrual cycles.
• Seasonal breeders: The mammals (living in natural conditions) that can reproduce only in
the favourable seasons are called seasonal breeders.
• Continuous breeders: The mammals that can reproduce throughout their reproductive phase
are called continuous breeders.

33. 3. Senescent phase:
• It is the period when an organism grows old and loses the ability to reproduce.
• During this, concomitant changes in the body (slowing of metabolism etc.) occur. It
ultimately leads to death.
• In plants and animals, hormones are responsible for transition between juvenile,
reproductive and senescence phases.
• Interaction between hormones and environmental factors regulate the reproductive
processes and the associated behavioural expressions of organisms.

34. Events in Sexual Reproduction
• Organisms reproducing sexually exhibit three
events
(1) Pre-fertilisation,
(2) Fertilisation and
(3) Post-fertilisation events

35. 1. Pre-fertilisation events
• These include all events that take place before fusion of gametes.
• It consists of (a) gametogenesis and (b) gamete transfer.
(a) Gametogenesis
• It is the process of formation of male and female gametes by meiosis. Gametes are usually haploid cells.
• Gametes are called homogametes or isogametes when both have same appearance. Homogamete or
isogamete: In this, the male and female gametes are morphologically and physiologically similar.
E.g. Algae.
• Gametes are called heterogametes when gametes are different. Heterogametes or an isogamete: In this,
the male and female gametes are distinct types. The gametes are morphologically dissimilar but
physiologically similar. E.g. Humans.
• Male gamete is called the antherozoid (sperm)
• Female gamete is called the egg (ovum).

36. Sexuality in organisms
• In Plants,
• Bisexual term is used for homothallic and
monoecious plants, whereby male and female
reproductive structures are found in the same
plant.
• Unisexual term is used for Heterothallic and
dioecious plants, whereby male and female
reproductive structures are on different plants.
• In dioecious (unisexual) flowering plants, the
male flower is called staminate (bearing stamens)
while the female is called pistillate (bearing
pistils). E.g. papaya and date palm.
• In monoecious flowering plants, male and
female flowers are present on same individual.
E.g. Cucurbits and coconuts.

37. • In animals,
• Bisexual animals: Animals having
both male and female reproductive
system are called bisexual animals or
hermaphrodites. E.g. Earthworms,
leech, sponge, tapeworm, etc.
• Unisexual animals: Animals having
one type of reproductive system is
called unisexual animals. E.g.
Cockroach, higher animals etc.
• Fungi may be homothallic (bisexual)
or heterothallic (unisexual).

38. Cell division during gamete formation
• Gamete formation takes place by cell division. Gametes are always
haploid irrespective of parents’ body.
• Haploid parental body (n) produces haploid (n) gametes by mitosis.
E.g. Many monera, fungi, algae and bryophytes.
• Diploid parental body (2n) produces haploid (n) gametes by meiosis.
Such specialized parent cell is called meiocytes or gamete mother cell.
E.g. Pteridophytes, gymnosperms, angiosperms and animals.

40. (b) Gamete transfer
• Male and female gametes need to be physically brought together to
facilitate fusion called fertilization.
• In most cases, male gamete is motile and the female gamete is
stationary, except few fungi and algae, whereby both gametes are motile.
• In simple plants like algae, bryophytes and pteridophytes, gamete
transfer takes place through water medium. Male gametes are produced
in several thousand times the number of female gametes produced to
compensate the loss during transport.

41. • In higher plants, male gametes are produced in the anther
and need to be transferred to the stigma for fertilization to
occur. This is easy in monoecious plants as both the anther
and the stigma are present close by. In dioecious plants, it
takes place by pollination.
• In dioecious animals, the fertilization helps for successful
transfer and coming together of gametes.

42. 2. Fertilization (syngamy)
• It is the most important event in sexual reproduction.
• It is the fusion of male and female gametes to form a diploid zygote.
• It is also known as syngamy.
• Parthenogenesis:
It is a phenomenon whereby egg formation takes place without
fertilization. The adults produced by parthenogenesis are often
haploid, and their cells do not undergo meiosis in forming new
gametes. E.g. Rotifers, honeybees, some lizards and birds (turkey).

43. The process of fertilization might take place either outside the female body or inside
the female body. On the basis of this, fertilization is divided into two types:
(a)External fertilization:
The fertilization that takes place outside the female body is i.e. in the external medium
(water) is called external fertilization. E.g. most aquatic organisms (many algae, bony
fishes etc.) and amphibians
• Advantages: Such organisms show great synchrony between the sexes and release a
large number of gametes into the surrounding medium in order to enhance the
chances of syngamy.
• Disadvantages: In external fertilization the eggs have less chances of fertilization.
This can lead to the wastage of a large number of eggs produced during the process.
• Further, there is an absence of proper parental care to the offspring. This may result
in a low rate of survival in the progenies.

44. (b) Internal fertilization:
• The fertilization that takes place inside the female body is called
internal fertilization. E.g. terrestrial organisms, belonging to fungi,
animals (reptiles, birds, mammals) and plants (bryophytes,
pteridophytes, gymnosperms and angiosperms).
• In this, non-motile egg is formed inside the female body, whereby
motile male gamete reaches and fuses.
• In seed plants, the non-motile male gametes are carried to female
gamete by pollen tubes.
• There is large number of sperms produced but the number of eggs is
very low.

45. 3. Post-fertilisation events
Zygote
• Every sexually reproducing organism begins life as a zygote.
• It is the vital link between organisms of one generation and the next.
• The haploid gamete fuses to form a diploid zygote in all organisms.
• In organism with external fertilisation, zygote is formed in the external
medium.
• In organism with internal fertilisation, zygote is formed inside body.
• The further development of the zygote depends upon the life cycle of an
organism and its surrounding environment.
The event that takes place after the formation of zygote is called post-fertilization events.

46. • ♦ In some organism, like fungi and algae, zygote does not
develop immediately. They develop a thick wall that is
resistant to desiccation and damage. Then they undergo a
period of rest before germination.
• ♦ In organisms with haplontic life cycle, zygote (2n) divides
by meiosis to form haploid spores that grow into haploid
individuals.
• ♦ In organisms with diplontic life cycle, zygote (2n) divides
by mitosis and develops into diploid embryo.

47. Embryogenesis
• It is the process of development of embryo from the zygote.
• During embryogenes is, zygote undergoes cell division (mitosis) and cell
differentiation.
• Cell divisions increase the number of cells in the embryo and cell
differentiation helps the cells to undergo modifications into various tissues
and organs to form an organism.

48. Based on how and where the development of zygote takes
place, animals are divided into two types:
(a) Oviparous:
• The animals that lay eggs are called oviparous animals.
• Eggs can be fertilized or unfertilized.
• E.g. In reptiles and birds, the fertilized eggs are covered by a hard
calcareous shell and are released into the outside environment.
• They development takes place inside the egg and the young one
hatches out.
• Unfertilized eggs are laid down in water.

49. (b) Viviparous:
• The animals that give rise to young baby are called viviparous
animals.
• Here, the zygote develops into a young one inside the female
body and the developed young one is delivered outside.
• E.g. most of mammals, including humans.
• Advantage:
Because of proper care and protection, the chances of survival of young
ones are greater in viviparous animals.

50. • In flowering plants, the zygote is formed inside the ovule.
• Parthenogenesis: It is the process, whereby the female gamete develops into new
organism. Seedless fruits are formed by parthenogenesis.

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