CBSE Board Class XII – NCERT Biology
Chapter 1, Reproduction in Organisms
(NCERT solutions of Class 12 Biology textbook chapter exercise
questions)
Question 1: Why is reproduction essential for organisms?
Solution: Reproduction is the ability of all
living organisms to produce young ones (offspring) similar to themselves in
most of characters. The offspring grow, mature and produce new offsprings thus,
completing the cycle of birth, grow and death. This way reproduction enables
the continuity of the species generation after generation.
Question 2: Which is better mode of reproduction sexual or
asexual? Why?
Solution: Sexual reproduction is a better mode
of reproduction because though the events of sexual reproduction are elaborate
and complex but they follow a regular sequence.
Question 3: Why is the offspring formed by asexual reproduction
referred to as clone?
Solution: Asexual reproduction does not
involve the formation or fusion of gametes. Thus, a single parent is capable of
producing offsprings. The offsprings so produced are identical to each other
and are exact copies of their parent. They are morphologically and genetically similar
individuals so, they are referred to as clone.
Question 4: Offspring formed due to sexual reproduction have
better chances of survival; why? Is this statement always true?
Solution: Sexual reproduction involves the
formation and fusion of gametes. These gametes are male and female either from
same individual or by different individuals of the opposite sex. These gametes
fuse (syngamy) to form zygote which develops to form new organism. This way the
offsprings are not identical to themselves or to their parents.
These
offsprings are genetically different from their parents as variations appear
due to new combinations of genes during crossing over, chance of seggregation
of chromosomes and chance of fusion of gametes. Thus, there are more chances of
elimination of unfavourable traits in sexual reproduction so giving better
survival to the offsprings. No, the above statement is not always true. If the
mother is suffering from any major disease or any other ailment the offspring
may not survive.
Question 5: How does the progeny formed from asexual
reproduction differ from those formed by sexual reproduction?
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Solution: In asexual reproduction the participation of two organisms is not required, no gametes are formed. Somatic cells of the parent undergo mitotic divisions and produce the offsprings. So, the next generation will be the exact copy of the parent.
Solution: In asexual reproduction the participation of two organisms is not required, no gametes are formed. Somatic cells of the parent undergo mitotic divisions and produce the offsprings. So, the next generation will be the exact copy of the parent.
Sexual
reproduction is generally biparental. It involves the production of specialised
sex cells i.e. male and female gametes. They undergo fusion and form zygote. It
involves the process of fertilisation. During fertilisation both the parental
traits fuse and variations appear. The offsprings are genetically different
from the parents. Thus, giving better chances of survival for the most
favourable ones. It plays important role in evolution.
Question 6: Distinguish asexual and sexual reproduction. Why is
vegetative reproduction also considered as a type of asexual reproduction?
Solution:
Asexual
Reproduction
|
Sexual
Reproduction
|
1.
Always uniparental reproduction.
2.
No gametes are formed.
3.
It involves only mitotic divisions.
4.
No fusion of gametes occurs.
5.
Offsprings are genetically similar to the parents.
6.
Rate of reproduction is faster.
7.
Units of reproduction can be whole parent body or bud or body fragment.
8.
Occurs in lower invertebrates and lower chordates and plants with simple
organizations.
|
1.
Generally biparental except Taenia, Fasciola.
2.
Male and female gametes are formed.
3.
Meiosis occurs at the time of gamete formation and mitosis occurs after fertilization.
4.
Male and female gametes fuse to form
zygote.
5.
Offsprings are genetically different from the parent.
6.
Rate of reproduction is slower.
7.
Unit of reproduction are gametes.
8.
Found in higher plants and animals.
|
Vegetative
reproduction involves a single parent and there is no formation and fusion of
gametes; hence, it is considered as asexual reproduction.
Question 7: What is vegetative propagation? Give two suitable
examples.
Solution: Vegetative propagation is the
process of formation or regeneration of new plants from a portion of a
vegetative part of the plant.
E.g.,
Eyes of potato, Leaf buds of Bryophyllum. (See figures below)
.jpg "CBSE Class XII NCERT Biology - Eyes of Potato and Leaf Buds of Bryophyllum")
Question 8: Define: (i) Juvenile phase, (ii) Reproductive phase,
(iii) Senescent phase
Solution: (i) Juvenile Phase
Period
of growth of an organism from birth till attaining reproductive maturity is
called "juvenile phase".
In
plant, it is called vegetative phase.
In
perennial plants, vegetative growth continues through the year. It is more in
spring and rainy season and less during winter and summer season.
(ii)
Reproductive Phase
Period
in the life of an organism after it attains sexual maturity and starts
reproducing is called "reproductive phase". In perennial plants,
flowering occurs in particular season of every year. In biennial plants,
flowering occurs in a particular season. E.g. cabbage, radish, carrot and sugar
beet.
(iii)
Senescent Phase
The
period in the life cycle of an organism between the end of sexual maturity and
death. Degradative/Deteroriate changes takes place in the structure/function of organs.
Question 9: Higher organisms have resorted to sexual reproduction
in spite of its complexity. Why?
Solution: In sexual reproduction, separate
male and female gametes fuse to form a zygote which develops to form embryo and
later, a complete organism. It is an elaborate and complex process. It involves
slow multiplication and units of reproduction are haploid gametes. Since, the
offsprings are genetically different from the parents as variations appear due
to new genetic combinations during crossing over, chance of seggregation of chromosomes,
and chance of fusion of gametes. So, better chances of survival are there in
the next generation. This leads to selection of better traits at each
generation and ultimately to the evolution.
For rest
exercise questions (10 – 18) and Solutions
of CBSE Hot Questions for Chapter 1, Reproduction in Organisms, click below –
Value Based Questions (VBQs) -
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