NCERT Solutions for Class 12 Biology Chapter 1
Reproduction in Organisms Class 12
Chapter 1 Reproduction in Organisms Exercise Solutions
Exercise : Solutions of Questions on Page Number : 17
Why is reproduction essential for organisms?
Which is a better mode of reproduction sexual or asexual? Why?
Why is the offspring formed by asexual reproduction referred to as clone?
A clone is a group of morphologically and genetically identical individuals.
Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
Sexual reproduction involves the fusion of the male and the female gamete. This fusion allows the formation of new variants by the combination of the DNA from two (usually) different members of the species. The variations allow the individuals to adapt under varied environmental conditions for better chances of survival.
How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Progeny formed from asexual reproduction |
Progeny formed from sexual reproduction |
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1. |
Asexual reproduction does not involve the fusion of the male and the female gamete. Organisms undergoing this kind of reproduction produce offspring's that are morphologically and genetically identical to them. |
Sexual reproduction involves the fusion of the male and the female gamete of two individuals, typically one of each sex. Organisms undergoing this kind of reproduction produce offspring's that are not identical to them. |
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2. |
Offsprings thus produced do not show variations and are called clones. |
Offspring's thus produced show variations from each other and their parents. |
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Q6 :
Answer :
Sexual reproduction |
Asexual reproduction |
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1 |
It involves the fusion of the male and female gamete. |
It does not involves the fusion of the male and the female gamete |
2. |
It requires two (usually) different individuals. |
It requires only one individual. |
3. |
The individuals produced are not identical to their parents and show variations from each other and also, from their parents. |
The individuals produced are identical to the parent and are hence, called clones. |
4. |
Most animals reproduce sexually. Both sexual and asexual modes of reproduction are found in plants. |
Asexual modes of reproduction are common in organisms having simple organizations such as algae and fungi. |
5. |
It is a slow process. |
It is a fast process. |
What is vegetative propagation? Give two suitable examples.
Vegetative propagation is a mode of asexual reproduction in which new plants are obtained from the vegetative parts of plants. It does not involve the production of seeds or spores for the propagation of new plants. Vegetative parts of plants such as runners, rhizomes, suckers, tubers, etc. can be used as propagules for raising new plants.
Examples of vegetative reproduction are:
Define
(b) Reproductive phase,
Answer :
(a) Juvenile phase:
It is the period of growth in an individual organism after its birth and before it reaches reproductive maturity.
(b) Reproductive phase:
It is the period when an individual organism reproduces sexually.
(c) Senescent phase:
Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
Explain why meiosis and gametogenesis are always interlinked?
Meiosis is a process of reductional division in which the amount of genetic material is reduced. Gametogenesis is the process of the formation of gametes. Gametes produced by organisms are haploids (containing only one set of chromosomes), while the body of an organism is diploid. Therefore, for producing haploid gametes (gametogenesis), the germ cells of an organism undergo meiosis. During the process, the meiocytes of an organism undergo two successive nuclear and cell divisions with a single cycle of DNA replication to form the haploid gametes.
Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
(b) Anther ———————————
(d) Pollen ———————————
Answer :
(a) Ovary Diploid (2n)
(b) Anther Diploid (2n)
(c) Egg Haploid (n)
(d) Pollen Haploid (n)
(e) Male gamete Haploid (n)
Define external fertilization. Mention its disadvantages.
External fertilization is the process in which the fusion of the male and the female gamete takes place outside the female body in an external medium, generally water. Fish, frog, starfish are some organisms that exhibit external fertilization.
In external fertilization, eggs have less chances of fertilization. This can lead to the wastage of a large number of eggs produced during the process.
Differentiate between a zoospore and a zygote.
Zoospore |
Zygote |
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1. |
A zoospore is a motile asexual spore that utilizes the flagella for movement. |
A zygote is a non-motile diploid cell formed as a result of fertilization. |
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2. |
It is an asexual reproductive structure. |
It is formed as a result of sexual reproduction. |
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Q14 :
Answer :
Gametogenesis |
Embryogenesis |
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It is the process of the formation of haploid male and female gametes from diploid meiocytes through the process of meiosis. |
It is the process of the development of the embryo from the repeated mitotic divisions of the diploid zygote. |
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Describe the post-fertilization changes in a flower.
What is a bisexual flower? Collect five bisexual flowers from your neighborhood and with the help of your teacher find out their common and scientific names.
A flower that contains both the male and female reproductive structure (stamen and pistil) is called a bisexual flower. Examples of plants bearing bisexual flowers are:
(1) Water lily ( Nymphaea odorata)
(2) Rose (Rosa multiflora )
(3) Hibiscus (Hibiscus Rosa-sinensis )
(4) Mustard ( Brassica nigra)
(5)
Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?
Cucurbit plant bears unisexual flowers as these flowers have either the stamen or the pistil. The staminate flowers bear bright, yellow coloured petals along with stamens that represent the male reproductive structure. On the other hand, the pistillate flowers bear only the pistil that represents the female reproductive structure.
Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Oviparous animals lay eggs outside their body. As a result, the eggs of these animals are under continuous threat from various environmental factors. On the other hand, in viviparous animals, the development of the egg takes place inside the body of the female. Hence, the offspring of an egg-laying or oviparous animal is at greater risk as compared to the offspring of a viviparous animal, which gives birth to its young ones.