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NCERT Class 12 Biology Chapter 1 Reproduction in Organisms
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Reproduction in Organisms
Chapter: 1
BIOLOGY
UNIT – I REPRODUCTION
TEXTUAL QUESTIONS ANSWERS
Q. 1. Why is reproduction essential for organisms?
Ans: Reproduction ensures the continuance of species from one generation to another.
Q. 2. Which is a better mode of reproduction sexual or asexual? Why?
Ans: Sexual reproduction is a better mode of reproduction as it involves fusion of gametes from two parents. It allows the formation of new variants by the combination of the DNA from two different parents.
Q. 3. Why is the offspring formed by asexual reproduction referred to as clone?
Ans: Offspring formed by asexual reproduction are produced from only one parent and are identical to each other. They are morphologically and genetically similar to their parents and are thus, called clones.
Q. 4. Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
Ans: Sexual reproduction involves the fusion of male and 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.
It is not always necessary that the offspring produced due to sexual reproduction has better chances of survival. Under some circumstances, asexual reproduction is more advantageous for certain organisms like individuals who do not move from one place to another and are well settled in their environment.
Q. 5. How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Ans: Progeny formed from asexual reproduction:
(i) Asexual reproduction does not involve the fusion of male and female gamete. It produce offspring’s that are morphologically and genetically identical to them.
(ii) Offspring’s thus produced do not show variations and are called clones.
Progeny formed from sexual reproduction:
(i) Sexual reproduction involves the fusion of male and female gamete of two individuals. It produce offspring’s that are not identical to them.
(ii) Offspring’s thus produced show variations from each other and their parents.
Q. 6. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
Ans: (i) Sexual reproduction involves the fusion of male and female gamete while asexual does not involves the fusion of male and female gamete.
(ii) Sexual reproduction requires two different parents while asexual requires only one parent.
(iii) Progeny of sexual reproduction is not identical to their parents. They show variations from each other and also from their parents. Progeny of asexual reproduction is identical to the parent and are also called clones.
Vegetative propagation involves the propagation of plants through vegetative parts like rhizome, sucker, tuber, bulb, etc. It does not involve the fusion of male and female gamete. It requires only one parent. Hence, vegetative reproduction is considered as a type of asexual reproduction.
Q. 7. What is vegetative propagation? Give two suitable examples.
Ans: Vegetative propagation is a mode of asexual reproduction. Vegetative parts of plants like runners, rhizomes, suckers, tubers, etc called propagules give rise to new plants.
Examples of vegetative reproduction are:
(i) Tubers [Eyes] in potato.
(ii) Leaves of Bryophyllum.
Q. 8. Define:
(a) Juvenile phase.
Ans: Juvenile phase: Stage of growth is called juvenile or vegetative phase.
(b) Repro-ductive phase.
Ans: Reproductive phase: It is the period when an individual organism reproduces sexually.
(c) Senescent phase.
Ans: Senescent phase: It is old age of organism and leads to death.
Q. 9. Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
Ans: Higher organisms have resorted to sexual reproduction in spite of its complexity because this produces new variations in progenies through the combination of DNA from two different individuals. These variations make the organism better suited for the environment. Variations also lead to the evolution and better chances of survival.
Q. 10. Explain why meiosis and. gametogenesis are always interlinked?
Ans: Gametogenesis is the process of the formation of gametes. Haploid gametes are produced from diploid parent body through meiosis.
Q. 11. Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
(a) Ovary.
Ans: Ovary is Diploid (2n).
(b) Anther.
Ans: Anther is Diploid (2n).
(c) Egg.
Ans: Egg is Haploid (n) ale.
(d) Pollen.
Ans: Pollen is Haploid (n).
(e) Male gamete.
Ans: Male gamete Haploid (n).
(f) Zygote.
Ans: Zygote Diploid (2n).
Q. 12. Define external fertilization. Mention its disadvantages.
Ans: External fertilization is the process in which fusion of male and female gamete takes place outside the female body in an external medium like water e.g. algae, fish, amphibians.
Disadvantages of external fertilization:
(i) Eggs have less chances of fertilization.
This leads to the wastage of a large number of eggs produced during the process.
(ii) There is an absence of parental care to progeny which results in a low rate of survival in the progenies.
Q. 13. Differentiate between a zoospore and a zygote.
Ans: Zoospore is a motile asexual haploid spore having flagella while zygote is a non-motile diploid cell formed as a result of
fertilization in sexual reproduction.
Q. 14. Differentiate between gametogenesis from embryogenesis.
Ans: Gametogenesis: It is the process of the formation of haploid male and female gametes from diploid meiocytes through meiosis.
Embryogenesis: It is the process of development of the embryo from the repeated mitotic divisions of diploid zygote.
Q. 15. Describe the post-fertilization changes in a flower.
Ans: After fertilization, the zygote divides several times to form an embryo. The fertilized ovule inside the embryo forms a seed. Ovary forms the fruit with thick wall called pericarp.
Q. 16. 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.
Ans: A flower with both male and female reproductive parts (stamen and pistil) is called bisexual flower.
Examples of 5 bisexual flowers are:
(i) Water lily (Nymphaea odorata).
(ii) Rose (Rosa multiflora).
(iii) Pea (Pisum sativum).
(iv) Mustard (Brassica nigra).
(v) Onion (Allium cepa).
Q. 17. 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?
Ans: Cucurbit plant bears unisexual flowers as these flowers have either stamen or pistil. The staminate flowers have androecium and pistillate flowers have gynoecium.
Examples of plants that bear unisexual flowers are coconut, papaya, date palm etc.
Q. 18. Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Ans: Oviparous animals lay eggs outside their body. As a result, the eggs of these animals are vulnerable to predators and adverse environment. Viviparous animals have the development of egg 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 viviparous animal which gives birth to its young ones.
