These Solutions are part of NCERT Solutions for Class 12 Biology. Here we have given NCERT Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms
Chapter 1 – Reproduction In Organism – covers different exercises. The questions in each exercise come with the answer and a detailed, step-by-step solution for better understanding by the student. This will prove to be most helpful to students in their home assignments and practice. The topics and sub-topics included in the chapter are the following:
Question 1.
Why is reproduction essential for organisms?
Solution:
An organism gives rise to young ones by reproduction. The offspring grow, mature, and in turn, produce new offspring. Thus, there is a cycle of birth, growth, and death. Reproduction enables the continuity of the species, generation after generation. So, therefore reproduction is essential.
Question 2.
Which Is a better mode of reproduction: sexual or asexual? Why?
Solution:
Sexual reproduction is a better mode of reproduction than asexual mode because the former contributes to the evolution of the species by introducing variation in a population and occurs much more rapidly. Variation in a population occurs because of the fusion of male and female gametes (sexual reproduction) carrying different sets of chromosomes.
Question 3.
Why is the offspring formed by asexual reproduction referred to as clones?
Solution:
In sexual reproduction, the offspring is morphologically and genetically identical to the parent and to each other. Hence, it is called a clone.
Question 4.
Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
Solution:
The offspring that are produced by sexual reproduction are not genetically identical to their parents. They exhibit variations because they receive chromosomes from two different parents. Since they show variation, they are highly adapted to the changing environment. Asexually produced organisms are genetically identical and all organism show similar adaptations. So, during any calamity, there is a possibility that the whole generation would destroy leading to extinction of species. However, this statement is not true always because of some inborn genetic disorder due to which organism have a risk in their survival, e.g., Haemophilia.
Question 5.
How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Solution:
The progenies have similar genetic make-up and are exact copies of their parents in asexual reproduction but the progenies have different genetic make-up and different from each other and dissimilar to the parent in sexual reproduction.
Variation is absent in asexual reproduction but it is a common phenomenon of sexual reproduction. In asexual reproduction, variation may occur due to mutation whereas variation occurs due to mutation, crossing over, and recombination in sexual reproduction.
Question 6.
Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
Solution:
The differences between asexual and sexual reproduction are given in the following table:
Question 7.
What is vegetative propagation? Give two suitable examples.
Solution:
In plants, the vegetative propagules (runner, rhizome, sucker, etc.) are capable of producing new offsprings by the process called vegetative propagation. As the formation of these vegetative propagules does not involve both the parents, the process involved is asexual.
Examples:
Question 8.
Define
Solution:
Question 9.
Higher organisms have resorted to sexual reproduction inspite of its complexity. Why?
Solution:
Higher organisms have resorted to sexual reproduction to:
Question 10.
Explain why meiosis and gametogenesis are always interlinked?
Solution:
Gametogenesis refers to the process of the formation of gametes. Gametes are haploid cells. If the organism is diploid it undergoes meiotic division to produce haploid gamete. So gametogenesis and meiosis are always interlinked.
Question 11.
Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
Solution:
Question 12.
Define external fertilization. Mention its disadvantages.
Solution:
In most aquatic organisms such as majority algae, fishes and amphibians, syngamy occurs in the external medium i.e., outside the body of the organism. This type of gametic fusion is called external fertilisation. A major disadvantage is that the offspring are extremely vulnerable to predators threatening their survival.
Question 13.
Differentiate between a zoospore and a zygote.
Solution:
Zoospores are The microscopic, flagellated (motile)
special asexual reproductive structures found in certain members of the kingdom fungi and simple plants like algae whereas zygote is a diploid cell formed by die fusion of male and female gametes. The zygote is usually non flagellated.
Zoospores are the structures that give rise to new organism whereas zygote is formed after fertilization which develops into a mature organism.
Question 14.
Differentiate between gametogenesis from embryogenesis.
Solution:
The differences between gametogenesis and embryogenesis are given in the following table :
Question 15.
Describe the post-fertilization changes in a flower.
Solution:
The post-fertilization changes that take place in a flower are as follows:
Question 16.
What is a bisexual flower?
Solution:
A bisexual flower possesses both male and female reproductive structures i.e., stamens and carpels are present in the same flower
e.g.. Rose (Rosa dim), Kikar (Acacia nilotica), China rose (Hibiscus rosa sinensis) etc.
Question 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?
Solution:
Other unisexual plants are com, papaya, cucumber etc.
Question 18.
Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Solution:
Cucurbit plant bears unisexual flowers as these flowers have either the stamen or the pistil. The staminate flowers bear bright, yellow-colored 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. Other examples of plants that bear unisexual flowers are corn, papaya, cucumber, etc.
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