NCERT Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms
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:
- ASEXUAL REPRODUCTION
- SEXUAL REPRODUCTION
- Pre-fertilisation Events
- Post-fertilisation Events
Why is reproduction essential for organisms?
Reproduction is essential for organisms because it maintains population of the young, adult and aged persons and the continuity of the species generation by generation and introduces variation in the organisms which are essential for adaptation and existence of life on earth.
Which Is a better mode of reproduction: sexual or asexual? Why?
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.
Why is the offspring formed by asexual reproduction referred to as clone?
Asexual reproduction results in the production of offsprings which are morphologically and genetically similar to one another and are also exact copies of their parents. Such a group of individuals are called clones.
Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
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.
How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Asexual reproduction is a process where offsprings are produced by a single parent without the involvement of gamete formation. No meiosis occurs in asexual reproduction and the progeny are genetically similar to parents and they do not show any variation.
But in sexual reproduction, the individual is produced as a result of meiosis and gametic fusion, exhibit genetic variation and differ from either of the two parents as well as among themselves.
Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
The differences between asexual and sexual reproduction are given in the following table:
As vegetative reproduction does not involve two parents and any meiosis and syngamy so it is considered as a type of asexual reproduction. This term is used in case of plants.
What is vegetative propagation? Give two suitable examples.
Vegetative propagation in plants is a method of asexual reproduction in which the parts other than seeds are used as propagules. In fact, it is a method of propagation in those plants which have lost their capacity to produce, seeds or produce non-viable seeds (e.g., Banana, seedless Grapes, Rose, Pineapple, etc.) Among flowering plants, every part of the body, such as root, stem, leaf or bud takes part in vegetative propagation. Modified tuberous roots can be propagated vegetatively when planted in soil (e.g., sweet potato).
Underground modified stems such as rhizomes (e.g., Ginger, Eichhornia or water hyacinth, etc.), corms (e.g., Colocasia, Banana, etc.), bulbs.(e.g., Garlic, onion, etc.), etc.
- Juvenile phase
- Reproductive phase
- Senescent phase
- Juvenile phase is the period of growth between the birth of an individual till reaches reproductive maturity. In plant, this is also called vegetative phase.
- Reproductive phase starts after vegetative phase (juvenile phase) and the organisms produce offspring during this phase. A few plants show unusual flowering phenomenon. Some of them such as bamboo species, flower only once in their life time, usually after 30-100 years. They produce large number of fruits and die. Among animals such as birds living in nature lay eggs seasonally while birds in captivity (as in poultry farm) can be made to lay eggs throughout the year.
- Senescent phase or old age begins at the end of reproductive phase. It is last phase of life span during which there is progressive deterioration in the body and loss in capability of reproduction. Old age ultimately leads to death of the organism. In plants, it is characterized by yellowing of leaves and leaf fall.
Higher organisms have resorted to sexual reproduction inspite of its complexity. Why?
Higher organisms though show complexity yet reproduce sexually because it enable these organisms to survive during unfavorable conditions. It contributes to evolution of the- species by introducing variation in a population much more rapidly than asexual reproduction.
Explain why meiosis and gametogenesis are always interlinked?
In sexual reproducing organisms, meiosis occurs during gametogenesis to reduce the diploid number of chromosomes (2n) to haploid number of chromosomes (n) in the gametes. Thus, gametes are formed as a result of meiosis so that their chromosome number.
Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
- Male gamete…..
- Ovary – Diploid(2n)
- Anther – Diploid(2n)
- Egg – Haploid(n)
- Pollen – Haploid(n)
- Male gamete – Haploid(n)
- Zygote – Diploid(2n)
Define external fertilization. Mention its disadvantages.
Malm External fertilization occurs outside the body of the organisms in water. It is also called external syngamy
e.g., most aquatic organisms (algae, fishes and amphibians).
The major disadvantage of this type of fertilization is that the offsprings are not protected from the predators and their survival is threatened upto adulthood. Moreover, a large number of gametes are wasted.
Differentiate between a zoospore and a zygote.
Zoospores are Ihe 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 nonflagellated.
Zoospores are the structures that give rise to new organism whereas zygote is formed after fertilization which develops into a mature organism.
Differentiate between gametogenesis from embryogenesis.
The differences between gametogenesis and embryogenesis are given in the following table :
Describe the post-fertilization changes in a flower.
After fertilization, the following changes occur in flower :
- The petals, sepals, stamens, style and stigma are shed. In some cases the sepals remain persistent e.g., pea.
- The zygote developed into embryo.
- The fertilised ovule changes into seed.
- The wall of ovary produces wall of the fruit called pericarp.
- The ripened ovary with pericarp and seeds is called fruit.
What is a bisexual flower?
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.
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?
In the staminate flowers stamens are present, but pistils are absent. They cannot produce fruits. In the pistillate flower, pistils are present, but stamens are absent and produces fruits. The example of unisexual flowers are – papaya and date palm.
Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
In oviparous animals, the development of the zygote takes place outside the body of the female parent whereas in viviparous animals, it takes place inside the body of the female. Because in oviparous animals, the fertilized eggs are laid in the open environment where they are not protected from the predators. Thus their survial rate is very less as compared to offspring of viviparous animals.
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