Class 12 Biology Chapter 1 Reproduction in Organisms The answer to each chapter is provided in the list so that you can easily browse through different chapters Assam Board HS 2nd Year Biology Chapter 1 Reproduction in Organisms Question Answer.
Class 12 Biology Chapter 1 Reproduction in Organisms
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III. QUESTIONS FOR – 3 MARKS.
Q.1. Explain with suitable examples why meiosis and gametogenesis are always interlinked.
Ans : The process of gametogenesis and meiosis has the linked because the gametes are formed only by the meiosis cell division. Generally meiosis cell division takes place in body cells where chromosome number always maintained as in. In gametogenesis the gametes are formed which are haploid in number and as a result of fertilization the chromosome number is, maintained. Hence, meiosis or reduction cell division is an essential process at the time of gametogenesis.
Q.2. Honeybees produce their young ones only by sexual reproduction. In Spite of this in a colony of bees we find both haploid and diploid individuals in the colony state the reasons behind their formation.
Ans : Honey bee reproduces sexual and by parthenogenesis only. In a hive 3 castes are found :
(a) Fertile female called queen.
(b) Fertile male called drone.
(c) Sterile female called worker.
Generally Queen lays two types of eggs- fertilized and unfertilized eggs. From the fertilized eggs either the queen (fertile female) or the worker (sterile female) can formed while from the unfertilized eggs only males are developed. Queen develops eggs by meiosis or reduction cell division while the haploid male develops gametes only by mitosis process. As a result of union of male and female gametes queen or worker may developed. The males are formed by a process of parthenogenesis.
Q.3. Briefly discuss, mentioning all the changes held in an angiosperm flower subsequent to pollination and fertilization with necessary diagrams.
Ans : In angiosperms, the pollen grain is transferred from another to the stigma where the pollen grain germinate and forms a pollen tube which leads the male gamete to meet the ovum is the ovary. Finally in the ovary, fertilization takes place.
Again in dioecious animals, male and females are found in different individuals where male gametes are to transfer to the female body. In side the female body fertilization takes place. It is done by the means of sexual reproduction. For this purposes the male gametes are produced in nature.
But in plants, for the transfer of pollen grains, they become sticky so that they can easily do the pollination.
Q.4. In the plants like Bryophyllum, Potato, Ginger, Mint etc. is it possible to consider vegetative propagation as a type of asexual reproduction. If it is so justify the statement with reasons.
Ans : In Bryophyllum, potato, ginger, mint etc. vegetative propagation is a mode of reproduction where new plant is developed from any part of the plant body. For example, in Bryophyllum, the leaf bud is developing a new plant body, in potato the eye can form a new plant, in ginger the rhizome can develop the new plant and in mint the new plant develops from the bud of each node. So, we can say that only by vegetative propagation these can multiply i.e. by asexual mode of reproduction.
Q.4. “Fertilization is not an obligatory event for fruit formation in certain plants.” Explain the statement with of examples.
Ans : We know that for the formation of fruit, fertilization is essential specially in angiosperms. After the fertilization the ovary is transformed into fruit and the ovule is transformed into seed. But in some plants fruit may develop without the fertilization process from the ovary and then this type of fruit is called parthenocarpic fruit as it is formed by parthenogenesis process only. It is also called as false fruit. It is found in Apple. Here actually the thalamus is modified into fruit in place of ovary.
Q.5. Explain why internal fertilization is found to be more successful than the external fertilization in the living bodies?
Ans : When the fertilization takes place inside the female body then it is called as internal fertilization and when it is taking place in the external medium i.e. water then it is called as external fertilization.
In the animals/organisms where internal fertilization is taking place there the male gametes are released in the female body and make sure to fertilization. But in the animals where external fertilization is taking place, there the male gametes are released in the medium and females also releases their gametes in that medium.
In case of internal fertilization, it is a sure short process but in external fertilization there is no certainty. Hence males gametes number should be several times more than the animals/organisms which fertilize internally. Hence internal fertilization is called more successful than the external fertilization.
Q.7. Mention atleast three points of differences found between asexual and sexual reproduction of living organisms.
Ans : Difference between Asexual and Sexual Reproduction :
| Asexual Reproduction | Sexual Reproduction | ||
| 1. | It is found in lower group of organisms. | 1. | It is found in higher group of organisms. |
| 2. | Here only one parent is involved. | 2. | Here both the parents are involved. |
| 3. | Here multiplication is taking place more. | 3. | Here less no. is produced. |
| 4. | No meiosis cell division takes place. | 4. | Meiosis cell division takes place. |
Q.8. Why higher organisms have resorted to sexual reproduction in spite of their complexity in all respect.
Ans : Sexual reproduction is a complex but slow process as compared to the asexual reproduction. Because, here fusion of male and female gametes takes place. Due to the fusion of male and female gametes, non identical offsprings are formed. In case of higher organism they can multiply when they attain the maturity. The sexuality develops along with the maturity. Thus these animals go for reproduction. But the reproduction in higher animals where sexual method is followed there the process is more complicated and very slow process. Although it is elaborate, complex and slow but the animals follow for the continuation of their life. Moreover very less number of offsprings are produced and after a long interval which have large life span also.
Q.9 . Give the definition of Juvenile phase, Reproductive phase and Senescence phase of an organism?
Ans : (i) Juvenile Phase : All organisms have to reach a certain stage of growth and maturity in their life, before they can reproduce sexually. These period of growth is called juvenile phase or vegetative phase.
(ii) Reproductive Phase : Reproductive stage in plants is represented by appearance of flowers. In animals the end of juvenile phase is indicated by many of them showing morphological and physiological changes prior to active reproductive behaviour.
(iii) Senescence Phase : The end of reproductive phase is one of the parameters of senescence or old stage. At this stage, body metabolism is slowed down and ultimately this stage leads to death.
Q.10. What do you mean by external and internal fertilization? Mention the disadvantages of external fertilization.
Ans : External Fertilization: The fertilization i.e. union of male gamete and female gamete when takes place in the external medium like water is called the external fertilization. It is found in fish, frog etc.
Internal Fertilization : When the fertilization takes place in side the female body i.e. mothers womb then it is called internal fertilization it is found in all mammals.
Disadvantages of External fertilization:
(i) It is not a sure shot process because it is dependent on the medium.
(ii) Here rate of production of male gametes should be several times more than these where internal fertilization takes place.
(iii) It is a wasteful process.
(iv) It is always found only in aquatic animals.
(v) After fertilization also the role of survivility not is very less.
(vi) The medium may not support the gametes for the fertilization process.
Q.11. What is meant by vegetative propagation? Discuss the importance of vegetative propagation in agriculture.
Ans : The vegetative like roots, stems and leaves can form a new plant body and it is called as vegetative propagation.
Vegetative propagation is important for the following reasons:
(a) Vegetative propagation has great survival value in nature.
(b) The plants raised through vegetative propagation can attain maturity within a short period.
(c) In agricultural field it plays two major role-firstly multiply the plants in rapid way and secondly it maintains the genetic qualities of the plant.
(d) During unfavourable condition also we can multiply the plant by vegetative way of multiplication.
Q.12. Explain how the meiotic process of cell division can be interlinked with the process of gametogenesis?
Ans : Meiosis cell division is the division where chromosome number is reduced to half and hence it is called as reduction cell division.
Generally the gametes are haploid but develops from the diploid cells in the reproductive organs. The cells undergoes a series of cell division which is called meiosis to reduce the chromosome number to half.
The process of formation of gametic from the diploid (2n) cells is called gametogenesis. The gametogenesis involves the process meiosis cell division by which from the diploid gamete mother cell (2n), haploid gametes (n) are formed. Hence we can conclude that meiotic process of cell division and gametogenesis has interlink.
Q.13. Explain that Embryonal protection and care comparatively better in Viviparous than Oviparous organisms.
Ans : In oviparous animals, the eggs are laid outside and whole of the period of embryonic development is exposed to harmful environment and biological factors, So chances of death are high in such cases. But in viviparous, the embryo is cared by the mother a female animal inside her body where the embryo has better chance of survival.
IV. QUES TION FOR (5 MARKS) (EXPLANATORY)
Q.1. What are the different events takes place in the process of sexual reproduction of an angiosperm plants. Describe briefly all the events with all necessary diagrams’.
Ans : In angiosperms, the different events that takes place in the process of fertilization can be divided into 3 parts-pre-fertilization, fertilization and post fertilization events.
(i) Pre-fertilization event: The pre fertilization events can be divided into two parts.
(ii) Gametogenesis : It involves the formation of gametes which are haploid and formed from diploid gametogonia by the process of meiosis. The gametogenesis may be of spermatogenesis or oogenesis.
Gamete Transfer: For fertilization both the gamete should unite together and here the motile male gamete coine to female gamete by any means. The transfer of male gamete a pollen grains from other to the stigma is done by self a with the help of other agents- which is called as pollination.
The pollination may be of two types self pollination and cross pollination. Cross pollination is done by agents like air, water, insects, other animals like man etc.
(i) Fertilization : Fusion of male and female gamete is called the syngamy and the mechanism of union of male and female gamete is called the fertilization. The haploid cells (n) combine together to form the diploid (2n) animal or organism.
(ii) Post Fertilization Events : Post Fertilization events include the formation of zygote and embryogenesis.
(a) Zygote : As a result of union of male and female gametes together, a diploid zygote is formed. It is, the first resultant of sexual reproduction.
(b) Embryogenesis : under goes a number of division which is called the cleavage and finally form a ball like structure called morula. Then it divides and form the embryo of the organism.
In angiosperm they develop seed. It is formed from the ovule and whole zygote is modified to embryo.
Q.2. What is post fertilization phase. Describe briefly with of diagrams the post fertilization changes held in an angiosperm flower.
Ans : In flowering plants zygote is formed inside the ovule. After fertilization, sepals, petals and stamens of the flower wither and fall off.
The Pistil remains attached to the flower. Zygote formes and the embryo and ovule having embryo forms the seed. Ovary wall develop into fruit wall (pericarp). Ovary develops into fruit. Pericarp is protective in function. After dispersal of fruits and seeds, seed germinate to form new plants in suitable germinating conditions.
Q.3. Although sexual reproduction is a long, energy – intensive complex form of reproduction, many groups of organisms prefers this mode. Why this is sco gives the reasons.
Ans : Sexual reproduction is found in most of the organisms. Even the organisms which depend upon asexual reproduction for their multiplication like algae and fungi, shift on to sexual mode of reproduction before the onset of adverse conditions. It is probably that gametes appeared from asexual spores under unfavourable conditions. Fusion of gametes had resulted in pooling of resources and combination of genetic potentialities of two. At the time of origin of sex benefits of this accidental fusion came to stay in life cycle. It is called a hunger theory of sex. These fusing gametes got specialized with evolution in higher organisms and gave rise to different types of heterogametes.
Q.4. Some plants like Rose produces large attractive bisexual flowers but they seldom produce fruits. Give the reasons for failure of fruit formation in this type of plants.
Ans : Rose is a neked seeded plant and so its seed is not found in side the fruit. Here the zygotes develops into embryo and ovules develops into seeds. But the ovary is unable to develop the fruit. So there is no fruit in some flowering plants like rose, but seldom they produce the fruit after fertilization.
Q.5. Define the different forms of sexuality found in Angiospermic plants. Explain the each type citing examples mentioning their common and scientific names.
Ans : On the basis of sexuality, the angiosperm plants are classified into :
(a) Unisexual Plant : The individual plant bears only one sex, either male or female. For e.g.. Papaya, cucurbita.
(b) Bisexual Plant : The plants which contains both the sexes in the single individual is called bisexual plant. Here the flower contains both male and female reproductive port together. For eg. coconut.
Q.6. Although Rose plants produce large, attractive bisexual flowers but they seldom produce fruits. Discuss the reasons for failure of fruits formation in Rose.
Ans : Rose is naked seeded plant and so its seed is not found inside the fruit. Here the zygotes develops into embryo and ovules develops into seeds. But the ovary is unable to develop fruit. So there is no fruit in some ring plants like rose, but seldom they produce the fruits after fertilization. Generally the multiply buy vegetative methods or asexual methods only.
Q.7. Describe with suitable examples the different modes of asexual reproduction found in Animals.
Ans : The development of female gametes into new individuals without the fertilization process is known as asexual reproduction. Sometimes it is also called as somatogenic reproduction.
Asexual reproduction may be of following types :
(i) Binary fission : It is the simplest division where cell is divided into two equal parts. It is generally found in lower group of organisms or animals. The binary fission may be of transverse binary fission which is found in Amoeba or may be longitudinal fission which is found in euglena and in some corals.
(ii) Multiple fission : It is very common among amoeba where the cell is divided by binary fission but tal:ing place in rapid way, producing numerous daughter amoeba. It is also called as sporogony.
(iii) Budding : Here a small bud develops and from it they can multiply. When getting mature, the buds get detached from the parent body an perform and independent life eg. Hydro, Sycon, Planaria etc.
(iv) Plasmotomy: Here cytoplasm divides two or more parts but without the nuclear division and hence each daughter cell has a few nuclei.
(v) Gemmule formation: Asexual reproduction occurs in fresh mater sponges by the formation of gemmules. Gemmules are composed of undifferentiated cells which contain some reserved food materials. When favourable conditions come again, gemmules hatch into the adult.
(vi) Regeneration: Several organisms have the power of regeneration. The organisms can regenerate a part of the body or the whole body. It is found sponge and planaria along with coelenterata and echinodermata.
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