1

Q1. What is protogynous condition? Give one example.

Solution

In the protogynous condition, the ovaries mature earlier than the testes. Example: Sycon

Q2. Why do plants like bryophytes and pteridophytes produce a large number of male gametes? 

Solution

In bryophytes and pteridophytes, pollination is facilitated by water. The male gamete is transferred to the female gamete through aquatic medium. In order to ensure sufficient number of male gametes reaching the female gamete and also to account for losses during transmission, the male gametes have to be produced in large numbers in bryophytes and pteridophytes. 

Q3. Do haploid organisms have meiosis in their lifecycle? If yes, state when does it occur? 

Solution

Yes. A haploid organism produces gametes by mitotic division. These gametes fuse to form a diploid zygote, which has to undergo mitosis to form haploid progeny.

Q4. How is the process of pollination different from fertilisation?

Solution

The transfer of pollen from the anther to the stigma is called pollination. Fertilisation is the fusion of the male gamete and the female gamete (syngamy) to form a zygote. This takes place with the help of the pollen tube, which travels through the style to reach the embryo sac in the ovule present in the ovary. 

Q5. Describe the post-fertilisation changes in a flower.

Solution

After fertilisation, the sepals, petals and stamens wither and fall off. In some cases, the sepals remain persistent. The ovules are transformed into seeds, the zygote becomes an embryo and the ovary becomes a fruit.

Q6. Distinguish between asexual and sexual reproduction.

Solution

Asexual and sexual reproduction Asexual reproduction Sexual reproduction 1. Involves the participation of a single individual parent. 1. Involves the participation of two separate parents. 2. Occurs without the formation of gametes. 2. Requires the formation of gametes. 3. Does not involve meiosis or reduction division. 3. Involves meiosis or reduction division. 4. Does not involve sexual fusion or fusion of gametes. Zygote is not formed. 4. Requires fertilisation to take place between two opposite gametes leading to the production of a zygote.  5. Offspring produced are genetically similar to the parents. They do not show variations. 5. Offspring produced exhibit genetic variation and are different from either of the two parents. 6. Very quick method of multiplication of individuals. 6. Very slow method of multiplication of individuals.  

Q7. What is budding? Describe gemmulation in Spongilla.

Solution

Budding is a type of asexual reproduction in which one or more unicellular or multicellular outgrowths called buds are formed on or inside the parental body. Budding is seen in sponges, coelenterates, annelids and tunicates. In Spongilla, budding is endogenous as a number of buds called gemmules are formed inside the parental body. Each gemmule of Spongilla is a mass of undifferentiated cells called archaeocytes surrounded by a protective coat of amphidisc spicules. Gemmules help in perennation and dispersal. During favourable conditions, archaeocytes come out of a gemmule through a micropyle and form a new sponge. 

Q8. What is menstrual cycle?

Solution

A series of cyclic changes occurring in the ovaries of the female genital tract every month constitute the menstrual cycle.

Q9. Mention the site where syngamy occurs in amphibians and reptiles.

Solution

In amphibians, syngamy occurs in water outside the body of the organism (external fertilisation and external development). In reptiles, syngamy occurs inside the body of the female (internal fertilisation and external development).

Q10. Distinguish between binary fission and multiple fission.

Solution

Binary fission and multiple fission   Binary fission Multiple fission 1. Forms two daughter individuals 1. Forms many daughter individuals 2. Divides only once 2. Divides repeatedly 3. No residue is left 3. Residue is left 4. Takes place in favourable conditions 4. Takes place in favourable as well as unfavourable conditions 5. Immortality is present 5. Immortality is absent Example: Amoeba reproduces by binary fission Example: Plasmodium reproduces through multiple fission  

Q11. Coconut palm is monoecious, while date palm is dioecious. Why are they called so?

Solution

In coconut palm, both male and female flowers develop on the same individual. This condition is called monoecious. In date palm, the male and female flowers develop on separate individuals. This condition is called dioecious.

Q12. Discuss the significance of vegetative propagation.

Solution

The significance of vegetative propagation is as follows: 1. Characters of the parent plant are preserved. A good variety produced can be propagated by vegetative means. 2. It is a quicker method. 3. It is an easier and cheaper method of propagation. 4. It is the only method of reproduction and perpetuation in plants which does not produce viable seeds. 5. It is easier to get rid of pathogen from any part of the plants by vegetative propagation. 6. Flowers produced on the scion are much superior in quality. 7. It is a less expensive method of multiplying plants. 

Q13. Why is reproduction essential for organisms?

Solution

Reproduction is essential for organisms because it enables the continuity of the species generation after generation.

Q14. Why is vegetative reproduction practised for growing some types of plants?  

Solution

Vegetative reproduction is practised for growing some types of plants because (i) Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds. (ii) Vegetative propagation is also applied to plants such as banana, orange, rose and jasmine which have lost the capacity to produce seeds. (iii) All plants produced by vegetative propagation are genetically similar to the parent plant. 

Q15. Both meiosis and fertilisation are essential to maintain chromosome number constant. Why?

Solution

Meiosis occurs and transforms diploid gametogonia into haploid gametes, while fertilisation involves the fusion of gametes and restores diploidy. If there is no meiosis during gametogenesis, then the gametes will be diploid and the individual produced will be a tetraploid (4n). However, when gametic meiosis is not followed by fertilisation, then the individual formed will be haploid (n). So, meiosis and fertilisation are two important processes involved in sexual reproduction which collectively maintain the chromosome number constant from generation to generation. 

Q16. Write the modes of asexual reproduction in the following organisms: Bryophyllum, Potato, Yeast, Rhizopus, Penicillium, Hydra

Solution

The modes of reproduction are as follows: 1. Bryophyllum: Reproduces asexually by formation of marginal adventitious buds in mature leaves 2. Potato: Buds in the eyes of potato tuber grow to form aerial shoots 3. Yeast: Budding 4. Rhizopus: Sporangiophores formed inside sporangia 5. Penicillium: Conidia formed on conidiophores 6. Hydra: Budding

Q17. Mention the advantages of artificial vegetative propagation.

Solution

Advantages of artificial vegetative propagation: 1. Allows quick production of new plants 2. Allows combination of good qualities of two different varieties 3. Provides an excellent method for propagating desirable varieties of plants economically with less attention and in comparatively shorter time 

Q18. What are gemmules? State their functions.

Solution

Gemmules are internal buds formed inside freshwater sponges, e.g. Spongilla. These are formed during unfavourable conditions and help in perennation and dispersal. 

Q19. Why is the offspring formed by asexual reproduction referred to as a clone?

Solution

Asexual reproduction results in the production of offspring which are morphologically and genetically similar. Such individuals are referred to as clones.

Q20. Why do internodal segments of sugarcane fail to propagate vegetatively even when they are in contact with damp soil?

Solution

Intermodal segments of sugarcane fail to propagate vegetatively even when they are in contact with damp soil due to the absence of adventitious buds.

Q21. Which type of asexual reproduction is found in Spongilla?

Solution

Gemmulation or internal budding is found in Spongilla.

Q22. State one difference between oviparous and viviparous animals.

Solution

Oviparous animals lay eggs (e.g. birds), while viviparous animals give birth to their young ones (e.g. humans, cats, dogs). 

Q23. What is external fertilisation? State its advantages and disadvantages.

Solution

In external fertilisation, syngamy occurs in the external medium (water), which is outside the body of the organism. Examples: Majority of algae, fish and amphibians   Advantage of external fertilisation: Organisms exhibiting external fertilisation show great synchrony between the sexes and release a large number of gametes into the surrounding medium in order to enhance the chances of syngamy.   Disadvantage of external fertilisation: The offspring are extremely vulnerable to predators threatening their survival up to adulthood. 

Q24. Define: (i) Juvenile phase (ii) Reproductive phase (iii) Senescent phase

Solution

(i) Juvenile phase is the period of growth between the birth of an individual up to maturity. (ii) Reproductive phase starts after the juvenile phase and remains up to the stage when an organism is capable of reproduction. (iii) Senescent phase is the phase of ageing when an organism loses its capacity of reproduction. In plants, it is characterised by yellowing and leaf fall.

Q25. Do you agree with the statement that only asexual reproduction can give rise to individuals resembling their parent? Support your answer with an example. 

Solution

No. There are examples of sexual reproduction taking place without actual fertilisation which produces individuals resembling their parents. Examples: Parthenogenesis in rotifers, unfertilised honeybee eggs develop into adults 

Q26. What are the different modes of vegetative propagation in flowering plants?

Solution

In flowering plants, vegetative propagation occurs by modified tuberous roots having adventitious buds, underground modified stems, creeping stems, leaves, bulbils and turions.

Q27. Write short notes on (a) Embryogenesis (b) Syngamy

Solution

(a) Embryogenesis: The process of development of the embryo from the zygote is called embryogenesis. Development of the offspring from reproductive units such as buds or fragments in asexual reproduction is called blastogenesis. Both embryogenesis and blastogenesis have the same target - to develop a new individual by the process of cell division and differentiation. (b) Syngamy: Syngamy is the process of fusion of one male gamete and one female gamete to form a zygote. It involves close association of gametes and all their acts resulting in the formation of a zygote including the fusion of nuclei. The fertilisation, however, includes all the associated events which ultimately lead to syngamy.

Q28. Name any three changes seen in human males and females which are indicative of reproductive maturity.

Solution

  Changes in males Changes in females 1. Testes mature and start producing sperms   1. Ovaries mature and start producing ovum; menstrual cycle begins   2. Pectoral girdle (shoulder girdle) grows   2. Pelvic girdle (hip girdle) becomes broad   3. Development of moustache and beard   3. Enlargement of breasts  

Q29. Which is a better mode of reproduction, sexual or asexual? Why?

Solution

Sexual reproduction is a better mode of reproduction as compared to asexual reproduction because it involves meiosis and the fusion of male and female gametes. Such a fusion involving two parents results in offspring which are not identical to the parents. It also causes variation which is essential for evolution and survival of the species under diverse changes in environmental factors.

Q30. Rearrange the following events of sexual reproduction in the sequence in which they occur in a flowering plant: Embryogenesis, Fertilisation, Gametogenesis, Pollination

Solution

Events of sexual reproduction in a flowering plant: Pollination, Gametogenesis, Fertilisation, Embryogenesis

Q31. What are vegetative propagules? Give two examples.

Solution

In plants, the units or structures of vegetative propagation which are capable of giving rise to new offspring are called vegetative propagules. Examples: Runner, rhizome, sucker, tuber, offset and bulb

Q32. Why are human beings called unisexual organisms?

Solution

Human beings are called unisexual organisms because the male and female sexes are separate.

Q33. What is vegetative propagation? Give two examples.

Solution

Vegetative propagation involves the production of new individuals from vegetative plant propagules such as buds, tubers and rhizomes. Examples: (1) Potato tubers possess buds which grow into new plants. (2) Adventitious buds of Bryophyllum leaves grow to form new plants.

Q34. Differentiate between self-pollination and cross-pollination.

Solution

Self-pollination and cross-pollination   Self-pollination Cross-pollination 1. It is the transfer of pollen grains from the anther to the stigma of the same flower. 1. It is the transfer of pollen grains from the anther of one flower to the stigma of another flower of a different plant of the same species. 2. It does not require any external agent, such as wind, water and insects, to carry out pollination. 2. It requires an external agent for pollination to occur. 3. It can take place even when the flower is closed. 3. It can occur only when the flower is open. 4. In self-pollinated flowers, the anther and stigma mature at the same time. 4. In cross-pollinated flowers, the anther and stigma mature at different times. 5. It preserves parental characters. 5. It does not preserve parental characters. 6. New varieties are not possible. 6. New varieties can be produced. 7. As new variations are not possible, the offspring cannot adapt to changing environmental conditions. 7. As new variations are possible, the offspring are healthier and are able to adapt to changing environmental conditions.  

Q35. What is the basic difference between binary fission and budding?

Solution

In case of binary fission, the unicellular organism divides by cell division to give rise to two equal and similar offspring. In case of budding, the organism produces a small bud which gradually grows in size and then separates from the parent.

Q36. Define: Life span

Solution

The period from birth to the natural death of an organism represents its life span.

Q37. Name the three phases of gametogenesis.

Solution

Multiplicative phase, growth phase and maturation phase are the three phases of gametogenesis.

Q38. Name the events of sexual reproduction in an angiospermic plant.

Solution

Sexual reproduction in angiosperms involves development of pollen, pollination, development of ovule, fertilisation, development of endosperm and embryo and finally the formation of fruit and seed. 

Q39. What is fission? What is the basic difference between fission in Amoeba and Paramoecium?

Solution

Fission is the division of an adult parental cell into two or more daughter cells. In Amoeba, binary fission can occur in any plane, while in Paramoecium, it occurs along a transverse plane. 

Q40. Why is banana considered a good example of parthenocarpy?

Solution

Banana is called a parthenocarpic fruit because it develops without fertilisation and is thus seedless.