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Q1. What is meant by monosporic development of female gametophyte?  

Solution

When the female gametophyte (embryo sac) develops from a single megaspore, it is called monosporic development. Usually, in most angiosperms, the megaspore mother cell divides by meiosis to form four haploid megaspores arranged in a linear fashion. The three haploid megaspores situated towards the micropyle degenerate, while one remains functional which develops into the female gametophyte.  

Q2. “Incompatibility is a natural barrier in the fusion of gametes”. Justify the statement. 

Solution

1. Nature has developed both structural as well as chemical barriers which restrict fertilisation in organisms. 2. Chemical incompatibility of pollen prevents fertilisation between unrelated plant species. 3. Structural barriers like placement of anthers and stigma at different positions prevent self pollination and promote cross pollination.

Q3. Name the type of flower which favours cross-pollination.

Solution

The flowers which favour cross-pollination are chasmogamous flowers. They develop exposed anthers and stigma.

Q4. Even though each pollen grain has two male gametes, why are at least 10 pollen grains and not 5 pollen grains required to fertilise 10 ovules present in a particular carpel?

Solution

Even though each pollen grain has two male gametes, atleast 10 pollen grains required to fertilise 10 ovules present in a particular carpel instead of 5 pollen grains because only one male gamete is involved in syngamy or the fusion of male gamete with the egg cell.

Q5. In the same species of Asteraceae and grasses, seeds are formed without the fusion of gametes. Mention the scientific term for such a form of reproduction.

Solution

In the same species of Asteraceae and grasses, seeds are formed without the fusion of gametes. This form of reproduction is called apomixis. 

Q6. If the diploid number of chromosomes in an angiospermic plant is 16, mention the number of chromosomes in the endosperm and antipodal cell.

Solution

The diploid (2n) number of chromosomes in an angiospermic plant is 16. So, the number of chromosomes in endosperm (3n) is 24 and that in antipodal cells (2n) is 16. 

Q7. How will you go about increasing the population of a certain plant introduced into a new environment which neither produces seeds nor responds to vegetative propagation? 

Solution

We can increase the population of a certain plant introduced into a new environment which neither produces seeds nor responds to vegetative propagation by using artificial techniques like tissue culture, meristem culture etc. 

Q8. Why is the process of fertilisation in a flowering plant referred to as double fertilisation? Explain.

Solution

Fertilisation in flowering plants is referred to as double fertilisation because both the male gametes of the same microspore take part in fusion. One fuses with the egg to form the diploid zygote, and the other fuses with the two polar nuclei (or secondary nuclei) to form the triploid primary endosperm nucleus.

Q9. Some plants have a mechanism of shedding of pollen before the maturation of stigma. Why? 

Solution

Some plants have a mechanism of shedding of pollen before the maturation of stigma to prevent self-pollination.

Q10. Mention the reasons for the difference in ploidy of zygote and primary endosperm nucleus in an angiosperm.

Solution

Zygote is formed by syngamy, so it is diploid in nature, and primary endosperm nucleus is formed by the fusion of secondary diploid nucleus with one of the male gamete, so it is triploid in nature.

Q11. Draw a labelled diagram of the sectional view of a mature pollen grain in angiosperms. Explain the functions of its different parts.

Solution

Structure of mature pollen grains in angiosperms.       Functions of the parts of pollen grain: A mature pollen grain has a two-layered wall—the outer exine and inner intine. The wall encloses a large vegetative cell containing vegetative nucleus and a lenticular generative cell. Their functions are as follows: 1. Exine: The outer thick exine layer is made up of sporopollenin which is resistant to physical and biological decomposition. It provides protection during the hazardous journey of pollen from the anther to stigma. There are one or many germ pores on the pollen surface which are directly or indirectly associated with its germination. 2. Intine: The intine is pecto-cellulosic in nature. It is associated with the formation of the pollen tube. 3. Vegetative cell: The vegetative cell is large and contains abundant food reserve. It has a large vegetative nucleus. The function of the vegetative cell is to provide the medium for the movement of male gametes inside the pollen tube. 4. Generative cell: The generative cell cytoplasm is highly reduced but it contains the usual cell organelles. It divides mitotically to produce two functional male gametes.

Q12. The microscopic pollen grains of the past are obtained as fossils. Mention the characteristic of pollen grains that makes it happen.

Solution

The outer exine layer of pollen grains is coated with wax and sporopollenin which is hard and not easily degraded by micro-organisms. This property of exine causes the pollen grains to stay intact in its fossilised form.

Q13. Give reasons why (i) Most zygotes in angiosperms divide only after certain amount of endosperm is formed. (ii) Groundnut seeds are exalbuminous and castor seeds are albuminous. (iii) Micropyle remains as a small pore in the seed coat of a seed. (iv) Integuments of an ovule harden and the water content is highly reduced as the seed matures. (v) Apple and cashew are not called true fruits.

Solution

(i) Endosperm is the food laden tissue formed during the development of angiospermous seed which provides essential nutrients to the growing embryo and also the young seedling at the time of seed germination. So, most zygotes in angiosperms divide only after certain amount of endosperm is formed. (ii) The seeds in which the endosperm is used up are called exalbuminous seeds. In groundnut, the endosperm is used and the reserve food material is stored in cotyledons. So, groundnut seeds are exalbuminous. The seeds having ample amount of endosperm tissue are called albuminous seeds. Castor seeds have persistent endosperm. So, castor seeds are albuminous.   (iii) Double fertilisation in angiosperms brings about some changes in the ovule during the development of seed. The micropyle remains in the form of a fine pore on the surface of seed to allow the entry of water during seed germination.   (iv) Integuments of an ovule harden and the water content is highly reduced as the seed matures to ensure the survival of seeds.   (v) The fruit derived from the ovary of a flower not associated with any non-carpellary part is called a true fruit. In apple and cashew, the main edible part of the fruit is the fleshy receptacle. So, they are not true fruits. Such fruits derived from the ovary along with other accessory floral parts are called false fruits.

Q14. Outer envelope of a pollen grain is made of a highly resistant substance. What is that substance and at which particular point is it absent?

Solution

The outer envelope of a pollen grain is made of a highly resistant substance called sporopollenin. Sporopollenin is absent at the germpore. 

Q15. In angiospermic plants, before formation of microspore the sporogenous tissue undergoes cell division. (a) Name the type of cell division. (b) What would be the ploidy of the cells of tetrad? 

Solution

(a) The type of cell division involved is meiosis or meiotic division. (b) The cells of the tetrad would be haploid in nature.  

Q16. Give the scientific name of a plant which came to India as a contaminant with imported wheat and caused pollen allergy.

Solution

Parthenium, which is a noxious weed, came to India as a contaminant with imported wheat and caused pollen allergy. 

Q17. Which is the triploid tissue in a fertilized ovule? How is the triploid condition achieved?

Solution

Endosperm is the triploid tissue formed by the primary endosperm nucleus containing cell resulting from the fusion of the secondary nucleus with the nucleus of one of the male gametes of pollen grain.

Q18. Among the animals, insects particularly bees are the dominant pollinating agents. List any four characteristic features of insect-pollinated flowers.

Solution

Characteristic features of insect-pollinated flowers: 1. Flowers are large. 2. Colourful petals of flower. 3. Presence of fragrance. 4. Rich in nectar.

Q19. Banana is a parthenocarpic fruit whereas oranges show polyembryony. How are they different from each other with respect to seeds? 

Solution

Banana fruits are seedless. Such fruits are called parthenocarpic, i.e., they produce embryo without fertilisation. The seeds of oranges have many embryos of different sizes and shapes. The orange seeds develop many embryos due to polyembryony.

Q20. Why are pollen grains produced in enormous quantity in maize?

Solution

Pollen grains are produced in enormous quantity in maize to ensure pollination as maize is pollinated by wind. 

Q21. Mention the pollinating agent of an inflorescence of small dull coloured flowers with well exposed stamens and large feathery stigma. Give any one characteristic of pollen grains produced by such flowers.

Solution

Small dull coloured flowers do not attract insects and birds. Therefore, these flowers produce large amount of small pollen grains which are dispersed in air and stick to large feathery stigma, Such flowers are thus, wind-pollinated.

Q22. Draw a longitudinal section of a post-pollinated pistil showing the entry of pollen tube into a mature embryo sac. Label the filiform apparatus, chalazal end, hilum, antipodals, male gametes and secondary nucleus.

Solution

Longitudinal section of a post-pollinated pistil showing the entry of pollen tube into a mature embryo sac.    

Q23. In a young anther, a group of compactly arranged homogenous cells were observed in the centre of each microsporangium. What is the name given to these cells?

Solution

Sporogenous tissue comprises of compactly arranged homogenous cells observed in the centre of each microsporangium. 

Q24. (a) Draw a labelled longitudinal view of an albuminous seed. (b) How are seeds advantageous to flowering plants?

Solution

(a) Longitudinal view of an albuminous seed       (b) Seeds contain food to nourish the embryo during germination and possess better adaptive strategies for dispersal to new habitats. These are formed by sexual reproduction with new variations and better genetic combinations. So, the seeds advantageous to flowering plants.

Q25. A bilobed and dithecous anther has 100 microspore mother cells per microsporangium. How many male gametophytes can it produce?

Solution

Each microsporangium has 100 microspore mother cells which form 400 microspores by meiosis (100 × 4). In an anther, there are four microsporangia. So, the total number of microspores will be 4 × 400 = 1600. As each microspore forms one male gametophyte, 1600 male gametophytes can be produced.

Q26. Pollen grains of water-pollinated species have a special characteristic for protection from water. Which is this characteristic?

Solution

Pollen grains of water-pollinated species show the presence of mucilaginous covering which offers them protection from water. 

Q27. An anther with a malfunctioning tapetum often fails to produce viable male gametophytes. Why?

Solution

Male gametophytes remain inviable because a malfunctioning tapetum cannot provide proper and adequate nutrition for microspore development. So, an anther with a malfunctioning tapetum often fails to produce viable male gametophytes.

Q28.  ‘Dehydration of seed increases their shelf life’—Explain. 

Solution

Dehydration reduces the water content and thus, minimises the metabolic activities that take place inside the seed which increases the shelf life of seeds.

Q29. Explain the process of artificial hybridisation to get improved crop variety in: (i) plants bearing bisexual flowers (ii) female parent producing unisexual flowers. 

Solution

If a plant breeder desires to cross a particular plant with desired pollen grains, a bisexual flower is artificially transformed into a female flower by removing its stamens in bud condition without affecting the female reproductive organs. This process is called emasculation. The emasculated flower is immediately enclosed in a bag to prevent pollination by unwanted pollen. This process is called bagging. Then, mature and viable pollen grains are collected from the male parent, the bag is opened and the pollen grains are dusted on the stigma. The bag is replaced immediately. The technique of emasculation is applied only when artificial pollination is carried out in a bisexual flower. If the female parent produces unisexual flowers, emasculation is not needed. The unisexual flower is bagged before the flowers open.

Q30. Differentiate between microsporogenesis and megasporogenesis. What type of cell division occurs during these events? Name the structures formed at the end of these two events.

Solution

Microsporogenesis: Process of formation of microspore from the pollen mother cell. Megasporogenesis: Process of formation of megaspore from megaspore mother cell. Meiotic division occurs in both the events. Microsporogenesis results in the formation of pollen grains, while megasporogenesis results in the formation of megaspores.

Q31. Trace the development of microsporocyte in the anther to a mature pollen grain.

Solution

As the anther develops, the cells of the sporogenous tissue undergo meiotic divisions to form microspore tetrads. As each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad, each one is a potential pollen or microspore mother cell. The process of formation of microspores from a pollen mother cell (PMC) through meiosis is called microsporogenesis. As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains. Inside each microsporangium, several thousands of microspores or pollen grains are formed that are released with the dehiscence of the anther.

Q32. Name the cell from which the endosperm of coconut develops. Give the characteristic features of endosperm of coconut.   

Solution

Endosperm of coconut develops from primary endosperm cell which divides repeatedly to form a triploid endosperm tissue. The endosperm of coconut is made up of coconut water which is free-nuclear stage and white kernal is cellular endosperm.

Q33. The flowers of brinjal are referred to as chasmogamous while that of beans are cleistogamous. How are they different from each other?  

Solution

Flowers of brinjal are similar to flowers of other species where anthers and stigma are exposed. Such flowers are called chasmogamous flowers. On the other hand, the flowers of beans remain closed to ensure self-pollination. Such flowers which remain closed so that cross-pollination does not occur are called cleistogamous flowers.

Q34. Mention two strategies evolved to prevent self-pollination in flowers.

Solution

Cross-pollinating flowers develop the following strategies to prevent self-pollination : 1. Protogyny (when gynoecium matures earlier than androecium) or Protandry (when androecium matures and sheds pollen before maturation of gynoecium) 2. Self incompatibility

Q35. Arrange the following in the correct developmental sequence: Male gamete, potential pollen mother cell, sporogenous tissue, pollen grains, microspore tetrad.

Solution

Sporogenous tissue potential pollen mother cell  microspore tetrad pollen grains male gamete.

Q36. Name the common function that is performed by cotyledons and nucellus. 

Solution

Nutrition is provided to the embryo by cotyledons and the embryo sac by nucellus, respectively.

Q37. (a) Draw a schematic labelled diagram of a fertilised embryo sac of an angiosperm.

Solution

(a) Fertilised embryo sac of an angiosperm        

Q38. Draw a vertical section of a maize grain and label (i) pericarp (ii) scutellum (iii) coleoptiIe and (iv) radicle.

Solution

Vertical section of maize grain      

Q39. Why pea flowers produce assured seed sets? Give reasons.

Solution

Pea flowers produce assured seed sets because they are cleistogamous, autogamous and homogamous. Hence, self-pollination occurs before the flowers open up at maturity.

Q40. (a) Draw the embryo sac of a flowering plant and label: (i) Central cell. (ii) Chalazal end. (iii) Synergids. (b) Name the cell that develops into an embryo sac and explain how this cell leads to the formation of embryo sac. (c) Mention the role played by the various cells of the embryo sac. (d) Give the role of filiform apparatus.

Solution

(a) Embryo sac of a flowering plant.       (b) Functional megaspore. The nucleus of the functional megaspore divides mitotically to form two nuclei which move to opposite poles and form the 2-nucleate embryo sac. (c) Egg: Fuses with the male gamete to form zygote or the future embryo. Synergid: Absorption of nutrients, attracts and guides the pollen tube. Central cell: After fusion with the second male gamete, it forms the primary endosperm cell which gives rise to the endosperm. (d) The filiform apparatus guides the entry of pollen tube into the embryo sac.