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18. What is apomixis and what is its importance?

The process of development of seeds from diploid cells of nucellus tissue without the process of fertilisation is called apomixis. This process is a form of asexual reproduction that mimics sexual reproduction. Apomixis is very commonly seen in grasses. Importance of apomixis Apomixis is used by horticulturists to produce hybrid seeds. Apomixis leads to the formation of infection-free...

17. Explain the role of tapetum in the formation of pollen-grain wall.

Tapetum is the nutritive innermost layer of microsporangium that provides nutrition to the developing microspores. The role of tapetum in the formation of pollen grain wall is as follows: Tapetum secretes ubisch granules required for the formation of sporopollenin in the exine (outer wall) of pollen grain Tapetum also secretes pollenkit substances required for the formation of pollen grain wall  

16. If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?

The fruits formed as a result of parthenocarpy are generally seedless. Hence, for parthenocarpy, we can select fruits which have a lot of seeds in them. Such fruits include watermelon, orange, muskmelon, lemon etc. So we can select watermelon to induce parthenocarpy because by this method we can have seedless watermelons.

15. What is meant by emasculation? When and why does a plant breeder employ this technique?

The process of removal of anthers from the flower with the help of forceps without affecting the female reproductive parts is called emasculation. This technique is used by plant breeders to allow suggestive breeding between plants in order to produce plants with desired seeds. Hence, it can be used to prevent self-pollination or prevent cross-pollination according to the need of the breeder. 

14. Why is apple called a false fruit? Which part(s) of the flower forms the fruit?

The fruits are formed from the ovary of a flower after fertilisation. Such fruits that develop from the ovary are called true fruits. On the other hand, fruits formed from any part of the flower other than ovary are called false fruits. Apple is called a false fruit because it develops from the thalamus and not from the ovary.  The parts of flower that take part in fruit formation are ovary,...

13. Differentiate between:

        (d)  perisperm and pericarp

The differences between perisperm and pericarp are as follows:  Perisperm Pericarp     Perisperm refers to the residual persistent nucellus The pericarp is the wall of fruit derived from the ovary wall Perisperm is non-functional to the seed The function of the pericarp is the protection of inside structures It is dry  It is fleshy.   

13. Differentiate between:

        (c)  integument and testa;

The differences between integument and testa are as follows: Integument Testa          It is a pre fertilisation structure that covers the ovule It is a post-fertilisation structure that covers the seed The integument is a thin layer consisting of living cells Testa is a thick coat consisting of dead cells The integument arises from chalaza Testa is derived from the integuments  

13. Differentiate between:

         (b)   coleoptile and coleorrhiza;

The differences between coleoptile and coleorrhiza are as follows: Coleoptile    Coleorrhiza  Coleoptile refers to the protective covering that surrounds plumule Coleorrhiza is the sheath that surrounds the radicle and root cap This sheath can come out of the soil, become green and perform photosynthesis.  Coleorrhiza remains in the soil only.   

13. Differentiate between:

            (a) hypocotyl and epicotyl;

The differences between hypocotyl and epicotyl are as follows: Hypocotyl Epicotyl This is the portion of the embryo present below the cotyledon. This is the portion of embryo present above the cotyledon.  Hypocotyl ends into radicle Epicotyl ends into plumule  

12. Why do you think the zygote is dormant for sometime in a fertilised ovule?

The zygote starts developing into an embryo only when a certain amount of endosperm has developed. This is because endosperm provides nourishment to the developing embryo. Thus, a zygote remains dormant in a fertilised ovule till the endosperm has developed. 

11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.

A pollen grain produces two male gametes. Out of these, one male gamete fuses with the egg cell and produces a zygote. The second male gamete fuses with the two polar nuclei of the central cell to produce primary endosperm nucleus. Since this fusion includes three haploid nuclei, it is called triple fusion. The process of triple fusion occurs in the central cell of embryo sac. The pollen tube...

10. What is bagging technique? How is it useful in a plant breeding programme?

 

Bagging technique - Bagging refers to covering of emasculated flowers with the help of butter paper or plastic bags to avoid contamination of stigma of these flowers to undesired pollens. This technique is used during artificial hybridisation experiments. This technique is useful in breeding programmes because it prevents contamination of stigma with unwanted pollens. So, through this technique, we can allow the breeding of species according to our need and obtain superior species. 

 

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9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?

 

Self-incompatibility refers to the genetic inability of fully functional pollen grains and ovules to produce viable seeds. This is mainly due to the presence of S or self genes. If these genes are present in pollen as well as ovule, they will not be able to produce viable seeds. Self-pollination does not lead to the formation of seeds in self-incompatible species due to the presence of certain...

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

Self-pollination refers to the transfer of pollen grains from the anther of a flower to the stigma of the same flower. Continuous self-pollination can reduce the variations in the progeny and cause a reduction in the vigour and vitality. Thus, plants have developed certain mechanisms to avoid self-pollination and ensure cross-pollination. The two of these mechanisms to prevent self-pollination...

7. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.

Flowers can be of two types i.e. chasmogamous flowers or cleistogamous flowers. Chasmogamous flowers are open flowers which have their anthers and stigma exposed. These flowers facilitate cross-pollination. On the other hand, cleistogamous flowers are closed flowers whose anthers and stigmas are not exposed. Since these flowers do not open at all, only self-pollination occurs in these and...

6. With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.        

The diagram of 7- celled 8- nucleate embryo sac of plants is as follows: The female gametophyte of plants is formed from a single functional megaspore with the help of four unequal mitotic divisions. These mitotic divisions give rise to 8 nuclei. Later, these nuclei assemble into 7 cells. To both chalazal and micropylar end three cells each move. The three cells at chalaza are called antipodal...

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

The female gametophyte of flowers develops from a single functional megaspore after continuous mitotic divisions. This type of development of female gametophyte from a single uninucleate megaspore is called monosporic development of female gametophyte. 

4.  With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.

The diagram of a typical angiosperm ovule is as follows: An ovule consists of funicle, micropyle, integuments, nucellus, embryo sac, hilum, chalaza etc.  Funicle - It is the stalk of ovule which connects ovule to the placenta. Funicle is short and multicellular.  Hilum - It is the point where funicle connects the main body of the ovule.  Integuments - These are the layers that surround the...

3. Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.

The correct developmental sequence is as follows: Sporogenous tissue    Pollen mother cell  Microspore tetrad   Pollen grain   male gametes

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

Differences between microsporogenesis and megasporogenesis are as follows Microsporogenesis  Megasporogenesis The process of formation of a functional haploid microspore is called microsporogenesis. The process of formation of a functional haploid microspore is called megasporogenesis. Microsporogenesis takes place in pollen sac of the anther Megasporogenesis takes place inside the...
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