Botany Chapter-02 Textual Activities Part-02

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

Continuous self pollination leads to decrease the vigour and vitality of particular race. So flowering plants have developed may devices to discourage  Self pollination and to encourage cross pollination. Dichomy and self sterility are two most common devices that ensure cross – pollination. 

1. Dichomy – maturation of anther and stigma at different times in a bisexual flower it prevents self pollination  

2. Self sterility due to the presence of self sterility gene in some flowers. Pollen grains do not germinate on the stigma of that flowers.Ex: tobacco, potato 

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

If a pistill have functional gametes fails to set seeds following pollination with viable and fertile pollen, capable of bringing about fertilisation in another pistill. The two are said to be incompatible.this phenomena is called sexual incompatibility. It may be inter specific or intra specific. It is a gene- physiological process.  

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

• Artificial hybridisation is one of the major approaches of crop improvement programme. In such crossing experiments it is make sure that only the desired pollen grains are used for pollination and the stigma is protected from contamination (from unwanted pollen). 

• This is achieved by emasculation and bagging techniques. 

• If the female parent bears bisexual flowers, removal of anthers fron the flower bud before the anther dehisces using a pair of forceps is necessary. This step is referred to as emasculation. 

•  Emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen. This process is called bagging. 

•  When the stigma of bagged flower attains receptivity, mature pollen grains collected from anthers of the male parent.are dusted on the stigma, and the flowers are rebagged, and the fruits allowed to develop. 

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

After entering one of the synergids, the pollen tube releases the two male gametes into the cytoplasm of the synergid. One of the male gametes moves towards the egg cell and fuses with its nucleus thus completing the syngamy. This results in the formation of a diploid cell, the zygote. The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid primary endosperm nucleus (PEN) . As this involves the fusion of three haploid nuclei it is termed triple fusion. 

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

The zygote after a period of rest develops into embryo. Most zygotes remain dormant till certain amount of endosperm forms. They do so to provide assured Nutrition to the developing embryo

13. Differentiate between: 

(a) hypocotyl and epicotyl; 

(b) coleoptile and coleorrhiza; 

(c) integument and testa; 

(d) perisperm and pericarp  


• It is part of embryonal axis between plumule and cotyledon node. 

• Terminal end is epicotyl plumule 


•  Embryonal axis between cotyledon and radicle. 

• Terminal end is Hypocotyl plumule. 

(b) coleoptile  

• It protects plumule during emergence from spill. 

• It is a terminal pore for emergence of first leaf.   Coleorhizza 

•  It does not protect the radicle during emergence from soil 

• It is a solid structure.  


• Cells are living. 

• Sclerids are absent. 

• Pre – fertilized structure    Integument 

• Cells are dead 

• Rich in sclerids 

• Post fertilized structure  

(d) Perisperm 

• It is part of seed 

• Usually dry part 

• Seen in only few seeds     


• It is part of fruit  

• Fleshy part 

• Seen in all fruits  

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

In most plants, by the time the fruit develops from the ovary, other floral parts degenerate and fall off. However, in a few species such as apple, strawberry, cashew, etc., the thalamus also contributes to fruit formation. Such fruits are called false fruits.   

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

If the female parent bears bisexual flowers, removal of anthers from the flower bud before the anther dehisces using a pair of forceps is necessary. This step is referred to as emasculation. Emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen. This process is called bagging. 

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

Parthenocarpic fruits are seedless. They develop from ovary without fertilization. Banana, grapes, pineapple are selected because these seedless of units are high economic importance. The fruits in which seeds or seed part from edible portion are not selected to induce parthenocarpy.

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

The innermost wall layer is the tapetum.It nourishes the developing pollen grains. Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus.At maturity, these cells degenerate and provide nourishment. The main function of tapetum is to provide Nutrition to pollens but it also secretes some substances of utmost importance like  Qallase enzyme, pollen kit substances. 

 18. What is apomixis and what is its importance?               

In  few flowering plants such as some species of Asteraceae and grasses, have evolved a special mechanism, to produce seeds without fertilisation, called apomixis. Thus  apomixis is a form of asexual reproduction that mimics sexual reproduction. There are several ways of development of apomictic seeds. In some species, the diploid egg cell is formed without reduction division and develops into the embryo without fertilisation. Hybrid varieties of several of our food and vegetable crops are being extensively cultivated. Cultivation of hybrids has tremendously increased productivity. One of the problems of hybrids is that hybrid seeds have to be produced every year. If the seeds collected from hybrids are sown, the plants in the progeny will segregate and do not maintain hybrid characters. Production of hybrid seeds is costly and hence the cost of hybrid seeds become too expensive for the farmers. If these hybrids are made into apomicts, there is no segregation of characters in the hybrid progeny.