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Q1 . Name the parts of an angiosperm flower in which development of male and female gametophyte take place .
- Male gametophyte- It develops in microsporangium inside the pollen grains
- Female gametophyte - It develops in the ovule .
- Microsporogenesis
- 1. It is process of formation of microspores from microspore mother cell .
- 2. It occurs inside the pollen sacs of anthers .
- Megasporogenesis
- 1. It is the process of formation of megaspores from megaspore mother cell .
- 2. It occurs in nucellus part of ovule.
- In both the events meiosis cell division occurs .
- Microsporogenesis results in the formation of microspores while megasporogenesis forms megaspores .
- Sporogenous tissue → Pollen mother cell → Microspore tetrad → Pollen grain → Male gametes .
Q4. With a neat , labelled diagram , describe the parts of a typical angiosperm ovule .
- Refer to the heading The Megasporangium ' in the text .
Q5 . What is meant by monosporic development of female gametophyte ?
- The formation of female gametophyte or embryo sac from a single functional megaspore is called monosporic . The nucleus of functional megaspore undergoes 3 successive mitotic divisions to form 8 haploid nuclei .
- Embryo sac is an oval multicellular structure which contains 8 nuclei but 7 cells
- Chasmogamous flowers have exposed anthers and stigma . Cross pollination cannot occur in cleistogamous flowers , as such flowers do not open at all .
- Flowering plants have developed many devices to discourage self pollination and to encourage cross pollination
- ( i ) Dichogamy : Maturation of anthers and stigmas of a flower at different times . It is of two types :
- ( a ) Protandry : Anthers mature earlier than the stigma .
- ( b ) Protogyny : Stigma mature earlier than the anthers .
- ( ii ) Self - incompatibility : The pollen grains of a flower are incapable of completing growth on the stigma of the same flower .
- The inability of certain gametes even from genetically similar plant species , to fuse with each other is called self - incompatibility . It is because of interaction between the chemicals of the pollen and those of stigma . ( Pollen - Pistil interaction ) .
Q10 . What is bagging technique ? How is it useful in a plant breeding programme ?
- The process of covering the emasculated flowers or the female flowers , after dusting with the desired pollen , with bags of butter paper .
- This technique ensures the use of only desired pollen grains for pollination and protection of stigma from contamination ( from unwanted pollen ) .
- Fusion of male gamete with secondary nucleus ( Polar nuclei ) is called triple fusion . It occurs in the embryo sac . It involves the fusion of one male gamete nucleus and two polar nuclei
- This is because the embryo develops only after the formation of endosperm . So the zygote waits for endosperm formation which supplies food material for developing embryo .
Q13 . Why is apple called a false fruit ? Which parts of the flower forms the fruit ?
- If the fruit is derived from the ovary alongwith other accessory floral parts , it is called false fruit . It is true in case of apple where thalamus also contributes in the formation of fruit alongwith the ovary .
- Thalamus of the flower is involved in fruit formation like in apple and cashew , while true fruits develop only from the ovary .
- Emasculation is the process of removal of anthers before maturation from the flower buds of female parent so that chances of selfpollination are eliminated . Plant breeders employ this technique for artificial hybridization for crop improvement programme .
- Watermelon , Orange and lemon because in these fruits the seeds are scattered within their edible parts and if seeds are removed they become more valuable .
- The tapetal cells provide nutrition to the developing pollen grains . Tapetum secretes both enzymes and hormones and special proteins for the pollen grains to recognise compatibility . Tapetum produce ubisch granules for the formation of exine of pollen grain . Tapetum secrete pollenkitt over outerside of mature pollen .
- Apomixis is production of seeds without fertilization . Hybrid seeds can be cultivated with the help of apomixis . It is still at research stage , but if experiments are successful then it may help in increasing the yield of better variety of crops
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