(a) Draw a diagram of an enlarged view of T.S. of one microsporangium of an angiosperm and label the following parts:

(i) Tapetum


(ii) Middle layer


(iii) Endothecium


(iv) Microspore mother cells


(b) Mention the characteristic features and function of tapetum.


(c) Explain the following giving reasons:


(i) Pollen grains are well preserved as fossils.


(ii) Pollen tablets are in use by people these days.


OR


(a) Why is the process of fertilisation in angiosperms termed as double fertilisation? Explain.


(b) Draw a diagram of an angiospermic embryo-sac where fertilisation is just completed. Label the following parts:


(i) Micropylar end of the embryo-sac


(ii) The part that develops into an embryo


(iii) The part that develops into an endosperm


(iv) The degenerating cells at the chalazal end


(c) Draw a labelled diagram of globular embryonic stage of an angiosperm.



(a)



A microsporangium is surrounded by 4 wall layers – the epidermis, endothecium, middle layers and the tapetum.


(b)The inner most wall layer of microsporangium is called tapetum. It nourishes the developing pollen grains.


(c) (i) Pollen grains are covered by a hard outer layer called exine which is made up of sporopollenin (one of the most resistant organic material). It can withstand high temperatures and strong acids and alkali. No enzyme is able to degrade sporopollenin. Due to the presence of sporopollenin, the pollen grains are well-preserved as fossils.


(ii) Pollen grains are rich in nutrients. Pollen grain tablets are used as food supplements. They are claimed to increase the performance of athletes and race horses.


OR


(a) Since two types of fusions, syngamy (fusion of one male gamete with nucleus of egg cell) and triple fusion (fusion of another male gamete with the two polar nuclei) take place in an embryo, the phenomenon is termed as double fertilization.


(b)


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Micropylar end of the embryo-sac is near the synergids,


The part that develops into an embryo is zygote.


The part that develops into an endosperm is primary endosperm cell (PEC).


The degenerating cells at the chalazal end are Antipodals.


(c)


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After fertilization, the embryo-sac develops into various stages like globular embryo, heart-shaped embryo and the mature embryo.


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