13. Which nuclei fuse to give rise to endosperm?
14. Name the part of gynoccium that determines the compatible nature of
pollen grains
15. What is shield-shaped single cotyledon of monocots called?
16. Who discovered double fertilization in angiosperms?
17. Name a plant in which dichogamy is found.
18. Name the tissue present in the fertilized ovules of angiospermic plants
that supplies food and nourishment to the developing embryo,
19. What is the site of microsporogenesis?
20. What is the site of megasporogenesis?
21. Which cell of male gametophyte produces the male gamete?
22. How many cells are found in a typical embryo sac?
23. What is an anatropous ovule?
24. What is nucellus?
25. What is funiculus?ed sin otyledot c ois called
26. What is the function of germ pore?
27. Name the substance of which the intine and extine is made.
Answers
1. One sperm nucleus fertilizes the egg cell, forming a zygote, while the other sperm nucleus usually fuses with the binucleate central cell, forming a primary endosperm cell (its nucleus is often called the triple fusion nucleus). That cell created in the process of double fertilization develops into the endosperm.
2. The pistil has the ability to recognize, the pollen, whether it is of the right type (compatible)or of the wrong type (incompatible). If it is of the right type, the pistil accepts the pollen andpromotes post-pollination events that lead to fertilization. If the pollen is of wrong type, thepistil rejects the pollen.The ability of the pistil to recognize the pollen is followed by its acceptance or rejection. It isthe result of a continuous dialogue between pollen grain and the pistil mediated by chemicalcomponents of the pollen interacting with those of the pistils.
3.single shield - shaped cotyledon of monocot seed is called SCUTELLUM .
4.The fusion of one sperm with the egg cell to form the embryo and of the other sperm with the polar fusion nucleus to give rise to the endosperm ('double fertilization') was discovered by Nawaschin in 1898 in the liliaceous plants, Lilium martagon and Fritillaria tenella.
5.The more usual form of dichogamy, which is found especially in such insect-pollinated flowers as fireweed (Epilobium angustifolium) and salvias (Salvia species), is protandry, in which the stamens ripen before the pistils.
6.
BRITANNICA
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Nutritional dependence of the embryo
During their early growth, the embryos of all vascular plants exist as virtual parasites depending for nutrition on either the gametophyte or the previous sporophyte generation through the agency of the gametophyte or, in the special case of the angiosperms, upon an initially triploid tissue, the endosperm, which is itself nourished by the parent sporophyte.
The early nutrition of the sporophyte in ferns, horsetails, and club mosses such as Lycopodium is clearly provided by the gametophyte. In these groups the young sporophyte produces a multicellular structure, the foot, which remains embedded in the tissues of the gametophyte throughout early development withdrawing nutrients. Ultimately, both shoot and root of the sporophyte grow out from the gametophyte, but, even after the first leaf has begun to photosynthesize and thus to produce its own food, the gametophyte may persist.
In Selaginella, the gametophytes are sexually distinct. The female gametophyte develops within the wall of the megaspore. The archegonia are exposed after the megaspore wall splits, but the gametophyte never escapes completely. After fertilization, the zygote cleaves, and the outer cell produces a long suspensor that pushes the embryo deeply into the tissues of the gametophyte. A foot is then formed, as in Lycopodium, and further development of the embryo continues at the expense of reserves transferred to the megaspore from the preceding sporophyte generation.
There are superficial similarities between the nutritional history of the embryo in gymnosperms and in Selaginella, for, in each, the female gametophyte, dependent upon reserves derived from the sporophyte, acts as an intermediary between one sporophyte generation and the next.
→It is a thin and continuous layer of pollen grain which encloses the PM of a cytoplasm.
→It is made up of cellulose and pectin.
→A newly differentiate and Pollen Grain has a central nucleus and cytoplasm.