Tag: evs

Gymnosperms are those seed plants in which the seeds remain exposed over the surface of the megasporophylls because the latter is not folded to form pistils and thus lack ovary. Flowers are absent and thus fruits are not formed.

In gymnosperms, the pollen grains and the megaspores are haploid and develop as a result of meiosis in the respective mother cells. The functional megaspore forms the embryo sac. The endosperm is formed prior to fertilisation, hence is haploid.

In Gymnosperms, the male and female gametophytes do not have an independent free living existence. They remain within the sporangia retained on the sporophytes i.e., female gametophyte within megasporangium and male gametophyte within microsporangium.

The gymnosperms are comparatively more ancient than the angiosperms in evolutionary terms. Most of the gymnosperms have now become extinct and the group is presently represented by only 900 living species. The living gymnosperms are widely distributed in the cold climates where snow is the source of water. Cycas and Ginkgo are referred to as living fossils .because they have not yet changed over the years while its related members or species have become extinct or fossilised. The living fossil represents a living unchanged example of an extinct group or genera etc. So, the correct answer is 'Both A and B'.

Gymnosperms grow in cold and dry climates and they don't have a need for water as compared to angiosperms and the second reason is that they didn't evolve to have vessels and vessels are considered as an advanced element of xylem but exceptionally the order Gnetales (considered as advanced gymnosperms) have vessels in their xylem. Also, in cold climates vessels can be too efficient, because the fast draw on water can lead to air locks when water freezes. That’s why deciduous broad-leaved trees in temperate climates - that do have vessels - cut their losses by going dormant in the winter. 

 Bordered pits are especially common in the tracheids of some gymnosperms. Their structure can be discerned best in a cross-section through neighbouring cells. The middle lamina between the cells is preserved within the pits. Their centre is made up by a disc of primary cell wall material, called torus. No secondary walls exists in the pit's structure. 

In siphonogamy, pollen tubes are developed for the transfer of male cells to the eggs. The seed plants are siphonogamous. But in the lower plants male cell actually swim to the egg. As a consequence, spermatocytes are sometimes called siphonogamous. It is a characteristic of all spermatocytes. So the correct answer is option A.

 Phloem is the vascular tissue responsible for transport of sugars and other liquid materials. Phloem is composed of several cell types including sclerenchyma, parenchyma, sieve elements and companion cells. The function of companion cells is uncertain though it appears to regulate the activity of the adjacent sieve elements. Albuminous cells have a similar role to companion cells, but are associated with sieve cells only and are hence found in gymnosperms.

Gymnosperms are archegoniate spermatophytes. Spermatophyte is another term from phanerograms which are the seeded plants- gymnosperms and angiosperms. Archegonia is the female sex organ which is present in bryophytes, pteridophytes and gymnosperms. So, the gymnosperms are the only one which are both spermtophyte and archegoniate.

Gymnosperm undergo double fertilization, therefore in haploid stage of the gynosperm life cycle the plants have only one set of chromosome, thus haploid microspores are released into air as pollen and in gymnosperm endosperm is formed before fertilization from the female gametophyte(n). Hence it is haploid.