Tag: pictorial feature of plant kingdom

Bryophytes are known as 'amphibians of plant kingdom' because they are adapted to land as well as water habitats. In their vegetative structure, bryophytes have become adapted to land. But they depend on water for sexual reproduction because the swimming habit is retained by their sperms.

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

Gymnosperms, example. Cycas, Pinus, Cedrus etc, bear reproductive structures in the form of cones. The cones that bear female reproductive structures are called female cones. Each female cone contains spirally arranged megasporophylls, that have ovules directly attached to them,  that is,ovules not enclosed in the ovary or are naked. After fertilization the ovule forms the seed and the ovary forms the fruit. Since, in gymnosperms ovary is  absent fruits are not formed.

Living gymnosperms are predominantly middle sized trees (Cycas) to tall trees (Pinus) and shrubs (Ephedra). Rarely they are woody climbers (Gnetum montanum). There are no herbs in gymnosperms.

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.