Botany and Plant Science

Apical zone of pollen tube contains abundant vesicles but lacks cell organelles. It is hemisphere in shape and transparent in nature. This transparent apical growing region of pollen tube is called as cap block. It exists only until the tube is growing. It disappears as soon as the growth ceases. 

Callose is a beta-1,3-glucan. It is the major component of the pollen tube cell wall. It is also deposited within the cytoplasm as distinct callose grains. This leads to the formation of callose plugs. Callose plugs separate the living, growing and functional part of the pollen tube in the tip from the remaining degenerating part.

Because hydrophtes are supported by water rather than by roots and stem structures, most hydrophtes as a result have roots that are small and feathery. These are designed to take in oxygen from the water, and since the plant is fully submersed in water at all times, there is less need for a long and thick root structure. One plant that has a feathery root is the Salvinia Molesta, which is a free-floating aquatic fern.

In submerged hydrophytes, the entire plant body is involved in the absorption of water and these plants not experiences much stress or pressure internally. So in these plants, xylem and mechanical tissues are poorly developed.

So, the correct option is ‘Poor development of xylem and mechanical tissues’.

Submerged hydrophytes live entirely underwater, so they do not need rigid mechanical tissues for support because the surrounding water provides buoyancy. Consequently, their xylem and supporting tissues are poorly developed.

Aerenchyma is a specialized spongy tissue with large air spaces that allows for gas exchange and provides buoyancy in aquatic plants.

Finely dissected or ribbon-like leaves in submerged plants increase the surface area for gas exchange and reduce resistance to water currents.

Hydrophytes live in water, which provides buoyancy, so they do not require extensive mechanical tissues like sclerenchyma to support their weight.

Aerenchyma is a spongy tissue that forms spaces or air channels in the leaves, stems and roots of submerged and aquatic plants. The floating leaves are there due to this feature of aerenchyma only. The aquatic plants or hydrophytes do not have submerged leaves or a well developed phloem, So the correct answer is 'Aerenchyma.'

Hydrophytes often have poorly developed roots or lack them entirely, and they frequently lack root caps because they do not need to penetrate soil in the same way terrestrial plants do.

Hydrophytes typically have reduced xylem and lack vessels, but they do possess tracheids. Therefore, the statement that tracheids are absent is incorrect.

Hydrilla is a submerged hydrophyte that absorbs water and nutrients directly through its leaves and stem, leading to a very poorly developed root system.

A characteristic feature of many hydrophytes is a poorly developed root system, as they are often suspended in water and absorb nutrients directly from the water column.

Vallisneria uses hydrophily (pollination by water) and has long-stalked female flowers. Casuarina is a xerophyte with phylloclades (or cladodes). Hydrilla is a submerged hydrophyte with aerenchyma. Tribulus is an annual but not typically classified as a root succulent.