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.

Often found on floating plants, many hydrophytes have air sacs that help the plant float on the surface of the water. The water chestnut is one example, which includes a beautiful cluster of green leaves with white flowers, attached to a fine root system. It is important to note that some aquatic plants will float slightly submerged in the water, such as the buttercup. Others, such as water lilies, will float up on top of the surface since their leaves distribute the weight across the surface of the water. 

Hydrilla is a genus of aquatic plant, usually treated as containing just one species, Hydrilla verticillata, though some botanists divide it into several species. Opuntia, touch me not and Calotropis lives on land. Thus, option B is correct and other options are wrong.

About 72% of the land on the Earth is a part of the oceans. This water of the oceans, rivers, lakes and ponds contribute to the aquatic ecosystem. So, about 72% of the Earth's surface is covered under the aquatic form of ecosystems. There are two types of aquatic ecosystem, freshwater and marine ecosystem. 

In a freshwater aquatic ecosystem like a pond, the organisms in the food chain include algae, small animals, insects and their larvae, small fish, big fish and a fish-eating bird or animal.

Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes. These plants require special adaptations for living submerged in water, or at the water's surface. The most common adaptation is aerenchyma, but floating leaves and finely dissected leaves are also common. Aquatic plants can only grow in water or in soil that is permanently saturated with water. They are therefore, a common component of wetlands. 

Succulent plants stores water in their stems, fleshy leaves, such as the aloe.

Victoria amazonica is commonly known as Giant Water Lily. They have the lagest floating leaves. They have large floating leaves, up to 3 meter in diameter. The leaves float on the surface of water on a submerged stalk.

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’.

A.Submerged hydrophytes – plants grow completely in the water, stomata are absent.

B.Hygrophytes – plants grow in wet conditions, stomata are present.

C.Mesophytes – plants grow in average climatic conditions. Stomata are present.

D.Xerophytes – plants grow in dry or arid conditions, sunken stomata are present.

So, the correct option is ‘submerged hydrophytes’.

In hydrophytes or aquatic plants, large intercellular air spaces are developed extensively in the parenchyma so as to form a connected system throughout the plant. Such a modified parenchymatous tissue is called aerenchyma. It provides buoyancy to the plants and helps in gaseous exchange also. Thus the correct answer is option B.

A. Nymphaea- Reserve food material in perisperm (Persistant nucellus). Perisperm occurs in the seeds of black pepper, coffee, castor, cardamom, Nymphaea. It is diploid.

B. Coconut- Reserve food material in endosperm.

C. Onion- Reserve food material in endosperm

D. Litchi- Reserve food material in cotyledons.

So, the correct answer is 'Nymphaea'.

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 are aquatic plants that live in water and are evolutionarily suited to thrive in aquatic environments. Hydrilla, also called waterthyme is a submerged hydrophyte, which is a troublesome aquatic weed at many places.

The plants which can live only in water are called hydrophytes. Among these hydrophytes, there are different sizes and classification based on them. The large sized hydrophytes are called macrophytes. As macro suggests large size.

• Benthic animals(benthos), refer to organisms who live at the lowest level(floor) of a water body(ocean or a lake or sea), sometimes even permanently attached to the bottom. For example, polychaete worms, bivalves, echinoderms, sea anemones, corals, sponges, sea squirts, turbellarians and larger crustaceans such as crabs, lobsters, etc.
• Hence Animals which live on the floor of the sea are called benthic is a true statement.
• So, the correct answer is 'True'.

The body of the fish is supported by endoskeleton made up of bones. Fish possess a streamlined body which helps them to swim in water. Fish swim with the help of their fins. Streamlined body helps in orientation of the fish movement in a particular path.

Generally, phosphorus is the limiting nutrient in freshwater aquatic systems. That is, if all phosphorus is used, plant growth will cease, no matter how much nitrogen is available. Phosphorus functions as the growth-limiting factor because it is usually present in very low concentrations. The natural scarcity of phosphorus can be explained by its attraction to organic matter and soil particles. Any unattached or free phosphorus is quickly removed from the aquatic system by algae and larger aquatic plants. Excessive concentrations of phosphoruscan quickly cause extensive growth of aquatic plants and algal blooms. Several detrimental consequences may result. Excessive algae and plant growth can lead to depletion of the oxygen, that is dissolved in the water. 

Root cap is present at the tip of the root and it contains meristematic cells which divide and increase the length of the root.
Mesophytes are terrestrial plants. Therefore, root cap is essential in mesophytic plants.
Epiphytes are plant which grows upon another plant or any object. They require physical support for the growth. Such plants also possess roots which anchor the plant to another plant or object.
Xerophytes are terrestrial plants which have adapted to survive in an environment with little water. Hence, roots are necessary for xerophytes. 
Hydrophytes grow in water. Hydrophytes have plenty of water hence, the root system takes secondary importance. Therefore, root cap is absent in hydrophytes. 
Therefore, the correct answer is 'Hydrophyte'.

A continuous system of air passages from leaves to roots is found in emergent hydrophytes because these are the type of plants that keep themselves up from the top of water and these air passages provide buoyancy to it. submerged plants are sinked in water, floating plants are there on the surface of water. suspended hydrophyte are the plants that are just below the surface of water. So the correct answer is ' Emergent hydrophytes '. 

The petiole is the stalk that attaches the leaf blade to the stem. Water hyacinth leaves in natural populations vary from being long and thin‐petioled to being short with inflated petioles. water hyacinth is a floating hydrophyte that has an inflated petiole which helps in keeping it on top of the water level thus allowing it not to sink. So the correct answer is ' Eichhornia or water hyacinth. '

The succulent stem of the cactus plants usually store water and carry out photosynthesis also. The cactus stem contains a tough and waxy outer layer, called cuticle. The cactus plants possess modified leaves shaped like thin spines or thorns that decrease water loss through transpiration. 

"Patther phul" or stone flower or rock moss is a xerophytic plant or xerophytic shrub occurring wild on rocky ground( not much water present) As it is a plant which needs very little water it is called a xerophyte and occurs in the region of Gujarat 

One of the most commonly found plants in deserts is opuntia. it is a type of cactus. It is also called prickly pear. It is used to treat burns, diabetes, ulcers, inflammation, etc.

Xerophytes have very small leaves or spines to reduce loss of water.

The osmotic concentration of cell sap is higher in xerophytes to allow them to absorb water in an otherwise water deficient environment. The higher osmotic concentration would mean a lower water potential. A lower water potential will be advantageous to xerophytes as water always flows from a higher water potential to lower water potential.

Most species of desert plants have lost true leaves, retaining only spines, which are highly modified leaves. As well as defending against herbivores, spines help prevent water loss by reducing air flow close to the cactus and providing some shade. In the absence of leaves, enlarged stems carry out photosynthesis.

The cuticle is a waxy coating over the surface of leaves and plants. It forms a waterproof coating over the surface of leaves and plants. It prevents water loss from plants and also prevents the plants from getting desiccated. It also prevents the intake of gases into the plants. 

In cacti, the succulence is mostly in the stems because the leaves of the cacti are reduced to thrones to minimize the surface areas and therefor the water evaporation through them. the cacti have a shallow widespread network of roots that enables them to absorb water, therefore the roots are not succulent. the cacti have thick stems that store maximum amount of water in the entire plant. So, the correct answer is 'Stem'.

A phreatophyte is a deep-rooted plant that obtains a significant portion of the water that it needs from the phreatic zone (zone of saturation) or the capillary fringe above the phreatic zone. Phreatophytes are plants that are supplied with surface water and often have their roots constantly in touch with moisture. These plants have very deep roots that are able to reach the water table. So the correct answer is ' Very deep reaching ground water fringe'. 

The xerophytic plants are the plants present in the desert and other dry environments. The rate of transpiration is high in xerophytic plants due to high temperatures. In order to minimize the rate of transpiration, they have sunken stomata.

Lamina is reduced in xerophytic plants. In xerophytes, the petiole is modified into expanded green structure which carries out photosynthesis in case of reduced lamina.  For example, in Australian acacia.

Xerophytes are the plants that survive in an environment having little supply of water or moisture. To survive with limited water supply they have anatomical modifications such as-

In non-succulent Perennial have extensive root systems, roots penetrate deep into the soil and establish contact with sub-soil water. 

• Some trees have deep, extensive root systems that anchor them to hillsides. Shrubs service berry is a deep-rooted deciduous shrub or small tree that grows best in well-drained, slightly acidic, moist soil. Ground covers, Vetiver Grass.

Acacia arabica is xerophyte because it is seen in desert places.

Xerophytes are made up of thick cuticles and contains parenchymal tissues. It does not contain Aerenchyma.

• Water storage in stem and tubers is an adaptation of plants to thrive in harsh environments with high temperatures and scarce water. Such plants called xerophytes usually develop succulent stems that can store water.
• They have a very extensive root system to absorb the maximum amount of water from the soil.
• Other adaptations include thick waxy cuticle, reduced leaf size, densely packed leaves, reduced number of stomata in pitted and grooved positions.

Vegetation of geographic region with low rainfall, high temperature, loose and sandy soil is of the type called xerophytic vegetation. It consists of spiny shrub, cactus. Caatinga is a type of xerophytic vegetation.

A xerophyte is the species of plants, that has the special characters to adapt in the environment with little water. Xerophytes plant have a thick waxy cuticle on the stem and leaves. This waxy cuticle reduces the water evaporation. In xerophytic plants, sunken stomata are present. which open during the night to prevent the water loss. To adapt in this environment, xerophytic plants leaves reduces into spines, which reduces the surface area of the leaf and reduces the amount of transpiration. The xerophytic plant makes their food through the CAM pathway.

Lithops (stone-faced as the plants appear stone-like)  is a genus of succulent plants in the ice plant family, Aizoaceae. They avoid being eaten by blending in with surrounding rocks and are often known as pebble plants or living stones. These are small succulent plants that survive in their harsh environment by having much of the plant body below ground. Each individual plant consists of two succulent leaves fused together in the shape of an inverted cone (although some species will produce multi-headed plants). The fissure at the top of the plant is the division between the two leaves and is spine-like. 

Vegetation of Rajasthan is xerophytic. It is a geographic region with low rainfall, high temperature, loose and sandy soil. It consists of spiny shrub, cactus. Caatinga is a type of xerophytic vegetation.

Answer is option A i.e. "Hydrophytes"
Hydrophytes are aquatic plants that live in aquatic environments either completely or partially submerged in water. As an adaptation, their vascular tissue and mechanical tissue are reduced. The cuticle is either completely absent or it is reduced, thin and poorly developed.
On contrary, xerophytes have heavy cuticle, vascular tissue and mechanical tissue. Mesophytes have moderate vascular tissue, mechanical tissue and cuticle and epiphytes are lower plants or mosses that live in marine environment, they are non-vascular.