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. 

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. 

• 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. 

Plants growing in bright light are called as sun plants or heliophytes, while plants growing in partial shade or low light intensity are called as shade plants or sciophytes. 

In succulent xerophyte, plants have fleshy organs, where water and mucilage are stored. Depending upon the organ, where succulence occurs, the succulents show chylocauly, i.e., fleshy stem, e.g., Opuntia, Euphorbia, Asparagus; chylophylly ie fleshy leaves, e.g., Agave, Aloe or chylorhizy, i.e., fleshy roots, e.g., Asparagus.

Plants living in dry conditions are called as xerophytes. These plants show many morphological and structural adaptations to survive in dry conditions. In stem the mechanical tissue is well developed and also bark is well developed to retain water

Xerophytes are plants of dry habitats, where the environment favours higher rate of transpiration than the rate of absorption. 

Hydrophytes possess special air storage parenchyma tissue, called as aerenchyma. It makes different parts of hydrophytes, light, spongy and flexible. It makes oxygen produced during photosynthesis, available to roots and other non photosynthetic regions. It can also help in exchange of gases with the atmosphere through stomata present in emerged regions of plants. Xerophytes show structural adaptations to discourage water loss through transpiration and increase water absorption. Such adaptations include thick cuticle, sunken stomata, well developed vascular tissue etc.

Hydrophytes are water loving plants. The hydrophytes with floating leaves have large leaves, stomata and waxy coating on the upper surface. The waxy coating prevent wetting and clogging of stomata.

Pneumatophores are specialized root structures that grow out from the water surface and facilitate the aeration necessary for root respiration in hydrophytic trees such as many mangrove species (e.g., Avicennia germinans and Laguncularia raecemosa), bald cypresses, and cotton (Tupelo) gum (Nyssa aquatica). So, the correct option is "B" (Pneumatophores).

Tropical desert areas are those where there is scarcity of water and extensive heat. Organisms in those areas adapt to survive in that ecological condition. Adaptations like thorns and succulents in flora helps the plants to survive without plenty of water. The leaves and stems undergo modification to conduct photosynthesis in less available water. Animals like frogs, rabbits, snakes, camels, etc. also go through modification in their characteristics to ensure their survival. Large surface of an any organism can lead to radiation of more body heat per unit of mass which can be fatal. Hence, such adaptations is not seen in organisms present in tropical desert.

In Opuntia (prickly pear), the stem is modified to a flattened green structure to perform the function of leaves. Leaf-like flattened modified stems are called phylloclades. 

CactI are among the most drought-resistant plants on the planet, due to their absence of leaves, shallow root systems, ability to store water in their stem, spines for shade and waxy skin to seal in moisture. Xerophytes can have smaller leaves or fewer branches than other plants. An example of leaf surface reduction are the spines of a cactus. Spines also protect the plants from animals and collect moisture too.

Myrmecophily is the term applied to positive interspecies associations between ants and a variety of other organisms such as plants, other arthropods, and fungi. Myrmecophily refers to mutualistic associations with ants, though in its more general use the term may also refer to commensal or even parasitic interactions. The term myrmecophile is used mainly for animals that associate with ants.

Halophytes grow in physiologically dry soil. The soil is having water but the soil solution has a high concentration of salts. Thus, the water is not easily available to plants, because water flows from a region of high water potential to a region of low water potential. 

Capparis decidua (family Capparidaceae) is commonly known as kair. It is 
distributed throughout the arid regions of India and other countries. Kair is a caducous plant, so in the foliage condition mainly stem and fruits are common. It is also known as Capparis aphylla.
Since the plant is xerophytic, it is generally found in dessert area and is highly draught resistant plant, which can survive for long. Tribal people prepare pickle from the fruits of kair. 

Hydrophytes are water loving plants and grow in aquatic environments. In these plants mechanical tissue is absent. Xylem is poorly developed or absent. Hydrophytes possess special air storage parenchyma, called as aerenchyma. It makes plant parts light, spongy and flexible.

Xerophytes are the plants that has adapted to survive in an environment with little liquid water, such as a desert or an ice- or snow-covered region in the Alps and Arctic regions. Succulents plants stores water. They have mucilage to retain water. Stomata are sunken and usually open only during nights. 

Typical plants that are found on the forest floor include a variety of ferns, mangrove trees, and vines. The canopy of trees spread their leaves to attract as much sunlight. Though the forest floor is the principal sites of decomposition, there is a stiff competition for sunlight and nutrients. The plants that occupy the forest floor are ones that require low light as they are adapted to grow under conditions of low light availability and have large dark  green leaves to absorb as much sunlight.

Xerophytes are plants of dry habitats, which are faced with the problem of more water loss through transpiration than is water available from soil, e.g., Acacia, Casuarina etc.
In these plants leaves or leaflets are often small, vertical, thick and leathery. Cuticle is thick and waxy. Stomata are sunken and restricted to lower surface of leaf.

• The root cap protects the growing tip of roots from soil and hard rock surface. 
• As hydrophytes are generally aquatic plants, no such protection is needed for their roots. 
• As a result of which root cap is absent in hydrophytes.
• In given options all are aquatic plants but utricularia, hydrilla and Limnophylla are rooted submerged plants there root are present in soil.
• Eichhornia is free floating aquatic plant and there root arr floating in water so they don't have the need of root cap they have root pockets.
• Option B is correct here.

Hydrophytes are water loving plants. Stomata are absent in submerged hydrophytic plants. But floating hydrophytes have stomata on upper surface. e.g., lotus. Exchange of gases occurs through general surface in submerged hydrophytes. Emergent hydrophytes possess special air storage parenchyma called aerenchyma. It makes their different parts light, spongy and flexible. It can also help in exchange of gases with the atmosphere through stomata present in emergent regions. Roots of hydrophytes are poorly developed or completely absent in Wolffia. 

Xerophytes are the plants of dry habitats, where the environment favours higher rate of transpiration than the rate of absorption. Xerophytes have various adaptations to check water loss and increase water absorption.

In hydrophytes, generally xylem is poorly developed. Tracheids are developed but vessels are completely absent. Hydrophytes possess special air storage parenchyma called aerenchyma. Cuticle is poorly developed.

Hydrophytes possess special air storage parenchyma tissue, called as aerenchyma. It makes different parts of hydrophytes, light, spongy and flexible. It makes oxygen produced during photosynthesis, available to roots and other non photosynthetic regions. It can also help in exchange of gases with the atmosphere through stomata present in emerged regions of plants. 

Exchange of gases occurs through general surface in submerged hydrophytes. 

• Minerals crystals are found in plant cell walls in the form of calcium oxalate, carbonate or silica.
• Calcium oxalate occurs in the form of a mass of crystals around a cellulosic core in few plants.
  
• Crystal sand is the calcium oxalate deposition in cells in the form of powdery mass and is seen in Atropa.
• So, the correct answer is 'Calcium oxalate'.

• Minerals crystals are found in plant cell walls in the form of calcium oxalate, carbonate or silica.
  
• Calcium oxalate occurs in the form of a mass of crystals around a cellulosic core in few plants.
  
• Calcium oxalate crystals occur in the form of needle-shaped in few plant cells and are called raphides.
  
• Eg- Water hyacinth.
  
• So, the correct answer is 'Calcium oxalate'.

There are various defense mechanism seen in plants. These are thorns, spines, prickles, glandular hair, stinging hair, alkaloids, tannins, raphides, etc. Tobacco has glandular hair for its defense. Glandular hair with sticky substances protect it from outer agencies. Lemon has thorns to protect itself from its enemies. Yucca has pointed spines at the leaf ends to protect itself from enemies.
Calotropis is known as milkweeds because of the latex they produce. Thus, the correct answer is 'Tobacco.'

A. Calcium oxalate crystals occur in the form of needle-shaped in few plant cells and are called raphides.

• Eg- Water hyacinth.

B. Calcium oxalate in the form of rod-like or cubicle shaped in few plant cells and are called prismatic crystals.

• Eg- dry scales of onions.

C. Calcium oxalate crystals occur in the form of star-shape in plant cells and are called sphaeraphides.

• Eg- phylloclades of Colocasia.

D. Calcium oxalate is deposited in the leaves within the vacuoles during early developmental stages in plants is called crystal sand. Eg- Beet root

So, the correct answer is 'Prismatic crystals'.

Many hydrophytes have production of different forms of leaves in the same plant i.e., heterophylly. In submerged aquatics with free-floating aerial leaves, the submerged leaves are generally linear, ribbon-shaped or finely dissected while the aerial leaves are complete and rounded or lobed.

Resource partitioning is the phenomenon of evolutionary changes seen in species in response to the selection pressure generated by interspecific competition. Due to this, no two organisms within the same species can coexist in the same niche if they have same resources. They have different foraging manner whether feeding type is different or same. Example of resource partitioning involves two tigers present in their own territories or niches and defending it from other tigers. 

To counter the herbivore attack, plants produce specialized morphological structures or secondary metabolites and proteins that have toxic, repellent effects on the herbivores. Plants confront the herbivores both directly by affecting host plant preference or survival and reproductive success (direct defense), and indirectly through other species such as natural enemies of the insect pests (indirect defense). Direct defenses are mediated by plant characteristics that affect the herbivores biology such as mechanical protection on the surface of the plants (e.g., hairs, trichomes, thorns, spines, and thicker leaves) or production of toxic chemicals such as terpenoids, alkaloids, anthocyanins, phenols, and quinones) that either kill or retard the development of the herbivores.

The submerged leaves are often highly dissected or divided. This has the advantage of creating a very large surface area for absorption and photosynthesis. It also minimises water resistance and hence, potential damage to the leaves since moving water (currents and waves) can be damaging to the leaves of the plant.

Xerophytes are plants, that have small amount of water or moisture, so they have adaptations that allow them to survive in these harsh conditions. These plants are like cactus and other succulents are typically found in deserts.