Question

Collect some aquatic plants- cut the leaves and stems. Observe them under a microscope and record your observations like air presence/absence of air spaces etc., and answer the below.
a) Why do they float on water?
b) What makes them float?
c) Are there any other reasons for their floating?
d) Draw a diagram of what you have observed under a microscope?

Answer 1

Aquatic plants are the plants that live in aquatic environments. They are also referred to as hydrophytes. They grow in the large abundance of water, with their roots, and sometimes leaves also, submerged in water.

Complete answer:
1)The leaves and stems of aquatic plants are found floating on the water surface for the process of gaseous exchange, which means the intake of carbon dioxide and release of oxygen. They have large, flat, and entirely floating leaves. Stomata will be present only on the upper side of the Leaves. Their cuticles are also poorly developed.
2. In aquatic plants, there are large air cavities present in the parenchyma. This gives buoyancy to the plants that help them to float. Such parenchyma type is known as aerenchyma. In floating leaves, mesophyll is differentiated into palisade and spongy parenchyma and contains gas-filled chambers for floatation.
3. The leaves come up to the surface to carry out the process of photosynthesis efficiently when there is no optimum temperature beneath the water. In them, the stomata are present only on the upper surface.

Additional Information:
-In an Aquatic environment the availability of water is high and the plants need not absorb water from the soil. So, in them, the root system has only secondary significance as organs of absorption.
-In general root systems may be secondarily modified, insignificant, poorly developed, or altogether absent.
-They have special mechanisms for the excretion of water from the body. They also have mucilage secretion to prevent desiccation and decay due to the action of water currents.

Note:
-Aquatic plants have very low osmotic pressure. They have several adaptations to withstand the conditions in aquatic environments.
-Their Morphological adaptations include modification of roots, stems, and leaves.
-Anatomical adaptations of Hydrophytes are of four main types namely, reduction of protecting structures, reduction of mechanical tissues, reduction of conductive tissues, etc.