Question

In hydrophyte stomata is absent so how does gaseous exchange takes place?????

Answer 1

In hydrophyte which is completely submerged in water, stomata is absent. Carbon dioxide is obtained from water, which is released during respiration by fish. Also, decomposition of organic matter that takes place in the water ecosystem contributes to carbon dioxide production.

Even though the rate of carbon dioxide dissolution in water is exceptionally low, traces of dissolved carbon dioxide are available to the submerged aquatic plants.

In fully submerged plants, an example is Elodea, there are many adaptations for the direct absorption of gases. The leaves will generally be thin and deeply divided/dissected for the purpose of creating a large surface area for the direct absorption of nutrients, gases such as CO2 for photosynthesis. Gases diffuse across cell membranes to and from the water in aquatic plants. Gases such as carbon dioxide diffuse much more slowly in water than in air

They have large and numerous parenchyma tissues which are sites for gaseous exchange. They use the epidermis for gaseous exchange. These plants however lack guard cells for gaseous exchange. The submerged plants also tend to lack stems and roots

Underwater leaves lack a waxy coating because carbon dioxide is easier to absorb without this layer. Some species supplement their carbon dioxide intake by extending a few leaves to the surface to absorb carbon dioxide from the air.