Contents
The study of cellular Biology Topics is essential to understanding the workings of all living organisms.
What are the Types of Aquatic Habitats ?
The habitats having water all around are called aquatic habitats. The important aquatic habitats are:
- Oceans, and
- Ponds, Lakes and Rivers.
Ocean water contains a lot of salts dissolved in it, so ocean water is very salty. Ocean is not a fresh-water habitat. On the other hand, ponds, lakes and rivers are called fresh-water habitats. The water of ponds, lakes and rivers does not contain much salts dissolved in it. Since the water of oceans is too salty, many animals and plants living in the fresh water of ponds, lakes and rivers are not found in ocean water. We will now discuss these aquatic habitats in detail, one by one.
1. Oceans
A very large area of sea is called ocean. The terms “ocean” and “sea” are usually used in the same sense. Ocean (or sea) is an aquatic habitat having water all around. When animals live in water, they must have special adaptations to help them survive in water. The adaptations in animals living in water are about their movement in water and obtaining oxygen for breathing. Some of the adaptations in animals living in the aquatic habitats like ocean (or sea) are as follows :
1. Many sea-animals have streamlined bodies to help them move in sea-water easily. For example, the fish living in the sea habitat have streamlined body shapes. The dolphins and whales living in the sea also have streamlined bodies. Some sea-animals like squids and octopus do not have streamlined body shape.
But when squids and octopus move in sea-water, they make their body shape streamlined. Such animals stay deeper in the ocean near the sea-bed and catch any prey that moves towards them. The streamlined shape of sea-animals is an adaptation for swimming in water.
2. Most of the sea-animals have gills which enable them to use oxygen dissolved in water for breathing. For example, the fish, squids and octopus living in sea water, all have gills to help them extract oxygen dissolved in water for breathing purposes. So, the presence of gills in sea-animals is an adaptation for breathing inside the water.
There are, however, some sea-animals like dolphins and whales which do not have gills. Dolphins and whales breathe in air through nostrils (called blowholes) which are located on the upper parts of their heads. Dolphins and whales breathe in air through blowholes when they swim near the surface of water. After breathing in air, they close the blowholes with flaps and dive into the sea.
Dolphins and whales can stay inside water for long time without breathing. They come to the surface of water from time to time to breathe in air. Thus, the presence of nostrils (or blowholes) in dolphins and whales is an adaptation for breathing.
2. Ponds, Lakes And Rivers
Ponds, lakes and rivers are “fresh-water” aquatic habitats. We can see many plants growing in the water of ponds, lakes, rivers and even drains. The plants which grow in water are called aquatic plants. There are three types of aquatic plants (or water plants). These are described below.
(a) Some aquatic plants float on the surface of water [see Figure (a)]. The two examples of aquatic plants which float on the surface of water are water-lettuce and water hyacinth.
(b) Some aquatic plants are partly submerged in water [see Figure (b)], The roots of partly submerged plants are fixed in the soil below water at the bottom of pond, lake or river. The stems of such plants grow up to the surface of water while the leaves and flowers float on the surface of water. The two examples of aquatic plants which are partly submerged in water are water lily and lotus.
(c) Some aquatic plants are completely submerged in water [see Figure (c)], The roots of submerged plants are also fixed in the soil below water at the bottom of pond, lake or river. All the parts of such plants (including stem, branches and leaves) grow under water. The two examples of completely submerged aquatic plants are Hydrilla and Vallisneria.
Adaptations in Aquatic Plants (or Water Plants)
The aquatic plants show a number of adaptations to their “water environment”. Some of the adaptations in aquatic plants are given below.
1. The aquatic plants have very short and small roots whose main function is to hold the plant in place. This adaptation in aquatic plants can be explained as follows: All the parts of an aquatic plant are surrounded by water, so an aquatic plant can absorb water and dissolved minerals directly from the surface of their stems, branches and leaves.
Since the aquatic plants do not have to depend on their roots to obtain water and dissolved minerals, their roots are very short and small. On the other hand, terrestrial plants (land plants) have to absorb water and dissolved minerals from the soil through their roots, therefore, land plants have large roots.
2. The stems of aquatic plants are soft, hollow and light, having large spaces filled with air. The aquatic plants do not need strong stems because the surrounding water of a pond, lake or river keeps them up.
3. The submerged aquatic plants have narrow and thin ribbon-like leaves which can bend in the flowing water of rivers and streams and hence do not obstruct the flow of water. In some submerged plants, the leaves are highly divided so that water can easily flow through them without damaging them. The thin leaves of submerged plants also allow the minerals to pass into them easily. The floating leaves of partly submerged plants are quite broad but flexible. The leaves of floating plants are, however, similar to those of land plants.
Animals Adapted to Live in Water and on Land
The animals like frog have ponds as their habitat (see Figure). Frogs are found in shady, damp conditions near ponds. Frogs can live inside water as well as on land near the pond. Actually, frogs spend most of their time on land but come back to water to lay their eggs. Frogs are adapted to live life in water as well as on land in the following ways :
1. Frogs have webbed back feet which help them to swim in water (Webbed feet are formed from thin skin between toes and work like paddles for swimming). This adaptation helps the frogs to live life in water.
2. Frogs have strong back legs for hopping (jumping) and catching their prey. This adaptation helps the frogs to live life on land.
Acclimatisation
Adaptations are very, very slow changes which take place in the bodies of organisms over thousands of years. There are, however, some changes which can occur in organisms over a short period of time to help them to adjust to some sudden changes in their environment (such as a change in altitude). For example, if we live in the plains and suddenly go to a high mountain region, we may experience difficulty in breathing for a few days. This is because the air is very thin at the “high altitude” on the mountain due to which we have to breathe faster (when we are on the mountains) so as to obtain sufficient oxygen.
After some days, however, small changes occur in our body due to which our body adjusts to the new environment of thin air on mountains. We say that our body has acclimatised (or got used) to the mountain environment. The process of becoming accustomed to a different environment (such as high altitude of mountains) over short periods is called acclimatisation. The changes which take place in the body of an organism during acclimatisation are temporary and can be reversed. On the other hand, the changes which take place during adaptation are permanent and cannot be reversed.