Question

From where do aquatic animals and terrestrial animals obtain oxygen for breathing and respiration?

Answer 1

Hint: Aquatic animals inhabit the water while terrestrial animals inhabit the land. The aquatic animals have gills for respiration while terrestrial animals use lungs.

Complete solution:
Let us talk about the aquatic animals. Where do they live? Well, aquatic animals are called so because they live in water. So accordingly, they have modified their bodies to suit the aquatic habitat. We know that water is composed of two molecules of hydrogen and one molecule of oxygen. So we say that the oxygen is dissolved in water.
The aquatic animals use this dissolved oxygen for their purpose of breathing and later for cellular respiration to oxidise the food in the presence of oxygen to obtain the energy.
Now, the aquatic animals are of different types. The unicellular organisms like Amoeba simply use the cellular surface for diffusion of gases, that intake of oxygen and giving out carbon dioxide. Animals like fish and frogs use the gills for extracting the oxygen from the water. The gills are heavily supplied with blood capillaries. As the water passes through the gills, the oxygen is filtered and absorbed in the blood
Moving on to the terrestrial animals, they live on land. For them, the source of oxygen is the atmosphere. The oxygen is released by the green plants during the process of photosynthesis. Terrestrial animals use respiratory systems made of lungs that are connected to the external environment via nasal chambers or openings. They inhale the oxygen along with other gases and exchange the oxygen with blood in the lungs. In this process, the carbon dioxide is expelled out.
Certain terrestrial animals like earthworms use the moist body surfaces for capturing the oxygen.

Note: Aquatic plants also obtain the dissolved oxygen in water from their surfaces. The terrestrial plants use stomata and lenticels for gaseous exchange