The aquatic animals can breathe under water due to the presence of dissolved________________.A. Carbon dioxideB. OxygenC. NitrogenD. None of the above

The correct answer is B. Oxygen.

Explanation:
Aquatic animals, such as fish and many invertebrates, can breathe underwater primarily because they extract dissolved oxygen from the water. Here’s how it works:

Dissolved Oxygen: Water contains oxygen in a dissolved form, which is essential for the survival of aquatic organisms. This dissolved oxygen is often produced by photosynthetic organisms, like phytoplankton and aquatic plants, during the day.

Respiration Process: Aquatic animals have specialized respiratory structures, such as gills, that allow them to extract this dissolved oxygen from water as it flows over them. When water passes over the gill membranes, oxygen diffuses from the water into the blood of the aquatic animal.

Oxygen Utilization: Once in the blood, the oxygen is transported to cells throughout the body, where it is used in cellular respiration to produce energy. This is similar to how terrestrial animals breathe atmospheric oxygen.

Other Options:
A. Carbon dioxide: While aquatic animals do release carbon dioxide as a waste product of respiration, they do not breathe it in; instead, they need oxygen.
C. Nitrogen: Nitrogen makes up a large portion of the atmosphere and is also present in water, but it is not utilized by aquatic animals for respiration.
D. None of the above: This is incorrect because dissolved oxygen is indeed present and is essential for the respiration of aquatic animals.
In summary, aquatic animals breathe underwater primarily due to the presence of dissolved oxygen in the water.