Answer:
The first necessity is to remove metabolic wastes from the body. The second necessity is to regulate the balance of water and electrolytes in the body. The third necessity is to remove excess substances from the body.
Explanation:
The first necessity is to remove metabolic wastes from the body. These wastes, such as carbon dioxide and nitrogenous compounds, are toxic and can disrupt normal cellular functions if they accumulate.
The second necessity is to regulate the balance of water and electrolytes in the body. This is important for maintaining homeostasis and ensuring the proper functioning of cells and organs.
The third necessity is to remove excess substances from the body. This includes substances that are ingested in excess, such as vitamins, and substances that are produced in excess by the body, such as hormones.