Final answer:
An essential nutrient is required by the body because it cannot synthesize the nutrient in sufficient quantities. These must be obtained from food, and examples include certain amino acids, fatty acids, and vitamins such as A and K.
Step-by-step explanation:
A nutrient required by the body due to the inability to make any or enough to meet needs is termed an essential nutrient. Essential nutrients are compounds that the body cannot synthesize in sufficient quantities and, therefore, must be obtained through the diet. Examples of essential nutrients include certain amino acids, fatty acids, vitamins, and minerals.
Non-essential nutrients, on the other hand, can be synthesized by the body in sufficient quantities for normal functioning and do not need to be obtained from food. Vitamins such as A and K are examples of essential vitamins because they perform critical functions such as maintaining connective tissue and assisting in blood clotting, respectively, and cannot be adequately produced by the human body.