Question

The main source of energy in humans beings is-
A. Fats
B. Carbohydrates
C. Proteins
D. None of the above

Answer 1

Hint: As we know every cell in our body needs energy to carry out a certain type of function. Whether we talk about physical work like holding, lifting and waking everything, requires energy whereas the work inside the cell could be production of certain materials,synthesis etc.

Complete answer:
Carbohydrates are the major source of energy required to do any work. They are further broken to its monomeric units. These are further metabolised and converted to Glucose. Glucose is used by cells so as to form Energy(ATP). They are necessary for cellular respiration in the mitochondria.

Hence the correct option is option B i.e. carbohydrates.

Additional information:- Lipids: They are the second source of energy after carbohydrates. If sufficient glucose or carbohydrates are not present then the body will produce Acetyl CoA from the fatty acids by the process of Beta-Oxidation. Acetyl CoA enters the mitochondria and continues to take part in Krebs Cycle to produce 14 ATP. Fatty acids are considered as a very high source of energy.

Proteins and Amino Acids: They tend to be the last source of energy. It is very difficult to extract energy from Amino Acids and Proteins in the form of ATP.

Ketone Bodies: Ketone bodies contain three water soluble molecules and their spontaneous breakdown product acetone, which is produced by the liver from fatty acids during periods of low food intake, fasting, starving, low carbohydrate diets, prolonged exercise etc. The brain has the capacity to metabolise ketone bodies and for ATP.

Note: Carbohydrates are the first molecules to be required to break down when we need energy. So, the order of first to last breakdown requirement will be carbohydrates, lipids, proteins and lastly ketone bodies. When a person is fasting we check for ketone bodies only.