Question: Compare the structure of fat (see Figure 5.9) with carbohydrates (see Figure 5.3). What features of their structures make fat a much better fuel?

Fat is the most commonly found substance in the human body. The body tends to store excess energy in the form of fat beneath the adipose tissues. During the starvation condition, the body tends to use this stored energy for its survival.

Carbohydrates are the primary energy source of the body. The glucose which is produced from the carbohydrates is used to form ATP. ATP acts as a fuel for the different types of metabolic processes.

Figure 5.9 depicts the structure of fats which is composed of fatty acids and glycerol. The basic units present in fatty acids are CH₂. The electrons sharing in fats are equal. The fats are in reduced form.

So, there is the liberation of more energy during the breakdown of fat molecules. This makes the fat molecules a good energy source.

Figure 5.3 depicts the structure of carbohydrates. The electron sharing present in the carbohydrates is unstable.The carbohydrates are slightly oxidized due to the presence of bonds such as C-O and O-H.

Hence, the liberation of more energy during the breakdown of fat makes them a more robust energy source than carbohydrates.