Question

If you take a sample of food and burn it in a device known as a bomb calorimeter, you will be able to measure the total kilocalories (a unit of energy) in that food. If you feed that same amount of food to an animal, the animal will only be able to use some of that energy. List the process through which an animal ingests food and the losses that occur between ingestion and absorption of its macro- and micro-nutrients.

Answer 1

The process of nutrition in animals is divided into following five stages :-

ingestion, digestion, absorption, assimilation and egestion.

Ingestion is a process of 'eating the food' or putting the food inside our body. When we take the food with our hands and put it in our mouth it is called ingestion. Mechanical breakdown  of food takes place by mastication with the help of teeth. The salivary glands and enzymes also help in breakdown of macromolecules into monomers.

The catabolic reactions like hydrolysis of food stuff into the monomers is an exothermic reaction.

Eg. Proteins breakdown into amino acids, starch into monosachrides, fats into fatty acids and glycerol.

The peptide bonds in a protein (which link the amino acids) when hydrolysed release 8 to 16 kilo joule per mole of energy. This indicates that some amount of energy is liberated in the gut. Though this energy is quite minimal in comparison to the energy that is later harvested and absorbed in the body by further breakdown of bonds to form the monomers during cellular respiration.