CBSE Class 11 Biology Digestion and Absorption Notes

Digestion and Absorption
Calorific value of carbohydrate, protein and fat: We all recognize the vital importance of food for life. A certain part of the nutrients that we take is used for building cell structures, synthesize functional molecules or replace worn-out parts. However most of the foods are used as sources of metabolic fuels. Carbohydrates, proteins and fats serve as the chief sources of energy in humans. These are oxidized and transformed into ATP, the chemical energy form used by cells to drive their multitudes of activities.
Since heat is the ultimate form of all energy, the energy value of food (or any fuel) is expressed in terms of a measure of heat energy it produces on combustion. The heat energy released by combustion of one gram of food is usually known as its gross calorific value. It is defined as the amount of heat produced in calories (cal) or in joules (J) from complete combustion of 1 gram food in a bomb calorimeter (a closed metal chamber filled with O2). The calorific value is usually expressed in terms of kcal per gram or kilojoules per gram. (1kcal = 4.184kJ) One kilocalorie is the amount of heat energy needed to raise the temperature of one kilogram of water through 10C (1.80F). Nutritionists traditionally refer to kcal as the Calorie or to kJ as Joules (always capitalized).The calorific values of carbohydrates, proteins and fats are 4.1 kcal /g, 5.65 kcal /g and 9.45 kcal /g, respectively. The actual amounts of energy liberated in the body by these nutrients, referred to as the physiologic value of the food, and are 4.0 kcal /g, 4.0 kcal /g and 9.0 kcal /g respectively.

DEFICIENCY DISEASES
Humans require a wide range of nutrients to perform various functions in the body and to lead a healthy life. You have already learnt about the functions of various nutrients in previous classes. Inadequate nutrients in the diet cause various deficiency disorders, particularly among the children and the poor.
The important deficiency disorders include protein energy malnutrition ( PEM) and disorders due to deficiencies of Vitamin A ,iron and iodine. Deficiency of protein and energy or both, called PEM, has been identified as major health and nutritional problems in India. Protein and energy intake are difficult to separate because diets adequate in energy are adequate in protein. Young children (0-6 years) require more protein for each kilogram of body weight than adults. So they are more vulnerable to malnutrition. Malnutrition is not only an important cause of childhood mortality and morbidity, but it also leads to permanent impairment of physical and mental growth of those who survive. The details of the disorders are given below.

PEM: it is an important nutritional problem among pre-school children.
It leads to various degrees of growth retardation. This is due to lack of adequate quantity of protein or carbohydrate or both.
PEM is of 2 types: Kwashiorkor and marasmus

The child suffering from PEM can recover if adequate quantities of protein and carbohydrate rich food are given.