Cell respiration converts oxygen and glucose into energy, water, and carbon dioxide. This energy obtained can be used for mechanical movement, maintaining body temperature, metabolic reactions, and transmitting nerve impulses. An individual's energy intake from food should equal their energy output from basal metabolism and physical activity to maintain energy balance. Basal metabolism is the minimum energy required to sustain life and can be calculated based on factors like age, sex, height, weight, and health. Food energy is measured in kilocalories, with 1 g of carbohydrates providing 4 kcal, 1 g of proteins providing 4 kcal, and 1 g of fats providing 9 kcal.

1. Nutritive Value of food
Sources and uses of food energy
Metabolism Cell respiration
Oxygen + glucose = energy + water + carbon dioxide
The waste products are water and carbon dioxide.
The energy obtained through cell respiration (38ATP) can be used as:
1. Mechanical energy is for movements of the whole body and organs
2. Heat is needed to keep the body temperature constant.
3. Chemical energy is present in all metabolic reactions.
4. Electrical energy is to transmit nerve impulses.
Energy Balance:
Energy input from the food eaten = Energy output (Basal Metabolism +Physical Activity)
Basal Metabolism: it is the energy required to keep the body functioning
(age, sex, body size like height and weight and the state of the body).
One kilocalorie is the energy needed to raise the temperature of 1 kg of
pure water to 1 degree centigrade.† The energy contained in food is
measured in kilocalories:
1 g of carbohydrates = 4 kcal
1 g of proteins = 4 kcal
1 g of fats = 9 kcal
1. Calculate the energy provided by yogurt (100 g) if its chemical
composition is 14% carbohydrates, 3% proteins, 3% fats.
2. Calculate caloric value of 250 g red meat, if its chemical composition
is 20% protein, 5 % fats.
3. Reading labels.