Explanation:
(a) Balanced Diet; is a diet containing all the six food classes/types of food in the right proportion to meet the body's requirement for growth, repair and maintenance.
(b) Classes of food:
-Protein
-Carbohydrate
-Vitamins
-Water
-Mineral salts/nutrients
-Fats and Oils/Lipids.
Importance of food classes

Food substances	Importance
Carbohydrate	Energy giving
protein	Growth/replacement/repair of worn out cells/repair of tissues
Fats and oil	Energy source/formation of adipose tissue for insulation
Vitamins	for proper functioning/maintenance of the body
Mineral salts/nutrients	play specific roles in metabolic processes/maintenance of the body
water	Medium for various metabolic processes/named processes

(c) The source, substrate and end products of ptyalin, pepsin and lipase are tabulated below:

Enzyme	Source	Substrate	End product
Pytalin	Salivary gland	cooked starch	maltose
pepsin	Gastric gland	protein	peptones/polypeptides/peptides
Lipase	pancrease	fat/oils/lipids	fatty acids and glycerol