Macronutrients:
With a few exceptions, heterotrophs require organic molecules such as carbohydrates, lipids and proteins in their diets. Enzymes breakdown these molecules into components that can be used for energy production or as sources for the “binding blocks” of life.
Carbohydrates: Carbon and energy from sugars and starches. The main dietary source of energy for heterotrophs is carbohydrates. Most carbohydrates come from plant sources. Various sugars (mosachharides) can meet this dietary need. Carbohydrates also are a major carbon source for use in organic compounds. Many plants also supply cellulose (polysaccharide) that human and other animals (except herbivores) cannot digest. Cellulose is called dietary fibre. It assists in the passage of food through the alimentary canal of mammals. Cellulose may also reduce the risk of cancer of the colon, because the mutogen and reduced if faecal elimination is more frequent.
Lipids: Highly compact energy – storage nutrients. Neutral lipids (fats) or triacyl glycerols are contained in fats and oils meat and dairy products, nuts and some fruits and vegetables high in fats such as avocados. Lipids are the good source of food energy. They produce about 9 calories (K. Cal) of usable energy per gram more than twice the energy available from equal mass of carbohydrate or protein.
Many heterotrophs have dietary requirement for lipids e.g. many animals require unsaturated fatty acids (e.g. linoleic acid, limolenic acid and arachidonic acid). These fatty acids act as precursor molecules for synthesis of steroids e.g. cholesterol. The steriols are also required for the synthesis of steroid hormones and cholesterol, which is a part of cell membranes. Other lipids insulate the bodies of some vertebrates and help maintain constant temperature proteins. Basic to the structure and function of cells. Animal sources of protein are other animals and milk. Plant sources are beans, peas and nuts. Proteins are needed for their amino acids which heterotrophs use to build their own body proteins.
Micronutrients:
They are usually small ions, organic vitamins, inorganic minerals and molecules that are used repeatedly in enzymatic reactions or as parts of certain proteins (e.g. copper in hemocyanin and iron in haemoglobin). Animals cannot synthesize them rapidly. Thus they must be oblaived from the diet.
Minerals: Some minerals are needed in large amount and are called essential minerals or macro-minerals. E.g. sodium and potassium are vital to the working of nerve and muscle in animal’s body. Animals lose large sodium, in the urine every day. Animals that sweat to help regulate body temperature lose sodium in their sweat. Daily supply of calcium is needed for muscular activity and with phosphorus for bone formation.
Other nutrients are known as trace minerals or micronutrients. Animals need these in only very small amount for various enzymatic functions.
Vitamins: Normal metabolic activity depends on small amount of more than a dozen organic substances that occur in many foods in small amount and necessary for normal metabolic functioning.
Vitamins may be water soluble or fat soluble. Most water soluble vitamins such as B vitamins and vitamin C are coenzymes needed in metabolism. The fat soluble vitamins have various functions. The dietary need for vitamin C and the fat soluble vitamins (A, D, E and K) tends to be limited to the vertebrates vitamin requirement vary in different vertebrates.
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