Question

Which one is not disaccharide?
(a) Lactose
(b) Sucrose
(c) Maltose
(d) Starch

Answer 1

Hint Carbohydrates may be defined as ‘organic substances having carbon, hydrogen and oxygen’. Carbohydrates are classified into monosaccharides and oligosaccharides.
Oligosaccharides are the compound carbohydrates by condensation of 2-9 monosaccharide molecules. These are classified according to the number of their monosaccharide units or monomers. For example- disaccharides, trisaccharides, etc.

Complete Answer- Disaccharides are the smallest and commonest oligosaccharides found in nature. They are formed by condensation of two monosaccharides molecules. The most important disaccharides are sucrose, lactose, and maltose.
Lactose or milk sugar is found in the milk of mammals. It is a unique product of mammary glands and not found in other parts of the animal body. It is a reducing sugar and formed by the condensation of two hexose molecules, glucose and galactose.
Sucrose is the common sugar of commerce and kitchen and also called household sugar. It is the storage product of photosynthesis in sugar cane and sugar beet plants. It is formed by the condensation of one molecule each of glucose and fructose by the elimination of a molecule of water from glycosidic hydroxyl groups. It is non-reducing sugar.
Maltose or malt sugar is found in germinating starchy seeds where starch is being broken down. It is formed by the two molecules of glucose and also by reducing sugar.
Starch is the reserved food material of the higher plants and is found in cereals, legumes, potatoes, etc. it is a polyglycan homopolysaccharide and is formed as the end product of photosynthesis.

So, the correct answer is option (D) starch.

Note- Oligosaccharides are soluble in water. They are commonly sweet in taste and all the carbohydrates are transported in oligosaccharide state. They form the component of the external surface of the plasma membrane and cell coat.
Polysaccharides contain a large number of monosaccharides residues and are usually tasteless. They form the component of the cell wall.