Question

An example of disaccharide made up of two units of the same monosaccharide, is:
(A) Maltose
(B) Sucrose
(C) Lactose
(D) None

Answer 1

Hint: The disaccharide that has two same monosaccharide units from the options is a reducing sugar. The glycosidic bond in this disaccharide is of $\alpha$-type. If it is $\beta$-type, then the disaccharide is called cellulose.

Complete step by step solution:
Carbohydrates are the hydrates of carbon which have free aldehyde or ketone groups alongside hydroxyl groups. However, they also exist in pyranose and furanose forms.
- Depending upon the number of monosaccharide units obtained upon hydrolysis, carbohydrates are classified into categories like monosaccharides, disaccharides, oligosaccharides and polysaccharides.
- Disaccharide is a carbohydrate which upon its hydrolysis gives two molecules of monosaccharides. We need to find a disaccharide from the given options that give two monosaccharide units. Let’s see all of them one by one to get the answer.
A) Maltose:

Thus, we can see that Maltose gives two molecules of D-Glucose upon hydrolysis. Thus, we can say that maltose is made up of two glucose molecules.
B) Sucrose:
When we hydrolyze sucrose, we get D-Glucose and D-Fructose. Thus, we can see that it is made up of two different monosaccharide molecules.
C) Lactose:
When we hydrolyze lactose, we get two monosaccharide units; galactose and glucose. Thus, it is also made up of two monosaccharide units.
So, from the above discussion, we can say that Maltose is a disaccharide which is made up of the same monosaccharide units.

Therefore the correct answer is (A).

Note: The disaccharides can be divided into broadly two categories; reducing and non-reducing sugars. In reducing sugars, the carbonyl group is free and in non-reducing sugars, there is no reducible centre present.