Question

Carbohydrates are ______________.
A) Used to make paper
B) Produced as an intermediate in the synthesis of proteins.
C) The polyhydroxy aldehyde or polyhydroxy ketone
D) All of these

Answer 1

Hint: Carbohydrates are also called saccharides. Recall that carbohydrates can be of two types i.e., aldoses and ketoses. General formula of carbohydrates is: ${C_x}{({H_2}O)_y}$. You must know that cellulose which is found in plants is also a carbohydrate. Also, give a thought to the process of synthesis of proteins.

Complete answer:
Carbohydrates, also termed as saccharides or sugars, one of the basic components of food, are composed of carbon, hydrogen, and oxygen. General formula of carbohydrates is: ${C_x}{({H_2}O)_y}$. Structurally, they are polyhydroxy carbonyl compounds and more specifically, they are polyhydroxy aldehydes or polyhydroxy ketones. The saccharides containing an aldehyde group are called aldoses and those with a ketone group are called ketoses. They are classified into four major groups- monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
- Monosaccharides: Carbohydrates that cannot be hydrolysed to simpler forms. Examples - Glucose, fructose etc.
 - Disaccharides: Carbohydrates which on hydrolysis gives two units of monosaccharides. Examples - sucrose, maltose etc.
- Oligosaccharides: Carbohydrates which on hydrolysis gives three to eight monosaccharides units. Examples – raffinosus etc.
- Polysaccharides: Carbohydrates which on hydrolysis gives more than eight monosaccharides units. Examples - cellulose, starch etc.
Let us discuss cellulose:
Cellulose is the most abundant polysaccharide. It is the major constituent of plant cell walls. It is used extensively in manufacturing paper, cellulose fibres, rayon, adhesives, and so on.
Carbohydrates are also produced as an intermediate in the synthesis of proteins. This is based on the fact that protein synthesis consists of two processes and these two processes can be summed up as:
${\text{DNA}} \to {\text{RNA}} \to {\text{Protein}}$
Now, the intermediate here is RNA, which is built with ribose sugar. Ribose is a simple sugar and carbohydrate. Its structure is as follows:

Thus, on summarising above all points, option D is the correct answer.

Note:
Cellulose on hydrolysis yields D-glucose. Glucose has a six-carbon straight chain with five hydroxyl groups and an aldehyde group. It can be identified as an aldohexose. Thus, it comes in the category of polyhydroxy aldehydes. Its structure is: