All Free Biology MCQs with Answers

4271. _ is the most abundant carbohydrate in nature.

• A. Waxes
• B. Glycerol
• C. Starch
• D. Cellulose

Explanation: A type of carbohydrate, cellulose contains chains of glucose rings, providing strength and rigidity. Cellulose forms the cell walls of plants and is the primary constituent of wood, making this organic compound the most abundant one on the surface of the Earth.

4272. Which of the following is a keto-sugar?

• A. Glyceraldehyde
• B. Dihydroxyacetone
• C. Ribose
• D. Glucose

Explanation: Glyceraldehyde, ribose and glucose are examples of aldose sugars while dihydroxyacetone is an example of keto sugar.

4273. Amino acid in which the R-group is hydrogen is:

• A. Glycine
• B. Alanine
• C. Leucine
• D. Valine

Explanation: Amino acids mainly differ due to the type or nature of R group. R may be a hydrogen atom as in glycine, or CH3 as in alanine, or any other group.

4274. Which of the following is purine?

• A. Guanine
• B. Cytosine
• C. Thymine
• D. Uracil

Explanation: Nitrogenous bases are of two types, single ringed pyrimidines and double ringed purines. Pyrimidines are cytosine, thymine, and uracil, while purines are adenine and guanine.

4275. The simplest monosaccharide containing a keto group is:

• A. Glyceraldehyde
• B. Dihydroxyacetone
• C. Glucose
• D. Ribose

Explanation: Glyceraldehyde, ribose, and glucose are aldose sugars while dihydroxyacetone is the simplest three-carbon keto sugar.

4276. Monosaccharides are major components of:

• A. DNA, ATP, Ribulose bisphosphate and Cysteine
• B. DNA, NAD and Insulin
• C. DNA, NADP, ATP and Ribulose bisphosphate
• D. DNA, RNA and Myosin

Explanation: Ribose is a five carbon sugar and a monosaccharide. It is a major component of nucleosides/ nucleotides, dinucleotides, nucleic acid and RuBP (carbon dioxide acceptor in dark reaction of photosynthesis).

4277. Number of base pairs in one turn of DNA is:

• A. 10
• B. 2
• C. 34
• D. 54

Explanation: The two strands of DNA are wound around each other so that there are 10 base pairs in each turn of the helix.

4278. Which molecular structure of enzyme is essential for activity of enzyme?

• A. Primary Structure
• B. Secondary Structure
• C. Quatemary Structure
• D. Tertiary Structure

Explanation: Globular structure of enzyme has a very important role in its activity and this globular structure attains at least tertiary level structure.

4279. The compounds which on hydrolysis yield polyhydroxy aldehyde or ketone subunits are:

• A. Lipids
• B. Proteins
• C. Polynucleotides
• D. Carbohydrates

Explanation: Carbohydrates are polyhydroxy aldehydes or ketones or complex substances which on hydrolysis yield polyhydroxy aldehyde or ketone subunits. Proteins are polymers of amino acids, Lipids are heterogeneous groups of compounds related to fatty acids, while the polynucleotide chain is made up of nucleotides.

4280. Secondary structure of protein is found in:

• A. Trypsin
• B. Keratin
• C. Insulin
• D. Glucagon

Explanation: Keratin is a fibrous protein having secondary structure and mostly found in nails and hairs. Trypsin is a protease while insulin and glucagon are the hormones and all are globular proteins.