All Free Biology MCQs with Answers

4211. Which of the following nucleotide sequence contain 4 pyrimidine bases?

• A. GCUAGACAA
• B. GATCAATGC
• C. UAGCGGUAA
• D. Both A and C

Explanation: In DNA and RNA, these bases form hydrogen bonds with their complementary purines. Thus, in DNA, the purines adenine (A) and guanine (G) pair up with the pyrimidines thymine (T) and cytosine (C), respectively.Normally the Nucleotides contain Nitrogenous base,pentose sugar,phosphate groups.

4212. What are the six elements that make up 99% of all elements found in a living system?

• A. C, H, O, P, Mg and Fe
• B. C, N, O, P, Mn and Cl
• C. H, O, C, N, Ca and P
• D. C, H, O, S, Fe, Ca

Explanation: Carbon, hydrogen, oxygen, and nitrogen are called the four big elements of the living body as they make up about 99% of the mass of most cells. As C, H, O, and N are the lightest elements, the bonds they form are the strongest covalent bonds.Hence, the compounds formed are stable and variable in size and shape. Carbon constitutes more than 50% of the dry matter while it has been observed that the human body contains 0.5% hydrogen, 18.5% carbon, 65% oxygen, and 3.3% nitrogen. Other elements are present in a lesser amount.

4213. What is glycogen, a polymer of?

• A. Galactose
• B. Glucose
• C. Fructose
• D. Sucrose

Explanation: Glycogen (animal starch) is a polysaccharide. It is a highly branched polymer of glucose occurring in animal tissues, especially in liver and muscle cells. It is the major store of carbohydrate energy in animal cells.

4214. Amino acids are mostly synthesized from:

• A. Mineral salts
• B. Fatty acids
• C. Volatile acids
• D. A-ketoglutaric acid.

Explanation: Amino acids are mostly synthesized from a­-ketoglutaric acid. These are the precursors of amino acids. A five-carbon compound formed during Krebs' cycle is an a­-ketoglutaric acid which is the first dicarboxylic acid formed. Pyruvic acid is converted into alanine, a­ketoglutaric acid into glutamic acid and OAA into aspartic acid. The polymerization of such amino acids results in the formation of proteins.

4215. Which is distributed more widely in a cell?

• A. DNA
• B. RNA
• C. Chloroplasts
• D. Phagosomes

Explanation: RNA occurs in the nucleus as well as in the cytoplasm of the eukaryotic cells and in a prokaryotic cell, it is found in the cytoplasm. DNA is found in the nucleus, mitochondria, and chloroplast. Chloroplast and phagosomes are found only in the cytoplasm.

4216. Living cells contain 60 - 95% water. The human body contains how much water?

• A. 60 - 65%
• B. 50 - 55%
• C. 75 - 80%
• D. 65 - 70%

Explanation: Water is the most abundant substance of living beings. The water content of actively living cells varies between 60-95%. In human beings, maximum water content is found in the embryo (90 - 95%). Water content decreases to 65-70% thereafter in adults.

4217. What are the components of a nucleotide?

• A. Purine, Pyrimidine and Phosphate
• B. Purine, Sugar and Phosphate
• C. Nitrogen base, Sugar and Phosphate
• D. Pyrimidine, Sugar and Phosphate

Explanation: A nucleotide is an organic compound consisting of a nitrogen­ containing purine or pyrimidine base linked to a sugar (ribose or deoxyribose) and a phosphate group.

4218. A segment of DNA has 120 adenine and 120 cytosine bases. The total number of nucleotides present in the segment is:

• A. 120
• B. 240
• C. 60
• D. 480

Explanation: According to Chargaff's rules, the amount of adenine is always equal to that of thymine, and the amount of guanine is always equal to that of cytosine i.e.,A = T (120) and G = C (120), therefore, the total no. of nucleotides would be 120 × 4 = 480.

4219. The basic unit of nucleic acid is:

• A. Pentose sugar
• B. Nucleoid
• C. Nucleoside
• D. Nucleotide

Explanation: The nucleic acids (DNA and RNA) are molecules having complex structures and very high molecular weights. A nucleic acid is composed of many nucleotide molecules joined into a linear, unbranched chain. A nucleotide is an organic compound consisting of a nitrogen­ containing purine or pyrimidine base linked to a sugar (ribose or deoxyribose) and a phosphate group.

4220. In the double helix of DNA, the two DNA strands are:

• A. Coiled around a common axis
• B. Coiled around each other
• C. Coiled differently
• D. Coiled over protein sheath
• E. A and b

Explanation: According to the Watson-­Crick model, the DNA molecule consists of two long, parallel chains which are joined together by short crossbars at regular intervals. The two chains are spirally coiled around a common axis in a regular manner to form a right-handed double helix.