All Free Biology MCQs with Answers

4191. Which of the following are not polymer?

• A. Proteins
• B. Polysaccharides
• C. Lipids
• D. Nucleic acids

Explanation: Lipids are fatty acid esters of alcohol and related substances. Polysaccharides are polymers of monosaccharides. Proteins are polymers of amino acids, and nucleic acids are polymers of nucleotides.

4192. Which of the following is the least likely to be involved in stabilizing the three­ dimensional folding of most proteins?

• A. Hydrogen Bonds
• B. Electrostatic Interaction
• C. Hydrophobic Interaction
• D. Ester Bonds

Explanation: Protein folding is the process by which a protein structure assumes its functional shape or conformation by allowing interaction between amino acids by various bond formations. All protein molecules are heterogeneous unbranched chains of amino acids. Different types of weak interactions hold the interacting segments together in protein. Hydrophobic interaction, H bonds, and electrostatic interactions are the weak ones and stabilize the tertiary structure of proteins, while ester bonds are covalent bonds and are least likely to be involved in stabilizing the three-dimensional folding of most proteins.

4193. The chitinous exoskeleton of arthropods is formed by the polymerisation of:

• A. N-acetyl glucosamine
• B. Lipoglycans
• C. Keratin sulfate and chondroitin sulfate
• D. D -glucosamine

Explanation: Chitin is a structural polysaccharide that constitutes the exoskeleton of arthropods. It is a complex carbohydrate in which N­-acetyl glucosamine monomers are joined together by (1,4) linkages. The chitinous exoskeleton provides strength and elasticity to arthropods.

4194. Macromolecule, chitin is a:

• A. Sulfur-containing polysaccharide
• B. Simple polysaccharide
• C. Nitrogen containing polysaccharide
• D. Phosphorous containing polysaccharide.

Explanation: Chitin is a structural polysaccharide that constitutes the exoskeleton of arthropods. It is a complex carbohydrate in which N acetyl glucosamine monomers are joined together by (1, 4) b­linkages. The chitinous exoskeleton provides strength and elasticity to arthropods. Chitin is a nitrogen containing polysaccharide.

4195. Uridine, present only in RNA, is a:

• A. Nucleoside
• B. Nucleotide
• C. Purine
• D. Pyrimidine.

Explanation: A nucleoside is a pentose sugar and a base together, without the phosphate group. Uracil is present as uridine in RNA only. Uracil + Ribose = Uridine

4196. Which one is the most abundant protein in the animal world?

• A. Trypsin
• B. Haemoglobin
• C. Collagen
• D. Insulin

Explanation: Collagen is an insoluble fibrous protein found extensively in the connective tissue of skin, tendons, and bone. Collagen accounts for over 30% of the total body proteins of mammals, and it is the most abundant animal protein.

4197. Which one of the following biomolecules is correctly characterized?

• A. Lecithin a phosphorylated glyceride found in the cell membrane.
• B. Palmitic acid ­an unsaturated fatty acid with 18 carbon atoms.
• C. Adenylic acid adenosine with a glucose phosphate molecule.
• D. Alanine amino acid­ contains an amino group and an acidic group anywhere in the molecule.

Explanation: Lecithin is a triglyceride lipid where one fatty acid is replaced by phosphoric acid, which is linked to an additional nitrogenous group called choline. It is a common membrane lipid. It is an amphipathic phospholipid, having both hydrophilic polar and hydrophobic nonpolar groups. The hydrocarbon chains of two fatty acids function as hydrophobic non­polar tails, whereas the phosphate and choline behave as a hydrophilic polar head group of the molecule. Palmitic acid is a saturated fatty acid (as it does not possess double bonds in its carbon chain) and contains 16 carbon atoms with formula C 16 H 32 O2. Adenylic acid or adenosine monophosphate is a nucleotide formed by the union of adenine (nitrogenous base), ribose (pentose sugar), and phosphate. It is formed through phosphorylation of nucleoside as phosphate combines with sugar molecule at its 5 carbon atom. Amino acids are organic acids with a carboxylic group (-COOH) having an amino group (- NH 2) generally attached to a­ carbon or carbon next to a carboxylic group. Alanine is a nonpolar and neutral amino acid having one methyl group and having an amino group attached to the carbon next to the carboxylic group.

4198. Which one of the following structural formulae of two organic compounds is correctly identified along with its related function?

• A. A: Lecithin - A component of cell membrane
• B. B: Adenine - A nucleotide that makes up nucleic acids
• C. A: Triglyceride - Major source of energy
• D. B: Uracil - A component of DNA

Explanation: A is the formula of Lecithin. Lecithin is a phospholipid and is the component of the cell membranes. B is the formula of adenine which is a nitrogenous base not a nucleotide.

4199. Carbohydrates are commonly found as starch in plants storage organs. Which of the following five properties of starch make it useful as a storage material? (1) Easily translocated (2) Chemically non­reactive (3) Easily digested by animals (4) Osmotically inactive (5) Synthesized during photosynthesis The useful properties are?

• A. (1), (3) and (5)
• B. (1) and (5)
• C. (2) and (3)
• D. (2) and (4)

Explanation: Starch is the major storage carbohydrate of plants. In most plant species it is accumulated in the chloroplast of leaves, whereas in storage organs it accumulates in the amyloplast as reserve starch. It is the osmotically inactive form of photosynthetic product and is a hexosan polysaccharide made of a large number of glucose units so it is chemically non-reactive.

4200. About 98 percent of the mass of every living organism is composed of just six elements including carbon, hydrogen, nitrogen, oxygen, and:

• A. Calcium and Phosphorus
• B. Phosphorus and Sulphur
• C. Sulphur and Magnesium
• D. Magnesium and Sodium

Explanation: 98% body mass of a living organism is composed of C H O N P ANd S according to New sindh text book