All Free Biology MCQs with Answers

4661. Condensation of a glycerol with two fatty acids and one phosphoric acid yields:

• A. One molecule of water
• B. Two molecules of water
• C. Three molecules of water
• D. Four molecules of water

Explanation: During the condensation reaction of glycerol with two fatty acids and one phosphoric acid to form phosphatidic acid, three ester bonds are created: two with the fatty acids and one with the phosphoric acid. Each esterification releases one molecule of water, resulting in a total of three water molecules being produced. This confirms that Option C is correct. Option A is incorrect because it underestimates the number of water molecules released; Option B is incorrect because it fails to account for all three ester bonds; and Option D is incorrect because it overestimates the number of water molecules produced.

4662. The most widely spread acylglycerol is:

• A. Triacylglycerol
• B. Diacylglycerol
• C. Monoacylglycerol
• D. Monoglyceride

Explanation: Triacylglycerol, also referred to as triglyceride, is the most widely spread acylglycerol because it is the primary form of stored energy in animals and plants. It consists of three fatty acids esterified to a glycerol backbone, making it the most abundant lipid. In contrast, diacylglycerol and monoacylglycerol have fewer fatty acid chains and are less common, often serving specific roles in metabolism or digestion. Thus, triacylglycerol is the correct answer due to its widespread presence and function.

4663. Biological macromolecules are polymers that are formed when _ are joined by a _ reaction.

• A. Monomers, Dehydration
• B. Subunits, Reduction
• C. Multimers, Dehydration
• D. Monomers, Hydrolysis

Explanation: Biological macromolecules are large molecules essential for life, formed from smaller units called monomers. The monomers are linked together through a dehydration reaction, also known as a condensation reaction, where a water molecule is removed during the bonding process. Option A is correct because it accurately describes this process. Option B is incorrect because reduction reactions are not involved in forming macromolecules. Option C is incorrect because it incorrectly uses 'multimers' instead of 'monomers.' Option D is incorrect because hydrolysis is the process of breaking down polymers, not forming them.

4664. Which one of the following characteristics is not common among carbohydrates, lipids, and proteins?

• A. They are composed of a carbon backbone with functional group attached
• B. They all play a role in cell signaling and communication
• C. Their polymers are broken apart by hydrolysis
• D. The molecules are held together by ionic bondings

Explanation: The molecules of all carbohydrates, lipids and proteins are held together by covalent bonds and not ionic bonds. The main bonds within these biological macromolecules are:Carbohydrates: Monosaccharide units are linked by glycosidic bonds, which are covalent bonds.Proteins: Amino acids are linked by peptide bonds (a type of amide bond), which are also covalent bonds. While ionic bonds can form between the charged side chains (R groups) of amino acids and are important for stabilizing the specific three-dimensional (tertiary and quaternary) structure of a protein, they are secondary interactions, and the main structural link between amino acids is the covalent peptide bond.Lipids: In the most common lipids like triglycerides, fatty acids are linked to a glycerol backbone by ester bonds, which are covalent bonds. The hydrocarbon chains themselves are composed of nonpolar covalent bonds.

4665. The first phospholipid identified in biological tissue was:

• A. Phosphatidylcholine
• B. Lethanolamine
• C. Phosphatidylserine
• D. Phosphatidic acid

Explanation: The first phospholipid identified in biological tissues was phosphatidylcholine, also known as lecithin. Theodore Nicolas Gobley discovered it in 1847 in the egg yolk of chickens. This marked a significant milestone in biochemistry, as phosphatidylcholine plays a crucial role in cell membrane structure and function. The other options, phosphatidylethanolamine, phosphatidylserine, and phosphatidic acid, were identified later and did not hold the distinction of being the first discovered phospholipids.

4666. The polar region of a phospholipid molecule is:

• A. Hydrophobic head
• B. Hydrophilic head
• C. Hydrophilic tail
• D. Hydrophobic tail

Explanation: Phospholipids are composed of a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails. The head is polar, allowing it to interact with aqueous environments, thus making it the correct answer. The tails are made from fatty acids, which are non-polar and do not interact with water, explaining why the other options are incorrect.

4667. The non-polar region of a phospholipid molecule consists of:

• A. Glycerol
• B. Choline
• C. Phosphoric acid
• D. Fatty acids

Explanation: Phospholipids are crucial components of cell membranes, featuring a unique structure with a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails. The head consists of glycerol and a phosphate group, which are polar, whereas the tails are composed of fatty acids, which are non-polar. This non-polar characteristic of the fatty acid tails is what allows them to repel water, forming the non-polar region necessary for the self-assembly of the phospholipid bilayer in cell membranes. Glycerol and phosphoric acid are both part of the polar head. Choline, if present, also contributes to the polar head. Fatty acids alone form the non-polar region, making Option D the correct choice.

4668. In phosphatidic acid fatty acids are attached to carbon no. _ of glycerol.

• A. 01
• B. 02
• C. 01 and 02
• D. 03

Explanation: In phosphatidic acid, the glycerol molecule has two fatty acids attached to the first and second carbons, forming ester bonds. This is a key feature of phosphatidic acid, which is a precursor in the biosynthesis of many lipids. The third carbon of glycerol is linked to a phosphoric acid group. This structural arrangement is crucial for forming phosphatidic acid. Options A and B are incorrect because they indicate only one carbon attachment, whereas both carbons 1 and 2 are involved. Option D is incorrect because it refers to the site of phosphoric acid attachment, not the fatty acids.

4669. In phosphatidic acid, phosphoric acid is attached to carbon no. _ of glycerol.

• A. 01
• B. 02
• C. 03
• D. 04

Explanation: Phosphatidic acid is formed when two fatty acids are esterified to the first and second carbon atoms of glycerol, and phosphoric acid is esterified to the third carbon. Options 1 and 2 are incorrect because these carbons are occupied by fatty acids, not phosphoric acid. Option 4 is incorrect because glycerol only has three carbon atoms, making this option impossible.

4670. For synthesis of a phospholipid, nitrogenous base is attached to _ of phosphatidic acid.

• A. First fatty acid
• B. Second fatty acid
• C. Phosphoric acid
• D. Glycerol

Explanation: In the synthesis of a phospholipid, the nitrogenous base is attached to the phosphoric acid, which in turn is connected to the glycerol backbone at carbon no. 3. This forms the hydrophilic head of the phospholipid. The fatty acids are esterified to the other carbons of glycerol, creating the hydrophobic tails. Options A and B are incorrect because the fatty acids do not participate in nitrogenous base attachment. Option D is incorrect because, while glycerol is part of the backbone, the nitrogenous base is specifically attached via the phosphoric acid.