All Free Biology MCQs with Answers

4331. It is an amino acid and also a part of phospholipid:

• A. Serine
• B. Ethanolamine
• C. Choline
• D. Aspartic acid

Explanation: Serine is an amino acid and is also a part of phospholipids. It is one of the 20 standard amino acids used in protein synthesis, and it serves as a head group in certain phospholipids, such as phosphatidylserine, which is a key component of cell membranes.

4332. Myelin sheath of neuron is composed of:

• A. Sphingolipids
• B. Ethanolamine
• C. Choline
• D. Waxes

Explanation: The myelin sheath is primarily composed of lipids, and sphingolipids are a major component of it. More specifically, a type of sphingolipid called "sphingomyelin" is a key constituent of the myelin sheath. Sphingomyelin is a combination of a fatty acid, sphingosine, and a phosphate group. It forms a part of the lipid-rich layer that makes up the myelin sheath.

4333. Which of following can form a biopolymer?

• A. Amino acid
• B. Nucleotides
• C. Monosaccharides
• D. All of these

Explanation: Option D is correct. Biopolymers are large molecules made up of repeating units of smaller molecules. Amino acids are the repeating units of proteins, which are the most abundant biopolymers in the human body. In the case of nucleotides, the monomers are linked together by phosphodiester bonds to form nucleic acids, which are the genetic material of all living organisms. Monosaccharides are the monomers that make up biopolymers called polysaccharides. Polysaccharides are very important molecules in living organisms. They are used for energy storage, structural support, and cell signaling.

4334. Muneeb is a chemistry student who is carrying out an experiment between an alcohol and acetic acid in the laboratory. The product formed at the end of the experiment will be:

• A. Glucose and Oxygen
• B. An ester and Water molecule
• C. Glycogen and Water molecule
• D. Glycerol and Sulfuric acid

Explanation: Option B is correct. The product formed at the end of the experiment will be an ester. An ester is a chemical compound that is formed by the reaction of an alcohol and an acid. The general formula for an ester is RCOOR', where R and R' are alkyl groups. In Muneeb's experiment, the alcohol will react with the acetic acid to form an ester. The type of ester that is formed will depend on the specific alcohol and acetic acid that are used. For example, if Sara uses ethanol and acetic acid, the product will be ethyl acetate. Ethyl acetate is a colorless liquid with a fruity smell. It is used in a variety of products, including perfumes, paints, and solvents. The reaction between an alcohol and an acid is called an esterification reaction. The esterification reaction is catalyzed by an acid, such as sulfuric acid. The acid helps to activate the alcohol and the acid, so that they can react more easily.

4335. Lipids contain double amount of energy as compared to the same amount of carbohydrates due to the presence of:

• A. Lower proportion of C-H bonds
• B. Higher proportion of C-H bonds
• C. Higher proportion of oxygen
• D. None of these

Explanation: Option B is correct. Yes, that is correct. Lipids contain more energy than carbohydrates because they have a higher proportion of carbon-hydrogen bonds and lower proportion of oxygen. Carbon-hydrogen bonds are very strong and require a lot of energy to break. When lipids are broken down, the energy from these bonds is released. Carbohydrates, on the other hand, have a higher proportion of oxygen-hydrogen bonds. Oxygen-hydrogen bonds are not as strong as carbon-hydrogen bonds, so they release less energy when they are broken down. This is why lipids are considered to be a more concentrated source of energy than carbohydrates. A gram of fat contains about 9 calories, while a gram of carbohydrate contains about 4 calories.

4336. Lipids are organic molecules which are insoluble in:

• A. Alcohol
• B. Ether
• C. Chloroform
• D. Water

Explanation: Option D is correct. Lipids are organic molecules that are insoluble in water. This is because lipids are non-polar molecules, while water is a polar molecule. Non-polar molecules do not dissolve in polar solvents, such as water. The solubility of lipids in alcohol depends on the structure of the lipid. Triglycerides have a very hydrophobic (water-fearing) structure, which makes them insoluble in alcohol. Phospholipids, on the other hand, have a more hydrophilic (water-loving) structure, which makes them soluble in alcohol. In general, lipids with shorter hydrocarbon chains are more soluble in alcohol than lipids with longer hydrocarbon chains. This is because the shorter hydrocarbon chains have more exposed hydrogen atoms, which can interact with the water molecules in the alcohol Lipids are organic molecules that are soluble in chloroform. Chloroform is a non-polar solvent, and lipids are also non-polar molecules. This means that the hydrophobic parts of the lipid molecules can interact with the hydrophobic parts of the chloroform molecules, allowing the lipids to dissolve in the chloroform. Lipids are organic molecules that are soluble in ether. Ether is a non-polar solvent, and lipids are also non-polar molecules. This means that the lipids can interact with the ether molecules through van der Waals forces.

4337. What type of linkage is formed when an alcohol and an acid react?

• A. Ionic bond
• B. Peptide bond
• C. Glycosidic linkage
• D. Ester bond

Explanation: Option D is correct. When an alcohol and an acid react, they form an ester linkage. An ester linkage is a type of covalent bond that is formed between an alcohol group and a carboxylic acid group. The general formula for an ester is RCOOR', where R and R' are alkyl groups. The reaction between an alcohol and an acid is called an esterification reaction. The esterification reaction is a condensation reaction, which means that it produces a water molecule as a byproduct. The esterification reaction is catalyzed by an acid, such as sulfuric acid. The esterification reaction is reversible, which means that the ester can be broken down back into the alcohol and the acid. However, the esterification reaction is usually carried out under conditions that favor the formation of the ester.

4338. The head of phospholipid molecule is polar (hydrophilic) due to:

• A. Fatty acids
• B. Phosphate
• C. Carboxylic acid
• D. Triacylglycerol

Explanation: Option B is correct. The head of a phospholipid molecule is polar (hydrophilic) due to the presence of a phosphate group. The phosphate group is negatively charged, which makes it attracted to water molecules. The water molecules surround the phosphate group, which helps to keep the phospholipid molecule stable in an aqueous environment. In addition to the phosphate group, the head of a phospholipid molecule may also contain other polar groups, such as a choline group or an ethanolamine group. These groups are also attracted to water molecules, which further contributes to the hydrophilicity of the head of the phospholipid molecule.

4339. Which of the following are the most prominent part of cell membranes in living organisms?

• A. Terpenoids
• B. Waxes
• C. Phospholipids
• D. Acylglycerols

Explanation: Option C is correct. Phospholipids are the most prominent part of cell membranes in living organisms. They make up about 50% of the mass of most cell membranes, and they are essential for the structure and function of the membrane. Phospholipids are amphipathic molecules, which means that they have both hydrophilic (water-loving) and hydrophobic (water-fearing) parts. The hydrophilic head of the phospholipid is made up of a phosphate group and a small group of other atoms. The hydrophobic tails of the phospholipid are made up of two fatty acids. The hydrophilic heads of the phospholipids are attracted to water, while the hydrophobic tails are repelled by water. This causes the phospholipids to spontaneously form bilayers in water. The hydrophilic heads of the phospholipids line up on the outside of the bilayer, where they are exposed to water. The hydrophobic tails of the phospholipids line up on the inside of the bilayer, where they are protected from water.

4340. An organic compound that belongs to lipids:

• A. C18H32O16
• B. C57H10O6
• C. C300H500O250
• D. C42H45O23N17S

Explanation: Option B is correct. The molecular formula C57H10O6 represents the compound triacylglycerol, also known as a triglyceride. It is a type of lipid that is made up of three fatty acids bonded to a glycerol molecule. Triglycerides are the most abundant type of lipid in the human body, and they are used for energy storage.