All Free Biology MCQs with Answers

4201. Which of the following is the simplest amino acid?

• A. Alanine
• B. Asparagine
• C. Glycine
• D. Tyrosine

Explanation: Glycine is considered the simplest amino acid as it has one amino group, one carboxylic group, and no substituent functional group.

4202. Nucleotides are building blocks of nucleic acids. Each nucleotide is a composite molecule formed by:

• A. Base­ sugar ­phosphate
• B. Base ­sugar­ OH
• C. Base­s
• D. Sugar ­phosphate

Explanation: Each nucleotide consists of three distinct units ­ a phosphate group derived from phosphoric acid, a pentose sugar, and a ring-shaped nitrogenous base. Nucleoside + Phosphoric acid= Nucleotide + H2O

4203. Carbohydrates, the most abundant biomolecule on earth, are produced by:

• A. Some bacteria, algae and green plant cells
• B. Fungi, algae and green plant cells
• C. All bacteria, fungi and algae
• D. Viruses, fungi and bacteria.

Explanation: Carbohydrates are organic compounds synthesized in the chlorophyll-containing cells of some bacteria, algae, and green plant cells, during photosynthesis. Certain photo­autotrophic bacteria e.g., Green sulfur bacteria, and purple sulfur bacteria contain pigments like Chlorobium chlorophyll and bacteriochlorophyll respectively that helps them in photosynthesis.

4204. The major role of minor elements inside living organisms is to act as?

• A. Co­factors of enzymes
• B. Building blocks of important amino acids
• C. Constituent of hormones
• D. Binder of cell structure

Explanation: Minor elements are those which are required in the quantity of less than milligram/gram of dry matter, but they are essential for proper growth and development of an organism e.g., Cl, Mn, B, Zn, Cu, Mo, etc. These elements work as non­protein cofactor in enzymes e.g., Zn, Cu, etc. They also take part in oxidation-reduction reactions, e.g., Cu, with variable valency. Chloride ion enhances the activity of salivary amylase. Zinc is required for the activity of carbonic anhydrase and alcohol dehydrogenase, etc.

4205. Lipids are insoluble in water because lipid molecules are:

• A. Hydrophilic
• B. Hydrophobic
• C. Neutral
• D. Zwitter ions

Explanation: Lipid molecules are insoluble or sparingly soluble in water but are freely soluble in organic solvents like ether, alcohol, and benzene. The insolubility of lipids in water is due to the fact that the polar groups they contain are much smaller than their nonpolar portions. The nonpolar chains are long, complex hydrophobic hydrocarbon chains. If shaken in water, lipids often form small droplets or micelles. The complex created is called emulsions. These nonpolar proteins give them water-repellent or hydrophobic properties.

4206. Which of the following have carbohydrates as a prosthetic group?

• A. Glycoprotein
• B. Chromoprotein
• C. Lipoprotein
• D. Nucleoprotein

Explanation: Glycoproteins are proteins that contain sugars like carbohydrates as a prosthetic group. In most glycoproteins, the linkage is between asparagine and N­-acetyl­ D-­glucosamine. Some glycoproteins are immunoglobulins, membrane proteins, and muscle proteins. Lipoproteins are protein complexed with lipids like triglycerides, phospholipids, etc. Nucleoproteins are proteins associated with nucleic acids and chromoproteins are proteins associated with pigments e.g., cytochrome, phytochrome.

4207. Cellulose, the most important constituent of the plant cell wall, is made up of:

• A. Branched-chain of glucose molecules linked by B-1,4 glycosidic bonds in straight-chain and Alpha­1,6 glycosidic bonds at the site of branching
• B. Unbranched chain of glucose molecules linked by b­1, 4 glycosidic bond
• C. Branched-chain of glucose molecules linked by Alpha-1,6 glycosidic bonds at the site of branching
• D. Unbranched chain of glucose molecules linked by a­1, 4 glycosidic bond

Explanation: Cellulose is the most abundant carbohydrate. Cellulose molecule is composed of 1600 to 6000 glucose molecules joined together. Those polymers form long-twisting macromolecules of cellulose. The chains are unbranched and linear. The successive glucose residues are joined together by B-1,4 linkages.

4208. Lactose is composed of:

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

Explanation: Lactose is popularly known as milk sugar. It is a disaccharide composed of one molecule of glucose and one molecule of galactose. The covalent bond that joins these two monosaccharide units is called glycosidic bond or glycosidic linkage. It is a reducing sugar.

4209. What are the most diverse molecules in the cell?

• A. Lipids
• B. Mineral salts
• C. Proteins
• D. Carbohydrates

Explanation: Proteins show enormous diversity because of different proportions and sequences of twenty amino acids within the protein molecule. A large number of permutations and combinations of these amino acids are responsible for the unlimited variety of proteins. Proteins are the most abundant and most varied of the macromolecules having one or more polypeptides (chains of amino acids). The proteins constitute almost 50% of the total dry weight of the cell. Proteins may be simple or conjugated. Among conjugated, proteins may be phosphoprotein, glycoprotein, nucleoprotein, chromoprotein, lipoprotein, flavoprotein, metalloprotein, etc. Functionally proteins may be structural protein, enzymes, hormones, respiratory pigment, etc.

4210. Which purine base is found in RNA?

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

Explanation: The bases are of two types­: purines and pyrimidines. The purine derivatives adenine (A) and guanine (G) are double ring structures whereas pyrimidine derivatives thymine, cytosine, and uracil are single ring structures. Thymine (T) and cytosine (C) are found in DNA and cytosine (C) and uracil (U) is found in RNA. Pneumonic for remembering purines: Pure As Gold.