All Free Biology MCQs with Answers

2211. Euglena belongs to the kingdom___________?

• A. Fungi
• B. Monera
• C. Protista
• D. Non of them

Explanation: Euglena is a unicellular eukaryote with a nucleus and membrane-bound organelles, so it is placed in kingdom Protista. It is not a fungus because it lacks the typical fungal body and nutrition, and it is not Monera because Monerans are prokaryotic and lack a true nucleus. The common mistake is selecting Monera simply because Euglena is single-celled.

2212. Nitrogen is present in___________?

• A. carbohydrates
• B. proteins
• C. lipids
• D. carbonates

Explanation: Proteins contain nitrogen because their amino acids have amino groups, written as -NH2, in addition to carbon, hydrogen, and oxygen. Most carbohydrates and lipids do not contain nitrogen in their basic structures, so students may choose lipids if they incorrectly generalize that all major organic molecules have the same elements.

2213. Proteins are made from amino acids by the process of ______________?

• A. Hydrolysis
• B. Pinocytosis
• C. Dehydration synthesis
• D. Active transport

Explanation: Amino acids join by peptide bonds through dehydration synthesis, in which a molecule of water is removed as the bond forms. Hydrolysis is the reverse process, breaking peptide bonds by adding water, so it is the likely mistaken choice.

2214. enzymes are actually composed of ___________?

• A. Carbohydrates
• B. Proteins
• C. Nucleic Acid
• D. Fats

Explanation: Most enzymes are globular proteins whose specific three-dimensional shapes form active sites for binding substrates and catalysing reactions. A small number of catalytic RNA molecules, called ribozymes, are exceptions, but proteins are the expected general answer in basic biology. Students may choose nucleic acid because RNA can act as a catalyst, but ribozymes are exceptions rather than the usual enzyme composition.

2215. Which of the following is a disease caused by deficiency of protein in children?

• A. Pellagra
• B. Marasmus
• C. Beri-Beri
• D. Rickets

Explanation: Marasmus results from severe deficiency of total calories and protein, producing marked wasting in children. Pellagra is due to niacin deficiency, beri-beri to thiamine deficiency and rickets to vitamin D deficiency, so students may choose a familiar nutritional disease without identifying the missing nutrient.

2216. The plant dye Henna imparts orangered colour to skin and hairs due to its reaction with which of the following?

• A. Lipids
• B. Carbohydrates
• C. Amino acids
• D. Protein and amino acids

Explanation: Henna contains lawsone, which reacts with proteins and amino groups in keratin of the skin and hair to produce an orange-red stain. Students may choose carbohydrates because henna is a plant product, but the colour-forming interaction is mainly with keratin proteins and their amino acids.

2217. Insulin is a human__________?

• A. Gene
• B. Protein
• C. Glucose
• D. Diabetes

Explanation: Insulin is a peptide hormone made of amino acids, so it is a protein that regulates blood glucose concentration. Students may choose gene because the insulin gene encodes it, but the gene is the DNA instruction, whereas insulin is the resulting protein.

2218. The simplest amino acid is_________?

• A. alanine
• B. glycine
• C. valine
• D. phenylalanine

Explanation: Glycine is the simplest amino acid because its side chain is only a hydrogen atom, giving it the smallest possible amino-acid structure. Alanine is a common mistaken choice because it is also simple, but its side chain contains an additional methyl group.

2219. Which of the following are proteins in nature?

• A. Antibodies.
• B. Interferons
• C. Antitoxins
• D. All of these

Explanation: Antibodies, interferons and antitoxins are protein molecules involved in defence, signalling or neutralising toxins. Students may select only antibodies because they most commonly associate proteins with immunity, but interferons and antitoxins are also protein-based defensive substances.

2220. helical structure is kept by the formation of _________ bonds among amino acids molecules?

• A. H bonds
• B. Disulphide Bond
• C. Ionic bond
• D. Hydrophobic bonds

Explanation: An alpha helix is stabilized by hydrogen bonds between the carbonyl oxygen of one peptide bond and the hydrogen of another peptide bond in the same polypeptide chain. Disulphide bonds and ionic interactions can stabilize higher levels of protein structure, but they do not produce the regular alpha-helical backbone pattern. Students may choose b because disulphide bonds are important in protein folding, confusing tertiary stabilization with secondary structure.