All Free Biology MCQs with Answers

821. Which test is used to detect proteins?

• A. Benedict's test
• B. Iodine test
• C. Biuret test
• D. Emulsion test

Explanation: Biuret test uses NaOH and CuSO4 to detect peptide bonds, giving a purple/violet color with proteins.

822. The secondary structure of protein includes

• A. α-helix and β-pleated sheet
• B. Quaternary folding
• C. Amino acid sequence
• D. Disulfide bridges

Explanation: Secondary structure involves local folding into α-helix or β-pleated sheet, stabilized by hydrogen bonds between backbone atoms.

823. Which lipid is a major component of cell membranes?

• A. Triglyceride
• B. Phospholipid
• C. Steroid
• D. Wax

Explanation: Phospholipids form the lipid bilayer of cell membranes due to their amphipathic nature (hydrophilic head, hydrophobic tails).

824. Starch and glycogen are polymers of

• A. β-glucose
• B. α-glucose
• C. Fructose
• D. Galactose

Explanation: Both starch and glycogen are polymers of α-glucose, linked by α-1,4 and α-1,6 glycosidic bonds.

825. Which vitamin is fat-soluble?

• A. Vitamin C
• B. Vitamin B12
• C. Vitamin D
• D. Vitamin B6

Explanation: Vitamins A, D, E, and K are fat-soluble. Vitamin C and B vitamins are water-soluble.

826. The enzyme that digests starch in the mouth is

• A. Pepsin
• B. Trypsin
• C. Salivary amylase
• D. Lipase

Explanation: Salivary amylase (ptyalin) begins starch digestion in the mouth, breaking it into maltose.

827. Which of the following has the highest energy content per gram?

• A. Carbohydrate
• B. Protein
• C. Lipid
• D. Nucleic acid

Explanation: Lipids provide about 9 kcal/g, while carbohydrates and proteins provide about 4 kcal/g each.

828. DNA and RNA differ in all EXCEPT

• A. Type of sugar
• B. Presence of uracil vs thymine
• C. Being nucleic acids
• D. Single vs double stranded

Explanation: Both DNA and RNA are nucleic acids. They differ in sugar (deoxyribose vs ribose), bases (T vs U), and structure (double vs single stranded).

829. The structure of DNA was discovered by

• A. Franklin and Wilkins
• B. Watson and Crick
• C. Mendel
• D. Avery

Explanation: Watson and Crick proposed the double helix model in 1953, based on Franklin's X-ray diffraction data.

830. DNA replication is

• A. Conservative
• B. Semi-conservative
• C. Dispersive
• D. Non-conservative

Explanation: Meselson and Stahl proved DNA replication is semi-conservative: each new DNA has one old and one new strand.