All Free Biology MCQs with Answers

841. The enzyme used in PCR to synthesize DNA is

• A. DNA polymerase I
• B. Taq polymerase
• C. RNA polymerase
• D. Reverse transcriptase

Explanation: Taq polymerase (from Thermus aquaticus) is heat-stable and used in PCR to withstand denaturation temperatures.

842. Gel electrophoresis separates DNA by

• A. Sequence
• B. Size
• C. Charge only
• D. GC content

Explanation: DNA fragments are separated by size (smaller fragments move faster) through an agarose gel matrix.

843. Insulin for diabetes treatment is now produced using

• A. Pig pancreas
• B. Human cadavers
• C. Recombinant bacteria
• D. Synthetic chemistry only

Explanation: Human insulin is produced by recombinant DNA technology using E. coli or yeast with the human insulin gene.

844. DNA ligase is used to

• A. Cut DNA
• B. Join DNA fragments
• C. Copy DNA
• D. Separate DNA strands

Explanation: DNA ligase seals nicks in DNA by forming phosphodiester bonds, joining DNA fragments together.

845. cDNA is synthesized from

• A. DNA template
• B. RNA template
• C. Protein template
• D. Lipid template

Explanation: Complementary DNA (cDNA) is synthesized from mRNA using reverse transcriptase; it lacks introns.

846. Stem cells that can form any cell type are called

• A. Multipotent
• B. Pluripotent
• C. Unipotent
• D. Differentiated

Explanation: Pluripotent stem cells (e.g., embryonic stem cells) can differentiate into any of the three germ layers.

847. Which of the following is NOT a characteristic of prokaryotic cells?

• A. Absence of membrane-bound nucleus
• B. Presence of 70S ribosomes
• C. Presence of histone proteins
• D. Circular DNA

Explanation: Prokaryotes lack histone proteins. Their DNA is not organized into nucleosomes with histones, unlike eukaryotes.

848. The fluid mosaic model of cell membrane was proposed by

• A. Robertson
• B. Singer and Nicolson
• C. Gorter and Grendel
• D. Danielli and Davson

Explanation: Singer and Nicolson proposed the fluid mosaic model in 1972, describing the membrane as a fluid lipid bilayer with embedded proteins.

849. Which organelle is responsible for the synthesis of proteins destined for secretion?

• A. Smooth ER
• B. Golgi apparatus
• C. Rough ER
• D. Lysosomes

Explanation: Rough ER has ribosomes on its surface and synthesizes proteins that are either secreted or inserted into membranes.

850. The powerhouse of the cell is

• A. Nucleus
• B. Mitochondria
• C. Chloroplast
• D. Ribosome

Explanation: Mitochondria are called the powerhouse because they produce ATP through oxidative phosphorylation.