All Free Biology MCQs with Answers

2101. Sickle cell anemia is an example of_________________?

• A. Chromosomal aberration
• B. Insertion of gene
• C. Deletion of gene
• D. Point mutation

Explanation: Sickle-cell anaemia results from a single nucleotide substitution in the beta-globin gene, which changes one amino acid in haemoglobin, so it is a point mutation. The likely alternative is chromosomal aberration, but that involves a large change in chromosome structure or number rather than a change at one gene position.

2102. Test cross is used to find_____________?

• A. Trait
• B. Phenotype
• C. Genotype
• D. Ratios

Explanation: A test cross mates an individual showing a dominant phenotype with a homozygous recessive individual. The offspring pattern reveals whether the tested parent is homozygous or heterozygous, so the test cross determines genotype. Phenotype is already visible, while ratios are only the resulting observations, not the purpose of the cross.

2103. An example of codominance is______________?

• A. A' blood group
• B. B' blood group
• C. O' blood group
• D. AB' blood group

Explanation: AB blood group demonstrates codominance because IA and IB alleles are both expressed in the phenotype, producing both A and B antigens on red blood cells. In blood group O, neither A nor B antigen is expressed, and A or B alone does not show codominance. The likely mistake is choosing A because it is a named blood group, without checking whether both alleles are expressed together.

2104. The innate tendency of offspring to resemble their parents is called________?

• A. heridity
• B. heridisk
• C. varaition
• D. none

Explanation: Heredity is the tendency of offspring to resemble their parents because genetic information is transmitted from one generation to the next. Variation means differences among offspring, so students may choose it if they confuse resemblance with inherited differences; option a is misspelled as “heridity” but clearly intends heredity.

2105. Release of the ovum from ovary is called__________?

• A. fertilization
• B. ovulation
• C. implantation
• D. none of these

Explanation: Ovulation is the release of a mature secondary oocyte from an ovarian follicle, usually around the middle of the menstrual cycle. Fertilization is the later fusion of gametes, while implantation is attachment of the embryo to the uterine lining.

2106. Yellowish glandular structure which produces progesterone is_____________?

• A. Graffian follicle
• B. Ovary
• C. Corpus luteum
• D. Placenta

Explanation: After ovulation, the ruptured Graafian follicle changes into the corpus luteum, a yellow endocrine structure that secretes progesterone. Progesterone maintains the uterine lining for possible implantation. The Graafian follicle is the precursor, so choosing it confuses the structure before ovulation with the progesterone-secreting structure after ovulation.

2107. Which one of the following remove nucleotides from the ends of DNA or RNA?

• A. Endonuclease
• B. Exonuclease
• C. S 1 nuclease
• D. Deoxyribonuclease

Explanation: Exonucleases remove nucleotides one at a time from the free ends of DNA or RNA strands. An endonuclease cuts within a nucleic-acid strand, so students who confuse end cutting with internal cutting may choose a.

2108. The active site of an enzyme______________?

• A. Never changes
• B. Forms no chemical bond with substrate
• C. Determined by structure and the specificity of the enzyme
• D. They are non specific in their action

Explanation: The active site's shape and chemical groups arise from the enzyme's three-dimensional structure, giving the enzyme specificity for particular substrates. A common mistake is choosing a because the active site may adjust slightly during induced fit, but it is not completely unchanging in every enzyme.

2109. Which statement is incorrect about Lock and Key Model________________?

• A. Specific enzyme can transform only a specific substrate
• B. Active site of an enzyme is a non flexible structure
• C. Active site does not change before during or even after the reaction
• D. It explains the mechanism of every chemical reaction

Explanation: The lock-and-key model proposes a relatively rigid active site and specificity between an enzyme and its substrate, but it does not explain every chemical reaction. Students may choose c because the model treats the active site as unchanged, but d is the broader and incorrect claim.

2110. A three dimensional dcavity bearing a specific charge by which the enzyme reacts with its substrate is called_________________?

• A. Active site
• B. Binding site
• C. Catalytic site
• D. Allosteric site

Explanation: The active site is the three-dimensional region of an enzyme with a specific shape and chemical environment that binds the substrate and carries out catalysis. The likely alternative is binding site, but a binding site may only attach a molecule, whereas the active site includes both binding and catalytic regions.