All Free Biology MCQs with Answers

2261. Organ rejection is caused by__________?

• A. B-Lymphocytes
• B. T-lymphocytes
• C. Both B and T lymphocytes
• D. RBCs

Explanation: Organ rejection is primarily a cell-mediated immune response in which T lymphocytes recognize foreign major histocompatibility complex molecules and attack the transplanted tissue. B lymphocytes mainly produce antibodies, so students may choose both B and T lymphocytes by treating all immune cells as equally responsible for rejection.

2262. Pus is formed by the dead _____________cells.

• A. RBCs
• B. Platelets
• C. White Blood Cells
• D. Hemoglobin

Explanation: Pus contains dead and living white blood cells, destroyed microbes and tissue debris accumulated during an inflammatory response. Students may choose red blood cells because they are abundant in blood, but RBCs transport oxygen and are not the main cells producing pus.

2263. BCG immunisation is for:__________?

• A. Leprosy
• B. Tuberculosis
• C. Cancer
• D. None of the above

Explanation: BCG is a vaccine used mainly to provide protection against tuberculosis, particularly severe forms of childhood TB. Students may choose leprosy because both diseases are caused by related bacteria, but BCG is not the standard vaccine for leprosy.

2264. Ingestion of bacteria by certain type of cells is termed as ________ ?

• A. Acclimatization
• B. Agglutination
• C. Paralysis
• D. Phagocytosis

Explanation: Phagocytosis is the process in which cells such as neutrophils and macrophages engulf and digest bacteria or other particles. Students may choose b because agglutination also involves microbes, but agglutination is their clumping by antibodies or other binding molecules, not their ingestion.

2265. Introduction of vaccine within the body to produce immunity is an example of____________?

• A. Artificially induced active immunity
• B. Naturally induced active immunity
• C. Artificially induced passive immunity
• D. Naturally induced passive immunity

Explanation: A vaccine is deliberately introduced into the body and stimulates the person's own lymphocytes to form antibodies and memory cells, so it produces artificially induced active immunity. Students may choose artificially induced passive immunity, but passive immunity involves receiving ready-made antibodies, such as by antiserum.

2266. An antibody is made of _________ polypeptide chains?

• A. 1
• B. 2
• C. 3
• D. 4

Explanation: A typical antibody has four polypeptide chains: two identical heavy chains and two identical light chains joined by disulfide bonds. The two-arm Y shape can mislead students into choosing b, but the arms are formed from parts of all four chains.

2267. The experiments on DNA molecules in chromosomes for knowing the basis of inherited diseases are conducted by ?

• A. Molecular biologists
• B. Microbiologists
• C. Freshwater biologists
• D. Social biologist

Explanation: Molecular biologists study DNA, genes, chromosomes, and mutations at the molecular level to determine how inherited diseases arise. Students may choose microbiologists because they study microorganisms, but that field is not specifically defined by analysing the molecular basis of inheritance.

2268. Functional unit of DNA Is____________?

• A. Nucleus
• B. Genes
• C. Chromosomes
• D. Nucleolus

Explanation: A gene is a specific segment of DNA that carries information for a functional product, such as a protein or functional RNA, making it the functional unit of heredity. A chromosome is a much larger DNA-protein structure containing many genes. Students may choose chromosome because it contains genes, but it is not the basic functional unit of DNA.

2269. Genetic information are carried in the form of long chain of molecules made-up-of _________?

• A. Amino acids
• B. RNA
• C. Nucleotides
• D. Polypeptides

Explanation: Nucleic acids carry genetic information and are long chains formed by joining nucleotides, each containing a sugar, phosphate group, and nitrogenous base. Amino acids form proteins, whereas polypeptides are chains of amino acids. Students may choose RNA because RNA can carry genetic information in some viruses, but the question asks what these information-carrying molecules are made of.

2270. The term 'gene' refers to __________?

• A. A portion of RNA
• B. A linkage group
• C. A portions of DNA
• D. A sequence of Amino

Explanation: A gene is a specific sequence of DNA that contains information for a functional product, such as a protein or functional RNA. The likely distractor is a portion of RNA, because RNA carries genetic messages in some processes, but in standard cellular genetics genes are DNA sequences.