All Free Biology MCQs with Answers

1851. Ribosomes are tiny Granules first studied in 1955 by__________?

• A. De-Duve
• B. Schwann
• C. August Weismann
• D. Palade

Explanation: George Emil Palade first studied ribosomes using electron microscopy and described them as small cytoplasmic granules in 1955. Schwann is associated with cell theory, so students may select him by confusing a general cell-biology contribution with the discovery of ribosomes.

1852. _____________________ contains the green chemical called chlorophyll.

• A. Cytoplasm
• B. Cell membrane
• C. Chloroplasts
• D. Vacuole

Explanation: Chlorophyll is the green photosynthetic pigment located in the thylakoid membranes inside chloroplasts. Students may choose cytoplasm because chloroplasts are suspended in it, but the pigment is contained within the chloroplast rather than freely dissolved in the cytoplasm.

1853. Carcinogens is __________ types of chemicals.

• A. Cancer causing
• B. Pneumonia causing
• C. Emphysema
• D. Asthma

Explanation: Carcinogens are chemical or physical agents that can cause cancer by damaging DNA or disturbing the control of cell division. Pneumonia, emphysema and asthma are diseases or conditions, not meanings of the word carcinogen. Students may choose emphysema because it is strongly associated with smoking, but a carcinogen refers to a cancer-causing agent.

1854. Which of the following gases readily combines with the haemoglobin of the blood?

• A. Carbon monoxide
• B. Methene
• C. Oxygen
• D. Nitrogen dioxide

Explanation: Carbon monoxide binds haemoglobin to form carboxyhaemoglobin, with an affinity about 200 to 250 times greater than oxygen, reducing oxygen transport to tissues. Students may choose oxygen because it normally binds haemoglobin, but the question asks which gas binds unusually strongly and dangerously.

1855. The respiratory problem most common in smokers is_________?

• A. tuberculosis
• B. emphysema
• C. asthma
• D. cancer

Explanation: Long-term smoking commonly causes emphysema, in which alveolar walls are destroyed, reducing respiratory surface area and impairing gas exchange. Cancer is also strongly associated with smoking, but emphysema is the characteristic chronic obstructive respiratory disease intended here.

1856. Of the following, which one is a contagious disease?

• A. Tuberculosis
• B. Lungs cancer
• C. Asthma
• D. Emphysema

Explanation: Tuberculosis is caused by Mycobacterium tuberculosis and spreads between people, especially through airborne droplets, so it is contagious. Lung cancer, asthma and emphysema are not ordinarily transmitted from one person to another. Students may choose lung cancer because it is a serious lung disease, confusing harmful disease with communicable disease.

1857. More than ___________ compounds of tar of tobacco smoke are involved to cause cancer?

• A. 5
• B. 90
• C. 15
• D. 10

Explanation: The question uses the conventional textbook figure that more than 10 compounds in tobacco tar contribute to cancer, so option d is intended. These carcinogenic substances can damage DNA and promote uncontrolled cell division. Students may choose 90 because tobacco smoke contains many harmful chemicals overall, but that is not the specific figure stated for the carcinogenic tar compounds in this syllabus.

1858. A chemical substance which can react (in place of substrate) with the enzyme but is not transformed into product/s and thus blocks the active site temporarily or permanently is called_______________?

• A. Co-enzyme
• B. Blocker
• C. Inhibitor
• D. Cofactor

Explanation: An inhibitor is a substance that reduces enzyme activity by binding to the enzyme; a competitive inhibitor can occupy the active site and prevent the substrate from binding. Cofactors and coenzymes assist enzyme activity rather than blocking it. Students may choose blocker because it describes the effect informally, but inhibitor is the accepted biological term for a substance that suppresses enzyme action.

1859. A substance which binds at the active site of the enzyme but does not result in the formation of the products is called________________?

• A. Irreversible inhibitor
• B. Reversible inhibitor
• C. Competitive inhibitor
• D. Non-competitive inhibitor

Explanation: A competitive inhibitor resembles the substrate and binds to the enzyme's active site, preventing the substrate from forming products. A common mistake is choosing a reversible inhibitor, but that describes the strength of binding rather than the specific location of binding.

1860. Inhibitors which block the enzyme by forming weak bond are called___________?

• A. Competitive inhibitors.
• B. Non-competitive inhibitors
• C. Irreversible inhibitors.
• D. Both a and b

Explanation: Weak, non-covalent bonds usually produce reversible inhibition, and both competitive and non-competitive inhibitors can act reversibly. Therefore, both types listed in a and b fit, making d the best choice. A likely mistake is choosing c because the inhibitor blocks the enzyme, but irreversible inhibitors usually form permanent or very strong bonds.