Explanation: The habitat of an organism is its natural living place where it finds food, water, shelter, and mates for reproduction. Examples include a pond for a frog, soil for an earthworm, and forest for a tiger. Each species has a specific habitat suited to its survival needs. The niche, on the other hand, describes the organism’s role or function in that habitat, such as how it obtains food or interacts with others.

Explanation: Vitamin A is essential for maintaining healthy vision, skin, and immune function. A deficiency of Vitamin A leads to night blindness (nyctalopia), a condition in which a person has difficulty seeing in dim light or at night. In severe cases, it can cause xerophthalmia (dryness of the cornea) and even blindness. Vitamin A is obtained from foods such as carrots, milk, butter, fish liver oil, and green leafy vegetables.

Explanation: All enzymes are proteins (except a few RNA-based enzymes called ribozymes). Enzymes act as biological catalysts that speed up chemical reactions in living organisms without being consumed in the process. They work by lowering the activation energy of reactions, ensuring that metabolic processes occur efficiently at normal body temperatures. Each enzyme is specific to a particular substrate, forming an enzyme-substrate complex to carry out its function effectively.

Explanation: Fibrinogen is a soluble plasma protein produced by the liver. During blood clotting, it is converted into insoluble fibrin threads by the enzyme thrombin. These fibrin threads form a mesh that traps red blood cells and platelets, creating a stable clot to stop bleeding. This process prevents excessive blood loss during injury and is regulated by clotting factors and platelets.

Simplified Reaction:

Fibrinogen → (Thrombin) → Fibrin → Blood Clot

The Taj Mahal is threatened primarily due to sulphur dioxide (SO₂) pollution. When sulphur dioxide released from nearby industries and vehicles mixes with moisture in the air, it forms sulphuric acid, leading to acid rain. This acid rain reacts with the white marble of the Taj Mahal, causing it to turn yellow and deteriorate — a phenomenon known as “Marble Cancer.”

Other options (for context)

• Carbon dioxide: Contributes to global warming but does not directly damage marble.
• Carbon monoxide: Harmful to health but has minimal effect on marble structures.
• Water vapour: Naturally present in the atmosphere and not harmful to monuments.

Explanation: Sulphur is used in the process of vulcanization of rubber. During vulcanization, sulphur forms cross-links between the rubber molecules, improving elasticity, strength, and resistance to heat and wear. This makes natural rubber more durable and suitable for industrial use.

Hepatitis is a disease that primarily affects the liver. It is characterized by inflammation of the liver tissues and can be caused by viral infections (such as Hepatitis A, B, C, D, and E viruses), excessive alcohol consumption, toxins, or autoimmune conditions. Symptoms include jaundice (yellowing of the skin and eyes), fatigue, nausea, and abdominal pain. Severe or chronic hepatitis can lead to liver failure or cirrhosis if left untreated.

Other options (for context)

• Pancreas: Affected by diseases like pancreatitis or diabetes, not hepatitis.
• Spleen: Involved in blood filtration and immunity, not affected by hepatitis.
• Small intestine: Responsible for digestion and absorption of food, not linked to hepatitis.

Explanation: Heavy water is chemically known as Deuterium oxide (D₂O). It is similar to ordinary water (H₂O), but the hydrogen atoms are replaced by deuterium — a heavier isotope of hydrogen containing one proton and one neutron. Heavy water is not suitable for drinking but is used as a moderator and coolant in nuclear reactors because it slows down neutrons, allowing a controlled nuclear fission reaction. It is also used in scientific research and isotope studies.