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: Nitrogen is an essential nutrient for plants, used in the synthesis of amino acids, proteins, nucleic acids, and chlorophyll. Plants absorb nitrogen from the soil primarily in the inorganic forms of nitrate (NO₃⁻) and nitrite (NO₂⁻). Urea, when applied as fertilizer, is first converted by soil bacteria into ammonia (NH₃) and then into nitrates through nitrification before being absorbed by roots.

Key Steps:

• Ammonification: Conversion of organic nitrogen (from dead plants/animals) into ammonia.
• Nitrification: Conversion of ammonia into nitrites and then nitrates by bacteria like Nitrosomonas and Nitrobacter.
• Assimilation: Uptake of nitrates by plants to form amino acids and proteins.

Nickel exposure commonly causes a skin disease called Dermatitis, specifically Allergic Contact Dermatitis. This condition occurs when the skin comes into direct contact with nickel-containing objects such as jewelry, coins, or belt buckles. It leads to redness, itching, and rashes, especially in sensitive individuals. Nickel allergy is one of the most common metal allergies worldwide.

Other options (for context)

• Itai Itai: Caused by cadmium poisoning, not nickel.
• Learning Disability: Not directly linked to nickel exposure.
• Asthma: May be aggravated by pollutants, but not typically caused by nickel.

Explanation: The blue whale (Balaenoptera musculus) holds the record as the largest mammal and the largest living organism on Earth. Adult blue whales can reach lengths of up to 30 meters (98 feet) and weigh over 180 tons. Despite their size, they feed mainly on small shrimp-like creatures called krill, filtering them through their baleen plates. Whales are warm-blooded, breathe air through blowholes, and give birth to live young — all key mammalian traits.

Comparison:

• Blue whale (largest mammal): up to 30 m long, ~180 tons
• African elephant (largest land mammal): up to 4 m tall, ~6 tons
• Rhinoceros: up to 2 m tall, ~2 tons

A fuse wire has high resistance and a low melting point. It is made of materials like tin-lead alloy so that it melts quickly when excessive current flows through the circuit. This breaks the circuit and prevents damage to electrical appliances due to overheating or short circuits.

• High resistance: Causes heating when excess current passes.
• Low melting point: Ensures the fuse melts easily to interrupt the circuit.

Explanation: Chlorofluorocarbons (CFCs) are the gases responsible for the depletion of the ozone layer. When released into the atmosphere, CFCs break down under ultraviolet (UV) radiation, releasing chlorine atoms that destroy ozone molecules (O₃), leading to thinning of the ozone layer and increased UV radiation reaching the Earth.

Explanation: Measles is a highly contagious disease caused by the Measles virus, which belongs to the Paramyxoviridae family, genus Morbillivirus. It spreads through respiratory droplets from coughing or sneezing by an infected person. Common symptoms include high fever, cough, runny nose, red eyes, and a characteristic red skin rash. Severe cases can lead to pneumonia or encephalitis. Measles can be effectively prevented by the MMR vaccine (Measles, Mumps, and Rubella).

Explanation: The hard structure of bones and teeth is primarily made of calcium phosphate in the crystalline form of tricalcium phosphate (Ca₃(PO₄)₂). It provides rigidity and strength. In tooth enamel, a small portion is converted into fluorapatite, which makes teeth resistant to bacterial decay.