Swine Flu is caused by the H₁N₁ virus, a subtype of the Influenza A virus. It primarily affects the respiratory system and is transmitted from person to person through droplets from coughs or sneezes. Symptoms include fever, cough, sore throat, body aches, and fatigue. The H₁N₁ pandemic in 2009 was declared a global health emergency by the World Health Organization (WHO).

Other options (for context)

• Dengue: Caused by the Dengue virus, transmitted by Aedes mosquitoes.
• AIDS: Caused by the HIV (Human Immunodeficiency Virus), not H₁N₁.
• Bird flu: Caused by the H5N1 virus, not H₁N₁.

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.

Explanation: Execution time is the period during which a job or program is actively processed by the computer’s CPU. It refers to the actual time taken to execute instructions, excluding waiting or idle times such as input/output delays or queue time.

Explanation: The phenomenon of radioactivity was discovered by the French physicist Henri Becquerel in 1896. He accidentally discovered that uranium salts emitted invisible rays that could fog photographic plates, even without sunlight. This led to the realization that certain elements spontaneously emit radiations — a property later termed as radioactivity. Subsequently, Marie and Pierre Curie expanded his work and discovered other radioactive elements like polonium and radium.

Explanation: The disease AIDS (Acquired Immuno Deficiency Syndrome) is caused by the HIV (Human Immunodeficiency Virus). HIV attacks the body’s immune system, specifically the CD4 or T-helper cells, weakening the body’s ability to fight infections and diseases. It spreads through unprotected sexual contact, sharing of infected needles, transfusion of contaminated blood, or from an infected mother to her child during birth or breastfeeding. There is no permanent cure, but antiretroviral therapy (ART) helps control the virus and prolong life.

Explanation: The spectrophotometer measures bacterial growth by determining the optical density (OD) or turbidity of a culture. As bacteria multiply, the suspension becomes more turbid and absorbs more light. The absorbance value is proportional to the number of bacterial cells present.

Explanation: SONAR (Sound Navigation and Ranging) is a system used in ships and submarines to determine the depth of the ocean or to locate underwater objects. It works by sending sound waves into the water and measuring the time taken for the echo to return after reflecting from the seabed or any object.

Explanation: The thyroid gland is located in the neck region, just below the larynx (voice box) and in front of the trachea (windpipe). It is a butterfly-shaped endocrine gland that secretes the hormones thyroxine (T₄) and triiodothyronine (T₃). These hormones regulate metabolism, growth, and energy production in the body. The thyroid also produces calcitonin, which helps control calcium levels in the blood. Iodine is essential for the synthesis of thyroid hormones.

Explanation: Fathom is a unit used to measure depth, particularly the depth of water in oceans and seas. One fathom is equal to 6 feet or approximately 1.83 meters. It is commonly used in navigation and marine studies.