Explanation: A microscope uses a system of convex lenses to magnify very small objects. Convex lenses, also known as converging lenses, bend light rays inward to a focal point, creating an enlarged and clear image of the specimen. A compound microscope typically contains two sets of convex lenses — the objective lens (near the specimen) and the eyepiece lens (near the observer’s eye). The objective lens forms a real, inverted, and magnified image, which is then further magnified by the eyepiece to produce a large virtual image.

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: Pathogenic parasites are those that invade the host’s body and cause disease. The presence of these harmful organisms stimulates the host’s immune system to produce antibodies that help neutralize or destroy the pathogens. Examples include Plasmodium (causes malaria) and Trypanosoma (causes sleeping sickness).

Explanation: Sodium (Na⁺) plays a crucial role in the transmission of nerve impulses in the human body. Nerve cells (neurons) transmit signals through an electrochemical process known as the nerve impulse or action potential. During this process, the movement of sodium (Na⁺) and potassium (K⁺) ions across the nerve cell membrane generates an electrical charge. The rapid influx of sodium ions causes depolarization, which allows the nerve impulse to travel along the neuron, ensuring proper communication between the brain, spinal cord, and body.

Deciduous trees are those that shed all their leaves once a year, usually during the dry or winter season to conserve water and energy. After a period of dormancy, they grow new leaves at the beginning of the next growing season. Common examples include teak, sal, neem, and peepal. This adaptation helps the trees survive unfavorable climatic conditions.

Other options (for context)

• Coniferous trees: Mostly evergreen and do not shed all their leaves at once; examples include pine and deodar.
• Evergreen trees: Retain their leaves throughout the year and shed them gradually.
• Both deciduous and coniferous trees: Incorrect — only deciduous trees completely shed their leaves annually.

Explanation: Lysosomes are known as the ‘suicidal bags’ or ‘disposal units’ of the cell because they contain powerful digestive enzymes capable of breaking down worn-out cell parts, foreign substances, and even the entire cell when it becomes damaged or obsolete.

Explanation: The liver is the largest gland in the human body. It is located in the upper right part of the abdomen, just below the diaphragm. The liver performs multiple vital functions, including the secretion of bile (which helps in digestion of fats), detoxification of harmful substances, storage of glycogen (energy reserve), and the synthesis of proteins and cholesterol. It also plays a crucial role in regulating blood sugar levels and metabolism. The average adult human liver weighs about 1.2 to 1.5 kilograms.

Biogas is a source of non-conventional (renewable) energy. It is produced through the anaerobic decomposition of organic waste materials such as animal dung, crop residues, and kitchen waste. Biogas mainly contains methane (CH₄) and is used as a clean fuel for cooking, lighting, and even power generation. It helps reduce dependence on fossil fuels and minimizes environmental pollution.

Other options (for context)

• Firewood: A traditional biomass fuel, not classified as a modern non-conventional source.
• Diesel: A conventional fossil fuel derived from crude oil.
• Petrol: Another conventional fossil fuel obtained from petroleum refining.

Explanation: Humans first landed on the Moon on July 20, 1969, during NASA’s Apollo 11 mission. American astronauts Neil Armstrong and Edwin “Buzz” Aldrin became the first and second humans to walk on the Moon, while Michael Collins orbited above in the command module. Neil Armstrong’s famous words, “That’s one small step for man, one giant leap for mankind,” marked this historic achievement in space exploration.