General Science Previous Year Questions (PYQ) with Answers – Page 32

A hydrogen ion (H+) is just a bare proton, so it cannot stay alone in water. It at once attaches itself to a water molecule and forms the hydronium ion, H3O+.

Plasmodium falciparum causes malignant, or cerebral, malaria, the most dangerous form of the disease. Red blood cells infected by it become sticky and block the small blood vessels of the brain and other organs, which can lead to coma and death if treatment is delayed.

Aluminium naturally forms a thin layer of aluminium oxide when it is exposed to air, and this layer protects it from further corrosion.

Haemodialysis uses a machine called an artificial kidney to clean the blood of a patient whose kidneys have failed.

Bronze is made by melting copper and tin together, with copper as the main metal. It is harder than pure copper and does not corrode easily, so it has been used for statues, bells, medals and utensils for thousands of years.

The pituitary gland sends out hormones that order the thyroid and the adrenal glands to release their own hormones. The pituitary is a pea-sized gland attached to the base of the brain, and it is called the master gland because it controls several other endocrine glands.

The rough strip of a safety matchbox is coated with powdered glass and a little red phosphorus, while the head of the matchstick carries antimony trisulphide and potassium chlorate.

The pancreas is both an exocrine gland, pouring digestive enzymes into the intestine, and an endocrine gland. Its endocrine part is made of small clusters of cells called the islets of Langerhans.

Each stoma is surrounded by two guard cells, and the pore opens or closes as these cells gain or lose water.

Aluminium oxide and zinc oxide behave like a base with acids and like an acid with bases, so both are amphoteric.

Thiamin (thiamine) is vitamin B1, a water-soluble vitamin that helps the body turn carbohydrates into energy and keeps the nerves and heart working well.

Isaac Newton built the first practical reflecting telescope in 1668. In it, light from the star falls on a large concave mirror at the bottom of the tube, and a small flat mirror set at 45 degrees near the top turns the light sideways to the eyepiece.

Levers are grouped by where the fulcrum, the load and the effort sit. In a second class lever the load lies between the fulcrum and the effort.

Galvanisation is the coating of iron or steel with a thin layer of zinc so that the iron underneath does not rust.

Newton's second law gives force = mass × acceleration. Mass has the dimension [M], and acceleration is velocity divided by time, that is [L T⁻¹] ÷ [T] = [L T⁻²].

Pellagra is caused by a lack of vitamin B3, niacin, also called nicotinic acid, and is remembered by the three Ds: dermatitis, a rough dark rash on skin exposed to sunlight, diarrhoea from the gut, and dementia from the nervous system; untreated, a fourth D, death, follows.

Period 2 holds the eight elements from lithium (3) to neon (10), and group 17 is the halogen column, whose members have seven electrons in the outer shell.

A microphone is a transducer that changes the pressure variations of sound into a matching electrical signal. In a common dynamic microphone, sound waves make a thin diaphragm vibrate.

By the conservation of momentum, the pistol moves back with 3 m s⁻¹, and the minus sign shows it moves opposite to the bullet.

The filament of an incandescent bulb must glow white-hot without melting, and tungsten has the highest melting point of all metals, about 3,400 °C. An incandescent bulb works by the heating effect of electric current: the thin coiled filament gets so hot, around 2,500 °C or more, that it gives…