General Science Previous Year Questions (PYQ) with Answers – Page 93

Each nucleotide of DNA is made of these three parts, and many nucleotides joined together form the polynucleotide chain. In a DNA strand, the sugar of one nucleotide is linked to the phosphate of the next by a phosphodiester bond, making a sugar-phosphate backbone.

Silk is the protein fibroin, spun by the silkworm, so it is a polymer made by a living organism and is therefore natural, like cellulose, starch, wool and natural rubber.

Concrete is the building material made by mixing cement with coarse aggregate such as gravel, fine aggregate such as sand, and water.

The principle says a body immersed wholly or partly in a fluid is pushed up by a force equal to the weight of the fluid it pushes aside, and that upward force is called buoyancy or upthrust.

Fluorine is the most electronegative element, so in every compound it pulls the shared electrons towards itself and always shows an oxidation number of -1.

The brain is the organ that interprets pain, but its own tissue has no pain receptors, so cutting or pricking it causes no sensation; the covering membranes, the blood vessels and the scalp do have receptors, which is why a headache hurts.

For the same pair of surfaces the order of friction is always static, then kinetic, then rolling. Static friction is the largest because the surfaces interlock while at rest and that grip has to be broken to start motion.

Inhalation, also called inspiration, is the phase of breathing in which the diaphragm flattens and the intercostal muscles pull the ribs up and out, so the chest cavity enlarges, the pressure inside the lungs falls below the pressure of the atmosphere and oxygen rich air rushes in through the nostrils…

Rayon is made by dissolving the cellulose of wood pulp in a chemical and forcing the solution through fine holes to form filaments.

A liquid boils when its vapour pressure equals the pressure of the air pressing on its surface, so lower air pressure means a lower boiling point.

Cones are the photoreceptor cells of the retina that respond to colour in bright light. The human retina carries two kinds of photoreceptors.

Among the four, the ant has the largest brain in proportion to its body. An ant’s brain is tiny in absolute terms, with about two hundred and fifty thousand neurons, yet it makes up roughly a sixth of the insect’s body weight, a share no vertebrate comes close to.

Opium is the dried latex of the opium poppy, whose botanical name is Papaver somniferum; the second word means sleep bringing.

Tungsten has the highest melting point of all metals, well above three thousand degrees Celsius, so a thin tungsten wire can be heated until it glows white without melting.

The British physicist said these words in a lecture in January 2016, using his own work on black holes as a message of hope for people facing depression.

Light keeps to a straight line only while its speed stays the same, which happens in a homogeneous, transparent medium.

Ferromagnetism needs the atomic magnets of a substance to line up together in fixed regions called domains, and this happens only in the ordered structure of a solid.

For a photon, energy equals momentum multiplied by the speed of light, E = pc, so a momentum of 10 MeV/c gives an energy of exactly 10 MeV.

Total internal reflection happens only when light inside a denser medium meets the boundary with a rarer one at an angle larger than the critical angle, and all of the light is reflected back.

By mass, an adult human body has the most oxygen, then carbon, hydrogen and nitrogen. Oxygen makes up about 65 percent of body mass, carbon about 18 percent, hydrogen about 10 percent and nitrogen about 3 percent.