General Science Previous Year Questions (PYQ) with Answers – Page 29

Chromosomes are made of DNA wound around proteins, mainly histones; together this DNA-protein material is called chromatin. In eukaryotic cells, a very long DNA molecule wraps around groups of eight histone proteins to form beads called nucleosomes.

A microphone turns sound into an electrical signal, and a speaker turns an electrical signal back into sound. Both are transducers, devices that change energy from one form to another.

Only this equation has the same number of iron, hydrogen and oxygen atoms on both sides. Iron reacts with steam to form iron(II,III) oxide and hydrogen gas.

Platelets plug a damaged vessel and start the chain that forms a clot. Platelets, or thrombocytes, are small cell fragments made from large cells called megakaryocytes in the bone marrow.

All three statements are correct; microbes called extremophiles live in all these conditions. Hyperthermophiles, many of them archaea living near deep-sea hydrothermal vents, grow above 100 °C; Methanopyrus kandleri and 'Strain 121' grow at about 120 °C, where high pressure keeps water liquid.

All four statements are correct; mushrooms show every one of these properties. Mushrooms are the fruiting bodies of fungi.

Buckminsterfullerene is C60, a cage-shaped molecule of sixty carbon atoms. The sixty atoms are arranged in 12 pentagons and 20 hexagons, the same pattern as the panels of a football, which is why the molecule is also called a buckyball.

Steel is an alloy of iron with a small amount of carbon, and carbon is a non-metal. Ordinary steel carries roughly 0.05 to 2 per cent carbon.

The liver cells (hepatocytes) are rich in smooth endoplasmic reticulum, whose enzymes break down drugs, alcohol and poisons into harmless forms.

Transfer RNA picks up a specific amino acid and brings it to the ribosome, where it is added to the growing protein chain.

Mitochondria carry their own circular DNA and their own ribosomes, so they can make some of their own proteins. Mitochondria are the sites of aerobic respiration, where ATP is produced, which is why they are called the powerhouse of the cell.

The sound travels to the cliff and back in 5 s, so it covers 340 × 5 = 1,700 m in all, and the cliff is half of that, 850 m away.

Slaked lime is calcium hydroxide applied as a watery solution, and it takes up carbon dioxide gas from the air to form solid calcium carbonate and water.

120 mmHg is the systolic pressure when the ventricles contract, and 80 mmHg is the diastolic pressure when they relax.

To see one's full image in a plane mirror, the mirror must be at least half the person's height: half of 1·5 m is 0·75 m. Light from Sita's feet must reflect from the mirror into her eyes, and so must light from the top of her head.

Nichrome has a high resistivity and does not oxidise easily when red hot, so it is the standard heating element.

Platinum is a noble metal and does not combine with oxygen even when heated in air. Metals low in the reactivity series, such as gold and platinum, hold on to their electrons very firmly, so oxygen cannot pull them away under ordinary conditions.

Bile has no digestive enzymes at all; it only prepares fats for digestion by other enzymes. Bile is made by the liver, stored and concentrated in the gall bladder, and poured into the duodenum through the bile duct.

In an isotonic solution the concentration outside the cell equals that inside, so there is no net movement of water.

All three symbols come from the Latin names of these metals: aurum, stannum and plumbum. Many metals known since ancient times take their symbols from Latin rather than English.