General Science Previous Year Questions (PYQ) with Answers – Page 62

It is caused by the bacterium Vibrio cholerae, which spreads through food and water polluted with human faeces. The bacterium was identified by Robert Koch in 1883.

Lysosomes are small membrane-bound sacs full of hydrolytic enzymes that digest worn-out parts and foreign material inside the cell. Lysosomes are formed from the Golgi apparatus and were discovered by Christian de Duve.

The enzyme breaks the β-lactam ring that gives penicillin its power. Penicillin was discovered by Alexander Fleming in 1928 from the mould Penicillium notatum.

An ECG records the electrical signals that make the heart muscle contract with each beat. Each heartbeat starts at the sino-atrial (SA) node, the natural pacemaker in the right atrium.

Both particles gain the same kinetic energy, but the electron is far lighter, so it ends up much faster. When a charge q is accelerated through a potential difference V, it gains kinetic energy equal to qV.

Ultraviolet rays have the shortest wavelength of the three, visible light comes next and infrared rays have the longest. The electromagnetic spectrum, in order of increasing wavelength, runs from gamma rays and X-rays to ultraviolet, visible light, infrared, microwaves and radio waves.

Silver is less dense, so a silver piece takes up more volume, loses more weight to buoyancy in water, and must therefore be heavier in air to show the same weight under water.

Apart from the Sun, Proxima Centauri is the star nearest to the Earth, about 4.24 light years away. Proxima Centauri is a small, dim red dwarf in the constellation Centaurus and cannot be seen with the naked eye.

Nylon 6 is made from a single monomer, caprolactam, whose ring opens on heating and joins up into long polyamide chains.

. A Fischer projection draws a molecule as a cross: the horizontal bonds point towards the viewer and the vertical bonds point away.

Functional group isomers have the same molecular formula but different functional groups. Alkyl halides such as C2H5Cl can only contain the halogen group, so no other functional group can be built from the same formula; they show chain and position isomerism instead.

Fluorine cannot be detected by Lassaigne's test, because silver fluoride is soluble in water and gives no precipitate. Lassaigne's test, or the sodium fusion test, detects nitrogen, sulphur and halogens in an organic compound.

Centrifugation separates very fine insoluble particles that are too small to settle on their own. The mixture is spun at high speed in a centrifuge.

Animal cells are bounded only by a flexible plasma membrane and have no rigid cell wall outside it. A cell wall is found in plants, where it is made mainly of cellulose, in fungi, where it is made of chitin, and in bacteria, where it is made of peptidoglycan.

In 1913 the English physicist Henry Moseley showed that atomic number, not atomic mass, is the fundamental property of an element.

Cotton soaks up sweat well, and as that sweat evaporates from the cloth it takes heat away from the body and keeps us cool.

Soap micelles are large enough to scatter the light passing through the solution, and this scattering makes soapy water look cloudy.

In graphite each carbon atom is joined to three others in a flat layer of hexagonal rings, like a honeycomb.

A monatomic element exists as single, separate atoms. Helium is a noble gas of group 18: its only shell, the first, is full with two electrons, so a helium atom has no tendency to share or transfer electrons and does not bond even with another helium atom.

A fuse must carry the normal current, so it must conduct, and it must melt quickly when the current becomes too large.