General Science Previous Year Questions (PYQ) with Answers – Page 92

Zika is spread mainly by the Aedes mosquito that also carries dengue, and it can pass between sexual partners. The Zika virus is a flavivirus first identified in Uganda's Zika forest in 1947.

Among the alkali metals, reactivity with water increases down the group, so lithium, at the top, is the least reactive.

Three equal resistors R in parallel have a combined resistance of R/3, and at the same voltage the power, V²/R, becomes three times as large.

Both gain the same kinetic energy, but the electron is far lighter, so it moves much faster. A charge q accelerated through a potential difference V gains kinetic energy qV.

The stinging hairs of the nettle plant inject methanoic acid, also called formic acid, into the skin. Each nettle hair is a fine, brittle tube that breaks on touch and pushes its contents into the skin like a tiny needle.

Aluminium has three valence electrons, one fewer than silicon, so each aluminium atom leaves a hole that acts as a positive charge carrier.

Temporary hardness comes from dissolved calcium and magnesium hydrogencarbonates (bicarbonates), and it can be removed simply by boiling. On boiling, calcium hydrogencarbonate breaks down into insoluble calcium carbonate, water and carbon dioxide, and the carbonate settles out; this is the scale seen inside kettles.

These are the signs of scurvy, the disease caused by a lack of vitamin C (ascorbic acid). Vitamin C is needed to make collagen, the protein that holds together gums, skin, blood vessels and bone.

A pearl is built up from layers of nacre, which is mostly calcium carbonate held together by a protein called conchiolin.

Of the three forms of carbon, only fullerenes are made of closed, hollow, cage-like molecules. The best-known fullerene is buckminsterfullerene, C60, a hollow sphere of 60 carbon atoms arranged in 20 hexagons and 12 pentagons, shaped like a football.

Syngamy is the fusion of a male and a female gamete, and since each gamete is haploid, their union gives a diploid zygote.

Humans have a single functional insulin gene, INS, on the short arm of chromosome 11, and both chains of insulin come from it.

A Mach number greater than 1 means the body is moving faster than sound in the surrounding medium. The Mach number is the ratio of a body's speed to the speed of sound in the medium around it, named after the Austrian physicist Ernst Mach.

The great majority of plant viruses carry their genes as single-stranded RNA. Viruses contain either DNA or RNA, never both, wrapped in a protein coat.

Cancer is uncontrolled cell division that follows the loss of the checks that normally govern growth. Normal cells divide only when signalled and stop when they touch neighbouring cells, a property called contact inhibition.

On the magnetic equator the angle of dip is zero, so the Earth's magnetic field there is entirely horizontal. The Earth behaves like a huge bar magnet.

HIV spreads through body fluids such as blood, so a transfusion of infected blood passes the virus directly into the bloodstream.

A mirage forms when light from the sky bends through hot, less dense air near the ground and is finally totally internally reflected.

Transcription is the step in which the genetic message of a gene is copied from one strand of DNA into a strand of RNA.

A transformer raises or lowers an AC voltage using electromagnetic induction between two coils. A transformer has a primary and a secondary coil wound on a common soft-iron core.