General Science Mixed Quiz: Set 73

A chemical reaction produces only internal forces, which cannot change the motion of the centre of mass but can change internal kinetic energy.

Accelerators speed up the vulcanisation of rubber; they are not a part of paint.

Mass is the same everywhere, but weight changes with g, so only statement II holds. Inertial mass measures how much a body resists a change in motion (F = ma); gravitational mass measures how strongly gravity pulls it.

A normal umbilical cord contains two arteries and one vein, three blood vessels in all. The umbilical cord joins the developing foetus to the placenta.

Latent heat is absorbed during a change of state while the temperature stays fixed. When water boils at 100 °C, adding more heat does not raise its temperature; the energy goes into breaking the attractions between molecules so that liquid turns into vapour.

The hepatitis B vaccine was the first vaccine made by recombinant DNA technology.

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.

Guava is the classic jam fruit because it is rich in both pectin and acid, the two things a jam needs to set into a firm gel.

Breaking calcium carbonate into quicklime and carbon dioxide needs a steady supply of heat, so the reaction absorbs energy. An endothermic reaction takes in heat from its surroundings, while an exothermic reaction gives heat out.

Galileo was the first to argue that, with air resistance removed, every body falls with the same acceleration regardless of its mass.

Baking soda, sodium hydrogen carbonate, is a mild base, so a small amount shifts fresh milk, whose pH is about 6.6, slightly above 7.

Litmus is a purple dye taken from lichens, and in the classification used in school science lichens are placed in Thallophyta, the group of simple plants whose body is an undifferentiated thallus with no true root, stem or leaf.

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.

An ordinary incandescent bulb is filled with an unreactive gas, nitrogen usually mixed with argon, so that the white-hot tungsten filament does not burn away.

Ethyne, C2H2, has its two carbon atoms joined by a triple bond, each carbon also holding one hydrogen. Carbon has a valency of four.

Both kinds of radiation carry energy that food absorbs as heat, and both are used in everyday kitchens. Infrared radiation is the heat radiation given out by hot bodies: a grill, a toaster, an oven element or glowing coals cook the surface of food mainly by infrared rays.

Both carry their own DNA and ribosomes and can make some of their own proteins. Mitochondria, the powerhouses of the cell, and plastids such as chloroplasts each contain a small circular DNA molecule and 70S ribosomes, much like bacteria.

Lactase breaks down lactose, the sugar in milk, so a person who still makes enough of it can digest milk at any age.

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

Adrenaline, released by the adrenal glands into the blood, speeds up the heart beat when the body faces stress or danger.