General Science Mixed Quiz: Set 23

In myopia the eyeball is too long or the lens of the eye too strongly converging, so rays from a distant object meet in front of the retina and the person cannot see far objects clearly.

Both are tiny algae grown in tanks and sold as protein rich food supplements, and both have been studied as food for astronauts.

Sound travels fastest in solids because their particles are packed closely and are strongly bound, so a disturbance is passed on to the next particle almost at once.

The BCG vaccine takes its name from Albert Calmette and Camille Guerin, the two French scientists who developed it from a weakened strain of Mycobacterium bovis.

A microwave oven does not cook by passing a current through a resistance. It generates microwaves in a magnetron, and these waves make the water molecules in the food rotate rapidly, so the food heats from within by dielectric heating.

Distillation separates a liquid from a solution or from another liquid by boiling it and condensing the vapour, so it is used when the components differ in boiling point, as in getting pure water from salt water or separating acetone from water.

Most alpha particles passed straight through the foil, a few were deflected through small angles and about one in twenty thousand bounced back.

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.

Gases move across the cell membrane by diffusion, the spread of particles from a region where they are more concentrated to a region where they are less concentrated.

A silicon diode in forward bias drops about 0.7 volt across itself, whatever the supply voltage is.

In humans the digestion of starch begins in the buccal cavity, that is the mouth. The salivary glands pour out about 1.5 litres of saliva a day, and the enzyme in it, salivary amylase or ptyalin, breaks starch into the simpler sugar maltose.

Calaverite is gold telluride, with the formula AuTe2. It is one of the very few minerals in which gold occurs chemically combined rather than as the free metal, because gold is a noble metal that usually resists reaction.

White blood cells are usually about 8 to 20 micrometres across, larger than red cells but not in the range given here.

Algae belong to Thallophyta, the simplest division of the plant kingdom. Their body is a thallus, which means it is not divided into root, stem and leaf, and they have no vascular tissue.

The brain is divided into fore-brain, mid-brain and hind-brain, and the fore-brain is the main thinking part. Its largest portion is the cerebrum, whose folded outer layer holds separate areas for hearing, sight, smell and touch, for reasoning and memory, and for ordering voluntary movement.

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.

Spirogyra is a green filamentous alga found in ponds, and when its filament grows long it simply breaks into two or more pieces.

Water behaves unlike most liquids between 0 and 4 degrees Celsius, a behaviour called the anomalous expansion of water. Almost every substance shrinks as it is cooled, but water shrinks only until it reaches 4 degrees Celsius.

In a suspension the particles of the solute are large enough to be seen and do not dissolve; they stay spread through the liquid only while it is stirred and settle to the bottom when it is left standing.

A tunnel diode, also called an Esaki diode after Leo Esaki who made it in 1957, is heavily doped on both sides, so its depletion layer is extremely thin and electrons cross it by quantum tunnelling.