General Science GK Questions with Answers – Page 50

The layers of graphite are held only by weak van der Waals forces, not by covalent bonds. Diamond and graphite are allotropes of carbon.

Soap lowers the surface tension of water, so water spreads into fine gaps and wets greasy dirt that plain water would bead up on.

Sound is a mechanical wave that needs a medium, so it cannot pass through empty space. Sound travels as a series of compressions and rarefactions passed from particle to particle of a medium.

In a dicot leaf most stomata are on the lower surface, so coating that surface blocks most of the water loss and the leaf stays fresh the longest.

Typhoid is caused by the bacterium Salmonella typhi; the other three are viral diseases. Salmonella typhi spreads through food and water contaminated with the faeces of an infected person, which is why typhoid is common where sanitation is poor.

Every living cell needs a cell membrane, and plant cells add a rigid cell wall outside it. The cell membrane, or plasma membrane, is the thin, selectively permeable boundary of every cell; it controls what enters and leaves.

The animal cell membrane is a phospholipid bilayer with proteins set in it and cholesterol between the lipid molecules. The fluid mosaic model of Singer and Nicolson (1972) describes the membrane as a double layer of phospholipids, whose water-loving heads face outward and water-fearing tails face inward.

Carbon monoxide reacts with neither acids nor bases to form a salt and water, so it is a neutral oxide.

Taking A as the reference level and ignoring air resistance, all the kinetic energy given at A turns into potential energy at the top, B. Mechanical energy is conserved when only gravity does work.

In each of the four changes a substance combines with oxygen from the air, which is oxidation.

Statements I and II are standard rules for oxidation numbers, but Statement III reverses what happens to a reducing agent.

Sleeping sickness, or African trypanosomiasis, is caused by the protozoan Trypanosoma brucei. Trypanosoma is a flagellated protozoan that lives in the blood.

Melanin absorbs the ultraviolet rays of sunlight and shields the DNA of skin cells from damage. Melanin is made by cells called melanocytes in the lower layer of the epidermis.

This is the order of the taxonomic ranks from the broader group to the narrower one. The full hierarchy set out by Linnaeus and used today runs Kingdom, Phylum (Division in plants), Class, Order, Family, Genus and Species.

Orthophosphoric acid, H 3 PO 4, has three replaceable hydrogen ions, so it is tribasic. The basicity of an acid is the number of hydrogen ions one molecule can give up in water.

Lime water is a solution of calcium hydroxide, Ca(OH) 2, not calcium carbonate.

Liquid pressure at a depth is P = hρg, so a taller column presses harder on the base. In P = hρg, h is the height of the liquid above the point, ρ is the density of the liquid and g is the acceleration due to gravity.

Photosynthesis gives off oxygen, and oxygen is what aerobic respiration needs to release energy from food. In photosynthesis, green plants use sunlight, carbon dioxide and water to make glucose, and release oxygen, which comes from the splitting of water.

The dogfish is a small shark, and sharks are true fishes of the class Pisces. Pisces are aquatic vertebrates that breathe through gills, swim with fins and usually have scales.

Bile breaks fat into tiny droplets and lipase then splits those droplets into fatty acids and glycerol. Bile is made by the liver, stored in the gall bladder and poured into the duodenum.