General Science GK Questions with Answers – Page 113

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

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.

Iron is a micronutrient, needed by plants only in very small amounts, and calcium is a macronutrient, needed in large amounts.

Arteries are the blood vessels that carry blood away from the heart to the different parts of the body. Because the heart pushes blood into them under high pressure, arteries have thick, muscular and elastic walls and no valves, and they are placed deep in the body.

Bos mutus is the scientific name of the wild yak, the long haired bovine of the high cold plateaus of Ladakh, Tibet and the Karakoram, which grazes above four thousand metres and is listed as Vulnerable on the IUCN Red List.

The lysosome is a small sac bound by a single membrane that is filled with digestive enzymes, so it breaks down food particles taken into the cell and clears out worn out parts of the cell itself.

These are the weak attractions that appear when the electron cloud of an atom becomes momentarily lopsided, creating a temporary dipole which then induces a matching dipole in a neighbouring atom.

Sodium benzoate is the sodium salt of benzoic acid and is the preservative most often added to sauces, salad dressings, jams, pickles and soft drinks.

Permanent tissues are made of cells that have stopped dividing and have taken on a fixed shape, size and function, and in simple permanent tissues such as parenchyma the loosely packed cells leave clear intercellular spaces through which gases can move.

Mendeleev arranged the elements by increasing atomic mass in 1869 and left blank spaces where his pattern demanded an element that was not yet known.

After discovering the electron in 1897, J. J. Thomson pictured the atom as a sphere of positive charge with negatively charged electrons stuck in it, a picture often compared to plums in a pudding or seeds in a watermelon.

Isotopes are atoms of the same element, so they have the same number of protons and therefore the same atomic number, but they carry different numbers of neutrons, which makes their mass numbers differ.

The modern periodic table has seven horizontal rows, called periods, and eighteen vertical columns, called groups.

John Newlands arranged the fifty-six elements known in 1866 in order of increasing atomic mass, beginning with hydrogen, the lightest, and ending with thorium, the fifty-sixth.

Henry Moseley showed in 1913, from the frequencies of the X-rays that elements emit, that the atomic number, the number of protons in the nucleus, is the more fundamental property of an element.

Electronegativity is the tendency of an atom to attract a shared pair of electrons towards itself. It increases from left to right across a period, as nuclear charge grows, and decreases down a group, as each new shell puts the outer electrons further from the nucleus.

The alkali metals are lithium, sodium, potassium, rubidium, caesium and francium. Each has a single electron in its outermost shell, loses it readily to form a positive ion, and therefore stands in group 1 of the modern periodic table.

The capacity of a shell is given by the formula 2n squared, where n is the number of the shell counted outward from the nucleus.

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

James Chadwick discovered the neutron in 1932 by bombarding beryllium with alpha particles and showing that the radiation produced consisted of neutral particles of nearly the same mass as the proton.