General Science GK Questions with Answers – Page 85

Xylem carries water along with the minerals dissolved in it from the roots up to the stem and leaves. Plants have two kinds of conducting tissue.

Bacteria have a cell wall and human cells do not, so a drug that attacks the cell wall harms only the bacteria.

Each nucleotide of DNA is made of these three parts, and many nucleotides joined together form the polynucleotide chain. In a DNA strand, the sugar of one nucleotide is linked to the phosphate of the next by a phosphodiester bond, making a sugar-phosphate backbone.

A magnesium atom sits at the centre of every chlorophyll molecule, so a plant cannot make chlorophyll without it. Chlorophyll is built around a ring-shaped structure called a porphyrin, with a single magnesium ion held at its centre.

A carbonate reacts with an acid at room temperature to give carbon dioxide, and only carbon dioxide turns limewater milky.

The body's weight stays the same, but standing puts it on the small area of the feet, so the pressure is greater.

Silver is the best conductor, nichrome is an alloy with high resistivity, and glass is an insulator with enormous resistivity.

During a hard sprint the muscles run short of oxygen and switch to anaerobic respiration, which leaves lactic acid behind.

Gravitational force varies inversely as the square of the distance, so halving the distance makes the force 2 × 2 = 4 times larger.

Plants need magnesium in fairly large amounts, so it is a macronutrient, not a micronutrient. Plant nutrients are grouped by how much of them a plant needs.

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

For a 4d orbital, n = 4 and l = 2, which gives l = 2 angular nodes and n − l − 1 = 1 radial node.

A bacterium is a living cell filled with cytoplasm, while a virus is only genetic material inside a protein coat.

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

Animal cells are bounded only by a flexible cell membrane; a rigid cell wall is found in plants, fungi and bacteria.

A liquid boils when its vapour pressure equals the pressure above it, so less outside pressure means boiling starts at a lower temperature.

Magnesium burns in air with a dazzling white flame, which is why it goes into fireworks, sparklers and flares. When magnesium ribbon is heated it reacts with oxygen to form white magnesium oxide (2Mg + O2 → 2MgO), giving out intense heat and brilliant white light, including ultraviolet.

A short-sighted (myopic) person sees near things clearly but distant things blurred, and a concave lens corrects it.

A compound microscope uses two convex lenses, and its magnification depends on the tube length. The objective is a convex lens of very short focal length that forms a real, enlarged image of the specimen.

The third law does not make one force the cause and the other the effect; action and reaction arise together, at the same instant.