General Science Previous Year Questions (PYQ) with Answers – Page 46

Human cells, like all animal cells, have only a flexible plasma membrane on the outside and no rigid cell wall.

In myopia, or short-sightedness, a person sees near objects clearly but distant objects look blurred because their image forms in front of the retina.

An electric generator converts mechanical energy into electrical energy and so produces electric current. A generator works on electromagnetic induction, discovered by Michael Faraday in 1831.

For a straight wire, the right-hand thumb rule links the current to the circular field lines around it. Hold the wire in the right hand with the thumb along the current; the curled fingers then show the direction of the magnetic field lines, which form concentric circles around the wire.

Cinnabar is mercury sulphide, HgS, the chief ore from which mercury is obtained. Cinnabar is a bright red mineral.

Coating iron or steel with a thin layer of zinc is called galvanisation, and it is the most common way to protect them from rusting.

The average atomic mass is the weighted mean of the isotope masses, taking each in proportion to how common it is.

Rutherford's gold foil experiment of 1911 showed that an atom's positive charge and almost all its mass sit in a tiny central nucleus.

For three equal resistors R in parallel, 1/Rp = 1/R + 1/R + 1/R = 3/R, so Rp = R/3.

In uniform circular motion the speed stays the same, but the direction changes at every point, so the velocity keeps changing.

Inserting a plate of thickness t in one arm makes the light cross it twice, so the extra path introduced is twice the thickness times the quantity refractive index minus one.

Work equals force multiplied by displacement, and 4 N multiplied by 0.25 m gives exactly 1 joule.

In every isolated system these three quantities stay constant, and no known process has ever been found to break these laws.

In Newton's second law, F = ma, the force on a body is proportional to its acceleration, and the constant linking the two is the body's mass.

Buoyancy, or upthrust, is the upward force a fluid exerts on any object immersed in it. A fluid presses on an object from all sides, but the pressure grows with depth, so the push on the lower surface is greater than the push on the upper surface.

Smallpox was caused by the variola virus, a large DNA virus of the pox family that spread from person to person through the air.

An allele is one of the alternative forms of the same gene, found at the same place on a pair of matching chromosomes.

The girth, or thickness, of a stem increases only through the lateral meristems, the vascular cambium and the cork cambium.

Parenchyma is the basic packing tissue of plants, and it is also present in both xylem (xylem parenchyma) and phloem (phloem parenchyma).

The name comes from the Greek words for naked and seed: gymnosperms bear seeds that are not enclosed in a fruit, and most of them are woody, evergreen trees.