General Science Previous Year Questions (PYQ) with Answers – Page 28

Two liquids that mix completely but boil at clearly different temperatures can be separated by heating the mixture and condensing the vapour of the lower-boiling liquid first.

This is double fertilisation, a feature found only in flowering plants. The pollen tube carries the two male gametes into the embryo sac.

Streptococcus mutans turns dietary sugar, especially sucrose, into a sticky slime that glues it to the teeth. The bacterium makes enzymes called glucosyltransferases that join the glucose units of sucrose into sticky chains called glucans.

Mitochondria are membrane-bound organelles, and only eukaryotic cells have membrane-bound organelles. Prokaryotes such as bacteria and cyanobacteria have no true nucleus and no membrane-bound organelles; their DNA lies in a region called the nucleoid, and they carry out respiration on their plasma membrane.

Meiosis makes gametes that differ from one another, and fertilization joins a gamete from each of two parents, so every offspring gets a new mix of genes.

Walls are whitewashed with a solution of slaked lime, calcium hydroxide, which is an inorganic compound; quicklime itself is not applied, and the shiny layer comes from Ca(OH)₂, not CaO.

Magnesium ribbon burns in air with a dazzling white flame, giving off heat and light and leaving a white powder of magnesium oxide.

Equal and opposite forces acting for the same time give equal and opposite changes in momentum, so the total stays the same.

The speed of the wave is frequency times wavelength, 700 m/s, and 2,100 m at 700 m/s takes 3 seconds.

Mercury(II) oxide is a red-orange solid, mercury is a liquid metal at room temperature, and oxygen is a gas. This is a thermal decomposition reaction: when mercuric oxide is heated, it breaks down into mercury and oxygen, written with states as 2HgO(s) → 2Hg(l) + O₂(g).

Magnesium combines with oxygen to form a new substance, magnesium oxide, so a chemical reaction takes place. When a magnesium ribbon is heated, it burns with a dazzling white flame and leaves a white powder: 2Mg + O₂ → 2MgO.

Power is the reciprocal of focal length in metres, and 10 cm is 0.1 m, so P = 1 ÷ 0.1 = 10 D. The power of a lens measures how strongly it converges or diverges light.

Velocity multiplied by time is displacement, so the area between a velocity-time graph and the time axis gives the displacement.

A bacterium is a prokaryote, so its DNA lies in an irregular region called the nucleoid, with no nuclear membrane around it.

A star is so far away that it is a point source of light.

A freely falling object moves with a uniform acceleration, the acceleration due to gravity, g, about 9.8 m/s² near the Earth's surface.

Biogas is mostly methane, usually about 50 to 75 percent, and it is the methane that burns with a clean blue flame and no smoke.

Orangutans shape sticks into tools and use them to pull insects, honey and termites out of holes in trees and logs.

This is the thermite reaction, which is highly exothermic: it gives out so much heat that the iron formed comes out molten.

Energy equals power multiplied by time: 0.1 kW × 30 hours = 3 kWh, which is 3 units. The bulb's power is 100 W, which is 0.1 kW.