General Science Previous Year Questions (PYQ) with Answers – Page 36

In water plants, parenchyma cells enclose large air cavities; this special form is called aerenchyma, and it helps the plants float.

Animal cells do have vacuoles; they are only small and often temporary, so the statement is wrong. A vacuole is a membrane-bound sac filled with cell sap: water, salts, sugars and waste.

The eye adjusts the focal length of its lens to bring both near and far objects into focus on the retina, and this ability is called accommodation.

Probiotics include both bacteria and yeasts, and some of them help break down lactose, the sugar in milk. Probiotics are live microorganisms that give a health benefit when eaten in adequate amounts.

A mutation is a change in the sequence of the DNA or RNA that carries a virus's genes. A virus is made of genetic material, either DNA or RNA, inside a protein coat.

Resistance varies inversely with the area of cross-section, and doubling the diameter makes the area four times larger. The resistance of a wire is R = ρl/A, where ρ is the resistivity of the metal, l the length and A the cross-sectional area.

Biofilms form on almost any moist surface, including implants and food equipment, and they are notoriously hard to kill with antibiotics.

Leucoplasts are colourless plastids that store food: starch, oils and proteins. Plastids are found only in plant cells and some algae, and they are of three main kinds.

Silver turns black in air because it reacts with sulphur compounds, mainly hydrogen sulphide, to form a thin black coating of silver sulphide (Ag₂S).

Growth with repair and metabolism are two of the features that mark living beings off from non-living things. A living body grows from inside by making new cells from the food it takes in, and it heals wounds and replaces worn-out tissue.

A nerve impulse is carried by the movement of sodium ions into the nerve cell and potassium ions out of it.

Litmus is a natural dye extracted from certain lichens, especially species of Roccella. A lichen is a partnership between a fungus and an alga (or a cyanobacterium): the alga makes food by photosynthesis, while the fungus gives shelter and absorbs water and minerals.

An ammeter measures the electric current flowing in a circuit, in amperes. An ammeter is always connected in series with the part of the circuit whose current is to be measured, so that the whole current passes through it.

The gastric glands in the stomach wall secrete hydrochloric acid, the only mineral (inorganic) acid among the options. Hydrochloric acid (HCl) makes the stomach strongly acidic, with a pH of about 1.5 to 3.5.

Pitch is the way our ear senses the frequency of a sound: the higher the frequency, the higher the pitch.

The ball keeps slowing down by about 9.8 m/s every second until its speed becomes zero at the top, which takes 40 ÷ 9.8 ≈ 4 seconds.

On heating, silver oxide breaks down into silver metal and oxygen, while zinc oxide and magnesium oxide stay unchanged. The reaction is 2Ag₂O → 4Ag + O₂.

Deep-sea divers breathe a mixture of oxygen and helium because helium does not dissolve much in blood under high pressure.

Starlight bends as it passes through air layers of changing density, and because these layers keep moving, the star seems to flicker.

Momentum is mass times velocity, 10 × 10 = 100 N.s, and kinetic energy is half the mass times the square of the speed, ½ × 10 × 10 × 10 = 500 J. Linear momentum, p = mv, measures the quantity of motion and is a vector; its unit…