General Science Previous Year Questions (PYQ) with Answers – Page 26

The method uses a natural bacterium to stop mosquitoes from passing on viruses. Wolbachia is a common bacterium that lives inside the cells of many insects.

The charge moves exactly opposite to the field, and a magnetic field exerts no force on a charge moving along its line.

Both quantities change with temperature, and resistance is directly proportional to resistivity, while resistivity does not depend on the wire’s size.

Of the four elements of xylem, only xylem parenchyma is made of living cells; tracheids, vessels and xylem fibres are dead at maturity.

In grasses the intercalary meristem lies at the base of the leaf blades and internodes, between tissues that are already mature.

Evaporation from the leaves pulls a continuous column of water up the xylem, and cohesion and adhesion keep that column from breaking.

Ramesh is short-sighted with a far point of 2 m, so he needs a concave lens of focal length −2 m, whose power is 1/(−2) = −0.5 dioptre.

A split-ring commutator reverses the coil's connection to the outer circuit every half turn, so the current outside flows in one direction only.

In plant cells RNA is found in the nucleus, the cytoplasm, mitochondria, chloroplasts and ribosomes. RNA is made in the nucleus, where DNA is copied into messenger, transfer and ribosomal RNA; the nucleolus in particular is rich in ribosomal RNA.

The tapeworm is an animal, and animal cells have no cell wall, only a cell membrane. A rigid cell wall lies outside the cell membrane in plants, fungi, most bacteria and many protists, giving the cell shape and protection.

Thyroxine is an iodine-containing hormone, so the thyroid gland cannot make it without iodine from the diet. The thyroid is a butterfly-shaped gland in the neck.

Mitochondria carry out respiration, chloroplasts photosynthesis, ribosomes make proteins and the rough endoplasmic reticulum transports them. Mitochondria are called the powerhouse of the cell because aerobic respiration in them releases energy as ATP.

The sour taste of tamarind comes from tartaric acid, not oxalic acid, so this statement is not correct. Many natural acids give foods their sour taste.

Cane sugar, or sucrose, is made of carbon, hydrogen and oxygen joined chemically in a fixed ratio, so it is a compound.

Both are pure forms of carbon, but their atoms are arranged differently, which gives them opposite physical properties. Diamond and graphite are allotropes of carbon.

When a candle burns, the wax first melts and turns to vapour, which is a physical change, and the vapour then burns in air, which is a chemical change.

Only pair 3 is right; the descriptions of Cepheids and nebulae have been swapped. Cepheid variables are pulsating stars that brighten and dim on a regular cycle.

The magnetic force depends on the sine of the angle between velocity and field, and sin 90° is the largest value.

Curd contains lactic acid, which reacts with copper and brass to form poisonous salts, so it should not be stored in them.

An accelerometer measures acceleration, including the pull of gravity, and each of the three actions depends on reading it. An accelerometer is a small sensor, today usually a MEMS (micro-electro-mechanical system) chip, that senses changes in speed and the direction of gravity.