General Science Previous Year Questions (PYQ) with Answers – Page 19

The retina is the light-sensitive layer at the back of the human eye; it is not a part of any microscope.

L4 lies on Earth's orbit 60° ahead of the Earth, so it is as far from the Sun as from the Earth.

The animal cell membrane is a phospholipid bilayer with proteins set in it and cholesterol between the lipid molecules. The fluid mosaic model of Singer and Nicolson (1972) describes the membrane as a double layer of phospholipids, whose water-loving heads face outward and water-fearing tails face inward.

All three are underground modified stems: the potato is a stem tuber, and onion and garlic are bulbs. A stem can be told from a root by its nodes and buds.

A wave moves forward by one wavelength in each cycle, so 150 wavelengths take 150 cycles, and 150 cycles at 300 per second take half a second.

Lysozyme kills bacteria by breaking down their cell walls, and it is found in saliva, tears and mucus. Lysozyme attacks peptidoglycan, the main material of the bacterial cell wall, by splitting the bonds between its sugar units; the weakened cell then bursts.

Presbyopia is an age-related loss of near focusing, and it is corrected with bifocal or progressive lenses. With age the ciliary muscles weaken and the eye lens loses its flexibility, so the power of accommodation falls and the near point moves away.

Microbodies are small vesicles bounded by a single membrane, filled with enzymes that carry out particular metabolic reactions. The main microbodies are peroxisomes and glyoxysomes.

A rainbow forms only because sunlight is refracted, dispersed and internally reflected inside raindrops. When sunlight enters a water droplet it is refracted and split into its colours (dispersion), because each colour bends by a different amount.

The water at the bottom warms, becomes lighter and rises, while cooler water sinks to take its place, and these convection currents carry heat through the pot.

X-rays can pass through solid materials and their wavelength is close to the spacing of atoms, so they serve both purposes.

Two vanadium atoms must balance five oxide ions, each of charge −2, so each vanadium carries +5. In a neutral compound the oxidation states add up to zero.

This is the false statement: glass cools into an amorphous solid without any regular crystal structure. When molten glass cools, its viscosity rises so quickly that the atoms have no time to arrange themselves in an ordered crystal lattice.

The body makes nitric oxide (NO) itself, and it relaxes the walls of blood vessels so that they widen and carry more blood.

Litmus is a purple dye extracted from certain lichens, such as species of Roccella, and it turns red in acid and blue in base.

These three oxides, made by heating limestone with clay, form the compounds that make cement set and harden. Portland cement was patented by Joseph Aspdin in England in 1824, and named after Portland stone, which the set cement resembled.

The weight we feel is really the push of the floor on us, and in orbit that push disappears. The space station and the astronaut are both in free fall around the Earth.

Filament bulbs are commonly filled with argon, often mixed with nitrogen, not helium. An inert gas in a filament bulb slows the evaporation of the hot tungsten filament.

Wet straw or gunny bags keep the fresh concrete moist, so water does not evaporate before the cement has hydrated properly.

Massive giant stars burn their fuel so fast that they live much shorter lives than dwarf stars, so Statement I is false and Statement II is true.