General Science Previous Year Questions (PYQ) with Answers – Page 77

Xylem carries water together with the minerals dissolved in it from the roots to the stem and leaves, so blocking it stops both.

It is called dry ice because, at ordinary pressure, it changes directly from solid to gas (sublimation) instead of melting, so it never makes anything wet.

Guttation is the loss of water in the form of liquid droplets from the edges and tips of leaves. Guttation happens mostly at night or early in the morning, when the soil is moist and the air is humid, so transpiration is slow.

Both statements are true, and the airborne spread of the TB bacterium is exactly why crowded places raise the risk.

A true fruit is a ripened ovary and nothing else. After fertilisation, the ovary of a flower develops into the fruit, its wall becomes the pericarp and the ovules inside become seeds.

Meristems are groups of actively dividing cells, and all new plant tissue comes from them. Meristematic cells are living, small and closely packed, with thin cellulose walls, dense cytoplasm, a large nucleus and few or no vacuoles.

The layers of graphite are held only by weak van der Waals forces, not by covalent bonds. Diamond and graphite are allotropes of carbon.

This is the order of the taxonomic ranks from the broader group to the narrower one. The full hierarchy set out by Linnaeus and used today runs Kingdom, Phylum (Division in plants), Class, Order, Family, Genus and Species.

Orthophosphoric acid, H 3 PO 4, has three replaceable hydrogen ions, so it is tribasic. The basicity of an acid is the number of hydrogen ions one molecule can give up in water.

Carrying water and food through the plant is the main job of the stem's vascular tissue, not of the leaf.

Mosses and liverworts have no xylem or phloem, so water moves through them cell to cell. Bryophytes, such as Funaria (a moss) and Marchantia (a liverwort), are called the amphibians of the plant kingdom because they live on land but need water for fertilisation.

Copper with dilute nitric acid gives copper nitrate, water and nitric oxide: 3Cu + 8HNO 3 → 3Cu(NO 3 ) 2 + 2NO + 4H 2 O. Nitric acid is a strong oxidising agent, so metals usually do not release hydrogen from it; instead the acid itself is reduced, and…

It is part of the kidney's nephron and filters blood to form urine; it plays no role in breathing. Bowman's capsule is the cup-shaped start of each nephron, wrapped around a tuft of capillaries called the glomerulus.

Boiling removes only temporary hardness; permanent hardness comes from salts that do not break down on heating. Temporary hardness is caused by the bicarbonates of calcium and magnesium.

Prokaryotic cells such as bacteria have no membrane-bound organelles, so they lack mitochondria. Prokaryotes have no true nucleus: their DNA lies in a region called the nucleoid, and they have no mitochondria, chloroplasts, endoplasmic reticulum or Golgi body.

AIDS is caused by HIV, a retrovirus whose genome is two copies of single-stranded RNA. After HIV enters a helper T-cell (CD4 cell), its enzyme reverse transcriptase copies the viral RNA into DNA, which is then built into the host cell's own DNA.

Both statements are true, and the magnetic field set up by the current (Statement II) is exactly why the compass needle turns (Statement I).

A candle gives light by burning wax, so it converts chemical energy, not electrical energy, into light and heat. In a burning candle the wax vapour combines with oxygen in the air; the chemical energy stored in the wax is released as heat and light.

Bleaching powder is an oxidising agent, not a reducing agent, so this statement is the false one. Bleaching powder, calcium oxychloride (CaOCl₂), is made by passing chlorine gas over dry slaked lime, Ca(OH)₂.

Washing soda is sodium carbonate decahydrate, sodium carbonate with ten molecules of water of crystallisation.