Hydrological cycle

Correct answer: B, deposition. A phase change is identified by comparing the starting and ending states. Here water starts as a gas, water vapour, and ends as a solid, ice crystals, without first becoming liquid. The direct gas-to-solid change is called deposition. Frost can form through this process when water vapour changes directly into ice on a sufficiently cold surface. A, evaporation, is liquid to gas. C, melting, is solid to liquid. D, condensation, is gas to liquid, such as vapour becoming liquid droplets. Condensation and deposition are therefore different even though both begin with water vapour. Memory cue: deposition is gas to solid; sublimation is the reverse, solid to gas.

Correct answer: B, oceans, in the usual global water-cycle pathway. Rain and melting snow can produce surface runoff. Streams join to form rivers, and rivers generally flow downhill because gravity carries water toward lower elevations. They commonly discharge into lakes, seas, or oceans. Lakes may also lose water by evaporation, feed rivers, or exchange water with groundwater, so not every drop follows one identical route; however, the major eventual reservoir for surface water is the ocean. A is not the normal destination. C, a desert, is a land environment, not the general receiving basin for rivers and lakes. D, clouds are formed when water evaporates and later condenses; rivers do not flow physically into clouds. Memory cue: runoff moves downhill; rivers ultimately carry water toward the oceans.

Correct answer: B. Infiltration is the entry of water from the ground surface into soil and underlying material. Urbanization often replaces permeable soil and vegetation with roofs, roads, pavements, and concrete. These relatively impermeable surfaces prevent or reduce rainfall from entering the ground. As infiltration decreases, a larger and faster share of rain becomes surface runoff, which can overload drains and increase the risk of urban flooding. A is generally the opposite of the common effect. C ignores the change in surface cover. D is scientifically meaningless: water does not disappear; it is redirected as runoff, evaporation, storage, or drainage. Green spaces, porous pavement, rain gardens, and recharge areas can reduce this effect. Memory cue: hard surfaces block infiltration and speed runoff.

Correct answer: B. Clouds are made mainly of extremely small liquid water droplets and, in colder regions, ice crystals suspended in air. Each tiny droplet has very little mass, so air resistance and rising or turbulent air currents can keep it suspended for some time. Warm air rises, cools, and may cause water vapour to condense around tiny particles, producing these droplets or crystals. A is wrong because water is still affected by gravity and larger drops fall. C is wrong because gravity has not disappeared; when droplets combine and become large enough, precipitation occurs. D alone is incomplete: wind may move clouds, but cloud formation and suspension also involve condensation, droplet size, and air currents. Memory cue: tiny droplets plus moving air can remain suspended; large drops fall as rain.

Correct answer: B, hail and snow. Water is solid when its particles are held in a fixed arrangement and it has a definite shape or structure. Snow consists of ice crystals, and hail consists of balls or lumps of ice, so both are solid forms of water. A, water vapour, is water in the gaseous state and spreads through the air. C, river water, is normally liquid and flows to fit the shape of its channel. D, dew, consists of liquid droplets formed when water vapour condenses on a cool surface. In the water cycle, heating can change ice into liquid water and liquid water into vapour, while cooling can produce ice, snow, or hail under suitable conditions. Memory cue: ice, snow, and hail are solid; water and dew are liquid; vapour is gas.

Correct answer: A. The biosphere includes living organisms and the regions where life exists. The water cycle continuously moves water among oceans, atmosphere, land, groundwater, rivers, lakes, ice, plants, and organisms. Evaporation, condensation, precipitation, runoff, infiltration, and transpiration help redistribute and renew freshwater supplies needed for drinking, photosynthesis, metabolism, growth, and habitats. The cycle does not make every water source pure or guarantee equal freshwater in every place, but it is essential for maintaining and replenishing usable freshwater. B is not its main purpose; temperature is influenced by many processes. C describes Earth’s rotation, not the water cycle. D weathering and erosion can involve water, but destroying rocks is not the cycle’s primary importance. Memory cue: the water cycle continually circulates and renews water needed by life.

Direct answer: B, precipitation. The water cycle moves water between Earth’s surface and the atmosphere. First, heat may change liquid water into water vapour by evaporation. The vapour cools and forms clouds by condensation. When water falls from clouds to the ground, the process is called precipitation. Rain is liquid precipitation, while snow, sleet and hail are solid forms. During a hailstorm, water droplets or ice particles are carried upward inside a cold, strong cloud, freeze or grow into ice, and eventually fall because of gravity. A is evaporation, which sends water upward, not downward. C is percolation, in which water moves through soil and rocks. D is transpiration, the loss of water vapour from plant leaves. Memory cue: precipitation means water “precipitates” or falls from the sky.

Direct answer: B, condensation nuclei such as dust particles. Atmospheric air contains water vapour, but tiny suspended particles provide surfaces on which vapour can begin forming liquid droplets or ice crystals. These particles are called condensation nuclei and may include dust, sea-salt particles, smoke or other aerosols. As moist air cools, water molecules gather around these nuclei, allowing clouds and mist to develop. A is wrong because oxygen is a gas in air, not the special surface needed for this process. C is wrong because water molecules are the material that condenses, not the nuclei that support condensation. D is too absolute: condensation can occur without particles under special conditions, but in the atmosphere nuclei make it much easier and are the expected school-level answer. Cue: nuclei are tiny “seeds” around which cloud droplets grow.

Direct answer: A, nutrient cycling and erosion. Flowing water has mechanical force. As a river moves downhill, it can loosen and carry soil, rock fragments and dissolved minerals; this removal and transport of material is erosion. When the river becomes slower on plains, some transported sediment and nutrients may be deposited. In this way, water movement connects places and helps redistribute materials involved in natural nutrient cycles. B is too narrow: pollution is contamination caused by harmful substances and is not an unavoidable meaning of river transport. C is not the described process; temperature may affect water movement but is not shown here. D is incorrect because water is transported and changes location or state, not destroyed. Memory cue: running water can “erode, carry and deposit.”

Direct answer: B, water vapour. Water exists mainly in three physical states: solid ice, liquid water and gaseous water vapour. Solar heating causes liquid water at oceans, rivers, lakes and soil to evaporate; plants also release water vapour through transpiration. The vapour rises, may cool and condense into cloud droplets, and later return as precipitation. A is solid water, so it is not gaseous. C, dew, consists of liquid droplets that form on cool surfaces when nearby air cools and water vapour condenses. D, fog, is a collection of tiny liquid droplets or sometimes ice particles near the ground, not invisible gaseous water. Thus, do not confuse a visible mist with vapour: vapour itself is a gas. Cue: evaporation produces water vapour.

Direct answer: B, infiltration and percolation. An aquifer is an underground layer of permeable rock or sediment that can store and transmit groundwater. After rain or other surface water reaches the ground, infiltration is the entry of water through the soil surface. Percolation is the further downward movement of that water through soil pores and permeable rock until it reaches the groundwater zone. This adds water to the aquifer and raises or restores its stored supply. A moves water from the surface into the atmosphere. C carries water across the land and may reduce the amount available to enter the ground. D transfers water from plant tissues to the atmosphere. Actual recharge depends on soil, rock, vegetation and rainfall conditions, but the key pathway is downward infiltration followed by percolation. Cue: recharge means water goes down into storage.

Direct answer: B. Global warming raises average temperatures, and warmer air and surfaces generally increase evaporation and the amount of water vapour that the atmosphere can hold. This can intensify parts of the water cycle. More available moisture may contribute to heavier rainfall and flooding in some regions, while altered circulation, earlier snow or ice melt, and drying of soils can increase drought risk in others. The exact effect differs by place and season, so the statement does not mean every area always becomes wetter. A is not the best answer because warming generally strengthens or speeds several water-cycle processes. C is false: rainfall has not stopped everywhere. D is opposite to the broad warming trend; glaciers generally lose mass, although individual short-term changes can vary. Cue: warming adds energy to evaporation, but rainfall distribution becomes less predictable.

Direct answer: A, condensation of water vapour near the surface. Fog forms when air close to the ground cools sufficiently for water vapour to change into countless tiny liquid droplets, often around condensation nuclei. These droplets remain suspended near the surface and reduce visibility. It is therefore similar to a cloud at ground level, but the defining condition in this question is near-surface condensation. B is wrong because evaporation changes liquid water into invisible vapour; it does not directly describe the visible fog. C is less precise: clouds form higher in the atmosphere, whereas fog is near the ground, even though both involve condensation. D concerns the movement of groundwater below the surface and has no direct role in defining fog. Memory cue: fog is a cloud that forms low, by cooling and condensation.

Direct answer: B, about 99%. Roots absorb water from the soil, and that water travels through the plant’s conducting tissues toward leaves. At leaf surfaces, especially through stomata, most of the water escapes as water vapour; this loss is called transpiration. In the commonly taught school-level estimate, approximately 99% of absorbed water is lost through transpiration, while only a very small fraction is retained or used in metabolic processes and growth. A, C and D are much lower than the accepted approximate value for this question. The figure is an estimate, not a universal constant: it can vary with plant species, humidity, temperature, wind, soil water and stomatal behaviour. Do not confuse transpiration with evaporation from open water; transpiration is specifically water loss from plant surfaces. Cue: plants absorb much water but use only a tiny fraction internally.

Direct answer: A, because Earth’s water is largely retained within the Earth system rather than continuously being lost into outer space. In the water cycle, the same water can evaporate, condense, fall as precipitation, flow as runoff, enter the soil, become groundwater, and return to oceans or the atmosphere. It changes location and physical state, but the global supply is recycled. Gravity helps retain water, while the atmosphere, land and oceans exchange it. B is false because the cycle operates in every season. C is false because water is constantly used by organisms and moved through ecosystems; “closed” does not mean unused. D is false because the cycle includes oceans, land, atmosphere, rivers, soil, groundwater, ice and living organisms. Scientifically, small exchanges with space exist, but at school level the Earth’s water cycle is treated as essentially closed. Cue: closed means recycled within the system, not locked in one place.

Direct answer: B, evaporation is extremely rapid for available water. Arid regions commonly have high temperatures, intense sunlight, low relative humidity and often moving air. Heat supplies energy for liquid water molecules to escape into the atmosphere, while dry air can accept additional water vapour. Wind can also remove moist air from the surface, allowing evaporation to continue. Therefore exposed water and wet soil may dry quickly, even though deserts receive little rainfall. A and C are wrong because dryness does not stop evaporation; it often increases the rate when some water is present. D is wrong because evaporation and condensation are different phase changes: evaporation changes liquid into gas, whereas condensation changes gas into liquid. The total water loss also depends on how much water is available, so “high rate” does not mean deserts contain abundant water. Cue: hot plus dry air promotes fast evaporation, but limited supply causes rapid drying.

Correct answer: B, rivers and lakes. Surface water is water found on or openly flowing across Earth’s surface. Rivers and lakes are visible surface-water bodies, as are ponds, reservoirs, wetlands, and oceans. B is correct because both named examples store or carry water above the ground. A, an aquifer, is a layer or body of permeable underground material that stores and transmits groundwater, so it is not normally classified as surface water. C is wrong because deep rocks are geological material; they may contain water in pores or cracks but are not themselves surface-water bodies. D is wrong because plant cells contain biological water, not an open surface-water reservoir. Memory cue: visible water bodies such as rivers and lakes are surface water; hidden water below ground is groundwater.

Correct answer: B. The water cycle moves water between Earth’s surface and the atmosphere. During evaporation, water needs energy to change from liquid to vapour, so it absorbs latent heat from the surroundings. When water vapour cools and condenses into droplets, this latent heat is released into the surrounding air. These processes transport and redistribute heat, helping moderate temperature rather than allowing heat to remain concentrated in one place. A is wrong because the cycle does not regulate temperature simply by heating water. C is wrong because melting ice is only one possible change and is not the main temperature-regulating mechanism. D is wrong because the water cycle does not stop wind. Memory cue: evaporation absorbs heat; condensation releases it.

Correct answer: B. Gravity pulls water toward Earth. In precipitation, water droplets or ice particles in clouds fall downward as rain, snow or hail when they become sufficiently large. After water reaches the ground, gravity makes it flow from higher land to lower land as surface runoff and helps it move into soil and groundwater. Evaporation in A is mainly driven by heat energy, especially solar energy, not by gravity. Sublimation in C is the direct change of ice into vapour and is caused mainly by energy and environmental conditions. Transpiration in D is the release of water vapour from plant leaves through stomata, also not a downward gravitational movement. Memory cue: gravity makes water fall and flow downhill.

Ocean water contains dissolved salts, but evaporation mainly removes water molecules from the surface. These molecules enter the atmosphere as water vapour, while the dissolved salts are non-volatile under ordinary natural conditions and remain in the ocean. When the vapour later cools and condenses, it forms droplets that are essentially fresh water. This separation is a natural part of the water cycle and helps produce freshwater precipitation.

Option B is correct. Wind can increase evaporation, and sunlight supplies energy, but neither is the reason that the vapour is not salty. The important reason is that dissolved salts do not normally pass into the vapour with water during evaporation. The original reference to boiling point gives a rough school-level idea, but the more accurate explanation is that salts are non-volatile and remain behind; boiling-point comparison alone should not be treated as the complete mechanism.

Correct answer: B. An aquifer is a layer or body of underground permeable rock, sediment or soil that can store and transmit groundwater. Rainwater and surface water may infiltrate into the ground and percolate downward until they reach a saturated zone. The aquifer then acts as an underground reservoir, and wells may obtain water from it. Some aquifers also allow slow groundwater movement toward springs, streams or other outlets. A is wrong because clouds form in the atmosphere when water vapour condenses. C is wrong because an aquifer does not stop rainfall; it may receive part of the infiltrated rainwater. D is wrong because storage underground is not the same as increasing evaporation. Memory cue: an aquifer is a natural underground water store, not an underground river in every case.

Water in soil is essential because it dissolves mineral salts and makes them available for absorption by plant roots. Root cells take up this soil solution, and the water helps carry minerals through the plant in conducting tissues. Water is also needed for photosynthesis, cell firmness, growth, and many chemical reactions, but the option specifically asks about the role connected with mineral salts. Without enough soil water, nutrients may remain present in the soil but cannot move readily into the roots.

Therefore, option B is correct. Supporting roots is important, but water is not present only for physical support. It acts as a solvent and transport medium for minerals. Changing leaf colour is not its basic purpose, and saying that water is unnecessary is false. The supplied answer correctly focuses on absorption and transport of dissolved mineral salts, while the broader functions explain why adequate soil moisture is vital for healthy plants.

Correct answer: B. Organisms temporarily take up water, but it can return to the environment through several routes. Animals release water vapour during respiration and lose water in urine, faeces and other excretory products; water may also leave through sweating where applicable. Plants release a large amount of water vapour through stomata during transpiration, and some water returns through plant tissues, litter and decomposition. Photosynthesis in A uses water as a reactant rather than being the general return process. Eating food in C does not itself return water to the environment, and D is false because water continuously cycles between organisms and their surroundings. Memory cue: organisms borrow water; respiration, excretion and transpiration return it.

Correct answer: B. Sunlight transfers energy to the water system. As water molecules gain energy, their average kinetic energy increases, meaning they move more actively. The fastest molecules near the surface may overcome attractive forces holding them in the liquid and escape into the air as water vapour; this process is evaporation. Not every molecule becomes vapour, and evaporation can occur even below the boiling point. A is opposite to the usual effect of absorbed solar energy. C is impossible for moving molecules in ordinary liquid water, and D ignores energy absorption. Temperature represents average kinetic energy, while individual molecules have different energies. Memory cue: more absorbed energy means faster molecules and a greater chance of surface escape.

Correct answer: B. Evapotranspiration is the combined transfer of water from land to the atmosphere by evaporation and plant transpiration. Evaporation occurs from soil, open water, wet surfaces and other exposed areas. Transpiration is the release of water vapour from living plants, mainly through stomata in leaves. Hydrologists often consider the combined amount when estimating how much water leaves a land surface, although the exact contribution of each process can vary. A cloudburst in A is intense rainfall, not atmospheric water loss. C is melting, which changes ice to liquid water. D is underground movement and does not describe the combined upward transfer to the atmosphere. Memory cue: evapotranspiration = evaporation + transpiration.