Part 1: Multiple choice
The word "environment" is derived from a French word meaning
Which of the following is an abiotic factor of the environment?
A community of organisms interacting with each other and with non-living components is called
How many interconnected spheres make up the natural environment according to the book?
The sphere that contains the solid rocky crust and soil is the
The approximate percentage of Earth's surface covered by water is
About what percentage of Earth's water is salt water?
The approximate share of Earth's water that is easily available fresh water is
Water stored as polar ice and glaciers is approximately
Sea water is not suitable for irrigation or drinking mainly because it
The continuous movement of water between its three states through an almost closed system is the
The two physical forces that drive the water cycle are
Formation of clouds results from
Rainfall and snowfall are examples of
Water that soaks through soil pores and porous rocks forms
The openings through which most transpiration occurs are the
The tissue that carries water and minerals upward in the plant is the
Transpiration lowers the temperature of a leaf because evaporation
Which of the following is a nitrogenous waste excreted by mammals?
Which nitrogenous waste is almost insoluble and needs very little water for removal?
Which process, if stopped, would most directly stop vapour reaching the atmosphere from the oceans?
Increasing the rate of plant transpiration will indirectly
Which environmental condition decreases the rate of transpiration?
Which of the following is NOT a biological contribution to the water cycle?
The water cycle is described as "almost closed" because
Frozen water in glaciers belongs to which sphere?
The Nile Delta was shaped largely by which effect of the water cycle?
Water vapour rising from the sea forms clouds mainly because of
Which of the following correctly orders the steps?
Respiration of an animal returns to the atmosphere
Surface runoff finally carries most water to
Which gives the best explanation of why fresh water is a scarce resource?
A guard cell is found around
Cutting down a large forest is likely to
Which is a nitrogenous waste typical of fish?
Groundwater is stored mainly in
A student says: "the hydrosphere distinguishes Earth from other planets in the solar system." The statement is
The instrument used to measure the depth of rainfall at a place is the
Which one of these is an example of a chemical effect of the water cycle on Earth's surface?
Which is the best reason for the unit's concern about population growth and water?
Part 2: Written questions and problems
1. [Give reasons] Give a reason: the water cycle is considered an almost closed system.
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- The total quantity of water on Earth stays practically constant; water only changes state and location among ocean, air, land, ice and organisms.
- Energy enters from the Sun, but almost no matter enters or leaves.
2. [Give reasons] Give a reason: sea water cannot be used directly for drinking or irrigation.
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It contains a high concentration of dissolved salts that dehydrate the body and damage most crops.
3. [Give reasons] Give a reason: plants are considered a part of the water cycle.
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They absorb water from the soil and release large amounts of water vapour to the air by transpiration, adding to atmospheric vapour and clouds.
4. [Give reasons] Explain: transpiration cools a plant.
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Water evaporating from leaf cells absorbs a large amount of latent heat from the leaf, so the leaf temperature decreases.
5. [Give reasons] Explain how transpiration helps the movement of water and minerals up a tall plant.
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Evaporation at the leaves creates suction; cohesion between water molecules (hydrogen bonds) pulls a continuous water column up the xylem, carrying minerals with it.
6. [Give reasons] Give a reason: the temperature of a rising air mass falls and clouds form.
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At higher altitude the pressure is lower, the air expands and cools; cooled air cannot hold all its vapour so it condenses into droplets.
7. [Give reasons] Give a reason: groundwater may take a very long time to return to the sea.
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It moves very slowly through the tiny pores of soil and rock, so it can take years to centuries to reach rivers or the sea.
8. [Give reasons] Give a reason: the hydrosphere is a feature that distinguishes Earth from the other planets of the solar system.
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Earth has large amounts of water in all three states on its surface, while other planets lack abundant liquid surface water.
9. [Give reasons] Give a reason: the rate of transpiration decreases on a very humid day.
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The air is already nearly saturated with vapour, so the vapour-pressure difference between leaf and air is small and less water evaporates from the leaf.
10. [Give reasons] Explain why fish can excrete ammonia while birds excrete uric acid.
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Ammonia is toxic but very soluble, so fish quickly dilute it in the surrounding water; birds live on land and must save water, so they convert nitrogen into insoluble, non-toxic uric acid.
11. [Give reasons] Give a reason: the water cycle can change the surface of Earth.
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Moving water erodes and deposits materials (physical), dissolves minerals (chemical) and supports organisms (biological).
12. [Give reasons] Give a reason: pollution that enters a river can end up far away from its source.
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Rivers, groundwater, evaporation and rain move water and the substances it carries from place to place around the cycle.
13. [Give reasons] Give a reason: respiration and excretion are described as biological processes of the water cycle.
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Both release water (vapour and liquid) from organisms into the environment.
14. [Give reasons] Explain: evaporation is the process whose stopping most directly disturbs the water cycle.
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Evaporation is the step that lifts water into the atmosphere; without it there would be no vapour, clouds or rain.
15. [Give reasons] Give a reason: the four spheres cannot be studied completely separately.
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- Matter and energy move continuously among them; a change in one (e.g.
- CO₂ in the atmosphere) affects the others (ocean acidity, life, rocks).
Part C — Define / compare
16. [Define] Define the hydrosphere.
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All the water found on, under and above Earth's surface in its solid, liquid and gaseous states.
17. [Define] Define an ecosystem.
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A community of living organisms interacting with each other and with the non-living components of their surroundings, adapting to changing conditions.
18. [Define] Define transpiration.
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The release of excess water as vapour from plant surfaces exposed to air, mainly through stomata of leaves and green stems.
19. [Define] Define precipitation and give two forms.
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Water falling from clouds to Earth's surface, as rain and snow (also hail, sleet).
20. [Define] Define infiltration.
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The movement of water downward through the pores of soil and rocks, forming groundwater.
21. [Compare] Compare biotic and abiotic factors.
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Biotic factors are living (plants, animals, microbes, humans); abiotic are non-living (light, air, water, soil, temperature).
22. [Compare] Compare surface runoff and infiltration.
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Runoff: water flows over the surface to streams, rivers and sea. Infiltration: water seeps into the ground and forms groundwater.
23. [Compare] Compare evaporation and transpiration.
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- Evaporation: physical change from liquid to vapour at any wet surface.
- Transpiration: a biological process, vapour lost from plants mainly through stomata.
24. [Compare] Compare the three nitrogenous wastes ammonia, urea and uric acid.
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- Ammonia: very toxic, very soluble, needs much water (fish).
- Urea: less toxic, soluble (mammals).
- Uric acid: non-toxic, almost insoluble, saves water (birds, reptiles, insects).
25. [Compare] Compare salt water, fresh water and frozen water as shares of the hydrosphere.
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Salt ≈ 97 % (oceans, seas), accessible fresh ≈ 1 % (rivers, lakes, groundwater), frozen ≈ 2 % (ice caps, glaciers).
Part D — Problems
26. [Problem] The total volume of water on a planet-model is 5000 litres with the real Earth percentages. Calculate the volume of salt water, frozen water and accessible fresh water.
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salt 4850 L, ice 100 L, fresh 50 L.
0.97 × 5000 = 4850; 0.02 × 5000 = 100; 0.01 × 5000 = 50; sum = 5000.
27. [Problem] Earth's surface area is about 5.1 × 10⁸ km². Find the area covered by water, taking 70 %.
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3.57 × 10⁸ km².
0.70 × 5.1 × 10⁸ = 3.57 × 10⁸ km².
28. [Problem] A pond receives 8000 m³ per year by rain and inflow and loses 3000 m³ by evaporation and 4500 m³ by outflow. By how much does its volume change?
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+500 m³ (increase).
8000 − (3000 + 4500) = 500.
29. [Problem] A tree transpires 120 litres of water per day in summer. How much does it release in 30 days, in m³?
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3.6 m³.
120 × 30 = 3600 L = 3.6 m³.
30. [Problem] Using L = 2.26 × 10⁶ J/kg, calculate the heat absorbed when the tree in Q69 evaporates its water in one day (1 L = 1 kg).
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2.71 × 10⁸ J.
120 kg × 2.26 × 10⁶ = 2.712 × 10⁸ J.
31. [Problem] A rain gauge collects 25 mm of rain. How many litres fall on a roof of area 40 m²? (1 mm over 1 m² = 1 L)
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1000 L.
25 mm × 40 m² = 25 × 40 = 1000 L.
32. [Problem] A city uses 150 L per person per day. How much does a city of 2 million people use in a day, in m³?
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300 000 m³.
150 × 2 × 10⁶ = 3 × 10⁸ L = 3 × 10⁵ m³.
33. [Problem] If accessible fresh water is 1 % of the total and the total water is 1.4 × 10⁹ km³, find the volume of accessible fresh water.
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1.4 × 10⁷ km³.
0.01 × 1.4 × 10⁹ = 1.4 × 10⁷ km³.
34. [Problem] A field of 3 hectares has 25 000 plants per hectare. Each plant transpires 0.3 L per day. Find the water vapour released per day in litres.
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22 500 L.
3 × 25 000 = 75 000 plants; × 0.3 = 22 500 L.
35. [Problem] A 60 kg person is 70 % water by mass. What mass of water is in the body and what is its volume in litres?
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42 kg, 42 L.
0.70 × 60 = 42 kg; water density 1 kg/L.
36. [Problem] A person loses 2.5 L of water per day and replaces it all. How many litres pass through the body in a year (365 days)?
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912.5 L.
2.5 × 365 = 912.5.
37. [Problem] A lake of volume 80 million m³ gains 20 million m³ and loses 18 million m³ in outflow and evaporation. What is the new volume, and what is the percentage change?
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82 million m³; +2.5 %.
80 + 20 − 18 = 82; 2/80 = 0.025.
38. [Problem] Of 500 mL of a sample of earth's water-model, 485 mL are salty. What is the percentage of non-salty water?
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3 %.
(500 − 485)/500 = 0.03.
39. [Problem] Evaporation from a sea takes 5 × 10¹² kg of water per day. Using L = 2.26 × 10⁶ J/kg, find the heat absorbed.
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1.13 × 10¹⁹ J.
5 × 10¹² × 2.26 × 10⁶ = 11.3 × 10¹⁸ J.
40. [Problem] If rainfall over a farm of 2 hectares (1 ha = 10 000 m²) is 12 mm, find the volume of rain in m³.
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240 m³.
Area = 20 000 m²; depth = 0.012 m; volume = 20 000 × 0.012 = 240 m³.