Year 7 Science · Unit 2 · Lesson 12

The Water Cycle

Challenge Worksheet

Name

Date

Class

Learning Goals

Find and correct errors in a description of the water cycle.
Use the lesson’s water figures to explain why less than 0.3% of Earth’s water is accessible.
Evaluate a water security strategy for a dry continent.

Warm Up

1. State the energy involved in each process: (a) evaporation, (b) condensation, (c) runoff.

Recall 3 marks

Your Turn

Find the error

A student wrote this description of the water cycle. Four sentences contain one error each. Write “correct”, or rewrite the sentence so it is correct.

Apply 4 marks

#	Student’s sentence	Correct, or the fixed sentence
1	The Sun heats water at the surface of the ocean, and it evaporates into water vapour.
2	High up, the water vapour forms clouds, which are made of water vapour.
3	When water vapour condenses, it takes in heat from the air around it.
4	Cloud droplets grow heavy and fall as rain, snow, sleet or hail.
5	Rain that soaks down into the soil and refills aquifers is called runoff.
6	Transpiration is water evaporating from the surface of rivers and lakes.

Go Deeper

Read the data: where Earth’s water is

Scenario: plenty of water, little to use

Table 1 shows where all the water on Earth is stored. The figures are rounded, so they do not add to exactly 100%.

Table 1. Share of all water on Earth

Store	Share of total water (%)	Where it is
Salt water	97.5	oceans and seas
Ice and glaciers	about 1.7	Antarctica, Greenland, mountain glaciers
Groundwater	about 0.76	underground aquifers
Surface fresh water	about 0.013	rivers, lakes, wetlands

Source: figures from Lesson 12.

2. Add up the three fresh water stores in Table 1. Show your working and round to one decimal place.

Apply 2 marks

Answer %

3. Aisha says: “Question 2 shows that about 2.5% of Earth’s water is fresh, so the lesson is wrong when it says less than 0.3% is accessible.” Explain how both figures can be right.

Analyse 3 marks

4. Groundwater is less than 1% of Earth’s water. Use Table 1 to explain why protecting shallow aquifers still matters in Australia.

Analyse 2 marks

Scenario: a farm dam in summer

A farm dam in western New South Wales is 1500 mm deep when full. In a hot, dry summer with no rain, about 8 mm of water evaporates from its surface every day. (Made-up figures, of a realistic size.)

5. How deep will the water be after 60 days with no rain? Show your working.

Apply 2 marks

Answer mm

6. The farmer plans a new dam that holds the same amount of water but is deeper and narrower. Explain why it would lose less water to evaporation, and say where the evaporated water ends up.

Analyse 3 marks

Show What You Know

7. A politician says: “Building more dams is the best way to make Australia’s water supply drought-proof.” Evaluate this claim. Use the water cycle, Australia’s climate and at least one other water strategy in your answer.

Analyse 6 marks

Answer Key (for teachers)

Question 1

(a) Solar energy absorbed (1). (b) Heat released (1). (c) Gravity (1). [3 marks]

Find the error

1 correct. 2 clouds are tiny liquid droplets. 3 condensation releases heat. 4 correct. 5 infiltration. 6 transpiration is vapour released by plants’ leaves. [4 marks: 1 per error fixed]

Question 2

1.7 + 0.76 + 0.013 (1) = 2.473, about 2.5% (1). [2 marks]

Question 3

2.5% is all fresh water; accessible is only what we can reach (1). Most ice is in Antarctica and Greenland; most groundwater is too deep or salty (1). Rivers and lakes plus shallow aquifers: under 0.3% (1). [3 marks]

Question 4

Groundwater (0.76%) is about 60 times all rivers and lakes (0.013%) (1). Shallow aquifers are among the few stores we can reach, by bores (1). [2 marks]

Question 5

8 × 60 = 480 mm lost (1); 1500 − 480 = 1020 mm (1). [2 marks]

Question 6

Evaporation happens only at the surface (1); a narrower dam has less surface, so less evaporates each day (1). The vapour condenses and falls as precipitation elsewhere (1). [3 marks]

Question 7

Marking guide: 1 dams refill only from precipitation and runoff; 1 Australian fact (about 470 mm rain, variable, or longer dry spells as it warms); 1 evaporation from the dam; 1 impact: less flow downstream; 1 comparison with desalination or recycled water; 1 judgement (a mix is needed). [6 marks]

Model answer: Too strong. A dam stores precipitation and runoff, so it refills only when it rains, and Australia gets about 470 mm a year, unevenly. In a long drought it empties, and loses water by evaporation. Dams cut flow to wetlands downstream. Desalination is drought-proof but energy-hungry. A mix is best.

Common error: counting ice and deep groundwater as accessible.