The water cycle

This task is about using a science diagram to think about the water cycle.

Teaching and learning:

Why is the water cycle an important idea in science?

Knowing that water exists in three different states within the normal range of temperatures on Earth is fundamental to understanding the importance of water to life on our planet. It is also a precursor for understanding the processes of changes of state such as freezing, melting, evaporation, and condensation. We need to know about both the states that water exists in, and the processes that lead to changes from one state to another, to understand Earth's systems, such as the water cycle. Knowing about the water cycle helps us to make decisions about important environmental issues such as water usage and climate change.

Key competencies and Nature of science

Diagrams are a common convention used for communicating in science. Exploring diagrams potentially incorporates Communicating in science from the Nature of science strand, and contributes to the development of the key competency Using language, symbols, and texts.
The main emphasis of the first question of this resource is about interpreting diagrams. Because students need to synthesise knowledge to complete the task, it also provides students with an opportunity to practice the key competency thinking.

Diagnostic and formative information:

Trial and reporting information
This resource was trialled with 655 students from Years 4-10, so the data collected provide a good indication of how students' ideas change over time. The number of students trialled were 99 (Y4), 15 (Y5), 115 (Y6), 51 (Y7), 128 (Y8), 64 (Y9) and 183 (Y10).

NOTE 1: In this section the data from the separate years are considered. However, Year 5 was a particularly small group of just 15 students from one school who performed better on some questions than older students, probably indicating a school effect. Their results are not shown.

NOTE 2: The results from the smaller samples of trial students will have a greater margin of error than the larger samples.

Question a) Draw arrows on the diagram to show the different directions of water movement in the water cycle.

Students are commonly taught what a conventional water cycle diagram looks like. Most students can reproduce this once they have learnt it. In this task, elements of the water cycle were placed differently from the conventional diagram. This task requires the synthesis of two different types of knowledge:

- knowledge about the water cycle; and
- knowledge about diagrams.

The assessment focus for this part of the task is on knowing about how diagrams work rather than knowledge about the water cycle. (Go to Key competencies and Nature of science.) However, some knowledge of the water cycle is necessary to complete the task. Check that students' ability to complete the diagram is not hampered by their lack of familiarity with the water cycle.
For those students who are able to transfer the information from a familiar to unfamiliar diagram, some assumptions can be made that they do understand connections between some parts of the water cycle at a simple level.

As well as looking at the students' responses, their comments about the task and teachers' feedback were also examined.

Marking schedule
The marking schedule for this task allowed us to capture each student’s overall pattern of response, in addition to recording the accuracy of their individual links. We did this by coding each arrow as shown in the diagram, and adding a 2 if the arrow was in the correct direction or a 1 if it pointed the wrong way, and a 0 if it was missing. Thus a correct pattern would read: A2 B2 C2 D2 E2

The water cycle diagram that students, especially younger ones, are likely to be familiar with incorporates elements of a simple drawing (e.g. a landscape) with some conventions of a diagram (e.g., arrows). What sense do they make of a less literal, partial symbolisation? The table below shows the most common patterns of overall responses, and likely reasons for these:

Pattern	% of all students doing this	Why this pattern?
A2 B2 D2 (E and C missing)	22	E and C are the arrows that appear to point “uphill” if the model is read literally, and there is confusion about the ocean being at the top and the clouds at the bottom. Students who think this are likely to be unaware that diagrams are a representation of a particular idea, not a drawing of reality. Even at years 9 and 10, a quarter of the students did this.
No response at all	11	This was most common at year 4 (20% of this group) – many younger students found the placement of the ocean at the top of the diagram confusing.
B2 C2 E1 (A and D missing)	7	This pattern makes a full cycle around the outside of the diagram in an anticlockwise direction – these students seemed to think a cycle should be literally that.
B1 C1 E1 (A and D missing)	3	In this version all the arrows added point “downhill” – i.e. in the direction rain would fall if this was taken literally – thus this appears to be a variation of the first pattern.
A2 B2 E2 (C and D missing)	2	Both links from falling rain are missing, others are correct.
B1 C1 E2 (A and D missing)	2	This is consistent with a full clockwise cycle around the outside of the diagram.

Question b) Explain why the rain is not salty

Student responses: Why isn't rain salty?

NOTE 1: There is no line linking the Y4 responses to the others because we did not include Y5 data.
NOTE 2: The thick blue line represents a clear and correct answer. The green, blue, and red lines represent partial answers, which may include some misconceptions. The purple broken lines show the percentage of incorrect or missing answers.

No year 4 students from the trials were able to provide a full answer. The biggest jump in understanding was shown between years 7 and 8. However, by Year 10 there were still only about 1/3 of students who gave a full and correct answer.

Examples of correct responses:

Because salt does not evaporate with the water. The fresh water goes up and comes down (Y6)
Because only water is evaporated not the salt, so there's no salt in rain (Y8)
Because the sun evaporated the water, not the salty minerals (Y9)
When water evaporates from the ocean only the pure water is taken up, so any solids or dirt that are in the water are left behind (Y9)
The heat from the sun only makes water evaporate, not salt (Y10)
Because salt cannot be evaporated. It is separated when the water is evaporated, so it is only water being taken (Y10)

Other common responses are summarized in the chart below.

Common response	Example of student responses	Likely misconception
*The salt is too heavy*	The salt is too heavy to rise with the water (Y8) Salt molecules are too big to be evaporated, unlike water (Y10)	These students understand that the salt gets left behind, but they don't clearly link this occurring because of a change of state from a liquid to a gas
*Not all rain water comes from the ocean*	Because the rain does not come from the sea (Y4) It's not salty, it's water from the clouds (Y6)	No obvious connection made between evaporation and clouds
	The rain is not usually salty because the sun doesn't absorb the sea water that much (Y10)	As above. Also has a misconception about evaporation (the sun absorbs water)
	Well I'm guessing that it doesn't always come from the ocean? (Y6) Because rain does not only come from the sea. It also comes from rivers, springs, even swimming pools (Y9)	Unaware that most evaporated water comes from the ocean
	Because it's mixed with unsalty and salty water from different places, sometimes the unsalty water overpowers the salty water (Y8)	As above, but also brings in the concept of dilution to explain away water that might come from the ocean. Does not demonstrate an understanding that salt does not evaporate.
*Some other misconceptions about evaporation and/or the water cycle*	Because the salt doesn't come back down (Y8) Because it gets filtered in the clouds (Y10)	No link is made to evaporation. There is some sort of filtering system in the clouds.
	Because different water has been evaporated differently so the rain is not always salty because the different waters cause the rain to fall in either salty or non-salty form (Y8)	Unaware that salt does not evaporate, or that the water cycle may involve water moving from one place to another, i.e., the water that evaporates from the ocean may not fall as rain back into the ocean.

Next steps:

What to look for at different levels
The students' understanding of science will impact on decisions about what to do next, as will the curriculum expectations for Communicating in science at their level (refer to your curriculum document). The chart shows a brief summary of the new curriculum expectations by level.

Level	Knowing about diagrams	Knowing about the water cycle (science context)
2	Talk about what simple diagrams show us. Use students’ own ways of representing ideas. Explore ways others (including peers) represent ideas.	Focus on what is observable and students’ explanations, e.g. the places water is found, the states of water, and what happens to water under certain conditions (such as warm, cool, and windy).
3 & 4	Talk about the purpose of and use scientific conventions, such as arrows.	Begin using scientific vocabulary to describe processes in the water cycle. At Level 4 begin to develop an understanding of how water particles behave in different states, and use this to develop explanations for what they observe.
5	Talk about the purpose of and use scientific conventions, such as arrows. Evaluate the effectiveness of examples of diagrams to portray science ideas.	Describe what is happening at the particle level at various points of a water cycle.

Self-assessment
Encourage students to think about why they have made their responses, and what they need to be working on. Older students can evaluate their own responses using the provided activity. After they have completed Part A, they are then asked to analyse their thinking (Part B). They may find it more useful to discuss their analysis in pairs, before completing the two final questions. The self-assessment activity can be adapted to use with younger students as a whole class activity.

Go to the self-assessment activity Thinking about my water cycle diagram.

Diagrams
Adapt the following activities to a level appropriate to your students.

If students are not aware that a diagram is a representation:

Make up cards of the different parts of the water cycle.
Ask students, in groups, to arrange on a sheet of paper however they like.
With a felt pen draw arrows between to show the direction the water is going.
Try several versions, and then get students to choose which one they like best.
More advanced students could label each arrow with the name of the process occurring.
Ask each group to share, explaining why this was their best version.
Look for explanations that show awareness that diagrams:
- Should be clear and easy to read ( e.g., not too many arrows crossing);
- Show how parts relate to each other;
- Are representations, not a picture.
Compare a range of water cycle diagrams.
- What does each diagram show?
- What does each diagram leave out?
Which diagram shows ……… more clearly? (For example, evaporation [transpiration] from plants, underground water, that water vapour moves from where it was evaporated, etc.)
What does this diagram show that this other one doesn't?
Identify the parts of the familiar water cycle diagram, and then find these parts on the ARB resource diagram.
What does the familiar diagram show that the ARB doesn't?
Why might they have been left out?
Why is the ocean at the top, and the clouds at the bottom?
If we change their position what difference does it make?
(If younger students find the positioning too challenging, redraw the task, putting the clouds at the top and ocean at the bottom. Edit the student task in a word processing program. See Changing an assessment resource.

If students are putting the arrows in the wrong direction:

Discuss what the arrows represent.
If we didn't have an arrow there what would we have to write to show our ideas?
Explore using different arrows to show different ideas. Could we use different arrows to show:

a) water moving from one place to another, and
b) changing state?

How will readers know what the different arrows mean?

If students are incorrectly linking elements of the water cycle:

Check understanding of the water cycle.
Check their understanding of diagrams being representations.

The water cycle
Students with misconceptions about the water cycle.

Make sure that students have observed and talked about examples of water changing state, including evaporation and condensation, that occur as part of their everyday life.
Set up a model of the water cycle (go to Other resources).
Observe what happens over a period of time.
Identify what each part of the model represents.
Identify where the model is different to the real water cycle.
To explore the idea that evaporated water may fall as rain elsewhere, look at weather maps of the South Island to investigate how water is picked up by the prevailing westerly wind.
Which way does the wind blow most often?
Where is the highest rainfall?
Where does it mostly rain?
Where did the water come from?
Students who think salt evaporates can boil salty water until only the salt is left. If it is possible to collect the condensing water, they can taste it for saltiness.
Grow crystals. Go to Other resources.

Students who understand particle theory can use this to develop explanations why salt does not evaporate.

		Y4, 6, 8, 10 (07/2007)
a)	Arrows going in correct direction, showing: Ocean to cloud	difficult (Y4 and Y6) moderate (Y8) easy (Y10)
	Cloud to rain	difficult (Y4 ) moderate (Y6) easy (Y8 and Y10)
	Rain to ocean	very difficult (Y4, Y6, and Y8) difficult (Y10)
	Rain to river	very difficult (Y4) difficult (Y6) moderate (Y10) easy (Y8)
	River to ocean	very difficult (Y4) difficult (Y6, Y8, and Y10)
	All correct	very difficult (all years)
b)	An explanation that includes: - a link (explicit or implicit) between the ocean and rain and/or - only water evaporates, not the salt	very difficult (Y4 and Y6) difficult (Y8 and Y10)

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The water cycle

The water cycle

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