Gill
Science
Stage 4
S
To the Solar System and
beyond
Courtesy NASA/JPL-Caltech)
What is the water cycle?
S 43924
Number: 43924
Title: The Solar System
This publication is copyright New South Wales Department of Education and Training (DET), however it may contain
material from other sources which is not owned by DET. We would like to acknowledge the following people and
organisations whose material has been used:
Extract from Science Syllabus Years 7-10 © Board of Studies NSW, 2003
Unit overview pp iv-vii
Various photographs, courtesy of NASA/JPL-Caltech
Front cover and Part covers,
The Earth pp 3, 34
The Solar System pp 3, 6, 9,
19-23, 25, 34, 39, 44-45, 4750, 57-59, 61, 66-67
The Universe p 36
Photograph of Weathering and Erosion in the Desert ©Rhonda Caddy
Photograph of a Glacial Valley ©Upgrade Business Systems
Photograph of the Crab Nebula ©Malin/Pasachoff/Caltech
Photograph of a Star ©Anglo-Australian Observatory
Photograph of Stars ©Anglo-Australian Observatory/Royal Observatory, Edinburgh
The Earth p 18
The Earth p 19
The Universe p 7
The Universe p 8
The Universe p 35
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© State of New South Wales, Department of Education and Training 2005.
What is the water cycle?
Have you found any books or CD-ROMs about Earth or space yet?
For this lesson, you could talk to someone older to find the answers.
What is the task?
In the send-in exercise for this lesson, you will answer this question,
‘What is the water cycle?’.
Your answer must describe the water cycle by outlining the physical
changes that occur. It must also discuss why people can have different
views about water pollution.
Here are some terms that you could investigate.
water cycle
condensation
respiration
evaporation
artesian
precipitation
aquifer
transpiration
hydrological
How should you answer?
However you decide to present the information, make sure that it answers
the question.
If you have decided to use this lesson, continue reading.
The Earth
33
The blue planet
Courtesy NASA/JPL-Caltech
Earth has an abundance of water, giving it a blue colour from space.
Taken together, all the water on Earth is called the hydrosphere.
Four-fifths of Earth’s surface is covered with liquid water. In the
atmosphere that surrounds Earth, clouds of water vapour form and swirl.
Earth is the only planet in our Solar System where water is readily
available. What processes occur to ensure that Earth continues to have a
good supply of fresh water?
34
To the Solar System and beyond
The water cycle
The water cycle is the name given to all the processes that continue to
make water available on Earth. The water cycle is sometimes known as
the hydrological cycle.
The following activity helps you to become familiar with the terms used in
the hydrological cycle.
The water cycle
1
What are the processes in the water cycle?
Use clues in the words below to draw a line to match each word on
the left with its meaning on the right.
2
condensation
As water vapour cools, it condenses to form
liquid water.
evaporation
Living things use food (glucose) and oxygen to
make carbon dioxide and water which are
released into the environment.
infiltration
Plants lose water (transpire) from their leaves
as they obtain the carbon dioxide they need
from air. This loss of water is sometimes
compared with perspiration in animals.
precipitation
Water can slowly seep down through soil and
rocks, being filtered as it travels. The water
may also pick up new substances that dissolve
in it as it moves underground.
respiration
Water precipitates as falling rain, snow, hail
and sleet.
transpiration
When liquid water is heated, it changes into
water vapour and evaporates into the air.
Now look at the words in the left column. What clue is there in each
one that the word refers to a process?
_______________________________________________________
The Earth
35
3
Here is a diagram of the water cycle. Cut out the boxes in the
Additional resources section and match the names of the processes
with parts of the diagram.
4
Now, write a sentence to describe each process. For example: Water
vapour in clouds is changed to liquid water by a process called
condensation.
a
How does water leave oceans, rivers, lakes and the soil?
___________________________________________________
___________________________________________________
b
How does water return to the earth?
___________________________________________________
___________________________________________________
c
How do living things form water from food and oxygen?
___________________________________________________
___________________________________________________
d
How do plants lose water?
___________________________________________________
___________________________________________________
36
To the Solar System and beyond
e
How does water spread through the soil into artesian reserves?
___________________________________________________
___________________________________________________
Check your answers.
Ideally, the water cycle could go around and around, with clean water
always being available to shape landforms and for humans and other
living things to use. But, this is not the case.
Pollution and the water cycle
You have probably seen pollution of some type in your local area. If you
live in a city you would have seen air pollution. If you live near a river
or stream you may have seen rubbish dumped into the environment.
Where can pollution enter the water cycle?
Cut out the poison symbols from the Additional resources section and
tape them onto the previous diagram at places where fertilisers, poisons
and other pollution could move into water.
What did you think? Most pollutants get into water as it runs over land
into oceans, rivers and lakes, and as it seeps through the soil. Some air
pollutants also dissolve in water during precipitation, while water is still
falling from the sky.
Why is pollution of the water cycle a problem?
Precipitation is Earth’s source of fresh water. If pollutants from the air
become dissolved in the water as it falls, gradually all water could
become polluted.
One of the main problems with air pollution is that it can cause acid
rain. This means that wastes such as sulfur oxides and nitrogen oxides
have dissolved in rain, making it more acidic than pure water. Acid rain
damages plants and animals, and weathers rocks and buildings more
quickly.
The Earth
37
Fertilisers, wastes from rubbish dumps and the street, oil and other car
wastes on roads, detergent from homes are all things that can be washed
into rivers, lakes and oceans. And when they are, the water becomes
unsuitable for some living things.
Waterways have been used as a dumping ground for wastes for
thousands of years. But, wastes don’t just go away. They can be carried
into the soil and into underground water reserves. This means that
springs and wells become polluted.
Australia is unusual in the world because when Australians pollute
waterways, it is other Australians who suffer. In most other countries,
the pollution from one country can move into another, carried in rivers,
in underground water or floating in the air.
Consider this fictional story
Scunia is a small, poor country with a long, ocean coastline. The people
of Scunia need industry for employment and to make money for their
country. But because Scunia is poor, the cheapest production methods
are used. These create considerable amounts of pollution. But winds
blow air pollution away from Scunia and polluted water quickly washes
into the ocean and away. The pollution has little effect on Scunians and
so people do not want to ‘waste’ money by reducing the pollution they
make.
Consider this story
Give your opinions to answer the following questions.
1
What kinds of water pollution would you expect in and around
Scunia?
_______________________________________________________
_______________________________________________________
2
Why do Scunians cause water pollution?
_______________________________________________________
_______________________________________________________
38
To the Solar System and beyond
3
Should Scunia behave differently?
_______________________________________________________
_______________________________________________________
You might have thought that was easy to decide. Of course most people
would think Scunia should stop causing pollution!
But it is not so simple really. What about all the people who would lose
their jobs if businesses in Scunia had less money? Would you be
prepared to pay more for things you want so that some of the money
could be used to make industrial processes cleaner?
Did you think the story about Scunia was silly? There are many places
around the world with similar problems. Even within Australia, one
town may be less concerned about its pollution if it affects another town.
One neighbour worries less about polluted water if it flows onto someone
else’s land. Spilt chemicals somehow seem less of a worry if you can
wash them away down the sink.
It is easy to say that no-one should pollute. And that would be the best
solution because it would keep unwanted substances out of the water
cycle. But sometimes there are situations where people are willing to
accept some pollution, at least until other situations can be changed.
Consider the following situations.
4
Suellen takes her dog for a walk every day. It is more like a run
really because she is usually in a hurry. Today, she rushed out of the
house so quickly that she forgot the plastic bag to clean up after her
dog, Fluffy. Well, Fluffy did as he always does and left a huge pile
of dog poo on the roadside a couple of blocks from home. Suellen
got a stick and pushed it into the gutter so that it would be washed
away down the drain. That way, no-one would walk in it.
Did Suellen do the right thing? Why? Why not?
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
The Earth
39
5
Kweek Wun Soffa’s cleaning company has a big problem. A large
drum of hazardous cleaning fluid has been knocked over during
unloading. It is a once-off accident and is never likely to happen
again. However, the company cannot afford to have the fluid
cleaned up safely. It would mean shutting down the business,
putting twenty people out of work and inconveniencing many others.
Kweek has applied to the local council for permission to hose the
waste away. The fluid will mildly affect a small area of weedy creek
only and then be quickly spread out into a large river where it would
be unnoticeable.
Should the local council give permission? Why? Why not?
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
A scientific understanding of the water cycle may help people see that
water pollution is undesirable. But in these simple examples, you’ve
thought about why different people may have different opinions and
make different decisions about water pollution. Scientists (and
scientifically trained people, like you) may make recommendations but
decisions have to take account of social and ethical considerations too.
(You have to consider how decisions will affect people.)
Check your answers.
Now complete Exercise: What is the water cycle?
40
To the Solar System and beyond
The Earth
41
Suggested answers
Check your responses against these suggested answers.
Water cycle
1
2
42
All of the words have the ending -ation.
To the Solar System and beyond
3
4
Here are some sample answers.
a
Water changes from a liquid into a gas when it leaves oceans, rivers,
lakes and the soil by a process called evaporation.
b
Water falls back to the earth as a liquid such as rain or frozen to a
solid such as snow and hail in a process called precipitation.
c
Living things form water and carbon dioxide from glucose and oxygen
inside their bodies by a process called respiration. (They release some
of this water as a gas into the air.)
d
Plants release water as a gas through their leaves in a process called
transpiration.
e
Liquid water seeps between particles in soil and rocks by a process
called infiltration.
Consider this story
The Earth
1
Scunia will have lots of kinds of water pollution. There will be wastes
from manufacturing (such as dissolved metals, soot and oil) and wastes
from people (such as food scraps and faeces [poo]). There will probably be
wastes from farms, too (such as fertilisers and animal faeces).
2
Scunians cause water pollution because they don’t want to (or can’t afford
to) spend money to avoid water pollution. Scunians don’t worry about
their water pollution because it doesn’t affect them (much).
3
You might say yes or no! There are reasons for choosing either answer.
4
There are at least two opinions. You could say that Suellen was wrong
because what she did will pollute waterways. You might think that she
acted sensibly by making the footpath a clean and safe place to walk.
It depends on your point of view. (Suellen’s local council would probably
say that she broke the law if she had left dog poo in the street.)
43
5
44
Some local councils would (and have) decided to give businessmen like
Kweek permission to pollute after an accident like this. They decide that it
would be more damaging for people’s lives if the business fails than if a
weedy creek is polluted. Other people would say that pollution must be
avoided since any pollution is likely to affect living things in the area or
wherever to water goes. (Pollution doesn’t disappear just because it
spreads out. It just means that there is a small amount of pollution over a
large area rather than a large amount of pollution in a small area.)
To the Solar System and beyond
Exercise: What is the water
cycle?
Name
____________________________
Teacher ____________________________
Your answer must describe the water cycle by outlining the physical
changes that occur within it. It must also discuss why people can have
different views about water pollution.
Your answer should show that you can:
•
construct a diagram of the water cycle
•
write a paragraph describing how water is cycled that includes a
description of the processes, e.g. evaporation, condensation and
precipitation
•
discuss an example of water pollution where social and/or ethical
issues also need to be considered.
Attach your own send-in exercise and answer or complete the tasks on
the following pages.
1
Use the drawings from Additional resources page to construct a
diagram of the water cycle. Add arrows and labels to make your
diagram meaningful.
Diagram of the water cycle.
The Earth
45
2
Write a paragraph about how water is cycled from the diagram you
have made. Make sure that your paragraph explains why
evaporation, condensation and precipitation are important in the
cycle.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
3
When you understand the scientific processes in the water cycle, it is
easy to see that water pollution must be avoided. Yet there are many
situations where water pollution is allowed to occur. Why do you
think this is the case?
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
46
To the Solar System and beyond
Additional resources
The diagrams on this page are for you to cut out and use.
Names of processes for the water cycle
condensation
evaporation
infiltration
precipitation
respiration
transpiration
Poison symbols
Water cycle components
The Earth
47