Senior Science
8.2 Water for Living
Section 1
Water is Essential
Section 1
Water is Essential
Focus - Water is essential for the health of humans and other living things
8.2.1.a
Identify the relative amount of water in a variety of living things
8.2.1.b
Describe the importance of water as a solvent in the
– bloodstream
– cells
– transpiration stream
8.2.1.c
Discuss ways in which plants optimise water uptake
8.2.1.d
Discuss ways, using examples, that plants reduce water loss such as
– thick outer coating (cuticle) on leaves
– reduced leaves
– dropping leaves in times of drought
8.2.1.e
Discuss ways, using examples, that animals reduce water loss such as:
– excrete uric acid instead of urea
– nocturnal behaviour
– reduced activity
– lying in the shade
– burrowing underground
8.2.1.i
Perform a first-hand investigation to demonstrate that substances dissolve in
water and to identify the solute and solvent in each case
8.2.1.ii
Plan, choose equipment or resources for and perform a first-hand investigation to
determine the amount of water present in a variety of fruits, vegetables and meat
8.2.1.iii
Perform a first-hand investigation to identify adaptations of some plants that assist
in reducing water loss
8.2.1.iv
Gather, process and analyse information to identify the different ways in which a
range of terrestrial animals reduce water loss
© P Wilkinson 2002-04
2
Describing aqueous mixtures
A mixture consists of two or more substances that can be separated by physical means.
Examples
 Dirty water – a mixture of dirt and water; the dirt can be separated by filtration.
 Sugar solution – a mixture of sugar and water; the sugar can be separated by
evaporating the water.
A liquid solution is a mixture in which a solid, liquid or gas (the solute) dissolves in a liquid
substance (the solvent). A solution:
 contains dissolved substances (particles)
 and these particles are spread out evenly throughout the liquid.
Also,

The particles are extremely small (cannot be seen with the naked eye).

The particles can remain suspended indefinitely.

The particles cannot be separated by filtration
 A solute is the substance that dissolves in the solvent.
 A solvent is a liquid in which the solute dissolves.
 A solution where the solvent is water is called an aqueous mixture.
 A solute is soluble if it dissolves completely in a solvent
 A substance is insoluble if it will not dissolve in a solvent.
 If two liquids mix they are said to be miscible.
Notes Questions
1. Which of the following mixtures are solutions?
Oil and water; Dirty water; sea water; air; mayonnaise; alcohol and water; paint
2. Explain why a solution is a mixture.
3. Suggest a reason why the diagram opposite could
represent a solution.
4. Copy and then complete the following table
Solute
Salt
Sugar, flavours and other …
© P Wilkinson 2002-04
Solvent
Solution
water
Coca cola
Beer
3
8.2.1.i
Perform a first-hand investigation to demonstrate the range of substances that will
dissolve in water and to identify the solute and solvent in each case
Solutes and Solvents
Aim
To identify the solute and solvent in a range of substances that dissolve in water.
Risk Analysis
Before any practical task is performed, a risk analysis should be completed. This means an
assessment of sources of risk needs to be made. Factors to consider include physical,
chemical and biological factors.
NB
See Humans at Work – Section 1 for more details
Method
1. Organise the following equipment:

6 medium test tubes

test tube rack

solids (solutes)
- sodium chloride, Phenolphthalein, iodine, copper sulfate,
polystyrene foam

liquids (solvents) - water, methylated spirits, acetone

Spatula
2. Mix small quantities of each of the solutes separately with each of the solvents.
3. Determine if a solution is formed.
4. Record the solubility of the solute using a table similar to the one below; (ie if the solute is
soluble, slightly soluble or insoluble).
Results
Solvent
Solute
Sodium Chloride
Phenolphthalein
Water
Conclusion Write an appropriate conclusion
Discussion / Questions
1.
2.
3.
4.
5.
6.
Name two safe working practices for a science laboratory.
[2 marks]
Outline how students did not waste resources doing this experiment. [2 marks]
Name a biological risk.
[1 mark]
Outline a physical risk.
[2 marks]
Describe a chemical risk.
[3 marks]
Explain why there might be a need to repeat some combinations of solvents and solutes
in the experiment.
[2 marks]
© P Wilkinson 2002-04
4
Marking criteria for investigation
Marking Criteria
Mark range
Perform planned practical (12.1) [3 marks] At all times


Carry out planned procedure safely
Use safe working practices
Data collection (12.2)



[2 marks]



Discussion
2
Sufficient criteria
[3 marks] Scaffold
used
1
Few criteria
[5 marks]
[2 marks]
1
Scaffold
partly used
2
1
Most criteria
Few criteria
3
1
3
All criteria
Ruled
Column headings
Units & Column headings
Accurate data recorded
Conclusion (14.1)
Occasionally
2
Neat
Uses Laboratory report scaffold
Results table (13.1)

3
Accuracy of measurements
Sufficient data collected
Presents information (13.1)

Mostly
5
Totally consistent
2
Logical
1
[12 marks]
Notes Questions
5. Write ONE complete sentence for each of the following groups of words.
 Each sentence must use every word from the group
 Each sentence must be a correct scientific statement
a.
b.
c.
d.
e.
Salt, solvent
Dissolved, water, when
Soluble, solution, is
Solid, insoluble, which
Solution, sugar, methylated spirits (careful!)
6. The following are all solutions: each contains a solute dissolved in a solvent.
a. For each solution:
i. Name the solute
ii. Name the solvent.
b. Present all this information in a table.
SOLUTION 1
SOLUTION 2
SOLUTION 3
SOLUTION 4
© P Wilkinson 2002-04
A cup of coffee
Sea water
Blood
Water that travels through plants
5
8.2.1.ii
Plan, choose equipment or resources for and perform a first-hand investigation to
determine the amount of water present in a variety of fruits, vegetables and meat
8.2.1.a
Identify the relative amount of water in a variety of living things
Part A
Planning an investigation
A scientific investigation must be planned so that valid and reliable data is collected. One
important aspect of planning is describing and trailing the method to be used. The method
needs to be repeatable.
Planning involves a number of points:
 A discussion about various issues related to performing the investigation.
To discuss means to identify issues and provide points for and against these issues.
 A risk analysis
 A written method using a text type called a “procedure scaffold”.
Pre planning questions
The following questions are to help in a discussion about various issues related to performing
the investigation. After these issues are considered, a draft method can be written.
1. Identify ONE fruit that would be suitable – ie cheap and easy to get.
2. Which of the questions below make it clear what needs to be done in the investigation.
 How much water is in a fruit?
 How much of the fruit is water?
 What is the percentage of water in the fruit?
 What is the amount of water in the fruit expressed as a percentage of total weight?
a. Identify problems with some of these questions
b. Explain which question is the best.
3. Outline some ways that could be used to remove the water from the fruit. What can
you do to the fruit to let the water escape?
4. In order to get the % of water by total weight two measurements need to be made.
What is measured before and what is measured after?
5. In this experiment use the same pieces of fruit BEFORE (with water) and AFTER
(without water). Therefore, in this investigation the material being tested will be
“destroyed”. This is acceptable since the fruit being tested should be cheap and
plentiful. In some scientific investigations the material is very important and would only
be destroyed in extreme circumstances. Name TWO examples of such materials.
Identify the situation where such materials might occur.
© P Wilkinson 2002-04
6
6. How many pieces of fruit will be used in this experiment (1, 2, 3, 5, 10 …)?
7. How many times will the experiment be repeated to get reliable data?
8. How does the experimenter know that all the water has been removed from the fruit?
Discuss the sequence: Weigh – Heat – Weigh – Heat – Weigh – Heat – Weigh. How
long would the sequence be continued.
9. Explain why an oven could be used.
10. Explain why a weighing machine could be used.
11. Explain why a scalpel or pin would be useful.
12. Name a container that would be acceptable to hold the fruit.
Risk analysis
Safe working practices involve care to be taken
 When using scalpels and pins.
 By wearing correct footwear in the laboratory.
 By being careful where bags are placed in the laboratory.
 By concentrating on the task to be completed and reducing distraction.
Write a sentence for TWO of the above safe working practices.
The procedure scaffold
The procedure scaffold has three main parts:
1. An statement outlining the aim or purpose of the investigation
 Generally a single sentence
2. Materials needed for the investigation
 This may be a list.
 This may be left out in some cases.
3. A sequence of steps in a logical order.
 Preferably in point form
 One idea per point
 Numbers can be used to show 1st, 2nd 3rd etc
 The order is usually important
 Words such as now, next and after this can be used.
 Many steps should begin with command words such as add, stir, and weigh.
 There is enough detail so that the investigation can be repeated.
© P Wilkinson 2002-04
7
Write-up of aim, … method
Once pre-planning occurs the draft method can be written and the experiment performed.
1. Heading Write a heading for the investigation.
2. Pre planning questions
Write down a summary of the various ideas and issues
raised in response to the pre planning questions above.
3. Write a draft method using the Laboratory Report Scaffold and the following headings
a. Write the purpose or aim of the investigation.
b. Write a list of materials or equipment needed
c. Write a method in point form.
d. Draw ONE diagram.
Marking Criteria
Planning investigation (11.2)
1. Heading for investigation
Mark range
[15 marks]
Good / Yes
[1]
2. Summary of issues raised in discussion
Poor / No
1
[2]
0
2
1
0
3. Appropriate headings used in written report [1]
1
0
4. Aim of investigation
1
0
[1]
5. Appropriate list of equipment selected.
[2]
2
1
0
6. Procedures are listed in logical steps.
[2]
2
1
0
7. Each step is numbered and in a sentence
[2]
2
1
0
8. Instructions are clear.
9. Diagram.
© P Wilkinson 2002-04
[1]
1
[3]
3
8
0
2
1
0
Part B
Performing the experiment
Write-up of results, conclusion
1. Perform the investigation
 Use your method or an edited version to perform the investigation.
2. Record your results.
 Construct a table to show the original weight and weight loss.
 Show your calculations of percentage weight loss for each food type.
% of water in food = % weight loss
=
original weight – final weight x 100
original weight
1
 Graph these measurements using a column graph.
3. Write a conclusion.
Discussion / Questions
a Outline what happens to the waste material after the experiment
[2 marks]
b Describe how this investigation could be repeated for other fruits, meat, and vegetables.
[3 marks]
Marking Criteria
Mark range
Perform planned practical (12.1) [3 marks] At all times


Carry out planned procedure safely
Use safe working practices
Data collection (12.2)






3
[5 marks]
All criteria
Few criteria
[2 marks]
1
Most criteria
Few criteria
3
1
5
Totally consistent
2
Discussion questions
© P Wilkinson 2002-04
1
2
Ruled
Column headings
Units & Column headings
Accurate data recorded
Conclusion (14.1)
Occasionally
2
Sufficient criteria
Accuracy of measurements
Sufficient data collected
% calculation completed
Results table (13.1)

[2 marks]
Mostly
9
Logical
1
8.2.1.b
Describe the importance of water as a solvent in the
– bloodstream
– cells
– transpiration stream
Water as a solvent
What to do
 Read the information on water and its uses in living things
 Answer the questions
 Describe the importance of water as a solvent in the bloodstream, cells and the
transpiration stream.
Every living thing is made up of cells. Living cells are made up from many different
substances, but the most important and abundant is water. The weight of a living organism is
between 60% and 99% water – therefore most organisms can withstand very little water loss.
Both plant and animal cells are dependent on water. Water allows cells to maintain their
shape and to function.
1. Polarity
Each water molecule has a formula H2O – a water molecule consists of two hydrogen
atoms and one, oxygen atom. The oxygen atom attracts (negative) electrons more
strongly than the hydrogen atom. This causes one end of the water molecule to be
negatively charged and the other end positively charged – the molecule is said to be
polar.
2. Cohesiveness
Water molecules are polar. Therefore the negative end of one molecule attracts the
positive end of the other. This attraction between the polar water molecules results in the
molecules “sticking together” – cohesive. It allows water to move up the conducting
tissue of plants and allows some insects to move across the surface of a pond without
sinking.
3. High Specific Heat
Because polar molecules attract each other, energy is needed to separate them. This
allows water to absorb more heat (high specific heat) than most other liquids. This means
that water can absorb and transfer heat. This is important to cells where chemical
reactions release large amounts of energy (heat), which might cause cells to overheat.
4. Water as a Solvent
The most important biological property of water is its ability to act as a solvent. A large
number of substances (sugars, gases, organic acids) dissolve in water. As well, water,
generally does not react with the solutes.
© P Wilkinson 2002-04
10
Uses of water in living things
Bloodstream - Multicellular animals need
to transport materials around their bodies;
eg digested food from the small intestine;
urea from the liver & kidneys and carbon
dioxide to the lungs. Since water is a good
solvent it dissolves many substances like
glucose, urea, salts, oxygen and carbon
dioxide. It is an ideal fluid for transporting
these substances. Blood plasma is 90%
water. The substances dissolve in the
water and are carried in solution around the
body.
Water is also necessary for
substances to enter the bloodstream. Eg
the lung surface needs to be moist so that
oxygen can dissolve and move across to
red blood cells.
Cells - Water is essential for all the cells reactions. Many
of these reactions only occur when the two reacting
substances are dissolved (in water). For example seeds
will not germinate without a certain amount of water in the
seed. Also, within the cell, water is still necessary for
transport and moves substances around the cell. [In plant
cells, water is necessary in making the cell turgid (stiff).
When the vacuoles of plant cells are full of water, they
cause the cells to push against the cell walls.]
Transpiration Stream - Multicellular plants need to
transport materials around their bodies. Salts and
other nutrients are absorbed by the roots and
delivered to the leaves via the transpiration stream.
This is only possible because these substances are
soluble in water.
[Water is also essential for
photosynthesis.]
© P Wilkinson 2002-04
11
Notes Questions
7. Research
What is a cell?
8. What is the main substance in cells?
9. How much water would there be in a living organism that weighed 100kg?
10. Why do cells need water?
11. Water has a number of properties that contribute to making it an important molecule for
living organisms.
12. What type of atoms (elements) make up a water molecule?
13. Why is water a polar molecule?
14. What causes water molecules to be cohesive (stick together)?
15. What type of substances will dissolve in water?
16. Research
What is the bloodstream?
17. Name three substances transported around the body.
18. Why can blood transport many of these substances?
19. Why is water essential for chemical reactions in cells?
20. Research
What is the transpiration stream?
21. Name one substance transported by the transpiration stream.
8.2.1.c
Discuss ways in which plants optimise water uptake
8.2.1.d
Discuss ways, using examples, that plants reduce water loss such as
– Thick outer coating (cuticle) on leaves
– Reduced leaves
– Dropping leaves in times of drought
Plants obtaining water
What to do
Using the information below, answer the following
1. Discuss ways in which plants optimise water uptake.
2. Discuss ways, using examples, that plants reduce water loss
It may be necessary to do further research to write a complete discussion.
© P Wilkinson 2002-04
12
In plants, water moves from the soil, into the root, through the stem, then the leaves and
finally into the air via stomata.
On a hot day, a large tree absorbs hundreds of litres of water from the soil. Very little of this
is used for photosynthesis. Most (99%) is evaporated from the leaves.
Water absorption occurs via the root hairs. The root hairs greatly increase the surface area in
contact with water bearing soil.
The 2nd column needs to be reorganised to match the 1st column.
Plant feature
Reason for plant feature
Extensive root systems
Reduces need to constantly absorb water via roots.
Roots may produce a chemical To direct water towards the roots – eg Hakea
that stops the growth of other
plants nearby.
Succulents store water in fleshy This reduces the competition for scarce water.
leaves (eg saltbush)
Well-spaced plants
To collect and store water
Leaves shaped special way
Decreases competition for water
Transpiration is defined as the loss of water from the leaves.
Transpiration is important because it causes water to be pulled through the plant.
The process of transpiration is very wasteful of water.
depending on their need for water and external conditions.
Plants control their water loss
Cacti store water in stem
Most water loss occurs through the stomata. Plants mainly control water loss by opening and
closing stomata (on the underside of the leaf)
Plants that live in dry or desert environments have a variety of special adaptations to help
reduce water loss. These adaptations are necessary for the plant to survive with little or no
water.
Leaves of plants in dry areas are often small
Stems covered with spines or needles, such a covering helps reduce grazing by animals
Stomata are often found on the underside of a leaf. As a result the stomata are protected
from the direct heat of the sun.
Other plants curl their leaves that have a “hairy surface” creating an inner cavity. This
increases humidity and reduces evaporation. It also protects the leaf from the drying effects
of the wind.
The leaves of plants in dry climates have fewer stomata when compared to plants from wetter
climates.
Eucalypts display another adaptation. They hang their leaves vertically, edge-on to the sun.
This means little of the surface is exposed to the heat of the sun’s rays.
© P Wilkinson 2002-04
13
8.2.1.iii
Perform a first-hand investigation to identify adaptations of some plants that assist
in reducing water loss
8.2.1.iv
Gather, process and analyse information to identify the different ways in which a
range of terrestrial animals reduce water loss
8.2.1.e
Discuss ways, using examples, that animals reduce water loss such as:
– excrete uric acid instead of urea
– nocturnal behaviour
– reduced activity
– lying in the shade
– burrowing underground
Writing the method of a first-hand investigation
In order to write a valid, experimental method, certain principles of experimental design need
to be known.
Why do experiments?
When planning a first-hand investigation the following principles
should be considered.
 A first-hand investigation is designed to discover new information.
 Experimenters are interested in the truth.
 The experiment must be able to be repeated by other scientists.
1. Outline the information that was discovered in the experiment to determine the amount of
water present in a variety of fruits, vegetables and meat.
2. Identify TWO reasons why this experiment could be repeated.
The writing genre To communicate the objectivity of the experiment the tradition is to never
use the words “I” or “WE”. It is normal to write in past tense using complete sentences.
Writing the method
The method is a description of steps to be followed and the
materials used. When writing the method the following topics should be considered.
V
G
C
M
A
N
S
© P Wilkinson 2002-04
Variables
Groups
Control
Measurements
Activity
Number
Safety
14
V
Variables
 In an experiment the effect of one variable on another is investigated.
 The independent variable is the variable deliberately changed by the
experimenter.
 The dependent variable is the variable that could change because of the change
in the independent variable.
 Controlled variables – The dependent variable and the independent variable can
change. All other variables are kept the same throughout the experiment – these
are called the controlled variables.
3. In this investigation on water content:
a] Identify the independent variable
[1 mark]
b] Identify the dependent variable
[1 mark]
c] Name 2 variables that could have been controlled. [2 mks]
G
Groups
 Groups occur because the independent variable is changed for different groups.
 The only difference between the groups at the start of the experiment is the
difference in the independent variable. In all other aspects the groups are the
same.
4. How many groups are there in the water content investigation?
C
Control
 There are two types of groups – the Control Group and the Experimental Group.
 The control is the reference against which experimental groups are compared.
 The control allows the experimenter to determine if the changes made to the
experimental group actually cause the dependent variable to change.
5. Outline the purpose of a control.
6. Is there a control in this experiment?
© P Wilkinson 2002-04
15
M
Measurements
 There are two types of measurement
 Qualitative: This measurement does not involve numbers. It uses words to
compare – eg green, greener; more, less; slower, faster
 Quantitative:
This measurement involves numbers. They should be
carefully measured.
Errors should be recorded and considered in the
Discussion section of the Laboratory Report.
 It can be very important to clearly describe how and what to measure in the
method.
7.
Identify the type of measurement in the water content investigation.
8.
Identify what was measured in this investigation.
A
Activity
 A scientific investigation can occur using a number of different activities. Types of
activities include:
 An experimental investigation
 Survey
 Model building
 Literature search, or other second hand investigation
 The method should be written so that
 Steps are outlined in a logical order.
 There is enough detail so that the investigation can be repeated.
N
Number
 Reliability depends on the number of results obtained. In some investigations only
three results may be necessary. In other investigations many hundreds of results
are necessary before reliability is certain.
 It is possible that a single unusual event could occur. A large number of results
reduces the influence of an unusual event on the overall results and the conclusion.
S
10.
How many results should be recorded for each fruit to obtain a reliable result?
11.
Would you consider your investigation reliable? Explain.
12.
Would have van Helmont’s conclusion changed if he planted many more trees?
Safety
 Identifying and minimising hazards must be considered for all investigations
 Identifying and using safe work practices is essential.
13. Identify TWO hazards that should be considered before performing this
investigation.
14. Identify TWO safe working practices required for this investigation.
© P Wilkinson 2002-04
16
OVERHEAD
OVERHEAD
OVERHEAD
OVERHEAD
Water as a Solvent
Bloodstream - Multicellular animals need to transport materials
around their bodies; eg digested food from the small intestine;
urea from the liver & kidneys and carbon dioxide to the lungs.
Since water is a good solvent it dissolves many substances like
glucose, urea, salts, oxygen and carbon dioxide. It is an ideal
fluid for transporting these substances. Blood plasma is 90%
water and carries these substances in solution around the body.
Water is also necessary for substances to enter the bloodstream.
Eg the lung surface needs to be moist so that oxygen can
dissolve and move across to red blood cells.
Cells - Water is essential for all the cells reactions. Many of
these reactions only occur when the two reacting substances are
dissolved. For example seeds will not germinate without a
certain amount of water in the seed. Within the cell water is still
necessary for transport and moves substances around the cell.
[In plant cells, water is necessary in making the cell turgid (stiff).
When the vacuoles of plant cells are full of water, they cause the
cells to push against the cell walls.]
Transpiration Stream - Multicellular plants need to transport
materials around their bodies. Salts and other nutrients are
absorbed by the roots and delivered to the leaves via the
transpiration stream. This is only possible because these
substances are soluble in water. [Water is also essential for
photosynthesis.]
© P Wilkinson 2002-04
17
Solvent
Solute
Sodium Chloride
Phenolphthalein
iodine
Copper sulfate
polystyrene
Water
soluble
insoluble
soluble
insoluble
methanol
acetone
insoluble
soluble
Slightly
soluble
soluble
soluble
soluble
soluble
insoluble
insoluble
insoluble
soluble
Conclusion: Water dissolved (ionic) salts such as sodium chloride and copper sulphate
completely and dissolved phenolphthalein only slightly. Acetone dissolved almost all the
solutes used, including polystyrene foam.
© P Wilkinson 2002-04
18