Explore…
Discover…
Inspire…
Practical Work
in Science
Foreword
What do I really remember about doing science at
school? Making a cardboard aeroplane in physics,
colourful and explosive experiments in chemistry,
looking at the intricate structure of plants and bodies
down a microscope in biology. Above all, science is
a practical subject. Most of what we know about
how the world works was discovered, not by sitting
in a chair and thinking hard, but by getting hands-on:
pulling things apart, putting them back together,
Photograph by Dave Pra
testing out ideas. Practical science is all about
tt
‘learning by doing’. Students achieve a deeper level
of understanding by finding things out for themselves,
and by experimenting with techniques and methods
that have enabled the secrets of our bodies, our
environment, the whole universe – to be discovered.
So – brains on, hands on, get practical!
Dr Alice Roberts
Anatomist
University of Bristol
“Practical work
mirrors the pioneering
investigative and
exploratory nature
of science”
Teacher response to SCORE questionnaire
www.score-education.org
Contents
Introduction
3
Activity grids
4
General health and safety guidance
6
Upper primary activities:
Bone mystery: Living things
Making sandcastles: Materials
Bishops can fly: Forces
10
12
13
Secondary biology experiments:
No stomach for it:
Modelling the effect of antacid medication
Biodiversity in your backyard:
Fieldwork using your school playing field
Going up in smoke:
Collecting and analysing the products of burning tobacco
Brine date:
Mating behaviour and sexual selection in brine shrimps
Microbes ate my homework:
Investigating how microbes help us to break down
cellulose and recycle plant material
A window on the past:
How stomatal density adapts in changing environments
Biology
Chemistry
Physics
18
20
26
30
36
41
1
2
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Contents
Secondary chemistry experiments:
A matter of balance:
The combustion of iron wool
Red cabbage indicator:
Making a pH indicator
Soot surveys:
Investigating air pollution
Hydrogels in the home:
Hair gel and disposable nappies
Discovering the formula:
Finding the formula of hydrated copper(II) sulfate
Preparing perfumes:
Making esters from alcohols and acids
Secondary physics experiments:
Bolt from the blue:
Timing a 100 m run accurately
Feeling the pressure:
Investigating the effects of atmospheric pressure
Power from the Sun:
What affects the output of a solar panel?
Does the Earth move?
Photographing the night sky
Kicking up a force:
Investigating the force used to kick a football
Making sparks:
Demonstrating the ionising effects of alpha radiation
Further information
48
50
52
56
59
61
66
69
71
74
76
79
82
www.score-education.org
Introduction
Hands-on learning experiences are
key to the development of skills and
the tying together of practical and
theory. Good quality practical work
can not only engage students with
the processes of scientific enquiry,
but also communicate the excitement
and wonder of the subject.
This booklet has been designed
to illustrate a range of reasons why
you might do practical work, and
to direct you to sources of high
quality practical activities for you to
use in your classroom. Whilst the
focus of this booklet is practical
work in secondary science, a few
primary level activities have also been
included to highlight the importance
of transition. Many secondary schools
have links with colleagues in primary
schools, and an understanding of
each phase is important to be able
to help students through the difficult
transition from Key Stage 2 to 3.
There is a wide range of possible
purposes for including practical work
in science lessons. Any particular
piece of work should have its
purposes made explicit to pupils if
they are to benefit fully from it. If not,
there is a danger of pupils seeing
practical work merely as a break
from the more routine activities of
speaking, listening and writing.
The activities chosen here illustrate
a range of purposes and highlight
different types of practical activity
that could be used to teach various
topics in the science curriculum.
The selections are purely illustrative
and we recommend that you take
a look at the original sources
(particularly www.practicalbiology.org,
www.practicalchemistry.org and
www.practicalphysics.org) for further
examples, and use the directory at the
back of the booklet to help you find an
activity to suit your needs.
The activities have been categorised
into Upper Primary (age 8-11),
Lower Secondary (age 12-14),
Upper Secondary (age 15-16), and
Post-16. Often, however, activities
can be adapted for use with more than
one age group. The activities have
also been categorised by purpose,
and as you will see in the table,
many of the activities fall into more
than one category: Investigations
including teamwork, Extended
enquiry, Challenging existing ideas,
Out of the classroom, Use of ICT, The
‘messiness’ of real data, Stimulating
demonstrations, and Developing skills.
We would encourage Heads of
Science to look at what is being
offered in terms of practical work
within their own institutions and
ensure that the full range of purposes
are covered. A blank table has been
provided that could be photocopied
and completed by departments.
“Science without practical is like
swimming without water.”
Teacher response to SCORE questionnaire
3
4
www.score-education.org
Developing skills
Stimulating demonstrations
The ‘messiness’ of real data
Use of ICT
Out of the classroom
Challenging existing ideas
Extended enquiry
Investigations inc. teamwork
Post-16
Upper Secondary
Lower Secondary
Upper Primary
Activities categorised by level
and purpose
Primary Science
Bone mystery: Living things
X
X X
X X
Making sandcastles: Materials
X
X
X
Bishops can fly: Forces
X
X X
X
Biology
No stomach for it
X
X
Biodiversity in your backyard
X
X X
X
X X X
Going up in smoke
X
X X
Brine date
X
X X X
Microbes ate my homework
X X X
A window on the past
X
X
X
X
X
X
X
X
X X
X
Chemistry
A matter of balance
X
Red cabbage indicator
X
X
X
X
Soot surveys
X
X
Hydrogels in the home
X
X
Discovering the formula
X
Preparing perfumes
X X X
X
X X X
X
X
X
Physics
Bolt from the blue
X
Feeling the pressure
X
X
X
X X X
Power from the Sun
X
Does the Earth move?
X
X X
X
X
Kicking up a force
X X
Making sparks
X
X
X
X
Developing skills
Stimulating demonstrations
The ‘messiness’ of real data
Use of ICT
Out of the classroom
Challenging existing ideas
Extended enquiry
Investigations inc. teamwork
Post-16
Upper Secondary
Lower Secondary
Upper Primary
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5
Complete this table with your own
activities, and assess their purposes
6
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General health
and safety guidance
See the health and safety notes in each experiment. The following is general
guidance. Health and safety in school and college science affects all concerned:
teachers and technicians, their employers, students, their parents or
guardians, as well as authors and publishers.
These guidelines refer to procedures in the United Kingdom. If you are
working in another country you may need to make alternative provision.
Health & safety checking
As part of the reviewing process,
the experiments in this booklet have
been checked for health and safety.
In particular, we have attempted to
ensure that:
• all recognized hazards have
been identified,
• suitable precautions are suggested,
• where possible, the procedures
are in accordance with commonly
adopted model (general) risk
assessments,
• where model (general) risk
assessments are not available,
we have done our best to judge the
procedures to be satisfactory and
of an equivalent standard.
Assumptions
It is assumed that:
• practical work is conducted in a
properly equipped and maintained
laboratory,
• rules for student behaviour are
strictly enforced,
• mains-operated equipment is
regularly inspected, properly
maintained and appropriate records
are kept,
• care is taken with normal
laboratory operations such as
heating substances and handling
heavy objects,
•
good laboratory practice is
observed when chemicals are
handled,
• eye protection is worn whenever
risk assessments require it,
• any fume cupboard used operates
at least to the standard of Building
Bulletin 88,
• students are taught safe techniques
for such activities as heating
chemicals, smelling them, or
pouring from bottles,
• hand-washing facilities are readily
available in the laboratory.
Teachers’ and their employers’
responsibilities
Under the COSSH Regulations,
the Management of Health and
Safety at Work Regulations, and
other regulations, employers are
responsible for making a risk
assessment before hazardous
procedures are undertaken or
hazardous chemicals used or made.
Teachers are required to cooperate
with their employers by complying
with such risk assessments.
However, teachers should be
aware that mistakes can be made.
Therefore, before carrying out any
practical activity, teachers should
always check that what they are
proposing is compatible with their
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employer’s risk assessments and
does not need modification for their
particular circumstances. Any local
rules issued by the employer must
always be followed, whatever is
recommended here. However, far
less is banned by employers than
is commonly supposed.
Be aware that some activities,
such as the use of radioactive material,
have particular regulations that must
be followed.
Reference material
Model (general) risk assessments
have been taken from, or are
compatible with:
CLEAPSS Hazcards (see annually
updated CLEAPSS Science
publications CD-ROM)
CLEAPSS Laboratory handbook
(see annually updated CD-ROM)
CLEAPSS Recipe cards (see
annually updated CD-ROM)
ASE Safeguards in the school
laboratory 11th edition 2006
ASE Topics in Safety 3rd edition, 2001
Procedures
Clearly, you must follow whatever
procedures for risk assessment your
employers have laid down. As far
as we know, almost all the practical
work and demonstrations in this
booklet are covered by the model
(general) risk assessments detailed
in the above publications. Therefore,
in most schools and colleges, you
will not need to take further action,
other than to consider whether any
customisation is necessary for the
particular circumstances of your
school or class.
Special risk assessments
Only you can know when your
school or college needs a special
risk assessment. But thereafter, the
responsibility for taking all the steps
demanded by the regulations lies
with your employer.
7
Upper primary
activities
www.practicalprimaryscience.org
Introduction
Practical work lies at the heart of primary science.
Children need opportunities to develop practical and
enquiry skills in order to engage with the world in a
scientific way and to make sense of what they are
learning about living things, the environment, materials
and physical processes. Hands-on experience promotes
curiosity and engagement and provides opportunities
for the discussion and questioning which develop
understanding. Practical work can take place inside
or outside the classroom, and can happen at any
point in a unit of work or lesson. It may be a five
minute demonstration, a short activity to practise
using an unfamiliar piece of equipment or an extended
enquiry. What it must be is a varied and integral part
of the learning process which promotes thinking as
well as doing.
Upper primary activities:
Bone mystery: Living things
Making sandcastles: Materials
Bishops can fly: Forces
“Practical work is doing
things with stuff.”
11 year old pupil
9
10
www.practicalprimaryscience.org
Bone mystery:
Living things
Introduction
This activity presents children with a mystery to be solved when a skeleton
is discovered during renovation work at a local site of historical interest.
It requires children to make decisions about what data to collect, to measure
accurately and to find patterns in their data. They will use their knowledge
that the skeleton grows until adulthood.
Lesson organisation
This activity takes place over two
lessons: one for planning and obtaining
data, the second for presenting the
data and drawing conclusions.
Measurements will need to be taken
from children of different ages and
from adults. Arrangements will need
to be made with colleagues to ensure
minimal disruption of lessons.
Children work in pairs to make the
measurements. You may wish them
to work in larger groups when planning
the investigation so that 2 or 3 pairs
can combine their data into a larger
total sample.
Equipment and materials
• Letter / news report
• Model skeleton or ICT / paper
images of a skeleton (see note 1)
• Selection of rulers, metre sticks and
tape measures, enough to allow
a choice for each pair of pupils.
Calipers may also be useful
if available.
• Spreadsheet or graphing software
(optional)
Technical notes and safety
1 If a model is not available an
archaeologists report, with data
about the skeleton, should be used.
Procedure
a Introduce the activity with a letter
or news report about the discovery
of a skeleton buried at a local
historical site. It is clearly ancient
but, as yet, archaeologists have very
little information about it. The task
for the class is to try to determine
what age the individual was when
they died. In order to answer the
question the children will need to
make comparisons between the
skeleton and people of various
ages in their school. The bones
have been disturbed and have not
yet been reassembled into a whole
skeleton so children will have to make
measurements of individual bones.
No measurements are available
yet but assure the pupils that the
archaeologists will send these by
the time of their next lesson.
b Using a model skeleton or suitable
images discuss what measurements
it would be possible to take from
a living person in order to make
comparisons with the skeleton.
Pairs or groups of children decide
what measurement to take and plan
their investigation. They then make
and record the measurements.
www.practicalprimaryscience.org
•
•
c In the second lesson the data is
presented as a bar chart grouped
by class or age or as a scattergraph
with age plotted against bone
measurement. This can be done
using ICT. Discuss patterns in the
sets of data.
d Reveal to the children that
the archaeologist’s data about
the skeleton has now arrived.
This will either be in the form of
measurements on a table or diagram
or, if a suitably sized model skeleton
is available, as a reconstruction of
the actual skeleton.
Children compare the
measurements of the skeleton
with their own findings and decide
on the likely age range of the mystery
individual. Older or more able
children can use combined evidence
from different measurements to
report an overall conclusion to the
archaeologist.
Teaching notes
When planning their investigation
you may want to prompt pupils to
consider and justify some or all of
the following decisions (depending
on age and ability):
What measuring equipment to use.
Where exactly to measure to and
from on each person.
• Which year groups to sample –
do they need to choose all years
to find a pattern?
• How many people in each year
group to measure.
• Whether they need the same
numbers of boys and girls.
• How they will choose which children
in a class to measure – the tallest,
the shortest, a random selection.
• Which adults to measure.
If doing this investigation for the first
time, without a model skeleton, you
will need to look at the data collected
by your pupils in order to choose
suitable measurements to include
in the archaeologist’s report for the
second lesson.
Children may also consider
evidence that people in the past
were, on average, shorter than we
are now. How might this affect their
conclusion?
The mystery can be further
extended into cross curricula work
by introducing evidence which allows
children to draw further conclusions
about when the person may have
lived and who they might have been.
11
12
www.practicalprimaryscience.org
Making sandcastles:
Materials
Introduction
In this investigation children mix sand and water to
find the ideal proportions for making a sandcastle.
It promotes discussion as they agree on their criteria
for identifying the best mixture. The activity can be
used across the primary age range: younger pupils can make observations and
simple measurements in a familiar context while older children are challenged
by finding more sophisticated ways to collect and present measured data.
Lesson organisation
This activity could be completed in
one lesson. It can be extended for
older children to provide the time
to explore and try different ideas for
data collection. Children work in small
groups (ideally not more than four).
Equipment and materials
Each group will need:
• Tray of dry sand (see note 1)
• Jug of water (more may be needed
if there is limited access to water)
• Small containers for making
sandcastles
• A range of equipment for
measuring volume e.g. beakers,
measuring cylinders
• Other equipment such as a camera,
timers / stopwatches and masses
may also be requested by
the children.
Technical notes and safety
1 Fine sand may blow or be rubbed
into the eyes. Sand should be
handled sensibly and pupils should
be reminded not to touch their eyes.
2 Wash hands after the activity.
Procedure
a Introduce the activity by attempting to
demonstrate making a sandcastle using
dry sand. Children should recognise that
you are unsuccessful because you have
not added water. Ask the children how
much water you need to add. There is
unlikely to be a consensus so the
challenge for the class is to investigate
‘What is the best mixture of sand and
water for making sandcastles?’
b Provide each group with a tray of sand
and jug of water. Other equipment should
be available for the children to choose.
The group will need to discuss how they
will judge / measure which is the most
successful sandcastle. They will also
need to consider how to present their
findings clearly to the rest of the class.
c Compare the results from each
group and discuss the reasons for
any differences.
Teaching notes
The investigation question is open ended
so it should stimulate discussion and
allow groups of children to make their
own decisions about what criteria they
will use and what measurements or
observations they will make.
Responses may range from a simple
ranking of the sandcastles based on
appearance, which could be recorded
by sketching or using a digital camera, to
measurements of how much weight each
sandcastle can support. Some methods
of data collection will be more successful
than others and children should be
encouraged to evaluate different
methods suggested by the group.
www.practicalprimaryscience.org
Bishops can fly:
Forces
Introduction
The initial problem solving challenge to make a piece of A4 paper float across
the classroom leads to the systematic exploration of the physical and material
phenomena of balance, friction, forces, gravity and the properties of common
materials. The activity starts with a problem solving approach and then
with further exploration leads to the identification and testing of trends and
patterns, followed by the communication of the processes used and tentative
explanations developed.
Lesson organisation
The introductory activity and exploration
involve students working individually
with their own paper model. This leads
to an investigation where they work in
small groups of not more than three.
Equipment and materials
• A4 paper, several sheets per pupil
• Scissors
• Paper clips
• Rulers
Technical notes and safety
If students are investigating releasing
their model from above their own
height (not essential but may be
part of exploratory activities) they
should stand on PE or playground
equipment and not classroom
furniture. (Refer to Be Safe! p12)
Procedure
a Setting the problem
Quite simply the students are
challenged to make a piece of
A4 paper float across the classroom.
They are allowed to cut and fold the
paper in any way they wish but are
not allowed to apply any force when
releasing the paper. The only forces
that can act on the paper as it falls
are gravity and the resistance caused
by air particles. The students spend
at least 5 minutes exploring a number
of options but invariably admit they
need help.
b Making the model
The students are shown how to make
a Bishop’s hat by folding and cutting
the paper to form an isosceles right
angle triangle and then folding the
hypotenuse twice inwards thinly like
folding a scarf, before joining the
ends to form a mitre or Bishop’s hat.
13
14
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All the students are required to make
a model that works. The model is
held horizontally near the tail with the
tail on the underside of the model and
released. As it falls the Bishops hat
will gently glide across the classroom.
c Exploring the model and
its flight pattern
Time needs to be spent making a
range of Bishop’s hats exploring ways
to improve the flight pattern, direction
and distance, by changing the centre
of balance, by adding paper clips or
the flow of air, by folding the tail up
and down. Following this exploration
a discussion of what is involved when
the paper floats across the room is
conducted including:
• Talking about the movement through
the air / and resulting air flow.
• Identifying the manner in which
the model moves.
• Identifying some questions
using the lead, I wonder what will
happen if…?
• Making a list of questions that could
be investigated.
• Identifying one that the whole class
can complete.
d As a class investigate
“I wonder what will happen to the
flight pattern if I change the way the
air flows over the tail by changing the
shape of the tail?”
Depending on their experience
the students, in small groups of no
more than three, can plan a simple
investigation to identify the effect
changing the tail has on the flight
pattern. It may be appropriate to
introduce the notion of multiple
testing when looking for patterns and
the use of symbols to communicate
what has been observed. For
example the students could draw
symbols to show the fold in the tail
and a curve to show the glide path.
The students will test their models a
number of times and as a class build
up a table to highlight patterns.
The teacher could use one group’s
results and record them in pictorial
form on the white board or large
sheet of paper. (See example in
teaching notes).
In a class discussion ask the
student to identify inferences that
can be drawn from these patterns
that can retested or evaluated
and then turn the inferences into
explanatory statements such as
“when the tail is folded down the
flow of air is changed and it causes
the flight pattern to change” or “with
our models it makes the model fall
directly down” If the students have
not made the connection to aircraft
and birds this would be a suitable
time to link this experience to other
similar situations.
www.practicalprimaryscience.org
e Finally discuss the activity from a
science perspective; ‘What makes
this activity a science activity?’,
‘What conventions of science
activity have been applied as we
have completed this exploration?’.
15
For example, a scientific idea is an
idea where the evidence supporting
the idea has been tested and
this testing can be replicated and
scientist use symbols to record
and communicate data and ideas.
Teaching notes
Example results table:
Exploring flight patterns / glide paths of Bishop’s hat when tail shape is changed
Tail shape
Test 1
Test 2
Test 3
Test 4
Biology
The science of the life processes and habits
of all living things, from tiny single cells to
whole organisms and how they interact
with each other and their environment.
www.practicalbiology.org
17
Introduction
Students come to understand how living things behave
through opportunities to engage in practical activities.
Biology involves making sense of complex systems at
the level of cells, organisms and whole ecosystems.
Often biologists have to devise models that isolate
individual processes for closer study, have to control the
many variables in a system to see the effect of each more
clearly, or have to study changes over long time scales.
A successful biologist will master key ideas in chemistry
and physics, and use mathematical tools for interpreting
and analysing data. Much of what students learn in
biology is directly applicable to their own lives, as a
growing understanding of other living things helps them to
learn about the human body and the wider environment.
Secondary biology experiments:
No stomach for it:
Modelling the effect of antacid medication
Biodiversity in your backyard:
Fieldwork using your school playing field
Going up in smoke:
Collecting and analysing the products of burning tobacco
Brine date:
Mating behaviour and sexual selection in brine shrimps
Microbes ate my homework:
Investigating how microbes help us to break down
cellulose and recycle plant material
A window on the past:
How stomatal density adapts in changing environments
“Doing practical work
is fun! We learn lots by
trying things out and then
explaining what we have
found out to others.”
15 year old pupil
18
www.practicalbiology.org
No stomach for it:
Modelling the effect of antacid medication
Introduction
This practical has been developed with support from the British
Pharmacological Society and the Physiological Society. Pupils monitor
the changing pH of a sample of dilute hydrochloric acid as doses of
over-the-counter antacid preparations dissolve. Typical doses of a range
of over-the-counter antacid preparations (powders, tablets and liquids) are
added to a volume of dilute hydrochloric acid that models the volume and
concentration of our stomach contents. Pupils monitor the changing pH,
and compare the effects of different preparations and discuss the short
and long-term consequences of using each medicine.
Lesson organisation
Organisation may depend on the
number of pH probes and meters
you have, or the range of antacids
you want to try. Students working
in pairs would each be able to
investigate one or two antacids.
Apparatus and Chemicals
For the class – set up by technician/
teacher:
• Hydrochloric acid, dilute, 0.01 mol
dm-3, 100 cm3 for each antacid
for each working group (refer to
Hazcard 47A and note 1)
• Universal indicator solution, in
dropping bottles (note 2)
• Antacids, with details of dosage
from packaging
For each group of students:
• Beaker, 100 cm3, 2 per antacid to
be tested
• Mortar and pestle
• Measuring cylinder, 100 cm3
Technical notes and safety
1 Hydrochloric acid is described
on Hazcard 47A as irritant at
concentrations above 2.0M, causes
burns and is irritating to the respiratory
system. The acid used here is much
more dilute and presents a minimal
hazard to students.
2 Universal indicator – see Hazcard
31 and Recipe card 32. The bottled
solution is highly flammable.
Procedure
SAFETY: Take care when making up
the dilute acid.
Preparation by the teacher
a Make up the dilute hydrochloric
acid by serial dilution (1 in 10, twice)
from 1 mol dm-3 acid. (See note 1.)
b Copy (and enlarge if necessary) the
details of typical doses of antacids
from the packaging.
c Set up a few beakers of 50 cm3 of
water with indicator to show what a
neutral pH would look like.
Investigation
d Measure 50 cm3 of dilute acid into
each of two beakers and add enough
Universal indicator to get a clearly
visible colour. (See note 2.)
e Sit both beakers on a sheet of
white paper.
f Keep one beaker for comparison as
small changes in the acid pH range
can be hard to see.
g Add a normal dose of antacid
to the other beaker and watch the
colour change. If the antacid is in
www.practicalbiology.org
tablet form, crush the tablet in a
mortar with a pestle before adding
to the acid.
h Repeat with other antacids.
i Decide which antacid is making
the greatest change, or the
quickest change. Record any
other observations – such as
effervescence.
j If using a pH probe, plot a graph of
pH against time over 10-15 minutes.
Teaching notes
The approximate relaxed volume
of our stomach is 50 cm3, but it
is able to expand to nearly 4 dm3.
The lowest pH of secreted acid is
about 0.8, but it is diluted in the
stomach to an ideal pH of around
1.4. The stomach secretes acid to
produce the optimum pH for the
action of pepsin. An excess of acid is
sometimes produced, which results
in acid indigestion (in the short term)
or could result in ulceration of the
stomach lining (if high concentrations
of acid persist). Antacids have
been developed to treat short-term
excesses. Other pharmaceuticals are
used to treat long-term imbalance of
acid production.
Students may be surprised how
little the pH changes when the
antacid is added.
It is interesting to compare liquids
with powders, and to see just how
slowly an uncrushed tablet reacts.
There are ingredients other than
antacids in many over-the-counter
preparations that have an effect
on indigestion. Some include a
mucilaginous component that coats
the stomach lining and may protect
the lining tissue from damage by acid.
This could lead into a more detailed
exploration of the structure of the
stomach and the different tissues that
make up the organ.
Discuss the issues associated
with long-term use of antacid
preparations. Ideas are listed below.
• Pepsin operates best at acid pHs,
so using antacids before meals, or
immediately after, could reduce the
rate of digestion.
• The body has many mechanisms
that maintain balance. Is it possible
that taking antacid medication
regularly would, in fact, stimulate
the gastric lining to make more
acid to restore normal pH?
Further information
www.rsc.org/education/teachers/
learnnet/pdf/LearnNet/rsc/
Kev51-60.pdf
This is from the RSC’s ‘Classic
Chemistry Experiments’ – a formal
titration of preparations of indigestion
tablets with hydrochloric acid. You
could use this as a more quantitative
extension activity linked to the above
investigation.
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Biodiversity in your backyard:
Fieldwork using your school playing field
Introduction
Introduce the core fieldwork technique of random sampling with quadrats in
your school grounds. Random sampling allows you to make an estimate of
the populations of different species in any area. It should eliminate sampling
bias introduced by the sampler selecting areas that look interesting or easier
to count. Develop an understanding of plant biodiversity in the grassland
typical of school playing fields. Use the Field Studies Council key Playing
field plants to identify the species that you find. Students are often surprised
by the biodiversity in an area they think of as ‘grass’. There is scope for
students to develop and investigate hypotheses about plant distribution based
on observations and measurements of factors such as soil, moisture, light
intensity and wind speed. Observations of human or other animal activity in
the area, and background information about the characteristics of common
playing field plants, provide further starting points for developing hypotheses
to test over short or long time scales
Lesson organisation
Students working in groups of three
(or four) can each take a role in the
survey. Depending on your students,
it should be possible to carry out
your survey of one or two areas of
the school grounds in one lesson.
Then, presenting and analysing
the results could be completed in
the next lesson. Collecting data to
investigate hypotheses might be
spread over several weeks. Each time
the students survey the area, they
will be more efficient as they become
more familiar with the technique and
the species present.
Apparatus and Chemicals
For the class – set up by technician/
teacher:
• Tape measure, 20 m, 2 (or string
marked into metres)
• Number cards, 1-20, in each of two
bags (or bowls or buckets)
OR 20-sided dice, 2 (ask someone
who plays war games or fantasy
role-play games)
•
Pinboard, or sheet of cardboard (for
step 1) with sticky tape or pins to
attach plants to the board
For each group of students:
• Quadrat – a wire frame
0.25 m x 0.25 m, or 0.5 m x 0.5 m
• Key to plants – see links
• Clipboard, 1
• Pencil, 1
• Record sheet – devised by teacher
or students
Technical notes and safety
1 Choosing your quadrat: A quadrat,
not a ’quadrant‘, is a frame used for
sampling an area and it is usually
square. Smaller quadrats present
a smaller number of species to be
identified. However, groups taking
10 samples each with 0.5 m x 0.5 m
quadrats will collect information about
a more significant sample of the area.
2 Refer to the supplementary
risk assessment (SRA 08) dated
October 2006 from CLEAPSS for
more details of hazards and control
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measures for working outdoors.
This risk assessment advises that it is
important to consider the following.
a How students are likely to behave
when working outdoors, and
suggests that the normal ratio for
classrooms or laboratories may not
be adequate to ensure safe working
outdoors.
b Provision for hand washing needs
to be readily available whenever
plants and soil are handled. You
might consider the use of alcohol
gels or other hand sanitisers with
paper towels.
c The low risk of diseases such
as toxoplasmosis and toxocariasis
from plants and soil contaminated
by cat or dog faeces. Covering any
cuts and grazes and ensuring that
children do not eat snacks or sweets
while working outdoors as well as
confirming thorough hand washing
reduce this risk.
d The possibility of allergic reactions
to substances encountered outdoors,
such as pollen, plant sap, contact
with leaves, insect bites and stings or
some hairy caterpillars. Be alert to the
development of any allergic reactions
or asthma symptoms and deal with
them according to your school’s
normal policy.
e The risk of sunburn on sunny
summer days if exposed for more
than 20-30 minutes.
f Risks of injury when using and
carrying tools or heavy loads of
unfamiliar equipment which should
be assessed for each individual in the
specific environment.
g Hazards such as building rubble,
pot holes in the ground, unsafe
structures or items such as broken
glass and other ‘litter’ that could be
hidden in grass or soil. Check the
area in advance and be aware of any
such risks that could cause wounds
or cause children to trip and fall.
Remove the hazards or identify them
with warning signs and keep children
away from them.
3 Sample size: You can test whether
your sample size is big enough by
comparing the results from two
groups sampling the same area.
If their results are very similar, your
sample size is big enough to be a
good estimate of the populations
in the area.
Ethical issues
It is useful to consider how the act
of surveying the area and collecting
plants might damage or change the
environment surveyed. Although
this is probably not an issue for a
school playing field (which is regularly
mowed and trampled in normal use),
it would certainly be an issue for a
natural or ‘wild’ area.
Procedure
SAFETY: Make a full risk assessment
for the outdoor activity and put
in place any necessary control
measures.
Preparation
a Check the area where you will be
working for hazards.
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b Make a preliminary survey yourself
to identify the most common plants
(other than grass).
c Collect your equipment together
and check it for hazards such as
sharp edges. Consider attaching tags
of brightly-coloured electrical tape to
make it easier to locate equipment
that gets ‘lost’ on the site.
d Organise your students in groups
of three (or four) and identify their
roles in the group.
Step 1: Preliminary observations
a Stand in the area to be surveyed
and make a simple plan drawing of
key features – the direction of north,
any nearby buildings, large plants
(trees and shrubs), favoured paths
across the area, slopes etc. Include
information about the use of adjacent
land and think about whether the site
is open and exposed or sheltered by
a belt of trees or buildings.
b Make a note of any clearly visible
features in the ‘grassland’ vegetation,
such as areas of flowering plants,
worn grass or darker vegetation.
Step 2: Identifying what species
are present
c Give the students a quadrat per
group. Place the quadrat on the
ground and ask students to look
closely at the plants and see how
many different plants they can see.
d Develop vocabulary to describe
the differences between plants –
for example key botanical features
such as leaf veins, sepals, or the
arrangement of flower clusters, and
the shapes of leaves, the patterns of
attachment of leaves to stems, the
habit of the plant (ground-hugging,
creeping, rosette etc). The table on
the inside of the FSC key Playing field
plants will guide such observations
and allow students to use them to
identify the main species of plants.
e Collect samples of the five most
common plants (other than grass).
Write their names on the board and
ask each group to bring and attach
a sample of each plant to the board.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
22
Put the quadrat
where you meet
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Step 3: Sampling the area –
a random sample
f Lay out your tape measures (or
marked string) at right angles along
two edges of the area to survey.
Lay the two bags of numbers near
the point where the tapes meet.
g With students working in threes,
ask one student to hold the quadrat,
a second to pick a number from the
bag on one line, the third to pick a
number from the other bag on the
other line. Then, the students who
have numbers should replace the
numbers and walk to that number
on their line. The student with the
quadrat uses their colleagues as
place markers and places the
quadrat where it is in line with both
of them. Then all three can work
together to identify the species in
their quadrat and record the results.
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h Send two students back to the
bags on the lines to pick more
numbers and randomly select the
next quadrat position. Repeat step g.
Count
Don’t
count
i Each group should assess the
contents of around 10 quadrats to
get a reliable estimate of the species
distribution.
Step 4: What to record
j In a preliminary investigation, or
with younger students, a presence
or absence of each species in each
quadrat may be enough information.
You can then collate the results to
show the percentage of quadrats in
which each species was found, which
will give you a relative abundance of
each species.
k With older students, or to
provide data you can analyse with
mathematical tools, you will need
to estimate and record the number
of plants of each species in each
quadrat or the percentage cover
of each species in each quadrat.
Step 5: Analysing the results
l Use a spreadsheet to analyse the
results and produce bar graphs or
other plots of the data collected.
m The simplest analysis would be
of the percentage of sample quadrats
that each species appears in.
n If you have information about
frequency (or percentage cover) you
can calculate the average frequency
(or average percentage cover) of
each species for each area sampled.
Teaching notes
It can be very rewarding with younger
students simply to open their eyes to
the diversity of plant species under
their feet. Developing observational
skills and learning which features
of plants are important when
distinguishing one species from
another are significant basic skills.
The detail of the data you gather
will depend on the investigation you
are exploring.
A 20 m x 20 m survey area covers
400 m2. A 0.25 m quadrat covers one
sixteenth of a square metre and a
0.5 m quadrat covers one quarter of
a square metre. So, with 10 groups
collecting data from 10 quadrats
each (100 quadrats surveyed), the
group will have sampled 6.25 m2 with
0.25 m quadrats (about 1.6% of the
area) or 25 m2 with 0.5 m quadrats
(6.25% of the area). (See note 3.)
A random sample will give you
some descriptions that characterise
an area. So it is useful if you want to
compare two contrasting habitats.
You could make random samples
on two different areas of grassland in
the school – such as the playing field
and any open areas that get less foot
traffic, or two different parts of the
playing field to see if there are
any differences.
It is possible using the method
here for selecting your random
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sample point that two groups of
students will survey the same square
metre. For introductory exercises
this should not pose a problem,
but for more thorough investigations
you could keep track of the areas
sampled and ensure you do not
survey any sample square twice.
There are several methods of
quantifying biodiversity – apart from
comparing a simple list of the number
of species identified in each area.
One measure is ‘species richness’.
Others include ‘range-size rarity’
and ‘taxic richness’. See links below,
or make a wider internet search.
Here is an example of a simple record sheet that you could use for your field survey.
Quadrat number
Species present
1
2
3
4
5
6
7
8
9
10
Numbers / percentages in each quadrat
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You could survey to answer
questions such as: Are there more
daisies in mown or unmown grass?
Is there more ribwort plantain
where the grass is less trampled?
Alternatively, after identifying
differences in distribution of species
between two areas, you can start
to develop hypotheses that might
explain the different distributions.
These might depend on being able
to collect further data about the
areas. For example: Is the soil wetter
where we find more buttercups?
You could collect and collate
information about the plants in
the field and maintain a database
of distribution information (with
photographs) over a number
of years.
This kind of random sampling
will probably not reveal any trends
or changes across an area (such
as differences near to or far from
a regular walkway where plants
are trampled). However, there are
systematic sampling techniques that
allow you to investigate changes
along a line from one part of an area
to another – such as a line transect
or a belt transect. A good guide to
ecological techniques will explain
these techniques in more detail.
An example of a simple record
sheet that you could use for your
field survey is shown.
Some questions to think about:
1 What are the 5 main species in
each area?
2 What do you think are the reasons
for any differences?
3 How would you investigate these
differences further?
4 What has surprised you most about
the diversity of plants on your school
playing field?
Further information
www.field-studies-council.org/
publications/pubsinfoaspx?
Code=OP97
Details of the Field Studies Council
key to Playing field plants. This will
be a great help in identifying the main
plants and provides supplementary
information about the plants to
support hypothesis development and
suggestions for further work. (Last
accessed November 2008.)
www.field-studies-council.org/
outdoorscience/diy.htm
Part of the London Outdoor
Science project – with details of
how to make and use your own
fieldwork equipment. (Last accessed
November 2008.)
www.field-studies-council.org/
resources/index.aspx
The index to all the Field Studies
Council on-line resources. (Last
accessed November 2008.)
http://internt.nhm.ac.uk/eb/
homepage.shtml
This is the homepage for a project
called Exploring biodiversity (dated
2001) on the Natural History Museum
(London) website. It includes
interactive models that explain how
to calculate species richness, rangesize rarity and taxic richness. You will
need to log in using Internet Explorer
to view these pages. (Last accessed
November 2008.)
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Going up in smoke: Collecting and
analysing the products of burning tobacco
Introduction
Draw the smoke from a burning cigarette through apparatus that traps and
analyses some of the components of the smoke. Establish the effect of unlit
cigarettes on the apparatus by running the filter pump for 10 minutes. (There
should be no effect.) Smoke at least two different cigarettes, and compare
their effect on the white-coloured mineral wool and on the indicator solution.
Discuss the differences between the cigarettes.
Lesson organisation
This procedure should be carried out
in a fume cupboard as a teacher-led
demonstration.
Apparatus and Chemicals
(see figure 1 & 2 below)
For the class – set up by technician/
teacher:
This apparatus must be set up in a
fume cupboard.
Filter pump or hand-operated
vacuum pump (see note 2)
Clamp stand, boss and clamp, 2
Matches
Dishes to collect ash from cigarettes
Apparatus as in diagram 1 or
diagram 2:
• Conical flask, 250 cm3, 1 or 2
• Glass tubes, bent to right angles, 2
or 4 (see note 3)
cigarette
holder
A
cottonwool
lighted
cigarette
Universal
indicator
Fig. 1
direction
of air flow
rubber
tubing
to
pump
cigarette
holder
lighted
cigarette
(type 1)
•
•
•
T-piece, glass
Rubber bungs, two-holed, 1 or 2
Hard glass tube, shaped to hold
a cigarette, 1 or 2
• White-coloured mineral wool,
superwool, glass wool or polymer
wool for aquarist filters
Alternatives / additions:
• connector to allow thermometer to
be held in the smoke stream near
the cigarette
• U-tubes containing white-coloured
mineral wool to replace tubes A
and B
• hydrogencarbonate indicator
(equilibrated with air) in place of
Universal indicator.
Technical notes and safety
1 Carry out the procedure in a
fume cupboard.
direction to
direction
of air flow pump of air flow
A
cottonwool
Universal
indicator
rubber rubber
tubing tubing
B
cottonwool
Universal
indicator
Fig. 2
lighted
cigarette
(type 2)
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2 If your water supply does not
support a filter pump, use a handoperated vacuum pump, or a syringe
to draw air through the apparatus.
3 Check that the tips of the longer
glass tubes are below the surface of
the indicator solution and the shorter
glass tubes are well above the
surface even if the liquid bubbles.
4 Disassemble the apparatus
in a fume-cupboard and avoid
skin contact with the tars. This is
essential. Wear protective gloves
(preferably nitrile) and place the
tar-soaked material in a plastic bag
which is sealed before disposal with
normal refuse. Wipe the glass with
a paper towel soaked in a suitable
solvent, such as ethanol (flammable)
and dispose of the paper towel with
the tarry wool. The apparatus is
difficult to clean so re-use in future
years. Store in a box or sealed
plastic bag to contain the smell.
(See CLEAPSS Laboratory
Handbook, section 9.6.)
Procedure
Cigarette packets carry health
warnings and schools/ colleges
are usually non-smoking premises
on the grounds of the stated health
risks of cigarette smoke. Set up the
apparatus in a fume cupboard and
avoid contact with the smoke and
skin contact with the contents of
the tubes at the end.
Parts of the apparatus near the
cigarette may be hot at the end,
so take care when disassembling
to weigh the tubes.
Preparation
a Find out the mass of tubes A and
B and write the masses on paper
associated with the apparatus.
Investigation
b This is often set up with one lit
cigarette and the second unlit as a
control. Consider running air through
2 unlit cigarettes (of different types)
for 10 minutes to establish that this
has no visible effect on the cotton
wool or the indicator. Then you
could use the apparatus to compare
two different types of cigarette – for
example normal and low tar, the
same brand with and without its filter,
packet cigarette vs hand-rolled.
c Start the filter pump. Light the
cigarette/s and run until the cigarette
is nearly smoked.
d Switch off the filter pump and
see what happens to the final few
millimetres of cigarette. (This will
be particularly interesting if you
are comparing packet cigarette
with hand-rolled as rolling tobacco
contains fewer ingredients to keep
it burning.)
e Note the visible changes to the
cotton wool and the indicator.
f Find the mass of tubes A and B
and calculate the increases in mass.
g Disassemble the apparatus
avoiding skin contact with the tar
(see note 3).
Teaching notes
This demonstration makes a good
starter activity for the subject of
smoking. Students may be surprised
at the amount of tar collecting in the
mineral wool from just one cigarette.
If you want to pass the wool around
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for children to smell (which can have
a dramatic impact), remove it from
the tube using a spatula and put
it in a beaker to remove the risk of
students touching the tar (note 4).
Cigarettes and smoking provide a
rich context for ethical discussions.
The first reported research indicating
links between lung cancer and
cigarette smoking was published in
1950, and relatively recently in the
UK smoking has been banned in
public places. There is scope for
debate about our rights to make
risky lifestyle choices as well as
the responsibility of government
to promote public health. The
commercial drive of tobacco
companies and the tax revenue to
government from tobacco sales
are factors that could influence the
reliability of information from different
sources. It is hard to find information
presented impartially on the subject
of smoking and cancer. It is worth
trying to identify who has funded
or supported any piece of reported
‘impartial’ or ‘scientific’ research.
Effects of tobacco smoke on the body
• Smoke from tobacco paralyses
cilia in the trachea and bronchi
for approximately an hour after a
cigarette has been smoked.
• Dry dust and chemicals in the
smoke irritate the lungs causing
more mucus to be secreted.
Cilia normally sweep this mucus
away, but smoke has paralysed
them. Mucus builds up and if this
becomes infected it can cause
bronchitis.
• Tar is a dark brown, sticky
substance, which collects in
the lungs as the smoke cools. It
contains carcinogens – chemical
substances known to cause cancer.
• Carbon monoxide is a gas that
combines with haemoglobin, the
oxygen-carrying substance in the
red blood cells, even more readily
than oxygen does. So it reduces
the oxygen-carrying capacity of the
blood by as much as 15% in heavy
smokers. Unlike the reaction with
oxygen, the reaction is irreversible.
• Nicotine is the addictive drug that
makes smoking such a hard habit
to give up. It is responsible for
the yellow staining on a smoker’s
fingers and teeth. Nicotine can
harm the heart and blood vessels
too – it makes the heart beat faster,
the blood pressure rise and the
blood clot more easily.
It is hard to find information
presented without an agenda on the
subject of smoking and cancer. There
are links below to a range of sources
of information.
As with many issues relating to
health and lifestyle choices it is
difficult to isolate the effects of any
individual factor. Some of the reports
indicate connections with socioeconomic profiles that may also
significantly influence health.
There is scope to discuss the meaning
of risk measurements and to try to
track down original research papers
in order to assess their methodology.
There is a link below to a report
on the detailed analysis of the
contents of the smoke from a range
of brands. This is an independent
analysis presented on the Tobacco
Manufacturers site. It doesn’t connect
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the smoke contents to specific
health risks, but it does mention
using ISO conditions for smoking
cigarettes (ISO 3308:2000). The idea
of an ISO standard routine analytical
cigarette smoking machine might
interest some students. The smoking
machine puffs with a puff volume of
35.0 ± 0.2 cm3 and with a 2.00 ±
0.02 second puff duration once every
60.0 ± 0.5 seconds.
The ISO standard machine makes
a much more detailed analysis than
the apparatus suggested above. The
instructions for a smoking machine
that would be acceptable for an ISO
accredited test list 24 factors that
must be controlled or measured by
the machine. These include:
• puff duration (the length of time
during which the port is connected
to the suction mechanism –
2.00 ± 0.02 seconds)
• puff volume (the volume leaving
the butt end of the cigarette and
passing through the smoke trap)
• puff frequency (the number of puffs
in a given time – one puff every
60.0 ± 0.5 seconds measured over
10 consecutive puffs)
• dead volume (the volume which
exists between the butt end of
the cigarette and the suction
mechanism)
• draw resistance (negative pressure
applied to the butt end under test
conditions to sustain a volumetric
flow of 17.5 cm3/ s, exiting the
butt end when the cigarette is
encapsulated in a measurement
device to a depth of 9 mm)
Ask students to evaluate your
apparatus compared to this list of
factors. What difference do you think
it makes if the apparatus smokes
continuously or puffs the cigarette?
Why is it important that there is an
internationally-recognised standard
way of assessing cigarettes?
Some reports of cigarette analysis
refer to NFDPM – which is nicotine
free dry particulate matter, otherwise
known as ‘tar’. TPM stands for total
particulate matter.
Further information
http://snipurl.com/7p46i
The UK Benchmark study report
of an analysis of tobacco from
cigarettes on the market in the UK.
P5 of Part 1 of the report lists all
brands tested and the components
of their smoke.
http://snipurl.com/7p47r
The Department of Health information
about tobacco and health.
www.ash.org.uk/
Action on Smoking and Health (ASH).
www.forestonline.org/
Forest.
http://snipurl.com/7rwhk
Cancer Research UK, the leading
funder of cancer research in the UK.
www.beep.ac.uk/content/493.0.html
The Bioethics Education Project,
pages on tobacco and health risks
and choices.
http://snipurl.com/7rwhv
Abstract from ‘The cumulative risk of
lung cancer among current, ex- and
never-smokers in European men’.
http://snipurl.com/7rwi0
Abstract from ‘Estimate of deaths
attributable to passive smoking
among UK adults: database analysis’.
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Brine Date: Mating behaviour and sexual
selection in brine shrimps
Introduction
This procedure is adapted from the ideas in the Survival Rivals kits produced
by the Wellcome Trust as part of the Darwin200 initiative and available for free
from Spring 2009.
Pupils develop practical skills of scientific enquiry in an investigation of living
brine shrimps – Artemia salina, and consider evidence that supports Darwin’s
ideas about sexual selection.
Artemia salina (brine shrimps) kept in a brightly-illuminated aquarium
provide an easily-observed and sustainable ecosystem for classroom-based
ecological and behavioural studies by students at Key Stages 3 and 4 or
Scottish Stages S1–S4 (Dockery and Tomkins, 2000).
The observable behaviours of brine shrimps allow students to investigate
the phenomenon of sexual selection. Students will see the brine shrimps
swimming and quickly distinguish between the sexes because mature animals
swim together, in pairs, one male and one female. The females may choose
the males they pair with. Once paired the males and females stay clasped
together. A clasped pair may have mated or be yet to mate, but the clasping
behaviour means the males guard the females which prevents other matings.
Lesson organisation
Begin by observing the shrimps (as
Darwin and other naturalists would
have done). Lead a discussion
of methods of investigating the
phenomenon of mate-guarding which
will generate hypotheses for students
to test – such as ‘larger females
pair with larger males’. Test the
hypotheses in subsequent lessons.
There are opportunities here for
students to work in groups with each
taking a different role in the team.
Collecting the data in a spreadsheet
and generating different kinds of
plot to search for relationships
allows development of ICT skills.
Completing the investigation could
include communicating their results
and conclusions to the class and
evaluating their method and findings.
Apparatus and Chemicals
For the class – set up by technician/
teacher:
• Brine shrimps – Artemia salina –
in a well-lit aquarium of salt water
(notes 1-4)
• Clean salt water (35 g dm-3) – the
best concentration for the shrimps
For each group of students:
• Pipettes to withdraw shrimps
(note 5)
• Beakers (100 cm3) to hold shrimps
withdrawn from the aquarium (note 5)
• Glass slide, 1 (note 6)
• Acetate measuring grid (note 6)
www.survivalrivals.org
Technical notes and safety
1 Use a very clean plastic or glass
vessel for your aquarium. An open
tank of 1-5 litres is fine. Cover the
bottom of the container with a layer
of sand or limestone (oyster shell
grit from pet stores is quite suitable)
to provide a surface on which
microorganisms can flourish. Fill the
aquarium with water containing salt
at a concentration of 35 g dm-3 (see
note 7). Use plain sea salt (solar salt)
or ‘artemia salt’ from an aquarium
store. The latter includes minerals
and algae that help newly-hatched
shrimp to thrive. It may also contain
microorganisms that contribute to
starting off a more natural ecosystem
for the shrimp. Iodine and anticoagulants in table salt are bad for
the shrimps! Use bottled mineral
water, or de-ionised water, or tap
water that has been left to rest for
48-72 hours to allow the chlorine to
escape from it.
2 Hatch eggs of Artemia salina in a
Petri dish containing a little of the salt
water from the aquarium, ideally at
25 °C, but no cooler than 20 °C. After
hatching, transfer the Artemia to the
larger aquarium (note 1). The shrimp
will grow if the aquarium is placed on
a warm well-lit windowsill. The lower
the temperature, the longer Artemia
will take to hatch. At 26-28 °C a
nauplius hatches within 24-48 hours,
gets pubescent in 8-14 days and
lives up to 5 weeks, depending on
the concentration of salt. The more
salt, the less the life expectancy.
You don’t need to illuminate your
aquarium constantly.
3 Feeding: In an open aquarium,
when the population density of brine
shrimps is low there is abundant
food and you will see a definite
green colour in the water. The
shrimp population will increase until
competition for food (the green
colour of the water disappears)
halts further expansion. If you want
to encourage larger populations for
this investigation, feed with algae
powder from aquarium suppliers
once a week. Add algae only if the
water is very clear and do not feed
too much! If the water gets cloudy
and green, there is too much food.
After some time you may see some
white/ yellow fluffy stuff at the bottom
of the aquarium. This is a brown
diatom, which Artemia can and will
eat. If it gets plentiful, you’re probably
feeding too much. Diatoms produce
oxygen, so it’s positively useful in
the aquarium at low levels. You can
keep Artemia in a closed drinks bottle
aquarium (see diagram below).
35% salt solution
Sand / limestone
granules
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An aquarium like this can develop
into a self-supporting, closed
ecosystem. The brine shrimps should
never need feeding and should
never run out of oxygen because the
algae on which they feed carry out
photosynthesis, grow and multiply
by asexual reproduction. The algae
never run out of carbon dioxide,
water or mineral salts because they
are recycled. Microorganisms in the
water cause decay of dead algae,
dead shrimps, shrimp droppings
and dead microorganisms. Stir the
substrate and water from time to time
to mix in the nutrients from decayed
organisms.
4 With an open tank, replace some
water (about 20%) every two weeks
or so to keep ammonia, ammonium,
nitrite and nitrate ion levels low, so
that hazardous bacterial populations
have no chance to develop and do
harm to the Artemia.
5 Catching shrimps: Use a sieve
with a mesh of 2-3 mm, such as
a tea strainer which will catch only
adults. Use soft plastic pipettes with
an inside bore of 3-5 mm with the
pointed end cut off. This should be
wide enough for adult shrimp to enter
when sucked up. The animals are
robust in water and should not be
handled outside this medium, but
should not be distressed by drawing
into a pipette like this. Return the
animals to their tank after 5 minutes.
6 Observing and measuring shrimps:
Water has a high surface tension and
will restrain the shrimp in the water
drop. Any detergent on the slide (or
in the water) will prevent the blob
from forming. Photocopy a sheet of
graph paper, with millimetre squares,
onto an overhead transparency
acetate sheet. A piece of this
on or under your glass slide will
provide a measure ideal for shrimp
observations with a hand lens (x10)
or a microscope on low power (x40).
7 Sodium chloride is described as
low hazard on CLEAPSS Hazcard
47b.
8 Observe good laboratory hygiene
after handling aquarium water.
Procedure
SAFETY: Ask students to wash their
hands after handling the aquarium
water.
Preparation
a Set up a population of brine
shrimps in a salt water aquarium
about 4 weeks before the
investigation begins.
b Spend part of one lesson observing
the behaviour of the brine shrimps
as an introduction to developing
hypotheses.
c Practice catching and measuring
the shrimps for the rest of the lesson.
Catching shrimps to measure
d Remove shrimps from the
aquarium by fishing them out with a
fine sieve. Don’t let them dry up in the
sieve. Lower them into a small beaker
of aquarium water and allow them to
swim free.
e Pick up the shrimps from this water
using a pipette that is wide enough
for adult shrimp to enter when
sucked up.
f Return the animals to their tank after
5 minutes.
www.survivalrivals.org
Measuring shrimps
g Take a clean glass slide and gently
rub it dry and shiny. Put just a few
drops of water with a shrimp onto
the slide from the pipette (below).
Suck up any excess water so that the
shrimp is confined in a blob of water
(note 6).
h Add one drop of water every
minute or two so that the shrimp
does not dry out.
i Use a hand lens (magnification x10)
or a microscope on low power (x40)
to observe the shrimps and measure
them against a scale (note 6).
Investigation 1: Pair choice
experiments
j Students will have developed their
own hypotheses to investigate, but
could investigate pair choice by
providing shrimps of different sexes
with a choice of mate of different
sizes and observing their behaviour.
To develop the investigation students
will need to make decisions for
themselves about the details of
what to look for and how to
interpret different behaviours.
Investigation 2: Measuring
relative sizes of paired individuals
k Students will have developed their
own hypotheses to investigate, but
could investigate the effect of size
on pairing choices by measuring
the relative sizes of pairs. This
would involve capturing pairs of
shrimps, measuring relative sizes and
analysing data to look for correlations
between sizes of males and females
in pairs.
Teaching notes
Teachers should be careful to
introduce these animals in a way
that promotes a good ethical attitude
towards them and not a simply
instrumental one. Although they
are simple organisms that may not
‘suffer’ in the same way as higher
animals, they still deserve respect.
This would be particularly true of any
experiments that established the
limits of parameters favoured by the
shrimps. Animals should be returned
promptly to the holding tank after
being examined. This supports ethical
approaches that are appropriate
to field work where pond animals
are returned to their habitat after
observations have been made.
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Charles Darwin proposed two
principal ideas to account for the
diversity of life on earth. While
the Origin of Species was mostly
concerned with natural selection,
Darwin noted briefly in that book
that sexual selection by mates was
also a force for evolutionary change.
He wrote:
“And this leads me to say a few
words on what I call Sexual Selection.
This depends, not on the struggle for
existence, but on a struggle between
the males for the possession of the
females; the result is not death to the
unsuccessful competitor, but few or
no offspring. [1]” [On the origin of
species, First edition, 1859,
Chapter IV]
By 1871 Darwin had expanded
those few words to take up the
greater part of his second book
on evolution: The descent of man
and selection in relation to sex.
Sexual selection, he suggested,
was largely responsible for human
diversity – a conclusion with which
many of today’s modern evolutionary
biologists would agree.
Teenagers find the social
arrangement between the males
and females inherently interesting
to investigate!
Brine shrimps are herbivores in
their ecosystem, feeding on algae
and bacteria. In a natural saltlake ecosystem there are no fish
predators, but birds such as avocet
and flamingos feed on the shrimps.
There is an opportunity here to
develop the concept of energy flow
and material transfer between trophic
levels. Natural selection operates
in this ecosystem as brine shrimps
compete with one another for food.
Brine shrimps exhibit sexual
dimorphism and pair for mating
– male with female. The special case
of sexual selection also operates.
Males are competing with one
another for larger females that
produce more offspring. Females may
be selecting male partners that are
larger and stronger and help them to
swim faster and so gather more food
for eggs. Sexual selection would thus
favour larger male shrimps. However,
larger shrimps will be captured more
easily from the water by flamingos.
Different selection pressures
operate on a living organism in its
environment. The result of selection
pressures is adaptation of a species
to suit the situation almost perfectly.
www.survivalrivals.org
Further information
www.survivalrivals.org
Brine Date is one of the Wellcome
Trust’s experiments to celebrate
Darwin 200. A kit containing
everything needed to run this
practical in school is available free
to all state schools across the UK in
2009. Details on this website. (Last
accessed November 2008. Full
website not available at that time.)
www.britishecologicalsociety.
org/articles/education/resources/
curriculum/brineshrimp
Details of how to get hold of, and
access to downloadable sample
material from, an invaluable book,
published by the British Ecological
Society, describing the culturing and
use of brine shrimps – Brine Shrimp
Ecology by Michael Dockery and
Stephen Tomkins ISBN 1900579103.
Price £14.50, including post and
packing. This includes a starter
kit with a substrate that includes
the necessary microorganisms to
colonise the salt water and start
off a self-contained ecosystem.
(Last accessed November 2008.)
http://www.captain.at/artemia/
Captain’s Universe provides
information about Artemia salina
– video clips, photographs, culture
details etc (Last accessed
November 2008.)
www.aquaculture.ugent.be
Very high level information about
culturing Artemia on a very large
scale from the Artemia reference
centre, University of Ghent.
(Last accessed November 2008.)
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Microbes ate my homework:
Investigating how microbes help us to break
down cellulose and recycle plant material
Introduction
Investigate the effects of cellulose-digesting enzymes in microbes on different
kinds of paper. This long-term activity allows students to explore the role of
microbes in decomposing organic waste and their place in the carbon cycle.
This practical investigates how quickly different kinds of paper decompose
under the action of soil microbes. Soil microbes are unusual in the natural
world in that they contain cellulases – enzymes that can digest cellulose the
fibrous substance that helps to provide plants with a rigid structure. Without
these cellulase enzymes in soil microbes, plant material would not decay and
the elements such as carbon contained in the material would not be recycled
for use by other living things.
Paper is made from woody plants and cellulose makes up 40-50% of the
mature plant cell wall therefore paper is largely made of cellulose. In this
investigation you will find out how microbes in the soil can break down paper
over a few weeks. This demonstrates how paper and plant material is broken
down in the compost bin.
Cellulase-producing microbes are found in the strangest of places from
termites’ stomachs through to the soil surrounding volcanoes. Scientists are
genetically modifying cellulase-producing microbes to get them to produce
larger quantities of cellulase. These microbes are being used commercially to
produce biofuels from non-food stuff. Currently, most biofuels are made by
fermenting edible plant material to produce ethanol. This means using plant
products that could be used as food to make fuel instead. If we could produce
ethanol from cellulose, we would be able to make use of a huge amount of
non-edible plant waste instead, such as stalks from farmland, sawdust and
wood chips from forestry operation.
Cellulase-producing bacteria in the guts of herbivores (for example, in the rumen
of ruminants and the appendix of rabbits) help those animals to survive by
breaking down cellulose so that the animals can use it as a source of energy.
Cellulase-producing microbes therefore play a key role in the carbon cycle,
breaking down carbon compounds and releasing methane and carbon dioxide
which are of enormous importance in their effects on global climate change.
Lesson organisation
Each group will set up six tubes
containing different paper/ card
samples with nutrient broth
containing soil microbes. The
practical work in the ‘set-up’ session
will take around 30 minutes and
each review session will take about
20 minutes. You need to leave at
least one week (and up to 3 weeks)
between set up and first review
and a further 1-3 weeks to each
subsequent review. Each review
will take only 10-15 minutes.
www.practicalbiology.org
Apparatus and Chemicals
For the class – set up by technician
/ teacher:
• Sterile nutrient broth
(50 cm3 per group) (see note 2)
• Soil
• Paper samples
For each group of students:
• Sterile 5 cm3 graduated pipette
and filler, 1
• Clean test tubes with aluminium foil
caps or cotton wool plugs, 6
• Clean conical flask (250 cm3), 1
• Test tube rack, 1 (to support the
tubes for up to 6 weeks)
• Sterile nutrient broth, 50 cm3
• Soil, 5 g
• Samples of different types of paper
in 1 cm x 2 cm strips (for example,
filter paper, tissue paper, unprinted
newspaper, heavily printed
newspaper, glossy magazine
covers, thin cardboard)
• Marker pen, 1
Technical notes and safety
1 Before embarking on any practical
microbiological investigation carry
out a full risk assessment. For
detailed safety information on the
use of micro-organisms in schools
and colleges, refer to Basic Practical
Microbiology – A Manual (BPM)
which is available, free, from the
Society for General Microbiology
(email education@sgm.ac.uk) or go to
the safety area of the SGM website
(www.microbiologyonline.org.uk/
safety.html) or refer to the CLEAPSS
Laboratory Handbook, section 15.
2 Make sterile nutrient broth
by rehydrating tablets (more
expensive) or powder according to
manufacturer’s instructions. Make
just enough (with a little extra for
mistakes). (See BPM p6 for
more details.)
3 Suitable disinfectants include
sodium chlorate(I) (hypochlorite) at
concentrations providing 1000 ppm
available chlorine for general surface
cleaning, or 2 500 ppm chlorine for
discard pots, or VirKon at 1% (follow
manufacturer’s instructions).
4 Cultures and contaminated
equipment and materials must be
autoclaved at 121ºC for 15 minutes
before disposal. After sterilisation,
all materials can be disposed of with
normal waste. Take care to package
glass to prevent injury.
Procedure
SAFETY: See Basic Practical
Microbiology – a Manual for more
information about hazards and risk
control measures.
Preparation
a Make up sterile nutrient broth
(note 2).
b Collect soil sample (5 g per working
group). Avoid areas where cats may
have buried faeces.
c Sterilise the pipettes.
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d Make cotton wool plugs for the
test tubes.
e Set up discard beakers with
appropriate disinfectant fluid (note 3).
Investigation
a Label 6 test tubes A - F, together
with your name and date.
b Use a graduated pipette and filler to
place 5 cm3 of nutrient broth in tube
A. Carefully drop in a 1 cm x 2 cm
sample of filter paper.
c Place 5 g of soil and 30 cm3
of nutrient broth in the conical
flask. Swirl the contents to form a
suspension. Allow this to settle for a
Tube
Treatment
A
B
C
D
E
F
Nutrient broth (sterile) + filter paper
Nutrient broth + soil + filter paper
Nutrient broth + soil +
Nutrient broth + soil +
Nutrient broth + soil +
Nutrient broth + soil +
minute to avoid blocking the pipette.
d Pipette 5 cm3 of the supernatant of
the nutrient broth / soil suspension
into each of the five remaining tubes.
Put the pipette into a discard beaker.
e Into tube B, carefully drop in a 1 cm
x 2 cm sample of filter paper.
f Put a 1 cm x 2 cm sample of a
different kind of paper or card into
each of the other four tubes C – F.
g Stopper each of the tubes with
either cotton wool or loosely cover
with aluminium foil.
h Record the contents of each of
the six tubes in a table.
Appearance
after … weeks
Appearance
after … weeks
i Leave the tubes at room
temperature for at least a week.
j Before reviewing the tubes, give
each a tap with your finger. Carefully
observe what happens to the paper
strip. Do not take out the cotton wool
stoppers.
k Record your results in the table.
l Dispose of the soil suspension
immediately after the first lesson and
the contents of the tubes safely at the
end of the investigation (note 4).
www.practicalbiology.org
Teaching notes
Cellulose is a fibrous substance that
helps to provide plants with a rigid
structure. It makes up 40-50% of
the mature plant cell wall and is the
most abundant carbohydrate. The
molecules are very large and very
long and contain carbon, hydrogen
and oxygen. In wood, forest and
agricultural wastes, and in waste
paper, cellulose occurs in a complex
mixture with lignin (another plant
polymer) called lignocellulose.
The microbes that can decompose
and thus recycle it are extremely
important in maintaining the turnover
of organic matter in the carbon cycle.
On land, the major decomposers
of cellulose are fungi aided by a
few bacteria. Cellulolytic bacteria
include species of Cellulomonas,
Pseudomonas and Ruminococcus.
Cellulolytic fungi include Chaetonium,
Fusarium, Myrothecium and
Trichoderma. Ask students to locate
the position of soil microbes on a
diagram of the carbon cycle.
Cellulose is not soluble in water,
so microbes cannot absorb it into
their cells. They secrete cellulase
enzymes which partly digest cellulose
and break it down to soluble sugar
molecules that can be absorbed
and used. Higher organisms do not
make cellulases which means that
herbivores cannot digest cellulose
themselves. They depend on
cellulolytic bacteria in their intestinal
tracts to do the job for them. This
can be a complicated process –
for example involving regurgitation,
chewing and swallowing in ruminants,
or re-ingestion of faecal pellets
in rabbits. This is an interesting
opportunity for students to carry out
some research into different methods
of digesting cellulose. Humans
cannot digest cellulose at all, so all
the cellulose we eat passes through
our digestive system unchanged.
This is called ‘dietary fibre’.
Students are often very aware of
issues associated with recycling and
may be interested to think about the
length of time paper of different sorts
would sit in landfill before rotting if it is
not recycled. This may also introduce
discussion about how different paper
treatments make them harder to
recycle.
If you have access to a compost bin
or wormery, you could compare the
results of this investigation with the
rate (and manner) of decomposition
of similar paper samples in the
compost bin and wormery. Be aware
of the risks posed by mould spores in
compost. If you choose to work with
material in a domestic compost bin,
make sure no cooked food or meat
products go into the compost, and
that there is no evidence of rodent
activity around the bin. Practise
good personal hygiene after handling
compost.
There is scope for higher level
investigations using this and related
techniques such as:
• exploring the effect of temperature
on the activity of cellulolytic
microbes or cellulases (from school
science suppliers),
• exploring the cellulolytic activity of
microbes from different soils,
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•
exploring the effect on cellulolytic
activity of adding nutrients to the
soil samples,
• exploring whether fungi or bacteria
are more important in terms of
cellulolytic activity in particular types
of soil.
These questions will help students
to focus their observations and think
about the purpose of the practical
procedure.
1 In this investigation, what is the
purpose of the tube containing filter
paper with sterile nutrient broth and
no soil?
2 Why is it important not to take out
the cotton wool stoppers?
3 How have the papers changed as a
result of the action of microbes from
the soil?
4 Which paper has decomposed the
least?
5 What would you do to develop
this investigation to give you more
information about soil microbes and
cellulose? How could you improve it?
Further information
www.microbiologyonline.org.uk
Society for General Microbiology
– source of Basic Practical
Microbiology, an excellent manual of
laboratory techniques and Practical
Microbiology for Secondary Schools,
a selection of tried and tested
practicals using microorganisms.
These booklets are available free of
charge. (Last accessed November
2008.)
www.microbiologyonline.org.uk/misac
MiSAC (Microbiology in Schools
Advisory Committee) is supported by
the Society for General Microbiology
(see above) and their websites
include more safety information and a
link to ask for advice by email.
(Last accessed June 2008.)
www.ncbe.reading.ac.uk/NCBE/
PROTOCOLS/pracbiotech.html
The NCBE is a rich source of upto-date protocols and practical
equipment for biotechnology
practicals in schools. These notes
(from 1993) show two more protocols
for assessing cellulase activity –
by digesting cellulose in an agar plate
(similar methodology to the starch
and protein methods on the Practical
Biology site) and by measuring the
change in viscosity of wallpaper paste
in syringe barrels! (Last accessed
July 2008.)
www.practicalbiology.org
A window on the past: How stomatal
density adapts in changing environments
Introduction
These notes describe how to measure the density of stomata on a leaf
epidermis. You can use the method to collect data about stomatal density
from a range of species of plants, or from plants that have been grown in a
range of conditions. The technique is straightforward, but requires care to
achieve good results.
Stomatal density usually varies between the upper and lower epidermis
of any leaf, will vary from species to species and may change with carbon
dioxide concentration in the surrounding atmosphere, and with light intensity.
Any change will take several weeks to occur, so there is an opportunity here
for a long term, self-directed investigation. Mathematical analysis of the data
gathered may be a challenge for some students – but is simplified with a
spreadsheet such as the one attached.
Lesson organisation
Demonstrate the technique and give
students an opportunity to practise
the skill of making epidermal peels
or impressions. Supply students with
plants kept for several weeks under
controlled conditions (such as varying
CO2 level, water supply, humidity,
temperature or light intensity) or offer
this as the groundwork for a longerterm self-directed investigation for
students.
Apparatus and Chemicals
For the class – set up by technician/
teacher:
• Plants to investigate (note 1 and note 2)
For each group of students:
Microscope with eyepiece
graticule (calibrated for different
magnifications) or stage graticules
on microscope slides to allow
simple measurement of field of view
(note 6)
• Nail varnish and sellotape OR
• Germolene ‘New skin’ to take
impressions from the epidermis
•
Technical notes and safety
1 Plants with hairy leaves are not
suitable for taking impressions.
Spider plants (Chlorophytum
comosum) work well in this
procedure. Red hot poker (Kniphofia)
is a common garden plant and an
easy to study monocotyledonous
example as you can peel its
epidermis and view it directly under
a microscope. Grey willow (Salix
cinerea) has been studied in modern
and fossil forms. Also useful are
the Mexican hat plant (Kalanchoe
diagremontiana), and Arabidopsis
thaliana (a popular model organism
for plant biology and genetics
which has one of the smallest plant
genomes and was the first plant
genome to be fully sequenced). Pot
geranium (Pelargonium) is also easy
to study and you can tear sections
of epidermis for direct viewing.
Variegated Tradescantia leaves can
be used for direct viewing of stomata
in the regions with little or
no chlorophyll.
2 Grow plants under clear domes
taped to a bench or tray so you
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can control the atmosphere around
them. You could use a large plastic
water container, a plastic garden
bell cloche or a laboratory bell jar.
Include a thermometer in each dome
so you can monitor temperature.
Reduce humidity levels by including
a desiccant such as silica gel or
calcium chloride (note 3). Increase
humidity levels by including an open
vessel of water (such as a deep Petri
dish), and topping it up regularly
before the liquid evaporates fully.
Reduce light levels by covering
domes with increasing numbers of
layers of fine fabric or horticultural
fleece. The level of carbon dioxide
in normal atmospheric air is low, but
plants will produce some from their
metabolic processes. You could
increase the carbon dioxide level by
breathing into the dome, or adding
a boiling tube with a few marble
chips (calcium carbonate) and 1020 cm3 of dilute hydrochloric acid
(approximately 0.1M). You could
reduce carbon dioxide levels by
including a carbon dioxide absorber
such as soda lime (note 4).
3 Desiccants: Silica gel (see Hazcard
86), for users in year 7 advises
wearing gloves and to beware of
dust from blue (self-indicating) silica
gel. The advantage of blue moistureindicating gel (containing < 0.5%
cobalt(II) chloride) is that it can be
reheated and used again. The risk to
health from cobalt(II) chloride is very
low. Calcium chloride (see Hazcard
19A) is an irritant as a solid. Wash
hands immediately if any gets on the
skin and wear eye protection when
handling the powder or granules.
4 Carbon dioxide: Calcium carbonate
is described as low hazard on
Hazcard 19B. Hydrochloric acid
(Hazcard 47A) at low concentrations
presents a minimal hazard to
students, and will be neutralised as
the marble chips react with it. Soda
lime is described as corrosive on
Hazcard 91. Ensure that students
do not handle the soda lime and
wear eye protection if there is any
risk of getting soda lime in their eyes.
Be aware of the necessary first aid
response if any soda lime should get
into anyone’s eyes.
5 Make an epidermal impression
by spreading a thin layer of nail
varnish on the leaf and leaving it
to dry. Remove the layer of varnish
by attaching clear sticky tape to it,
peeling it from the leaf surface and
sticking it to the slide. You could
try Germolene ‘New skin’ as an
alternative to nail varnish. It has
slightly different elastic properties
and may make a clearer impression.
You won’t need to use sticky tape
with ‘New skin’.
6 Graticules printed on plastic
are available at reasonable prices
– around £20 for 10 – if your
microscopes are not already
equipped with them
(see Suppliers section).
Procedure
SAFETY: Plant sap can be irritating to
the skin. Students may have allergic
reactions to nail varnish or Germolene
‘New skin’. Be alert to any students
suffering allergic responses to the
materials handled. Offer gloves as
skin protection if necessary and make
www.practicalbiology.org
sure students wash their
hands thoroughly at the end of
the procedure.
Preparation
a Grow plants in different conditions
for 4-6 weeks. Useful varieties of
plants are suggested in note 1. Ideas
for creating different conditions for
the plants are suggested in note 2.
b Make sure students know what
stomata look like, and understand
something about their function in
the plant.
Investigation
c Collecting epidermal evidence:
The epidermis will peel from some
leaves quite readily. First cut the leaf.
Use your fingernails to catch hold of
and peel off the epidermis, or use
a sharp razor blade to peel off the
epidermis. Mount the peel in a drop
of water on a microscope slide with
a coverslip. Alternatively, make an
epidermal impression with nail varnish
(or another clear substance) and
place that on a microscope slide to
view it (note 5).
d Discuss and decide how many
impressions or epidermal samples
should be taken, and from where on
each plant, to get a representative
sample. Try to be consistent about
which part of the leaf to use.
e View the epidermal impressions
using a calibrated microscope fitted
with an eyepiece graticule (note 6).
f Calculate the true area of the field of
view. You can calculate this using the
formula area = πr2 when you have
measured the true radius of the field
of view (r). (See also table overleaf.)
g Count the stomata visible in each
of three areas of the impression.
h Calculate the stomatal density for
each impression. (See table overleaf.)
i Analyse average density for each
impression and for each plant. (See
table overleaf.)
j Plot a graph of average stomatal
density against light intensity.
Teaching notes
Stomata control the movement of
gases and vapours into and out of a
leaf. They are often discussed primarily
in the context of controlling loss of
water from a leaf – as shortage of
water is a common stress experienced
by plants. The stomata of wilting
plants close which minimises further
water loss from the leaf.
However, closed stomata will also
reduce the availability of carbon
dioxide for a photosynthesising leaf.
So at low concentrations of carbon
dioxide, in light conditions, stomata
are stimulated to open wide which
permits photosynthesis to continue.
In low light conditions, carbon dioxide
concentration is not a limiting factor
for photosynthesis and stomata can
be closed without affecting carbon
dioxide uptake.
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c
(a+b+c) /3
= F/B
6
7
6.0
1.9
1.0
= total of column F I: Average number of
divided by number stomata in the plant
studied
of samples
E: Number of
stomata in third area
of impression
b
5
G: Average stomatal
density (number per
square micrometre
D: Number of
stomata in second
area of impression
a
3.14
F: Average number
of stomata in one
field of view
C: Number of
stomata in first area
of impression
= πr2
1
A: True radius of
field of view (µm)
B: Area of field
of view (square
micrometres)
(See the link to Annals of
Botany below.)
There are potentially commercial
implications when stomatal density
changes in plants grown under
artificial light or with additional
atmospheric CO2 to improve crop
production. This is because stomatal
reaction to high light intensity or
high CO2 levels could result in plants
having altered water requirements
r
Over short time scales, reducing
the size of the aperture in each
stoma reduces the loss of water
vapour from a leaf, but also reduces
the amount of carbon dioxide that
the plant can absorb. Therefore, at
high light intensities (which are often
accompanied by high temperatures
and low water levels) reducing water
loss has the concomitant effect of
limiting photosynthesis.
H: Number of
samples assessed
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and hence incurring additional costs
for supplying water to that crop.
If students are struggling with the
calculations, a spreadsheet with
these headings and formulae to ‘fill’
the spreadsheet would be useful.
Some species of plant have
stomata on both sides of the leaf,
and others have stomata only on
the lower epidermis. The shape of
stomata (and the mechanisms for
controlling the size of the aperture)
differ between monocotyledonous
plants (such as grasses) and
dicotyledonous plants.
Some species seem to respond
to prolonged ambient levels of light
intensity and carbon dioxide by
developing leaves with an altered
density of stomata. For example,
at high CO2 levels, a lower density
of stomata will not limit the rate of
photosynthesis, but will reduce water
loss and at higher light intensities,
a higher density of stomata will
maximise the rate of photosynthesis,
but with the risk of enhanced
water loss.
Interaction between factors is
complex and varies from species to
species. A literature search will find
many suggestions of factors already
investigated which could promote
ideas for further work in the school/
college laboratory.
Studies of stomatal density of
plant samples up to 300 years old
in botanical libraries have been
used alongside evidence of recent
changes in carbon dioxide levels in
the atmosphere. Studies of stomatal
density in fossils has been correlated
with information from ice cores to
give evidence of how carbon dioxide
levels in the atmosphere have
affected plants in the past.
Further information
www-saps.plantsci.cam.ac.uk/docs/
post16/article2.pdf
This link is to an 8-page booklet
published by SAPS (‘Seeing without
eyes – how plants learn from light’
by Stephen Day) that explains how
phytochromes in plants react to light
intensity and provide a mechanism by
which plants can respond to light.
www.plantscienceimages.org.uk
The SAPS plant science images
database which includes images of
stomata from dicotyledonous plants
such as Kalanchoe lower epidermis
and Arabidopsis thaliana.
http://aob.oxfordjournals.org/cgi/
content/abstract/76/4/389
Link to abstract of Annals of Botany
76: 389-395, 1995 – an article
entitled Stomatal Density and Index
of Fossil Plants Track Atmospheric
Carbon Dioxide in the Palaeozoic by
Jennifer C. McElwain and William G.
Chaloner. This research correlates the
stomatal density of forest tree species
collected over the last 200 years with
changes in carbon dioxide levels in
the atmosphere. It goes on to link
stomatal density in fossil specimens
from the Palaeozoic with carbon
dioxide levels as deduced from
ice cores.
45
Chemistry
The science of materials, their structure,
physical and chemical properties, and
how they interact.
www.practicalchemistry.org
47
Introduction
Chemistry is about the study of atoms, how they interact,
the structures they form and the materials they make.
Practical activities provide opportunities for students to
explore the chemistry of materials, and observe patterns
in reactions. They can also be used to demonstrate the
applications of chemistry, increasing its relevance to
students. Practical work is vital in the development of
students’ skills of manipulating and handling apparatus
and data, working with others, and scientific enquiry.
They can also provide opportunities for students to
collect their own data and use this to apply and develop
mathematical skills. Chemistry demonstrations should be
exciting and stimulating and some of the most memorable
experiences that students will take from science.
Secondary chemistry experiments:
A matter of balance:
The combustion of iron wool
Red cabbage indicator:
Making a pH indicator
Soot surveys:
Investigating air pollution
Hydrogels in the home:
Hair gel and disposable nappies
Discovering the formula:
Finding the formula of hydrated copper(II) sulfate
Preparing perfumes:
Making esters from alcohols and acids
“Practical work mirrors the
pioneering investigative and
exploratory nature of science.
Teaching is not about simply
passing on what we (think we)
know but the thrill of the chase”
Teacher response to SCORE questionnaire
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A matter of balance:
The combustion of iron wool
Introduction
Iron wool is heated in air on a simple ‘see-saw’ balance. The increase in mass
is seen clearly.
Lesson organisation
This demonstration takes around
5 minutes once it has been set up.
Apparatus and chemicals
For one demonstration:
• Eye protection
• Bunsen burner
• Heat resistant mat
• Wooden metre rule (see note 1)
• Aluminium cooking foil, about
10 cm x 10 cm
• Retort stand, boss and clamp
• Plasticine, few grams
• Knife edge, triangular block or
something similar
• Steel wool (Low hazard), about 4g
Technical notes and safety
Steel wool (Low hazard) Refer to
CLEAPSS Hazcard 55A
1 A shallow groove cut across the
width of the ruler at the 50 cm mark
will help when balancing it on the
knife edge. Cover the end of the
meter ruler with foil to protect it from
the Bunsen burner.
Procedure
a Cover one end of the metre ruler with
foil to protect it from the Bunsen burner.
Take about 4 g of steel wool and tease
it out so that the air can get around
it easily. Use a few of the strands to
attach it to the end of the ruler.
b Balance the ruler on a knife edge
or triangular block at the 50 cm mark.
Weight the empty end with plasticine
until this end is just down (see the
diagram). This part is critical.
Steel wool
Plasticine
Before
After
Foil to
protect ruler
Knife edge
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c Place a heat resistant mat
underneath the steel wool.
d Wear eye protection. Light the
Bunsen burner and heat the steel
wool from the top with a roaring
flame. It will glow and some pieces
of burning wool will drop onto the
heat resistant mat. Heat for about a
minute by which time the meter ruler
will have over-balanced so that the
iron wool side is down.
Teaching notes
As you are setting up, ask the students
whether they think the iron wool will
go up, down or remain the same.
Many will predict a weight loss.
If fine steel or iron wool is used
then it may be possible to light it
using a splint.
Equation:
iron oxide
Iron + oxygen
Fe2O3(s)
2Fe(s) + 3/2 O2(g)
This demonstration could be
complemented by a class experiment
such as ‘The change in mass when
magnesium burns’ which can be
found at www.practicalchemistry.org.
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Red cabbage indicator:
Making a pH indicator
Introduction
A pH indicator is a substance which has one colour when added to an acidic
solution and a different colour when added to an alkaline solution. In this
experiment pupils make an indicator from red cabbage.
Lesson organisation
The experiment is in two parts. The
first part involves boiling some red
cabbage in water. In the second
part the students test their indicator.
Between the two parts the mixture
must be allowed to cool. The first part
takes about 10 to 15 minutes. The
cooling takes about 15 minutes and
the testing less than 5 minutes.
The cooling period could be used
as an opportunity to discuss the
background to the experiment –
see Teaching notes below.
Apparatus and chemicals
• Eye protection for all
Each working group will require:
• Beaker (250 cm3)
• Bunsen burner
• Tripod
• Gauze
• Heat resistant mat
• Test-tubes, 3 (see note 1)
• Test-tube rack
• Dropping pipette
• Several pieces of red cabbage
Access to (see notes 2 and 3):
• Dilute hydrochloric acid, 0.01
mol dm-3 (Low hazard at this
concentration)
• Sodium hydroxide solution 0.01
mol dm-3 (Low hazard at this
concentration)
• De-ionised or distilled water
Beaker
Water
Pieces of red cabbage
Gauze
Tripod
Bunsen burner
www.practicalchemistry.org
Technical notes and safety
Dilute hydrochloric acid, 0.01 mol dm-3
(Low hazard at concentration used).
Refer to CLEAPSS Hazcard 47A
Sodium hydroxide solution 0.01 mol
dm-3 (Low hazard at concentration
used). Refer to CLEAPSS Hazcard 91
1 Small test-tubes of capacity about
10 cm3 are ideal.
2 Each group of students will need
access to the hydrochloric acid and
sodium hydroxide solutions. Dropper
bottles are ideal. Alternatively small
beakers (100 cm3) with dropper
pipettes could be used. Students
need to be able to pour the acid and
alkali solutions easily and safely into
test-tubes.
3 Provide similar containers for deionised or distilled water. Label the
containers ‘Acid’, ‘Alkali’ and ‘Water’.
4 A good tip is to attach a pipette to
each bottle with an elastic band, to
avoid cross-contamination.
Procedure
SAFETY: Wear eye protection
throughout. Consider clamping
the beaker.
a Boil about 50 cm3 of water in
a beaker.
b Add 3 or 4 small (5 cm) pieces
of red cabbage to the boiling water.
c Continue to boil the red cabbage
in the water for about 5 minutes.
The water should turn blue or green.
d Turn off the Bunsen burner and
allow the beaker to cool for about
15 minutes.
e Place 3 test-tubes in a test-tube
rack. Half-fill one of the test-tubes
with acid, one with alkali, and one
with distilled or de-ionised water.
Label the test-tubes.
f Use a dropper pipette to add a
few drops of the cabbage solution to
each test-tube. Note the colour of the
cabbage solution in each of the three
test-tubes.
Teaching notes
Discussion points could include
any or all of the following.
Many plant colouring materials
in berries, leaves and petals act
as indicators.
Some of these will not dissolve in
water easily. A solvent other than
water (e.g. ethanol) could be used,
but it may be flammable. Discuss
how the risk of fire can be reduced
by using a beaker of hot water to
heat the mixture.
Possible variations on this
experiment might include using
beetroot, blackberries, raspberries,
copper beech leaves, or onion
skins in place of the red cabbage.
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Soot surveys:
Investigating air pollution
Introduction
This experiment is adapted from a series of activities from a Field Studies Council
project ran between 2005-07 called London Outdoor Science. The investigation
looks at whether the levels of particulates vary in urban green spaces.
It is often difficult to measure air pollution, as sophisticated equipment and
long-term monitoring are usually needed to obtain worthwhile data. In this
investigation, on the other hand, particulate pollution (i.e. soot) adhering to
tree bark can rapidly be measured using nothing more complicated than
sticky tape.
Lesson organisation
The complete investigation will take
about three lessons, and pupils
will need a basic understanding
of the key pollutants before they
begin. Because there are a variety
of measurements to be taken, it is
best if pupils work in groups and are
assigned roles; i.e. recorder, distance
measurer, sampler, noise pollution
monitor. If groups start taking their
measurements at different points
along the transect this will give them
more room to work.
The location and transect should
be carefully identified in advance,
and could be determined by the
teacher, or chosen by students
during planning. An ideal transect for
this investigation would use a row of
trees (about 8 or more) of the same
species and similar age, that start at
a road and move progressively into a
green space.
If time permits, the class could be
taken outside to a local site before
designing the method, to be shown
the basic techniques. If time is
limited, the distances between the
trees along the transect could be
measured prior to the lesson and the
trees marked using site numbers.
Apparatus and chemicals
For fieldwork, each working group
will require:
• Clipboard, 1
• Plain paper to record results,
about 3 sheets
• Sticky tape, 1 roll
• Scissors, or sellotape dispenser
• Tape measure, 1
• Trundle wheel, 1
• Tree identification key (see note 1)
• Microscope slides (optional), 1 for
each site studied
• Noise sensor / datalogger (optional)
• Air pollution sensors – ozone, CO ,
2
SOx, NOx (optional)
• Key to lichens (optional)
For analysis of results, each working
group will require:
• Hand lens, 1
• Mini-quadrats (see note 2)
• Microscope, 1
Technical notes and safety
1 The Tree Name Trail is a tree
identification key available from the
Field Studies Council, and can be
bought online.
(www.field-studies-council.org/
publications/pubsinfo.aspx?
Code=OP51)
www.practicalchemistry.org
2 Mini-quadrats are small square
frames used for sampling. Miniquadrats can be made by
photocopying graph paper onto
acetate sheets (See Fig. 2).
3 An appropriate risk assessment
specific to the site being used, and
in line with school policy, must be
carried out. It is important that pupils
are always properly supervised when
working near roads. Risks to pupils
on out-of-school activities make it
vital that all trips which take pupils
any distance away from school
are planned carefully and well in
advance. The leader of the field trip
has particular responsibilities which
must be taken seriously. Most local
authorities will have regulations and
guidance for the conduct of out-ofschool activities and complying with
these is essential.
Hazards need to be identified in
advance and precautions taken; pupils
must be warned and supervised with
these hazards in mind.
Refer to CLEAPSS Laboratory
Handbook Chapter 17: Monitoring in
the Field and Laboratory.
Procedure
Lesson 1
a Introduce the area to be studied.
This research could be carried
out and presented by pupils as a
preparatory task. The internet can
be used to find relevant sites that list
pollution data for the region. Students
should be introduced to lichens as air
pollution bio-indicators at this stage.
b Provide students with knowledge
of the basic techniques for taking
measurements and samples,
including use of the datalogger if
applicable. The detailed planning
of the investigation could then be
left to them allowing for a variety
of methods to be discussed and
evaluated later.
c Ask students to make a prediction:
e.g. ‘The amount of pollution will
decrease further from the road,
Site 1
Fig. 1: Use of sticky tape for sampling
Site 2
Site 3
Fig. 2: Mini-quadrats, for use under a
microscope, placed over each strip of
sticky tape.
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into the middle
of the park’,
and consider
how it will be
measured.
d Put students
into small
groups to write the method for their
investigation, and assign roles to all
members of their group.
Lesson 2
e On arriving at the site, demonstrate
taking a sample on the bark using
sticky tape. Place a 3 cm length of
sticky tape firmly onto the bark of the
tree, leave for 10 seconds, and then
remove it. Soot and other particles
from the air will have adhered to the
tape, along with debris such as loose
bark and moss from the tree (Fig. 1).
f Ask students to get into their
groups. Give them their starting
points along the transect, and begin
taking and recording measurements.
- Distance: Measure the distance
from the road to the first tree and
to subsequent trees using a trundle
wheel, or tape measure. Each tree
should be numbered, starting from
the road as ‘site 1, site 2, site 3… etc’.
- Samples: Take two samples from
the bark of each tree using sticky
tape, 1 m from the base of the tree.
Stick the samples onto plain paper
and label it with the site. If time, a
third sample can be taken and placed
onto a labelled microscope slide.
- Tree species: Use a suitable
identification chart and record the
tree species.
- Tree age: Measure the girth of the
tree trunk using a tape measure held
at shoulder height. The tree age can
be estimated by dividing the tree girth
(in cm) by 2.5.
- Noise (optional): A data logger /
sensor may be used to record noise
levels at each site.
- Bio-indicators (optional): Observe
and record the presence of lichens
on the tree.
- Other pollutants (optional): If
sensors are available, use these to
measure the levels of other pollutants
e.g. CO2, SOx, NOx.
Lesson 3
g Look at the microscope slide from
site 1 under a microscope to observe
in detail the types of items that are
found on tree bark.
h Lay a mini-quadrat (acetate grid) over
the first pollution sample (sticky tape
stuck to paper) for site 1. Randomly
select a small (1 mm) square to
look at, using random coordinates.
Estimate the percentage of that
square that is covered with black
particulates and record your estimate.
Only black particles of soot should be
recorded; ignore bark and moss.
A hand lens may be useful.
i Repeat this 15 to 20 times, each
time randomly selecting another
small square, and estimating the
percentage of that square that is
covered with black particulates.
j Calculate an average percentage
cover of particulates for the sample
site, by adding together the
estimated values and dividing by
the number of repeats.
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k Repeat steps h to j for the second
sample from site 1 and calculate an
overall average. Record the overall
average for site 1.
l Repeat steps g to k for all sample
sites.
m Put the data into a spreadsheet to
be analysed, or plot a graph by hand,
with distance from the road along the
x-axis and average percentage cover
of particulates along the y-axis. If
applicable, plot a second graph over
the first, with the sound reading, or
concentration of other pollutants on
the y-axis.
n Analyse and evaluate the
results. Consider the variables
that were difficult to control, and
how secondary data could be
used to assess the reliability of the
experimental results.
Teaching notes
The investigation could be put into
a context, suitable for the location,
such as ‘Investigate the most suitable
site for a café in the park by collecting
and analysing the deposition of
airborne particulates on trees, and
noise levels.’
A discussion of validity will be
valuable, before and after the
fieldwork. The discussion could
begin with ‘do particles on the
sticky tape actually indicate air
pollution?’ Repetition and standard
procedures are important, e.g. taking
measurements at the same height
from the ground each time, and either
always from the same aspect or from
all round the circumference of the
tree. Using the same type of tape
and technique for applying the same
pressure each time is important.
The investigation has many
interesting areas to consider and
highlights the way scientists work
in the ‘real world’. Pupils can go on
to consider primary data collected by
nearby pollution monitoring stations
(available on the internet) and observe
how these data vary on a daily and
seasonal basis.
An alternative method for
investigating levels of air pollution
by using lichens as indicators has
been developed by the Natural
History Museum. See www.nhm.
ac.uk/jdsml/nature-online/lichenid-guide/
Further information
The original investigation and other
fieldwork activities can be found
at www.field-studies-council.org/
outdoorscience.
Secondary data can be found at:
www.defra.gov.uk/noisemapping
www.airquality.co.uk/archive/index.php
www.research-tv.com/stories/health/
airpollution/bb/
Activity adapted from:
Melissa Glackin’s activities at London
Outdoor Science (www.fieldstudies-council.org/outdoorscience).
Contactable at melissa.glackin@kcl.
ac.uk
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Hydrogels in the home:
Hair gel and disposable nappies
Introduction
In this pair of activities students investigate hydrogels – polymeric smart
materials. They are found in many commonly available products including
disposable nappies and cheap hair gel. The practical work is fun to do
and the results are sudden and dramatic.
Lesson organisation
To do all the practical work takes
about 30 mins. The hair gel experiment
is a good quick introduction to
hydrogels, while the nappy experiment
is more detailed.
If time is available, it is worth
considering combining this
experiment with another experiment
with hydrogels, using plant water
crystals. This experiment can be
found at www.practicalchemistry.org
It is a good idea to ask students to
make detailed observations of each
part of the experiment.
Apparatus and chemicals
• Eye protection
Hair gel – each group requires:
• Hair gel (see note 1)
• Salt
• Petri dish or lid
• Teaspoon or similar – an ordinary
spatula is a bit small
Nappies – each group requires:
• A disposable nappy (see note 2)
• Scissors
• A large ice cream tub or similar
container (see note 3)
• Dessert spoon or similar measure
• Stirring rod
•
Large beaker or plastic tub to
hold at least 600 cm3
• Plastic gloves for those with
sensitive skin
Access to:
• Distilled water, about 500 cm3
per group (see note 4)
• Salt
Technical notes and safety
1 For the hair gel the cheaper and
nastier the better. Allow about one
large teaspoonful per group.
2 Pampers Baby Dry® nappies
work well, but any ultra absorbent
disposables should be fine. As an
alternative to using nappies and
extracting the hydrogel, it is possible
to order sodium polyacrylate (Low
hazard) from Sigma Aldrich.
3 The ice cream tub is for collecting
the inside of the nappy and is safer
than collecting it over newspaper
or similar. If tubs are in short supply,
large zip-lock bags can be used.
Students put the nappy in the bag,
zip it up and manipulate it until all
the hydrogel is extracted and then
proceed as per the directions.
4 If distilled water is not available,
tap water can be used but the
results are not so spectacular.
www.practicalchemistry.org
Procedure
SAFETY: Wear eye protection
Hair gel
a Put a blob of hair gel onto the petri
dish lid. A large teaspoonful is fine.
b Gently sprinkle salt from a spatula
over the hair gel.
Disposable nappy
a Cut the middle section out of the
nappy – the thicker piece that is
designed to absorb the urine.
Discard the other piece.
b Make sure the ice cream
container is completely dry – wipe
it with a paper towel if necessary.
Any moisture in the tub stops the
experiment from working properly.
c Put the centre piece of the nappy
into the ice cream container and
gently take it apart. Small white
grains should start coming away and
this is what you are trying to collect.
Keep gently pulling the nappy apart
until you have collected as many of
the grains as you can. Do not do this
roughly or you will lose your product
and put a lot of dust and fluff into the
air. Avoid breathing in any of the dust.
d Remove and dispose of all the fluff
and other parts of the nappy, keeping
the grains in the bottom of the tub.
They are heavier and fall to the
bottom, which makes it easier
to separate them out.
e Estimate the volume of the grains.
f Pour them into the large beaker and
add about 100 cm3 of distilled water.
Stir. Keep adding distilled water,
100 cm3 at a time, until no more can
be absorbed and stir between each
addition. Estimate the final volume of
the hydrogel.
g Add a dessert spoonful of salt and stir.
Teaching notes
This activity can be used to enhance
the teaching of ionic and covalent
bonding, or hydrogels can be
considered as an interesting polymer
as well as an example of a smart
material. Hydrogels are smart
materials because they change
shape when there is a change in their
environment – in this case it is the
change in the concentration of ions.
Students need to have some
knowledge and understanding of
ionic and covalent bonding, reversible
reactions, and acids and bases to
understand what is happening.
+ H3O+
+ H2O
n
n
O
O
–
O
H
O
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Hydrogels are polymers that can
retain many times their own weight
in water. They are often polymers
of carboxylic acids that ionise in
water, leaving the polymer with
several negative charges down its
length. This has two effects. First, the
negative charges repel each other
and the polymer is forced to expand.
Secondly, polar water molecules are
attracted to the negative charges.
This increases the viscosity of the
resulting mixture still further as the
polymer chain now takes up more
space and resists the flow of the
solvent molecules around it.
The polymer is in equilibrium
with the water around it, but that
equilibrium can be disturbed in
a number of ways. If the ionic
concentration of the solution is
increased – e.g. by adding salt –
the positive ions attach themselves
to the negative sites on the polymer,
effectively neutralising the charges.
This causes the polymer to collapse
in on itself again. Adding alkali
removes the acid ions and moves
the equilibrium to the right; adding
acid has the opposite effect.
There are a large number of
hydrogels and they are sensitive to
different pHs, temperatures and ionic
concentrations. By using a mix of
monomers to create the polymer these
characteristics can be fine-tuned.
The hydrogels that are commonly
available and are used in this
practical activity are sensitive to
salt concentration, but do not show
much change across the pH range
that can be readily investigated in
the classroom. However, they do
lend themselves very well to a range
of investigative practical work. For
example, their volume in different
amounts of water or in different salt
concentrations can be measured.
For this type of investigation it is best
to use either plant water crystals or
to order sodium polyacrylate from
Sigma Aldrich – this has a smaller
crystal size and gives faster results.
Students should make detailed
notes on their experiments, noting
changes in volume, colour and any
other observations. Some expected
observations could include:
Hair gel
The hair gel shrinks in size very
quickly when the salt is added.
After a couple of minutes all that is
left is some liquid in the petri dish.
Disposable nappy
About 10 cm3 of hydrogel can be
extracted from the nappy core.
(Exactly how much depends on the
make and the size of the nappy.) The
hydrogel swells up extremely quickly
(much quicker than with plant water
storage crystals). It absorbs about
500 cm3 of distilled water giving a
very viscous mixture. When salt is
added, the viscosity immediately
reduces and the mixture is easier to
stir. The hydrogel releases the water
and settles on the bottom of the
beaker.
Further information
Inspirational chemistry on Learnnet
has more information about hydrogels.
www.chemsoc.org/networks/
learnnet/inspirchem.htm
www.practicalchemistry.org
Discovering the formula:
Finding the formula of hydrated copper(II) sulfate
Introduction
In this experiment, a known mass of hydrated copper(II) sulfate is heated to
remove the water of crystallisation. The mass of water is found by weighing
before and after heating. This information is used to find x in the formula
CuSO4.xH2O, using mole calculations.
Lesson organisation
This is a class experiment suitable for
students who already have a reasonable
understanding of the mole concept.
The degree to which the mole
calculations need to be structured
will depend on the ability and
mathematical competence of the
class. The outline structure given
in the Procedure below is intended
for students with reasonable
mathematical competence and
experience of mole calculations.
Given adequate access to toppan balances, and skill in their use,
students should be able to complete
the experimental work in 30-40
minutes.
Apparatus and chemicals
• Eye protection
Each working group will require:
• Crucible (see note 1)
• Crucible tongs (see note 2)
• Tripod
• Pipe-clay triangle
• Bunsen burner
• Heat resistant mat
Access to:
• Top-pan balance (± 0.01 g)
• Hydrated copper(II) sulfate
(Harmful, Dangerous for
environment), 2 - 3 g (see note 3)
Crucible
Copper sulfate
Pipe clay triangle
Tripod
Bunsen burner
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Technical notes and safety
Hydrated copper(II) sulfate (Harmful,
Dangerous for environment) Refer
to CLEAPSS Hazcard 27C
1 Crucibles may be of porcelain,
stainless steel or nickel, of capacity
about 15 cm3, and should sit safely
in the pipe-clay triangles provided.
Lids should not be used.
2 Crucible tongs should have a bow
in the jaws of the right size to pick up
the hot crucibles safely.
3 The copper(II) sulfate should be
provided as fine crystals. If large
crystals are used, these should be
ground down before use by students.
Procedure
a Weigh the empty crucible, and then
weigh into it between 2 g and 3 g of
hydrated copper(II) sulfate. Record
all weighings accurate to the nearest
0.01 g.
b Support the crucible securely in the
pipe-clay triangle on the tripod over
the Bunsen burner.
c Heat the crucible and contents,
gently at first, over a medium
Bunsen flame, so that the water of
crystallisation is driven off steadily.
The blue colour of the hydrated
compound should gradually fade
to the greyish-white of anhydrous
copper(II) sulfate. Avoid overheating, which may cause further
decomposition, and stop heating
immediately if the colour starts to
blacken. If over-heated, toxic or
corrosive fumes may be evolved.
A total heating time of about
10 minutes should be enough.
d Allow the crucible and contents
to cool. The tongs may be used
to move the hot crucible from the
hot pipe-clay triangle onto the heat
resistant mat where it should cool
more rapidly.
e Re-weigh the crucible and contents
once cold.
f Calculation:
• Calculate the molar masses of
H2O and CuSO4 (Relative atomic
masses: H=1, O=16, S=32,
Cu=63.5).
• Calculate the mass of water driven
off, and the mass of anhydrous
copper(II) sulfate formed in your
experiment.
• Calculate the number of moles of
anhydrous copper(II) sulfate formed.
• Calculate the number of moles of
water driven off.
• Calculate how many moles of water
would have been driven off if 1 mole
of anhydrous copper(II) sulfate had
been formed.
• Write down the formula for hydrated
copper(II) sulfate.
Teaching notes
Remind students to zero the balance
before each weighing.
Students will probably also have to
be reminded about the need to allow
the crucible and contents to cool
thoroughly before weighing.
Metal crucibles (stainless steel
or nickel) are more robust than
porcelain crucibles.
Further information
An alternative version of this
experiment, illustrated with videoclips, can be found at: http://dwb4.
unl.edu/chemistry/smallscale/
SS041c.html (This website is
intended for teacher use.)
www.practicalchemistry.org
Preparing perfumes:
Making esters from alcohols and acids
Introduction
In this experiment students investigate the reactions between a range of
alcohols and acids on a test-tube scale, to produce small quantities of a
variety of esters quickly.
Lesson organisation
As a class experiment this can be
organised, if desired, as a classcooperative investigation of the
ability of a range of alcohols to
react with a range of organic acids.
Working groups could compare their
results with others to build a general
overview of this route to the formation
of esters, with an interesting variety
of smells.
Depending on the actual way the
lesson is organised, this may be
designed to take from 15 minutes
to an hour.
Apparatus and chemicals
Each working group will require:
• Eye protection
• Glass specimen tubes, 4 (see note 1)
• Plastic dropping pipettes, access to
adequate supply
• Beaker (100 cm3)
• Test-tubes, 4
• Test-tube rack
• Bunsen burner
• Heat resistant mat
• Tripod and gauze
• Crucible tongs
Access to the following alcohols –
about 10 drops of each required
(see note 2)
• Methanol (Highly flammable, Toxic)
• Ethanol (Highly flammable,
Harmful)
•
Propan-1-ol (Highly flammable,
Irritant)
• Butan-1-ol (Harmful)
One or more other alcohols, as
available, from:
• Propan-2-ol (Highly flammable,
Irritant)
• Butan-2-ol (Irritant)
• 2-Methylpropan-1-ol (Highly
flammable, Harmful) (see note 2)
•
Ethanoic acid, pure (Corrosive),
about 2 cm3
• Benzoic acid (Harmful), about 0.2 g
• Propanoic acid (Corrosive) (if
available), about 2 cm3
• Concentrated sulfuric acid
(Corrosive), 5 - 10 drops (see note 3)
• Sodium carbonate solution,
0.5 mol dm-3 (Low Hazard at
concentration used), about 10
cm3 per ester
Technical notes and safety
• Methanol (Highly flammable, Toxic)
Refer to CLEAPSS Hazcard 40B
• Ethanol (Highly flammable,
Harmful) Refer to CLEAPSS
Hazcard 40A
• Propan-1-ol (Highly flammable,
Irritant) Refer to CLEAPSS
Hazcard 84A
• Butan-1-ol (Harmful) Refer to
CLEAPSS Hazcard 84B
• Ethanoic acid, pure (‘glacial’)
(Corrosive) Refer to CLEAPSS
Hazcard 38A
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plastic pipettes for each. Ideally each
pipette is held on to each bottle with
an elastic band.
3 For younger students, prepare the
specimen tubes by adding one drop
of concentrated sulfuric acid to each.
This minimises the risks involved
with such students handling this
substance. Advanced students may
be reliable enough to prepare their
own tubes in this way.
•
Benzoic acid (Harmful) Refer to
CLEAPSS Hazcard 13A
• Propanoic acid (Corrosive) Refer to
CLEAPSS Hazcard 38B
• Propan-2-ol (Highly flammable,
Irritant) Refer to CLEAPSS
Hazcard 84A
• Butan-2-ol (Irritant) Refer to
CLEAPSS Hazcard 84B
• 2-Methylpropan-1-ol (Highly
flammable, Harmful) Refer to
CLEAPSS Hazcard 84B
• Concentrated sulfuric acid
(Corrosive) Refer to CLEAPSS
Hazcard 98
• Sodium carbonate solution (Low
hazard at concentration used)
Refer to CLEAPSS Hazcard 95A
and Recipe Card 61
1 The essential requirements for
these tubes are:
• neutral borosilicate glass
• a wide flat base, so that they are
stable when stood in a beaker. If not
available, small test-tubes could be
used instead, standing in a larger
(250 cm3) beaker.
2 The alcohols and acids may be
best provided as a central resource,
away from flames, with a supply of
Procedure
SAFETY: Wear goggles throughout
a Add 10 drops of ethanoic acid (or
propanoic acid) to the sulfuric acid in
the specimen tube.
b Add 10 drops of ethanol (or other
alcohol) to the mixture.
c Put about 10 cm3 of water into the
100 cm3 beaker. Carefully lower the
tube into the beaker so that it stands
upright.
d Heat the beaker gently on a tripod
and gauze until the water begins to
boil, then stop heating.
e Stand for 1 minute in the hot water.
If the mixture in the tube boils, use the
tongs to lift it out of the water until
boiling stops, then return it to the hot
water.
f After 1 minute, using tongs, carefully
remove the tube and allow it to cool
on the heat resistant mat.
g When cool, pour the mixture into
a test-tube half-full of 0.5 M sodium
carbonate solution. There will be
some effervescence. Mix well by
pouring back into the specimen tube
– repeat if necessary. A layer of ester
will separate and float on top of the
aqueous layer.
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h Smell the product by gently wafting
the odour towards your nose with
your hand – do not put your nose
near the top of the tube!
i Repeat this procedure for up to
three more different esters.
Compare the odours of the different
esters prepared by your group and by
other groups. Write word equations
for each reaction, and (for advanced
students) chemical equations using
structural formulae.
For solid acids, the procedures in
steps 1 and 2 need to be changed:
j Add 1 cm3 of methanol (or other
alcohol) to the sulfuric acid in the
specimen tube.
k Weigh out 0.2 g of benzoic acid (or
another solid acid, such as salicylic
(2-hydroxybenzoic) acid (Harmful –
refer to CLEAPSS Hazcard 52) and
add it to the tube. Then proceed as
above. Yields from solid acids are not
as great, but odours are detectable
and distinctive.
Teaching notes
This method is an updated version
of the traditional test-tube scale
approach to ester preparation,
which minimises the risks involved
in handling the reagents involved.
For further information about this
method of ester preparation, consult
CLEAPSS Guidance Leaflet PS67-07
‘Making esters’.
This method is only suitable
for preparing small samples for
characterisation by odour. Advanced
students could scale up the
quantities using larger test-tubes,
but this would still not give sufficient
product for isolation, characterisation
by boiling point, or calculation of
percentage yield.
Do NOT be tempted to use butanoic
(butryric) acid, because of its very
unpleasant odour (of rancid butter).
Further information
For a broad review of esters, and
interesting details of their odours and
some uses, go to: http://en.wikipedia.
org/wiki/Esters
Another site which looks extensively
at the odours and uses of esters
in flavours and perfumes is: www.
hartnell.cc.ca.us/faculty/shovde/
chem12b/esters.htm
And for information from a
manufacturer of an amazingly
wide range of esters for uses
from flavourings and perfumes to
lubricants and paints, go to:
www.esterchem.co.uk/index.htm
63
Physics
The science of matter and its motion, as
well as space and time. Concepts such
as force, energy, mass and charge, and
learning to understand how the world
around us behaves.
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Introduction
Practical work in physics is important in showing things to
learners, as well as giving them an experience or feeling
of a phenomenon, particularly an abstract one such as
momentum. Experiments can sharpen students’ powers
of observation, stimulate questions, and help develop
new understanding and vocabulary. Practical work
plays a particularly important role in developing pupils’
understanding of the physical world around them. Everyone
remembers a number of dramatic practical activities from
school – often demonstrations or activities with unexpected
outcomes. These vivid memories of dramatic events can
help students to retain scientific knowledge.
Secondary physics experiments:
Bolt from the blue:
Timing a 100 m run accurately
Feeling the pressure:
Investigating the effects of atmospheric pressure
Power from the Sun:
What affects the output of a solar panel?
Does the Earth move?
Photographing the night sky
Kicking up a force:
Investigating the force used to kick a football
Making sparks:
Demonstrating the ionising effects of alpha radiation
“Practical work is doing
things with different types
of materials”
Teacher response to SCORE questionnaire
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Bolt from the blue:
Timing a 100 m run accurately
Introduction
This is an exploration of issues of measurement, such as precision, range of
values, uncertainty or ‘error’, repeat measurements and mean values.
Apparatus and materials
For each student or student group:
• Stopwatch or stopclock
• String
• Statistics board (see note 1)
• Masses (50 g), 5 or 6
• Cones/Track markers, 10 (optional)
• Video camera (optional)
• Tape measure, long (at least 10 m)
(optional)
Technical notes and safety
1 A statistics board is made from a
piece of wooden board about 0.5 m
square. 10 slotted channels are glued
to it and metal (or other suitable
material) discs are cut so that they
fit into the channels. The board is
supported vertically. Assign values
to each channel. Students drop in a
disc for the value they achieve. The
distribution of results grows as results
are added.
2 If working outside, students must
be appropriately supervised.
3 If a trolley is used in the lab, ensure
that the trolley cannot land on
anyone’s feet or legs.
Procedure
a One student runs a distance of
100 metres. You, and other students,
all independently time the run.
b Compare all of the measurements.
What is their range (the difference
between the highest and the
lowest values)?
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c What is the mean of all the
measurements? A mean is a kind
of average. Work this out by adding
them all together and then dividing
by the number of measurements.
d Did everybody make
measurements with the same
precision? For example, did
everybody make measurements
using tenths of seconds (0.1 second
is a tenth of a second) or hundredths
of seconds (0.01 seconds is a
hundredth of a second).
e How certain can you be about
the actual time taken for the run?
You can’t be perfectly certain!
There must be some uncertainty
in the measurements. The mean
measurement could be 14.8
seconds. Perhaps you think that the
‘true’ time for the run is in between
14.6 seconds and 15.0 seconds.
Then you can say that the uncertainty
is ± 0.2 seconds.
Teaching notes
The times can be collated as lists
of numbers or, using a computer,
as bar charts, or using a statistics
board. Bar charts enable students
to understand range, mean and
error visually.
Statistical treatment plays a very
important part in science. In advanced
experiments students are expected to
treat errors with some statistical care.
In kinetic theory the steady pressure of
a gas is recognised as an average of
innumerable individual bombardments.
Statistical methods are used to
delve into details of molecular speeds
or sizes. In atomic physics statistical
views are of prime importance. So
you might well make a gentle start
now by showing how scientists look
at a number of measurements of the
same thing.
It is worth pointing out that there is
such a thing as too much precision
in a quoted value. A student who
uses a stopwatch and gives a time
of 14.77 seconds is crediting the
timing process with more precision
than it has. Answers of 15 seconds
or 14.8 seconds may be acceptable
(depending on the procedure and
the stopwatch).
‘Mean’ is here used to indicate a
particular kind of average – that found
by dividing the sum of values by the
sample size.
In more advanced work, uncertainty
is conventionally called ‘error’. Here,
the word uncertainty more clearly
describes the concept. You could
repeat the activity for a different
motion, such as for a trolley pulled
across a metre distance on a table,
or the fall of a mass.
Again, all students should measure
the time for the same motion. Range,
mean, precision and uncertainty
can be compared with those for the
student’s 100 metre run.
You may want to compare timings
for real sports races. Information on
sporting records can be found on the
Internet. For example see Usain Bolt’s
record breaking 100 m run in the
2008 Olympics www.youtube.com/
watch?v=YFE1ctdRc88. Precision
of measurement in different sports
can be compared, and students
can discuss the idea of uncertainty
in the values.
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•
How Science Works extension:
This experiment already covers many
of the areas relating to accuracy
and reliability of data, as well as
experimental errors. The scope could
be increased further, as follows:
• Arrange pairs of students every
5 m or 10 m apart along the
100 m running path. Use some
kind of signal (e.g. dropping a raised
arm) to start both the runner and
everyone’s timers. As the runner
passes each student, they stop
their timer and record the time
taken to reach them.
Students then plot this data
graphically (distance against time).
This will make it easier for students
to understand average speed
and get a feel for the variation in
measurements. A ‘true’ velocity
can be calculated from the gradient
of the best fit line.
• If you placed cones/markers
along the track, you might be able
to video each student running, with
a stopclock also in the camera view.
This would generate a second set
of results that could be compared
numerically or graphically to the
class set. Students could comment
on whether this method improves
on the previous one.
www.practicalphysics.org
Feeling the pressure: Investigating
the effects of atmospheric pressure
Introduction
It is not always easy to get students to understand the effects of atmospheric
pressure, but here are a couple of simple activities to challenge existing ideas
and allow the development of a more sophisticated understanding of this concept.
Lesson organisation
Although these can readily be done
as demonstrations, the simplicity of
the equipment allows the activities
to be done individually or in small
groups as well.
Apparatus and materials
Each group/individual will need:
• Two straws
• A plastic cup of water
• A clear plastic bottle up to 1 litre
in size
• A clear plastic bottle up to 1 litre
in size, with a small hole on its base
• 2 well stretched balloons
• A drawing pin to make a hole in
a straw
Technical notes and safety
Each student who tries the two
straws activity should use fresh
straws and used straws should be
thrown away.
Procedure
Activity 1 – atmospheric pressure
and suction
1 Put a straw in the clear cup of
water.
2 Hold a second straw outside the
cup as shown.
3 Try sucking the water up through
the straw.
4 Now make a small hole in one of
the straws with the drawing pin about
3 cm from the top and try drinking
through it.
Suck here
Plastic bottle
Balloon
Plastic cup
Small hole
Water
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Activity 2 – balloon in a bottle
1 Place a balloon inside each bottle;
spread its neck over the top of the
bottle.
2 Try blowing up the balloon in each
case – only with the bottle with a hole
in will it work.
3 Air will exit the bottle via the small
hole in the base of the bottle. Quickly
seal the hole with your thumb and the
balloon will stay inflated.
4 By slowly allowing air to enter the
bottle, the balloon will deflate under
your command.
Teaching notes
Both activities can be run after some
discussion to encourage students
to make predictions and attempt
explanations that use the idea of a
pressure difference to explain what
happens.
Activity 1
The student will find it impossible to
drink if one of the straws is outside
the glass.
If both straws are placed in the
mouth it is difficult to maintain a
sufficiently low pressure to cause the
water to be sucked up, because air
enters the mouth through the second
straw. In order for the water to be
forced into your mouth, the pressure
outside (atmospheric pressure) needs
to be greater than the pressure inside
your mouth. This means that no
matter how you suck, a straw won’t
work if air can get into your mouth.
A similar effect is achieved by
making a small hole in a straw about
3 cm from the top and putting this
straw in the water.
Extension activities could include
exploring how many straws put
IN the water can drink be sucked
through – increasing the surface
area makes it harder.
By joining straws together find the
longest straw it is possible to drink
through.
Activity 2
Discuss why it is not possible to
blow up the balloon without the hole
in the bottle and why the balloon
stays inflated when the hole in
the bottle is covered. Encourage
students to use the idea of pressure
differences in their answers.
Putting the lid on the bottle, or tape
over the hole, can leave the balloon
inflated.
By sucking air through the hole in
the bottom of the bottle it is possible
to inflate the balloon.
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71
Power from the Sun:
What affects the output of a solar panel?
Introduction
This experiment is copyright of Gatsby Science Enhancement Programme,
and is reproduced with permission.
A solar power system for a house is not always going to give the same power
output. It will depend on the time of day, the season, the weather, and so on.
In this activity, the factors that affect the power output of a solar panel are
looked at, and may lead to an investigation of quantitative aspects of some
of these factors.
Lesson organisation
This can be done in small groups as
a qualitative activity to get a feel for
the factors that affect the output of a
solar panel, in which case the activity
may only take up part of a lesson.
If this is followed by a quantitative
investigation of one of the factors,
then this might be done in pairs and
will take longer.
The class could be organised so
that different groups each look at
a different factors in more detail,
and then report back to the whole
class. Students should be asked to
explain how their results relate to real
conditions with the Sun, and if there
is an opportunity, they could take the
panel outside and look at the effect
of tilting the panel, of partially
covering the panel or using
different kinds of filters.
Fig. 1: A solar panel connected
to an electric motor
Apparatus and materials
Each group will need:
• Solar panel unit
• Small motor unit
• Desk lamp
• Digital multimeter (or voltmeter)
• Plug-plug leads (red), 2
• Plug-plug leads (black), 2
• Metre rule
• Piece of cardboard
• Translucent sheets (e.g. tracing
paper) cut a suitable size to cover
the solar panel
• Coloured filters
• Clamp stand
V=
V
A=
Fig. 2: A solar panel connected to an
electric motor and a voltmeter
72
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Technical notes and safety
Desk lamps with metal shades can
get very hot and care needs to be
taken when moving them.
Half metre rule
Clamp stand
Lamp
v
Voltmeter
Solar panel
Procedure
1 Connect a solar panel to an
electric motor (see Fig. 1). Shine a
desk lamp on the panel so that the
motor turns.
2 Next, connect a voltmeter to the
solar panel (see Fig. 2).
The voltmeter can be used to get an
idea about the output of the solar
panel. A voltmeter does not measure
power (power = voltage x current),
but the voltage can be used to make
comparisons.
3 Explore the effects of:
• moving the lamp closer and
further away
• partially covering and uncovering
the solar panel
• tilting the panel backwards and
forwards
• putting a translucent sheet between
the lamp and the panel
• putting different coloured filters
between the lamp and the panel.
Teaching notes
In this activity, students will get
the opportunity to use a range of
investigative skills, including the
identification of different kinds of
variable, the tabulation of data and
drawing different kinds of graphs
and charts.
The activity works best if done in a
room with blackout or low light levels
as ambient light may overwhelm the
variations in light levels being observed.
Students should find that the
maximum output is given with a high
light intensity and the biggest surface
area, and with no tilt in relation to the
light source. The translucent sheet
and coloured filters reduce the
power output.
This investigation could be used as a
starting point for further investigations,
such as finding out how the voltage
across the panel is affected by the
distance of the lamp. A suitable
range of distances is from 10 to 25
cm (if using just the motor); with the
voltmeter, a suitable range of distances
would be from 10 to 50 cm. To help
students to measure the distance of
the lamp from the panel, it is helpful to
make a mark on the lamp casing level
with the centre of the light bulb.
Another factor that would be worth
investigating is the relationship between
the area of the panel exposed and the
voltage. Students could also try other
factors of their own, such as putting
glass, clear plastic sheet, white paper,
etc over the solar panel.
www.practicalphysics.org
Students should be asked to relate
their results to answer the question
‘If you were using this solar panel
outside with the Sun, what factors
would affect its power output?’ Even
on a clear day, much of the radiation
from the Sun is absorbed or scattered
as it passes through the atmosphere;
clouds will obviously reduce the
radiation still further. We can’t control
the amount of radiation coming from
the Sun, but we can tilt the panel to
make the best use of it. If a panel is
mounted horizontally, the maximum
output would be produced at noon,
when the Sun is highest in the sky.
When the Sun is low, the radiation is
spread over a larger area of the panel.
(In addition the radiation is reduced
because it travels a further distance
through the atmosphere thus leading
to greater absorption and scattering.)
At the equator, the Sun is overhead at
noon, but at other latitudes, the best
output is achieved by tilting the panel
(in the northern hemisphere, towards
the south). The optimum angle of tilt
depends on the latitude. Even better,
is to have a panel that is able to track
the position of the Sun and which can
move so that it is always perpendicular
to the radiation, though this adds
considerably to the cost of the system.
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Does the Earth move?
Photographing the night sky
Introduction
This demonstration uses a time exposure photograph to illustrate the apparent
motion of the stars.
Apparatus and materials
Tripod, or other means of holding
camera still during exposure
Camera with B (open shutter) setting.
Technical notes and safety
It is a good idea to cool down the
camera by leaving it outside for some
time before the exposure is set up, so
that no condensation forms inside the
camera.
The photograph will be more
impressive if the picture includes the
silhouette of the school building or
of well-known trees near by. Avoid
doing this at a time of month near a
full moon.
To get a B (Bulb) setting (open
shutter) on a digital camera, you
need to have your camera on manual
setting and then decrease shutter
speed. You will also need a cable
release that you can lock. Otherwise
the shutter only stays open as long
as you keep your finger down on
the button!
Have the lens aperture as wide open
as possible so that you photograph
more than just the brightest stars.
A digital camera or colour film will
show the different colours of the stars.
Use a torch when setting up the
camera and tripod. If students
do this at home, they should make
arrangements with parents or
guardians to do it in a safe place.
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Procedure
a Take a photograph of the night sky
by exposing a film in a rigidly fixed
camera for two hours or more, and
make it available for discussion.
b Encourage students who are
interested to make a photograph
themselves. To take such a
photograph, attach a simple camera
with an ordinary lens (not telephoto)
to a firm stand or tripod. Point it
towards the Pole Star, open the
shutter on a setting that keeps it
open indefinitely, (though the aperture
will usually have to be found by trial),
and leave undisturbed for the period
chosen (at least 2 hours, preferably
4 to 8 hours).
6 November at 11 p.m.
Teaching notes
1 The photograph will show arcs
of a circle as the stars appear
to revolve around the Pole Star.
The length of the arc, as a fraction
of the circumference of the circle of
which it forms a part indicates the
time for the exposure as a fraction
of 24 hours.
2 For the southern hemisphere,
there is no bright star close to the
celestial pole. The southern polestar,
Sigma Octantis, is only of the 5th
magnitude, so the direction to point
the camera will have to be judged
from other stars.
6 December at 11 p.m.
Aldebaran
Betelgeuse
Orion
Betelgeuse
Orion
Rigel
Procyon
Rigel
Sirius
A view of the stars through a window in Britain at the same time of night,
but one month apart. Can you explain why the stars appear to have moved
in this case?
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Kicking up a force:
Investigating the force used to kick a football
Introduction
This demonstration uses impact time and change of momentum of a football
to measure the force needed to kick the ball.
Apparatus and materials
• Scaler, or electronic timer,
accurate to 0.001 s
• Round football
(rugby type not suitable)
• Flexible leads, 30 cm
• Crocodile clips, 2
• Stopwatch or stop clock
• Balance (to measure mass of ball)
• Aluminium foil square,
15 cm by 15 cm
• Aluminium foil square,
7.5 cm by 7.5 cm
• Sellotape
• Plasticene
Technical notes and safety
Take care that the football is aimed so
that it does not cause damage, and
there is no danger of the timer being
knocked off the bench.
The large foil is Sellotaped to the
football: the small foil is taped to the
toe of the kicker’s foot.
Connections to the foil are made
with crocodile clips. The other ends
of the leads should be a loose fit in
the ‘timer input’ sockets so that they
will come out easily in the event of
an accident. It is sensible to have
a student holding the timer on
the bench.
Providing that the flexible leads
are arranged so that the period of
contact takes place before the ball
pulls the foil away from the crocodileclip contact, no difficulties should arise.
You should obtain consistent results.
It is possible to get a value for the
time of flight of a ball kicked with
medium force down a 10 m corridor
(or even a 5 m laboratory).
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Procedure
a Place the ball on three small lumps
of plasticene to stabilize it.
b Kick the ball in a horizontal
direction from a standing position on
a laboratory table, with only medium
force. More vigorous kicks can be
used out of doors to show the longer
time of contact.
c Find the time of contact of the ball
with the foot from the scaler or timer,
t, seconds.
d Find the mass of the ball, m kg,
using a balance.
Teaching notes
1 Measure how far the ball travels
horizontally before it hits the floor,
s, then s = vT. The time of flight, T,
can be found from the height of
the table, h = 1/2 gT2.
The acceleration due to gravity
= 10 ms-2
T2 = 2h/g
T = √2h/g.
Substituting in the equation v = s/T
gives a value for the initial velocity
of the ball.
Therefore using Ft = (mv) the force,
F, on the ball can be calculated.
Alternatively, film the flight of the ball
using a camcorder, and use frame
by frame playback mode to calculate
its speed. Multiflash photography
creates successive images at regular
time intervals on a single frame, and
further details can be found on
www.practicalphysics.org.
2 Once students have learnt about
the conservation of momentum in
a collision then a different method
can be used to calculate the force.
The football is kicked into
a cardboard box which is fixed
to roller-skates or a skateboard.
or
h
to
scaler
by multiflash
photo
s
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The box should be made massive
so that it moves slowly enough for
the time of motion to be measured
with a stopwatch. The flaps on the
box should trap the ball. All the
momentum of the ball is shared
with the box. The momentum of the
box is calculated from its mass and
velocity (= distance travelled in the
measured time). This is equal to the
initial momentum of the ball after it
is kicked. Using Ft = (mv) then the
force can be calculated if the time of
contact is measured on the scaler.
Cardboard box
Door flaps
trap the ball
www.practicalphysics.org
Making sparks: demonstrating
the ionising effects of alpha radiation
Introduction
The spark counter demonstration is a highly visible (and audible) way of
showing and counting ionisation of the air caused by alpha radiation (or a
match). It is a useful step towards understanding the Geiger-Müller tube.
Apparatus and materials
• Power supply, EHT, 0-5 kV
(with option to bypass safety
resistor)
• Spark counter
• Sealed source of radium, 5 µC
(if available)
• or sealed source of americium-241,
5 µC
• Holder for radioactive source
(e.g. forceps)
• Connecting leads
Technical notes and safety
The spark counter is a special piece
of apparatus (see image below).
It consists of a metal gauze with a
wire running underneath. Philip Harris
call it a Spark discharge apparatus.
Any kink or bend in the wire in
the counter is liable to cause a
spark discharge at that point. If that
happens the wire should be replaced.
A continuous spark (which will
very soon damage the wire) shows
the voltage is too high.
The spark counter should be dust
free. Dust around the stretched wire
can usually be blown away.
The gauze on top is connected to
the earth on the EHT supply as a
safety precaution.
Radium is a source of alpha, beta
and gamma radiation. Beta and gamma
radiations do not cause enough
ionisation of the air to start a spark.
Refer to CLEAPSS for further
guidance on managing radioactive
materials in schools.
A school EHT supply is limited to
a maximum current of 5 mA which
is regarded as safe. For use with a
spark counter, the 50 MW safety
resistor can be left in circuit so
reducing the maximum shock
current to less than 0.1 mA.
Metal gauze
Wire beneath
metal gauze
Spark discharge apparatus
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Although the school EHT supply
is safe, shocks can make the
demonstrator jump. It is therefore
wise to see that there are no bare
high voltage conductors; use female
4 mm connectors where required.
Procedure
Setting up
a Connect the positive, high voltage
terminal of the spark counter to the
positive terminal of the EHT supply
without the 50 MW safety resistor.
(The spark counter’s high voltage
terminal is joined to the wire that runs
under the gauze.)
b Connect the other terminal on the
spark counter to the negative terminal
of the power supply and connect this
terminal to earth.
–
c Turn the voltage up slowly until it is
just below the point of spontaneous
discharge. This is usually at about
4,500 V.
Carrying out
d Use forceps to hold a radioactive
source over the gauze. You should
see and hear sparks jumping between
the gauze and the high voltage wire
underneath each time an alpha
source is brought near to the counter.
e Move the source slowly away from
the gauze and note the distance at
which it stops causing sparks.
Teaching notes
1 Draw attention to the random
nature of the sparks and hence of
the radiation. By counting sparks
you are counting the number of
alpha particles emitted.
+
–
+
www.practicalphysics.org
2 You should find that the range of
the alpha particles is about 5 cm.
3 You could mention that this is alpha
radiation which is the most ionising of
the three main types of radiation.
4 The sparks are similar to those
produced by the Van de Graaff. The
alpha particles ionise the air forming
positive and negative ions. When
these ions recombine to form neutral
atoms then blue light is emitted. The
noise of the spark is due to warming
the air in the narrow region of the
avalanche current producing a sound
wave just like in a lightning strike.
5 A thin sheet of tissue paper or gold
foil held between the spark counter
and the source will show a reduced
range for the alpha particles or even
prevent them getting to the counter.
6 A version of this apparatus can be
seen in the CERN visitor centre (if
you happen to be passing). It detects
cosmic rays and makes them visible
using a 3D array of wire meshes
with high voltages between them.
The paths of rays can be seen by
the trail of sparks that they leave as
they ionise the air between the wire
meshes. This type of 3D array of
high voltage meshes is the principle
used to detect the paths of particles
produced in the collision experiments
at CERN.
7 Before you use the spark counter
showing ionisations from an alpha
source, you could use the spark
counter to count matches (as in
‘Counting matches with an
EHT supply’ available on
www.practicalphysics.org).
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Further information
General
CLEAPSS: www.cleapss.org.uk
SSERC: www.sserc.org.uk
ASE: www.ase.org.uk
ASE Upd8: www.upd8.org.uk
SciCast: www.planet-scicast.com
Field Studies Council (FSC): www.field-studies-council.org
Gatsby Science Enhancement Programme: www.sep.org.uk
Science Learning Centres: www.sciencelearningcentres.org.uk
Triple Science Support Programme: www.triplescience.org.uk
Earth Science Education Unit: www.earthscienceeducation.com
Earth Learning Idea: www.earthlearningidea.com
Primary science
ASE Primary Upd8: www.primaryupd8.org.uk
CREST STAR Investigators: www.the-ba.net/the-ba/ccaf/CRESTStarInvestigators/
Biology
Practical Biology: www.practicalbiology.org
BioEthics Education Project (BEEP): www.beep.ac.uk
Science and Plants for Schools (SAPS): www-saps.plantsci.cam.ac.uk
Survival Rivals: www.survivalrivals.org
Great Plant Hunt: www.thegreatplanthunt.org
Chemistry
Practical Chemistry: www.practicalchemistry.org
Nuffield Re:Act: www.chemistry-react.org
RSC Classic Chemistry Demonstrations:
www.rsc.org/education/teachers/learnnet/classic.htm
RSC Classic Chemistry Experiments:
www.rsc.org/education/teachers/learnnet/classic_exp.htm
RSC Microscale Chemistry:
www.rsc.org/education/teachers/learnnet/microscale.htm
RSC Video material for teachers of chemistry:
www.rsc.org/education/teachers/learnnet/videoclips.htm
Physics
Practical Physics: www.practicalphysics.org
Physics & Ethics Education Project (PEEP): www.peep.ac.uk
Teaching Advanced Physics (TAP): www.iop.org/activity/education/Teaching_
Resources/Teaching%20Advanced%20Physics/page_8325.html
Demonstrating physics – forces: www.teachers.tv/video/2505
Demonstrating physics – radioactivity: www.teachers.tv/video/27400
This booklet has been produced by
SCORE partners:
Association for Science Education
Biosciences Federation
Institute of Biology
Institute of Physics
Royal Society
Royal Society of Chemistry
Science Council
in association with:
CLEAPSS
Field Studies Council
Nuffield Curriculum Centre
The Wellcome Trust
Supported by Department for Children, Schools and Families
and The Gatsby Charitable Foundation.
Apart from any fair dealing for the purposes of research or private study,
or criticism or review, as permitted under UK Copyright Designs and Patents Act,
1988, this publication may not be reproduced, stored, or transmitted, in any form or
by any means, without prior permission in writing of the publishers, or in the case of
reprographic reproduction, only in accordance with the terms of the licences issued
by the Copyright Licensing Agency in the UK, or in accordance with the terms of
licences issued by the appropriate Reproduction Rights Organisation outside the UK.
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