Ask participants to retrieve handout 3.7, which sets out a number of these
possible misconceptions. Quickly run through the instructions on the first page of
the handout. Ask participants to work in pairs. There are 15 minutes available for
this task.
Handout 3.7
Handout 3.7
Task G Using appropriate
teaching and models to
address misconceptions
1 of 2
Here is a list of some frequent misconceptions about particles held by pupils at
about this age.
1
When a solid dissolves in water it is no longer there; its particles have
disappeared.
2
Particles exhibit the macro properties of the material. For example, the particles
expand when a material is heated; a solid melts when heated because the
particles melt; copper metal is ductile because copper atoms are ductile.
3
The particles are destroyed when a substance is burned, so it loses mass.
4
Compounds are mixtures. The elements can be mixed in any proportions. The
name isn’t systematically related to the constituent elements.
5
Reactions where gases are formed result in a loss of mass.
6
When two elements react together the atoms from the reactants are
transmuted into new atoms (of the products). The reaction is a ‘magical’
change.
Select one of these misconceptions to work on. Decide how you would plan to
overcome it in your teaching. Explain the teaching sequence, the practical work
and/or the model(s) you might use. Complete your notes on page 2 of this
handout.
Treatment of one misconception is illustrated below.
When a solid dissolves in water it is no longer there; its particles have disappeared.
Weigh samples of salt (sodium chloride) and water prior to mixing. Then mix the
two together to dissolve the salt.
Ask the question ‘what evidence do we need to show whether or not the salt has
disappeared?’ to provoke thought about reweighing the solution.
Weigh the solution to show that the mass of the salt has not been lost.
Under hygienic conditions show that the taste of the salt is still there in the solution.
Allow a group of pupils to evaporate a sample of the solution to demonstrate that
there is still salt there.
Demonstrate the bright yellow colour produced by adding a few grains of salt to a
Bunsen burner flame. Then show the flame colour produced by the salt solution,
indicating the presence of the salt.
Use small beads (or rice grains) to represent the particles in salt. Add these to a
large measuring cylinder of larger beads which represent water particles. The way
the ‘salt particles’ are able to fit between the ‘water particles’ is one possible
explanation for, although not evidence for, the way salt appears to vanish when
dissolved in water.
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| Strengthening teaching and learning of particles in Key Stage 3 science | Session 3
| Notes for tutors
© Crown copyright 2003
Circulate around the groups as they work. Use this time both to offer support and
to look for any particular suggestions to pick out in a brief report back from groups.
Additional guidance
T
If most of the participants are hesitant in their understanding of particles, focus
most on misconceptions 3, 4 and 5 on the handout, for which it is easier to
suggest teaching sequences.
You may wish to nominate a particular misconception for each group, to ensure
that all are tackled.
You may wish to demonstrate the suggested model (with beads or spheres of two
different sizes) that illustrates one possible mechanism for dissolving.
Using particle theory to understand
digestion
25 minutes
Say that:
60
•
During Key Stage 3 pupils learn about the structure of the digestive system, the
names of organs and their function, in simple terms.
•
Understanding about these aspects is generally good.
•
Understanding about how food is broken down and absorbed, and why it
needs to be broken down, is often less good.
•
The visking tubing model of the gut can confuse pupils about the process of
digestion and absorption rather than clarify; the model has limitations.
•
Task H presents an alternative approach to the standard visking tubing practical
work. Pupils have first to research information and then predict likely outcomes,
before carrying out the practical work.
| Strengthening teaching and learning of particles in Key Stage 3 science | Session 3
| Notes for tutors
© Crown copyright 2003
Additional guidance
T
You may wish to introduce this section by modelling how the subject could be
introduced in a contemporary context to a Year 8 class. Pass some bottles of
glucose-based sports drinks around to participants and ask four prompt-questions:
•
What is the main ‘energy-rich’ ingredient?
•
Does the drink supply quick or slow release energy stores?
•
How do these drinks work?
•
Can you use the idea of particle size to explain this?
Most such drinks supply glucose at an appropriate concentration to be absorbed
through the stomach wall almost immediately. This is because glucose is a small
carbohydrate molecule and does not have to be broken down into smaller
molecules before it can be absorbed into the blood. Other, more complex,
carbohydrates do require digestion before absorption and are better for longer-term
energy supply. More sophisticated sports drinks contain complex mixtures of
different-sized carbohydrate molecules, designed to match the energy requirements
of the athlete and nature of the sport.
If you wish participants to carry out the ‘Digestion – true or false?’ task you will
need to prepare sets of the cards from page 3 of handout 3.8. This task is unlikely
to be necessary for the majority of teachers.
Handout 3.8 simplifies the chemical changes slightly by referring only to glucose
as the sugar produced in the digestion of starch. This is appropriate to learning in
Year 8.
Task H
8 minutes
Show slide 3.8, which helps to summarise handout 3.8.
Slide 3.8
Alternative method of teaching digestion and absorption
Slide 3.8
Emphasising the role of particle size to improve understanding of digestion
• Find handout 3.8.
• Skim read items 1–4 on page 1 of the handout.
• Study item 5 onwards of the handout.
Ask participants to retrieve handout 3.8 and look at pages 1 and 2. This
represents the main activities from a series of lessons intended to give pupils a
better understanding of the mechanisms of digestion and absorption. Ask
participants to scan quickly through items 1 to 4, which may represent a fairly
typical start to this topic. Spend more time on item 5 onwards, which focus on the
role of molecule size within digestion.
Handout 3.8
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| Strengthening teaching and learning of particles in Key Stage 3 science | Session 3
| Notes for tutors
© Crown copyright 2003
Handout 3.8
An alternative method of
1 of 4
teaching digestion and absorption
Skim read items 1–4. Study item 5 onwards.
1
The topic can be introduced in the usual way. For example:
•
drawing a life-size body on paper (e.g. wallpaper) and adding internal
organs and labels
•
check size and position of organs with textbook
•
teach names of the parts (oesophagus, stomach, small intestine etc.) and
other key words, with careful pronunciation and other vocabulary strategies.
2
Ask pupils to think about the possible process of digestion and to suggest how
food is digested. Scaffold their answers suggesting the framework: first …, then
…, next …, etc.
3
Ask pupils to find out the role of enzymes in the digestion of food using
standard textbooks as a source of reference.
4
Use the ‘Digestion – true or false?’ cards as a card sort activity. Then take just
the true cards and sort them into an approximate sequence to represent the
process of digestion. There is more than one possible sequence. These could
be attached to appropriate places on a wall poster if one is displayed.
Faster workers could explain the mistakes in the false cards. Cards 1, 6, 9, 10,
11, 13 and 16 are the deliberately false statements.
5
Ask pupils to explain why enzymes are needed for digestion. Scaffold their
answers by giving them the root ‘Enzymes are needed in the process of
digestion because …’
Review their answers.
6
72
Once pupils are clear about their explanation, introduce the visking tubing
experiment. Get them to predict what will happen and why.
•
What do you know about the connection between glucose and starch?
•
What do you know about the action of enzymes (amylase) on starch?
•
What do you know about the visking tubing walls?
•
What do you expect to happen?
•
How will you test to show that this has happened?
7
Alternatively, you could use the ‘Predicting the digestion of starch’ diagram
labelling exercise as a group work activity.
8
Pupils can now carry out the visking tubing practical with a greater certainty of
understanding the purpose and details of the practical work and how this is a
model of digestion.
| Strengthening teaching and learning of particles in Key Stage 3 science | Session 3
| Notes for tutors
© Crown copyright 2003
Handout 3.8
2 of 4
9
It is possible for pupils to model the process of digestion on a larger scale.
A By drawing using:
to represent a water molecule;
to represent a glucose molecule (which is approximately
hexagonal in structure);
to represent a starch molecule.
B A bead model using:
a small bead to represent a water molecule;
a single poppet bead to represent a glucose molecule;
a string of poppet beads to represent a
starch molecule;
a length of net tubing (used to sell oranges)
to represent the intestine.
C A wet model using:
a length of leg from a pair of tights to
represent the intestine;
spaghetti in tomato sauce or chopped tomatoes to represent the ‘soup’ of
large and small molecules.
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| Strengthening teaching and learning of particles in Key Stage 3 science | Session 3
| Notes for tutors
© Crown copyright 2003
Handout 3.8
Digestion – true or false?
74
3 of 4
1
The food molecules that get
through the gut wall get passed
out of your body when you go to
the toilet.
9
In the stomach all the goodness
is removed from the food to
leave just waste.
2
Enzymes help break down large
food molecules into smaller
molecules.
10 Chewing protein molecules
breaks them up into small
molecules.
3
Enzymes such as amylase in
saliva start breaking down the
starch in potato as you chew it.
11 Enzymes in the human body
work best at a temperature of
87°C.
4
Many food molecules are large
and need to be broken down
into smaller molecules.
12 The food molecules that get
through the gut wall are picked
up by the blood supply and
carried round the body.
5
In the large intestine water is
extracted from the ‘soup’ to
leave a more solid waste.
13 As the mashed-up food goes
along the small intestine big
molecules of starch can get
through the intestine wall.
6
Starch molecules are much
smaller than molecules of sugars
such as glucose.
14 More digestive juices are added
to the food in the stomach.
7
The food and liquid is churned
up to make a liquid like soup.
15 Only some molecules are able to
go through the gut wall.
8
As the mashed-up food goes
along the small intestine small
molecules can get through the
intestine wall.
16 Enzymes are powerful acids that
break down other chemicals.
| Strengthening teaching and learning of particles in Key Stage 3 science | Session 3
| Notes for tutors
© Crown copyright 2003
Handout 3.8
Predicting the digestion of
starch
4 of 4
Draw arrows from each label to the correct part of the diagram
At the start
Tap water
Starch, water and amylase
(enzyme)
This will turn dark blue with
iodine
This is like the food inside
the intestine
This is like a piece of
intestine
At 37°C, like body
temperature
The small molecules can
get through the wall of the
tubing
During the experiment
This represents the blood
supply
This now contains water
and sugars
The enzyme is breaking
down the starch into
sugars
This will go brown with
Benedict’s test
This won’t change colour
with iodine
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| Strengthening teaching and learning of particles in Key Stage 3 science | Session 3
| Notes for tutors
© Crown copyright 2003