CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Learner’s Book answers
Unit 1 Respiration
Topic 1.1 The human
respiratory system
Activity: Gases in and out
1 and 3
Getting started
Respiration happens in all the cells in your body.
Respiration releases energy from food.
Respiration happens in all living things.
green
arrow
Questions
1
nose or mouth, voicebox (larynx), windpipe
(trachea), bronchus, bronchiole, air sacs
2
air sacs, bronchiole, bronchus, windpipe,
voicebox, nose or mouth
blue
arrow
Think like a scientist: Looking at lungs
1
Learners can give a basic description: they
look big, soft and pink, for example.
2
2
The lungs feel spongy, because they are full of
air sacs.
Think like a scientist: Why are air sacs
so small?
3
a
trachea
1
b
It has hard ridges on it, with softer areas
between.
The dye moving (diffusing) into the jelly is like
oxygen moving (diffusing) into the blood.
2
Learners should find that the dye diffuses
more quickly into the jelly when there are
many small holes. Some learners may be able
to relate this to surface area, and explain that
many small holes have more surface in contact
with the jelly than a few large holes.
3
Learners may or may not think this is a good
model. Accept any sensible suggestions. For
example, both the dye and oxygen move by
diffusion; the dye is a liquid, whereas oxygen
is gas; blood moves past the alveoli, but in this
experiment the jelly does not move.
c
bronchi
d
The larynx or voicebox; it makes sounds.
Topic 1.2 Gas exchange
Getting started
1
diagram C
2
In a gas, the particles are far apart.
In a gas, the particles move freely.
1
Two – one in the wall of the alveolus, and one
in the wall of the capillary.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Think like a scientist: Comparing the
carbon dioxide content of inspired air
and expired air
1
Expired air bubbles through tube B.
2
Inspired air bubbles through tube A.
3
The one that expired air bubbles through.
4
carbon dioxide
5
The limewater went cloudy first in tube B.
This is the limewater that expired air
bubbles through.
Think like a scientist: Using a model to
represent breathing movements
1
lungs = balloons; trachea = hole through the
bung; diaphragm = plunger; rib cage = syringe
2
As the plunger is pulled out, the volume of air
inside the syringe increases. This makes the
pressure decrease. As the air pressure outside
the syringe is now higher than the air pressure
inside, air moves into the syringe through the
small hole in the bung. The only place for it to
go is into the balloon, so the balloon inflates.
3
The movement of the plunger represents the
movement of the diaphragm, which causes the
pressure to reduce in the chest cavity when it
moves downwards. This draws air through the
trachea, inflating the lungs.
4
There are several points that learners could
make. For example, the ‘rib cage’ in the model
cannot move, as there is nothing to represent the
intercostal muscles. There are no ‘air sacs’ in the
balloons. There are no ‘blood capillaries’ around
the balloons.
Our results show that expired air contains
more carbon dioxide than inspired air.
Topic 1.3 Breathing
Getting started
Gas exchange is the movement of oxygen and carbon
dioxide between the air in the lungs and the blood.
It happens in the air sacs (alveoli).
The air you breathe in contains more oxygen than
the air you breathe out.
There is a small quantity of carbon dioxide in the
air you breathe in.
Questions
1
There is still quite a lot of oxygen in the air you
breathe out.
Think like a scientist: Measuring the
volume of air you can push out of
your lungs
1
This will depend on the results the
learners obtain.
2
Plans could include the following ideas.
•
The variable to be changed (the
independent variable) is the type of
musical instrument that the person plays.
•
The variable to be measured (the
dependent variable) is the volume of water
they can displace when they breathe out.
•
2
Some attempt should be made to
standardise other variables, but in
practice this is almost impossible, so the
experiment cannot really be a fair test.
2
Action
What do the
diaphragm
muscles do?
What do the
intercostal
muscles do?
Breathing
in
contract
contract
Breathing
out
relax
relax
When we breathe in, the muscles in the
diaphragm and between the ribs increase the
volume of the chest. This makes air move into
the lungs.
When we breathe out, the muscles in the
diaphragm and between the ribs decrease the
volume of the chest. This makes air move out
of the lungs.
Topic 1.4 Respiration
Getting started
To make something happen, energy has to be
transferred or transformed. Learners may be able
to suggest a range of energy changes (e.g. energy
in electricity to energy in light).
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Questions
Activity: Thinking about a thermogram
1
1
The object with the highest temperature is the
computer screen. Computers change electrical
energy to other forms (e.g. light) and some
energy is dissipated as heat.
2
About 30 °C (Note that this is the temperature
of her skin surface, which is lower than her
core temperature would be.)
3
The woman’s cells are respiring. Respiration
releases some energy as heat, raising her
temperature above the temperature of the
non-living chair.
2
3
a
The reactants are oxygen and glucose.
b
The products are carbon dioxide and water.
The air we breathe out contains less of the
reactants (because these have been used up by
respiring cells) and, therefore, less oxygen. It
contains more of the products and, therefore,
more carbon dioxide.
Topic 1.5 Blood
Getting started
Think like a scientist: Investigating
respiration in peas
Learners should recall that red blood cells are
small, round and red with a dent on the surface.
1
The condition of the peas (alive or dead).
2
size of the flasks; quantity of peas; insulation
on the flasks; temperature the flasks were
kept at; position of the thermometer bulb in
the flask
Red blood cells transport oxygen, and contain
haemoglobin that helps them to do this. They have
no nucleus, to make space for more haemoglobin.
3
temperature
4
The live, germinating peas were respiring.
In the mitochondria in their cells, oxygen
combined with glucose and released energy.
Some of this energy was dissipated as heat,
causing the temperature to rise. The dead peas
did not respire.
5
6
3
Neurones need a lot of energy to transfer
electrical signals around the body. Cheek
cells do not need much energy, as they just
stay in place, forming a lining on the inside
of the cheek. Mitochondria are where energy
is released from glucose, through aerobic
respiration, so neurones need a lot of them.
It is very unlikely that exactly the same results
would be obtained. Different peas might
respire at a different rate – they might be
different sizes, for example. Learners should
appreciate that it is not always possible in
biology experiments to standardise all the
variables that might affect the results.
Accept any suggestions that would improve
this experiment. Do not accept any that would
make it a different experiment – such as using
beans or small animals instead of peas. Good
suggestions would be: counting the number
of peas in each flask to make sure they are
the same; measuring the mass of the peas;
taking steps to make sure the insulation on
each flask is the same; taking readings on the
thermometers at more frequent intervals; using
three or more replicates of each flask and then
calculating the mean temperature change.
Questions
1
Roughly 30 to 40 times more.
2
Learners may mention differences in colour,
in shape, and the knobbly surface of the white
cell in contrast to the smooth red cell.
3
Aerobic respiration happens inside
mitochondria, in which oxygen reacts with
glucose to release energy.
4
Component Appearance Function
of blood
red blood
cell
5
round with a transport
dent in the
oxygen
middle; red;
no nucleus
white blood spherical;
cell
have a
nucleus
protect against
pathogens
plasma
transport
blood cells,
nutrients and
carbon dioxide
liquid
Red blood cells, white blood cells, dissolved
glucose, dissolved carbon dioxide.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Check your progress
d
Arrow labelled C from the blood capillary
into the air sac.
1.1 trachea, bronchus, bronchiole, alveolus
(air sac)
e
Reference to haemoglobin which combines
with oxygen in the lungs and releases it
when it reaches respiring cells.
1.2
1.3 a
A
b
B
c
C
d
B
O
wall of air sac
C
blood capillary
1.4 a
Labels to cell membrane and cytoplasm
both correct.
b
nucleus
mitochondria
a
Blood capillary correctly labelled.
c
Description of how the cell takes in a
pathogen; kills pathogen once it is inside
the cell
d
They produce antibodies which are
chemicals which attach to pathogens and
kill them OR make it easier for other white
cells to destroy them (by phagocytosis).
Wall of air sac correctly labelled.
b
Two red cells drawn inside
the capillary.
c
Arrow labelled O from the space inside
the air sac into the blood capillary.
Unit 2 Properties of materials
Topic 2.1 Dissolving
Questions
Getting started
1
Water is the solvent; sugar is the solute.
Most learners should be able to explain that an
element is made of one type of atom, a compound
is made of two or more different types of atom
which a bonded together and that a mixture is
different items, element and/or compounds that
are mixed together but not chemically bonded.
Illustrations should reflect this. Look for confusion
and misunderstandings about compounds and
mixtures especially the ideas of mixtures of
compounds such as sugar and salt.
2
When something dissolves, such as sugar in
tea, there are two substances involved. The
sugar is the solute, which dissolves in the tea,
which is the solvent. When something melts,
such as ice cream on a hot day, only one
substance is involved.
3
59 g; the mass of water is 50 g and the mass of
the salt is 9 g so together it is 59 g.
4
No; a solution is transparent and if there
are lumps and it is cloudy, it is not a solution.
The green powder was insoluble.
5
Credit any sensible suggestions such as:
Think like a scientist:
Dissolving and mass
1–3
4
4
These will depend on the practical task.
Credit an answer that explains that the solvent
and solute both have mass so that, when the
two are placed in the same beaker, none of
the mass suddenly disappears. The salt is
still present even though you cannot see the
particles because they have dissolved.
the choice of a suitable measuring cylinder
(a 10 cm3 one if using small volumes); using a
pipette to top up to the correct level; ensuring
that the meniscus is read at eye level
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Topic 2.2 Solutions and solubility
5
mass of solute dissolved in grams up the
vertical axis; a suitable scale used; bars drawn
with pencil and ruler; bars labelled; space
between bars
6
510 g
7
395 g (at 80 °C, 905 g of sugar could be
dissolved in 250 cm3 water.
So, 905 g − 510 g = 395 g)
Think like a scientist: Making different
concentrations of a solution
8
For all three salts: the higher the temperature
of the water, the greater the solubility.
1
9
73 g/100 g water
Getting started
Most learners should be able to define the terms
as: solvent such as water that a substance dissolves
in; solute as the substance that dissolves solution
as being what is produced when a solute dissolves
in a solvent. The point here is to discuss the
definitions and to look for any misunderstandings.
Learners should notice the differences in the
colour of the various solutions. They should
also notice that they have the same volume.
2
The paler the colour, the more dilute the
solution is.
3
No, because there is no colour to help you.
The salt or sugar dissolves to give a clear,
colourless solution.
4
So that you have the exact volumes you need
to make the different solutions.
5
No, it would make the task very difficult
because the small volume would be hard to
measure in such a large measuring cylinder.
The graduations on the scale would not be
clear enough.
6
There would be more food dye particles in the
most concentrated solution than in the most
dilute solution.
Think like a scientist: Solubility in water
1 and 2 Answers will depend on the solutes
provided.
3
You could find the mass of the test tube of
water and then find the mass of the solute
added by using a top pan balance. This would
be much more accurate than just counting the
number of spatulas because they will not all
carry the same quantity.
10 sodium nitrate
11 potassium nitrate
Topic 2.3 Planning a solubility
investigation
Getting started
Many learners find it difficult to understand that
their results can be reliable but not accurate.
Reliable means they get similar results every time
but accurate means as near to the true answer/
measurement as possible. The point here is to
discuss this and look for any misunderstandings.
Questions
1
The students have identified the following
variables: the volume of water used, the
temperature of the water and the number of
spatulas of the solute used.
2
If different volumes of water are used, then
they will not be able to account for the change
in the quantity of solute used. The change
could be due to the volume of water or to the
temperature; would not be able to tell which,
so the results would be of no use.
3
temperature
4
The volume of water is a control variable.
Another control variable is the size of the
spatula and how full each spatula is.
Questions
5
1
A saturated solution is one that cannot have
any more solute dissolved in it.
5
The dependent variable is the number of
spatulas of sodium chloride that will dissolve.
2
32 g
6
3
14 g
The number of spatulas of sodium chloride
that dissolves in 50 cm3 of water.
4
18 g
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Think like a scientist: Plan and carry
out an investigation into the effect of
water temperature on the amount of
sodium chloride (common salt) that will
dissolve in it
2
brown
3
blue
4
brown
5
There is one that is not permitted, substance C.
1
A line graph (which would be better as you
can read off the solubility at intermediate
temperatures) with the number of spatulas
of sodium chloride dissolved in water up the
vertical axis and the temperature along the
horizontal axis. Credit: a suitable scale; axes
labelled; points plotted accurately; pencil and
ruler used; points joined appropriately as a
line of best fit.
6
She repeats the investigation to ensure the
results are reliable.
7
Substance D is the most soluble because
it has been carried the furthest along the
chromatography paper by the solvent.
This will depend on the results; expect a
simple statement such as the higher the
temperature, the more salt dissolves. Specific
comments on the results obtained should also
be expected.
1
Ethanol was used because the green pigment is
not soluble in water but is soluble in ethanol.
2
The pigment is not pure. The evidence for
this is that the chromatogram shows there is
more than one colour present. Allow answers
that reflect the learner’s evidence from the
investigation. If they do not get separation, this
requires some discussion about why this may
have been. Sometimes the colours are very faint
and are difficult to see.
2
3
Yes, similar results should be expected.
Topic 2.4 Paper chromatography
Getting started
These could include dissolving then filtering,
evaporating off water and day to day ideas such as
using a sieve, picking out the larger items. The idea is
that the learners are reminded that chromatography
is another way of separating a mixture.
Think like a scientist: Separating the
colours in ink
1
To show where the spot of dye was to be
placed. Pencil is used because it will not
dissolve and interfere with the results.
2
It was important not to let the ink spot
go under the water so that the ink did not
dissolve into the water in the beaker.
3
It was important to remove the strip of paper
before the water level reached the end of the
strip so that the different colours in the ink
could be seen separated and the ink did not
run off the end of the paper.
4
The answer will be based on learners’ results.
They should get a separation into different
colours of pigment so the answer should state
that the pigment is not pure.
Questions
1
6
Think like a scientist: Is the green
colour in plant leaves pure?
Check your progress
2.1 A solute is a solid that dissolves in a liquid.
The liquid it dissolves into is called a solvent.
Together they make a solution.
A solid that does not dissolve in a liquid is
called insoluble.
The solubility of a solid measures how much
of a solute will dissolve.
When you measure the solubility of a solute
you must use the same volume and type of
solvent at a given temperature.
2.2 a zinc carbonate
b
colourless
c
Note: learners are asked to describe what
they would do, so they do not need to
explain the reasons for each step in the
process. The information in brackets
below does not need to be included in
their answer.
Place the mixture of copper carbonate
and iron sulfate in water and stir. (The
iron sulfate is soluble and will dissolve in
the water. The copper carbonate will not
dissolve.)
blue and yellow
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Filter the mixture. (The copper carbonate
will remain in the filter paper and the green
iron sulfate solution will pass through.)
2.3 a
b
c
The interval they used for the
temperatures was 10 °C.
d
Heat the filtrate to concentrate the
solution, which is then allowed to cool.
(You will be left with iron sulfate
crystals in the evaporating basin.)
The learners should keep the volume of
water used the same.
e
The independent variable is the
temperature of the water.
a saturated solution
f
The point at 60 °C should be identified.
g
The hotter the water, the more copper
sulfate will dissolve in it.
b
i
thrust
ii
lift
i
lift
ii
drag
The range of temperatures the learners
used was 20 °C to 80 °C.
Unit 3 Forces and energy
Topic 3.1 Forces and motion
Getting started
newton or N
2
Arrows: the length of the arrow shows the size
of the force and the direction of the arrow
shows the direction of the force.
3
True: weight or the force of gravity always acts
on all objects on Earth; there may or may not
be other forces acting on the objects.
4
a
D
b
B
c
C
Activity: Balanced or unbalanced forces?
Questions
These statements go in the balanced forces column:
1
a
Forces that are equal in size and opposite
in direction. This can be shown in an
annotated force diagram.
•
a bowling ball rolling at constant speed in a
straight line
•
a computer sitting on a desk
b
•
a helicopter going straight upwards at a
constant speed
2
3
7
c
1
i
Box drawn on a surface; upward and
downward arrows (coming from any
position); arrows of approximately
equal length; down arrow labelled
weight or gravity; up arrow labelled
contact force.
ii Same diagram as in part i; two
sideways arrows in opposite
directions; length of sideways arrows
approximately equal to each other
(length relative to vertical arrows is
not important); one sideways arrow
labelled push and the other friction.
a
orces are balanced; force from Team A is
F
equal and opposite to the force from Team B.
b
Force from Team B increases; force from
Team A decreases.
a
i
Thrust and drag are equal and opposite.
ii Lift and weight are equal and opposite.
The others go in the unbalanced forces column.
Think like a scientist: Measuring
balanced and unbalanced forces
1
Opposite directions/away from each other.
2
Forces are balanced; forces have equal sizes
and opposite directions.
3
a
The string moves toward the side with the
larger force.
b
4
Force diagram showing opposite direction
arrows of unequal lengths; forces that were
used in the investigation written on the
arrows with units, such as 8 N and 7 N.
String moves faster/moves more suddenly
(not moves further unless moves further in a
shorter time).
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
5
Forcemeters should give the same reading
when the same force is applied.
6
The forcemeters represent the teams/the
people who are pulling.
4
a
b
Topic 3.2 Speed
Getting started
1
2
Learners may not know what the speed limits
are as they do not drive, but they could be
prompted to find out. In some areas the speed
limits for cars and motorcycles are different
from the speed limits for heavier commercial
vehicles – learners could be asked why this is so.
In most countries, this will be in kilometres per
hour or km/h; learners may see this written in
some contexts as kmh, but this is scientifically
incorrect as it represents kilometres multiplied
by hours (distance × time), which is not the
correct way to calculate speed.
Questions
1
a
b
c
2
distance
speed = ________
​​
​​
time
m/s or metres per second (not sec
for seconds)
distance = speed × time
d
distance
time = ​​ ________
​​
speed
a
distance
​​
speed = ​​ ________
time
100
= ____
​​   ​​
10
= 10 m/s
b
3
a
b
c
5
distance = speed × time
= 800 × 6
= 4800 km
distance
time = ________
​​
​​
speed
7125
= _____
​​
​​
950
= 7.5 h
distance
speed = ​​ ________
​​
time
3
= __
​​   ​​
2
= 1.5 m/h
Activity: Speed, distance and time
Provide learners with distances if required. A range
of different distances should be used and a range
of different methods of travel used for calculation.
Care should be taken where distances are in
km because the unit of speed in the table is m/s.
Distances should be converted from km to m rather
than risking mistakes by converting m/s to km/h.
Learners should be asked why some methods of
travel are not suitable for certain distances in terms
of the three variables time, distance and speed. For
example, an aeroplane would not be suitable for
100 m distance as the aeroplane may need a longer
distance than 100 m to take off.
Think like a scientist: Calculating speed
The speed of the runner changes over the
100 m distance.
distance
speed = ​​ ________
​​
time
210
= ____
​​   ​​
6
= 35 m/s
distance = speed × time
= 35 × 14
= 490 m
1
The table should have columns for height in
cm or m, time to travel 1 m in s, and space for
repeat measurements. Averages and calculated
speeds can be in the same table or a separate
one. See answer for 2 below.
2
If the distance used on the horizontal surface
is 1 m then we can divide 1 m by the time
taken in seconds to obtain the speed in m/s.
3
The graph is not expected to be a straight
line, so a curve should be drawn if the points
look like they show a curve. Learners are not
to know what the relationship between height
and speed should be, so a straight line of
best fit is acceptable if the points are not very
obviously showing a curve.
4
a
b
distance
time = ________
​​
​​
speed
1925
​​
= _____
​​
35
= 55 s
8
c
distance
speed = ​​ ________
​​
time
8100
= _____
​​   ​​
9
= 900 km/h
Height of the ramp.
Time taken to travel 1 m or speed.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
5
Any two from: same object, same method
of release, same distance on the horizontal
surface, same release point on the ramp/same
distance travelled down the ramp.
6
To identify anomalous results and to calculate
an average.
7
As the height of the ramp increases, the speed
of the object increases.
Topic 3.3 Describing movement
Getting started
The intention here is to allow learners to think
about what the shape of the graph will be like, so
that you can discover their reasoning, rather than
for them all to get the correct answer. This activity
will allow you to refine your planning about how
to approach distance/time graphs.
d
e
Think like a scientist:
Walking and running
The safety precautions should include:
•
•
•
•
•
ensure the surface is not slippery
ensure there are no obstacles in the way
ensure the area for slowing down is clear
wear suitable shoes
run at a sensible, comfortable speed.
1
a
he average speed is calculated by
T
dividing the total distance in m by the
total time in s.
b
The average speed is calculated in the
same way and should be a value greater
than that in part a.
Questions
1
a, b and c
faster
distance
2
Axes should be labelled with distance in m
on the vertical axis and time in s on the
horizontal axis and a linear scale used to
include zero on both axes; lines should be
ruled and clearly labelled.
3
The line for running is steeper than the line for
walking; when running, you are moving faster,
so cover more distance in a fixed time; when
walking, you are moving slower, so cover less
distance in a fixed time.
slower
time
2
a and b
first, faster
part
stopped
distance
from home
last, slower part
time
3
a
80 m
b
distance
speed = ________
​​
​​
time
80
= ​​ ___ ​​
40
= 2 m/s
c
9
distance
speed = ________
​​
​​
time
time = 132 − 100
= 32 s
80
speed = ​​ ___ ​​
32
= 2.5 m/s
132 s
Topic 3.4 Turning forces
Getting started
This is an open-ended activity where learners
could give many types of examples, such as bottle
tops, control knobs, rotary switches, and so on.
The object is for learners to think of forces being
used to turn objects rather than the more obvious
pushing and pulling effects of forces that they may
have considered previously.
100 − 40
Questions
= 60 s or 1 minute
1
a
the turning effect of a force
b
moment = force × distance
c
N m, accept N cm
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
2
a
A
5
Comment based upon their original prediction.
b
This force is furthest from the pivot; this
force will make the object turn in the
correct direction.
6
Improvements should refer to the equipment
or the method and not how well the learner
worked. Reference can be made to specific
difficulties of their set-up, but also stopping
the pivot from moving, keeping the metre rule
aligned correctly and keeping the downward
pull on the metre rule constant.
3
4 × 0.12
= 0.48 N m
4
moment = force × distance
moment
​​
force = ________
​​
distance
5
1.8
​​
= ____
​​
0.09
= 20 N
moment caused by Zara = force × distance
= 450 × 1.5
= 675 N m
To balance, the moments on both sides must
be equal.
Topic 3.5 Pressure between solids
Getting started
Learners should be able to give examples, such as
knives, scissors, pins, and be able to link these to
cutting or pushing into other objects.
Questions
1
a
b
moment caused by Sofia = force × distance
moment caused by Sofia
distance = _____________________
​​
​​
force
675
​​
= ____
​​
500
= 1.35 m
1
2
10
There should be reference to making sure
the clamp stand supporting the metre rule is
stable; making sure the elastic band is in good
condition; not stretching the elastic band too
far; ensuring that the loops of string do not
break or come off their support.
3
x-axis labelled with distance in m; y-axis
labelled with force in N; linear scale with zero
on both axes so points cover at least half the
grid; points plotted correctly; smooth curve or
line of best fit drawn.
4
Trend description that matches the results.
The line is not theoretically straight, but if
learners have drawn a straight line, then they
can describe this. The statement should be
that as distance from the pivot increases,
the force decreases.
To make the area as large as possible,
so the pressure is as small as possible.
a
N/m2
b
N/cm2
c
N/mm2
force
pressure = _____
​​  area ​​
60
= ___
​​   ​​
0.5
= 120 N/m2
4
Total weight = 8000 N
8000
weight on each tyre = _____
​​   ​​
4
= 2000 N
Table should have distance in m in the first
column and forces in N in the following
columns, with repeats if needed. There should
be at least five distances, equally spaced.
3
i
To make the area as small as possible,
so the pressure is as large as possible.
ii
2
Think like a scientist:
Calculating moments
force
pressure = _____
​​  area ​​
force
pressure on each tyre = _____
​​ area ​​
2000
= ​​ _____ ​​
150
= 13.3 N/cm2
5
force
pressure = _____
​​  area ​​
force = pressure × area
= 40 × 0.5
= 20 N
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Think like a scientist:
Calculating pressure
a
1
A value should be given as a whole number
of cm2.
2
The value from 1 should be doubled and given
in cm2.
3
a
From the method, learners should have
a value of the person’s mass recorded in
kg, converted to weight, and given in N.
The pressure is the weight of the person
divided by the value given in 2. The
answer should be a pressure in N/cm2
b
This is the weight of the person divided by
the value given in 1. The answer should be
a pressure in N/cm2, and should be double
the answer to 3 a.
4
The pressure when standing on one foot is
greater/double because the same weight is
pressing on a smaller area / half the area.
5
A value should be given as a whole number of
cm2 that is smaller than the answer to 1.
6
Walking / running / dancing etc.
8
a
b
Draw around the person when lying
down. Then a workable method for
finding the area of the shape.
iThe pressure when lying down will
be lower.
iiThe weight or force remains the same,
but the area is larger, meaning the
pressure is smaller.
Topic 3.6 Pressure in liquids
and gasses
Getting started
Learners should recall the arrangements of
particles in liquids and gases. The common
misconception here is the particles in a liquid are
not all touching at least one other particle. If these
particles are not touching, they have drawn the
particles in a high pressure gas.
11
Questions
1
2
a
ressure increases with depth in water;
P
submarines must be very strong to
withstand this pressure / not be damaged
by the pressure.
b
Pressure increases with depth in water; the
wall needs to be stronger at the bottom than
at the top to withstand the greater pressure.
a
Pressure increases with depth / pressure is
directly proportional to depth.
b
When the depth in the liquid doubles, the
pressure in the liquid doubles.
3
C
4
a
Particles in the air inside the ball colliding
with the inside surface of the ball.
This is calculated by dividing the person’s
weight by the answer to 5. It should be a
pressure in N/cm2 and be greater than the
answer to 3 b.
7
b
5
b
More particles inside the ball, so more
collisions with the inside surface.
c
Particles move faster at higher temperature;
collisions with the inside surface have more
force and occur more frequently.
a
There are no particles to collide.
b
Particles in the air collide with the outside
of the container; there are no particles
colliding with the inside of the container;
the forces on the container are not balanced
and the force from the outside is greater.
Think like a scientist: Observing the
effects of pressure
1
The answer will depend on the prediction.
2
The diagram should show water coming out
with increasing pressure from the lower holes;
the water should be drawn in a curve from
each hole and landing further from the bottle
lower down.
3
Pressure increases with depth; water comes
out faster through the lower holes; as water
flows out, depth decreases, so the pressure at
each hole slowly decreases.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
4
The bottle should appear to be its normal
shape before; after being in the cold, the bottle
should be dented or squeezed in.
5
The pressure inside decreased.
6
Particles in air move slower at lower
temperature, so will collide less frequently
and with less force with the inside surface of
the bottle; the pressure on the outside of the
bottle remains the same; the pressure of air
in the bottle in the warm place was equal to
atmospheric pressure because the lid was off;
the pressure inside the bottle became less than
atmospheric pressure in the cold place, so
the forces on the sides of the bottle were
not balanced.
7
The bottle would be pushed outwards/become
harder; particles in air move faster at higher
temperature, so will collide more frequently
and with more force with the inside surface
of the bottle; the pressure on the outside of
the bottle remains the same; the pressure of
air in the bottle in the cold would be equal to
atmospheric pressure because the lid was off;
the pressure inside the bottle would become
greater than atmospheric pressure in the warm
place, so the forces on the sides of the bottle
would not be balanced.
Topic 3.7 Particles on the move
Getting started
1
2
Learners should be able to offer the idea that
the smell of the food spreads outwards from
the food.
Learners should suggest that the orange
mixes with the water and spreads throughout
the water.
Questions
1
2
3
a
B
b
A
Overall random movement of particles from
an area of higher concentration to an area of
lower concentration.
a
Gas; because the particles are not
touching each other.
b
12
The concentrations are the same because
there are the same number of blue
particles in the same space/volume.
c
4
a
By diffusion; particles move randomly and
spread from an area of high concentration
to an area of low concentration.
b
5
The concentration is higher in B because
there are more red particles in the same
space than in A.
Sofia is not correct; particles continue
to move randomly even though the
overall movement of the orange colour
has stopped.
A, C and D
Activity: Watching diffusion
1
The method should be written in a logical
order and be workable.
2
There should be a minimum of three drawings
depicting the start of the process where colour
has not yet begin to spread, an intermediate
stage where colour is spreading and a final
stage where colour is uniform in the water; the
colour should be less intense each time.
3
The prediction should have the idea of the
colour spreading more quickly.
Think like a scientist: The effect of
temperature on the speed of diffusion
1
The higher the temperature, the faster the
colour spreads.
2
Diffusion happens faster at higher
temperature because particles move faster.
3
The volume of water is a control variable /
makes the investigation a fair test; it would
take longer for the colour to diffuse through a
larger volume.
4
Any two from: Do each temperature
separately so that the stopwatch can be started
at the correct time; keep each beaker at a
constant temperature while diffusion
happens; repeat the experiment; use a
larger range of temperatures; use smaller
temperature intervals.
Check your progress
3.1 A and C (both required)
3.2 a
b
c
The bicycle will slow down.
The car will speed up/accelerate.
The ball will change direction/curve/move
in a circle.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
3.7 can be measured
3.3 B
3.4 Sketch graph with ‘distance run’ on the
vertical axis and time on the horizontal axis
(ignore units or scale); line sloping upward;
second part of line sloping upward with
shallower gradient.
3.5 a
Graph with distance in m on the vertical
axis, scaled from 0 to at least 550; time in
s on the horizontal axis, scaled from 0 to
at least 10; graph drawn to cover at least
half the available grid; straight line ruled
from (0, 0) to (10, 550).
distance
550
​   ​ ​​ = 55 m/s
​​ ​​ or ____
speed = ________
​​
time [ 10 ]
3.6 a
People’s feet are different lengths / 16
people may not be available / a rod is not
a fixed length.
b No special equipment is needed / one
person could measure a rod using their
own left foot.
b
must be calculated
force
moment
length
area
time
pressure
speed
3.8 a
moment = force × distance (Accept any
correct arrangement)
b Larger moment is created by increasing
the distance of the force from the pivot.
force
3.9 a
pressure = _____
​​  area ​​(Accept any correct
arrangement)
b
i
ii
B
C
3.10
A
3.11
ny two from higher temperature; higher
A
concentration; smaller/lighter particles.
Unit 4 Ecosystems
Topic 4.1 The Sonoran Desert
2
Getting started
Deserts are difficult for organisms, because there
is little water available. Learners may also say that
they are very hot, but this is not always true; there
are cold deserts (e.g. the Gobi desert) and many
deserts become very cold at night.
Cacti are plants that have very reduced leaves –
in many, the leaves have become spines. Instead
of leaves, they use their green, thick stems for
photosynthesis. This reduces the surface area of
leaf that is exposed to the air, which reduces the
loss of water vapour from the leaves. The spines
also protect the plant from grazing animals, which
would otherwise eat the plant to obtain water
as well as food. The stems store water. Learners
may also know about the root systems of cacti,
which sometimes spread very widely just below
the surface to catch rainwater almost as soon as
it falls. Roots may also go very deeply into the
ground to reach groundwater. Some species have
both types of root.
13
4
5
Activity: How a species fits into the
desert ecosystem
1–2 Answers will depend on the sources that
learners used to find information, and how
they selected the best.
Topic 4.2 Different ecosystems
Getting started
Questions
1
3
The producers use energy from the Sun to
make food by photosynthesis; this makes
energy available for all other organisms in the
food web.
The arrows represent energy, in the form of
chemical energy in food, passing from one
organism to another.
For example: Gila woodpeckers use saguaro
cacti to make nests; fruit bats pollinate
saguaro cacti.
A habitat is a place where an organism lives.
An ecosystem is a network of interactions
between living and non-living things; an
ecosystem contains many different habitats.
prickly pear cactus and brittlebrush
Sofia is correct. An ecosystem does include a place,
but it also includes all of the interactions between
the living and non-living things in that place.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Topic 4.3 Intruders in an ecosystem
4
The quantity of DDT in an animal’s body
increases at each level of the food chain,
because:
• one animal eats a lot of other animals in
its lifetime
• all the DDT stays in the animal and does
not break down.
5
Learners will differ in their views, so be
prepared to accept any relevant suggestions.
For example, the model does help to show
that one animal eats many animals, or what
happens over a long period of time, and it
does not model a complex food web.
Getting started
Learners are likely to suggest that the introduced
species ‘will take over’. Because it grows and
reproduces more quickly than the native saguaro,
there will be less light, water and space for the
saguaros to grow.
If the saguaros disappear, or are reduced in
numbers, this would reduce the numbers of other
species that depend on the saguaros, such as the
Gila woodpecker, termites, sap beetles and so on.
Questions
Questions
1
A species that has always lived in that country;
a species that ‘belongs’ in a country.
1
2
This will depend on the learner’s country.
3
Accept any sensible ideas. For example,
individuals of the species will have spread all
over the country, so it can be very difficult
to find them all and kill them. People may
become fond of the introduced species, and
not want it to be killed.
Minnow concentration is 0.50 ppm;
cormorant concentration is 26.40 ppm. The
cormorant concentration is 52.8 times greater
than the minnow concentration.
2
4
It is an invasive species.
DDT does not break down inside the
cormorant’s body, so all the DDT that the
cormorant eats in its lifetime builds up in its
body. Cormorants eat a lot of minnows, so all
the DDT from all the minnows accumulates in
its body.
5
Answers will be partly determined by learner’s
pictures in Topic 4.1. They are likely to suggest
that native plants, including the saguaro, will
not be able to grow. This will then affect other
species that rely on the saguaro.
Check your progress
4.1 a
A tree branch; the pool in
a bromeliad.
b
They get a lot of light; they are safe from
being eaten by herbivores on the ground
(Accept other correct ideas.)
c
It has a constant supply of water; it is
protected from predators.
d
Any two from:
An ecosystem is a network of interactions
between organisms and non-living parts
of their environment.
A habitat is a place where an organism lives.
An ecoystem contains many different
habitats.
Topic 4.4 Bioaccumulation
Getting started
1
A decomposer is an organism that breaks down
dead bodies or waste from animals and plants.
2
Organic substances – ones that have been
made by living organisms.
3
Substances that have not been made by living
organisms – for example: metal, glass, rock,
most plastics.
Think like a scientist: Modelling DDT in
a food chain
1–2 Answers will depend on the results of
the activity.
3
14
At each stage, there are fewer animals. So all
the red tokens from many animals go into the
body of one animal.
4.2 a
There are many different habitats in the
reef; these provide suitable habitats for
many different species.
b
It is poisonous.
c
single-celled alga → herbivorous fish →
carnivorous fish → human
d
bioaccumulation
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
e
c
The concentration of ciguatoxin is
higher in the carnivorous fish because the
concentration builds up along the food
chain/reference to biomagnification.
d
It reduced the (mean) number of visits
from 35 to 26 / by nine.
There are fewer insect visits and fewer
seeds produced; idea that seed production
follows successful pollination.
They could repeat it to check if the results
are always the same; they could time
insect visits for longer than 15 minutes
because one 15-minute period may not
be representative of what happens over a
long period of time. (Accept other good
suggestions and explanations.)
4.3 a
A species that has been moved to a
country/place/ecosystem where it
does not naturally live.
b To count visits to winged loosestrife with
and without purple loosestrife, so they
could compare the number of visits;
this was how they changed their
independent variable.
e
Unit 5 Materials and cycles on Earth
Topic 5.1 The structure of the atom
Getting started
Most learners will identify the largest cup as being
the heaviest. They cannot know this for certain.
You should follow the instructions in the teacher's
resource and, before the lesson, hide a piece of
modelling material or a stone in the middle or
smallest cup before filling them with water. Then
ask the class to predict which is the heaviest. Then
ask one learner to come and lift each cup, ask them
if they want to change their mind about which
is heaviest. Do not allow them to tell the class
directly what they found out by lifting the cups.
Challenge the class about this learner's decision. Is
this result true? Is this classmate trying to trick you?
The whole point of this exercise is to discuss the
evidence you need in order to come to a conclusion.
Questions
15
9
Ernest Rutherford discovered the proton in
1909 and the nucleus in 1911.
10 Rutherford’s model of the atom has a nucleus
but it doesn’t have any neutrons in it because
neutrons had not been proved to exist when
his model was formed.
Topic 5.2 Purity
Getting started
1
It is made of only one thing.
2
oxygen; gold; potassium
3
Elements: oxygen; gold; potassium.
Mixtures: sea water; orange juice; black
ink; soil.
Compounds: sodium chloride; copper oxide;
silver nitrate.
Questions
1
proton
2
electron
3
protons and neutrons
4
No charge; they balance each other out.
5
The individual atoms are held together
by electrostatic attraction between the
positively charge protons and the negatively
charged electrons.
6
Thompson’s model of the atom has no
nucleus, unlike the model we use today.
7
J. J. Thompson discovered the electron in
the 1890s.
8
James Chadwick proved the neutron existed
in 1932.
1
37.5%
2
90%
3
boron
4
nitrogen, nickel or hydrogen.
5
6
Salt
Percentage
sodium chloride
68.0
magnesium chloride
14.6
sodium sulfate
11.4
calcium chloride
3.1
other salts
2.9
​​
14.6
____
​​× 35 = 5.11 g
100
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Think like a scientist: Finding the mass
of salts in seawater
1–3
4
Questions
1
This will depend on their experiment.
There should be some similarity between the
results obtained and those suggested in the
Learner’s Book. If not, suggestion might be:
different seawater samples, spilling some of
the seawater or other practical issues.
Scotland: The weather is cold, there is snow
on the ground. There is no precipitation.
It is cloudy.
5
This is dependent on what they did and any
attempts they made to address these difficulties.
6
•
Wearing safety glasses.
Namibia: The weather must have very little
rain as there is only sparse vegetation. The sun
is shining as you can see shadows. There are
white clouds in the distance.
•
Care when heating in the evaporating
basin as the solution may spit.
New Zealand: The weather is wet; it is raining
heavily. The sky is cloudy and dark.
•
Care when moving the hot evaporating
basin or heating equipment.
Canada: The sky is grey with low cloud or
mist above the trees.
Republic of Ireland: There are many white
clouds in the sky but the sun is shining, you
can see it on the grass. There is a rainbow.
Think like a scientist: Reactions with
more than one product
1
These should be specific to what the learners
have done in the practical. Ensure word
equations are written on one line.
2
Look for suggestions, such as where there is
a solid and liquid formed, filtering (to obtain
the liquid) and collecting and drying (to
obtain the solid) for example silver nitrate and
sodium chloride.
Evaporating the solution; for example, in a
neutralisation reaction.
The suggestions are the important thing based
on the knowledge they have. The suggestion
does not need to be what you would do but it
needs to be discussed in class.
3
Specific suggestions for each reaction or
general suggestions, such as care with acids
and alkalis; not spilling liquids; any spills
cleared up at once; replacing bottle stoppers
as soon as possible; bottle tops placed upside
down on the work surface; any spills on the
skin washed with water; wearing safety glasses.
Bangladesh: It is very windy and the branches
of the trees are bent over in the wind. The sky
is grey.
2
So that we can use the information to build up a
picture of what is likely to happen in the future.
3
This will depend on where you live.
4
Credit any correct answers, such as Mali,
Chad, Oman, Saudi Arabia, and Yemen.
5
Credit any correct answers, such as S/SW
Australia, central Chile, the Western Cape,
SW of USA.
6
Credit any correct answers, such as Cameroon,
Democratic republic of Congo, Uganda,
Brazil, Columbia, Malaysia, Indonesia,
Thailand, Costa Rica, Cuba and Jamaica.
7
The climate in the arid zone is hot and dry all
year, whereas the climate in the tropical zone
is hot and wet all year.
8
The climate in the temperate zone has cold
winters and mild summers, whereas the
Mediterranean zone has mild winters and hot,
dry summers.
Topic 5.3 Weather and climate
Getting started
Accept any relevant words such as rain, hail, snow,
cloudy, hot, humid, monsoon, hurricane, storm;
aim for a variety of terms and use a dictionary to
help define the terms.
16
Credit answers that are correct and use the
correct vocabulary even if they do not cover
every aspect shown in the photograph. The
following answers are examples only.
Activity: Recording the weather
1
So that a comparison can be made. The
temperature tends to be higher in the middle
of the day, so if you took the temperature at 9
am and the next day at 2 pm you would not be
comparing the same thing.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
2
3
So that they are not affected by direct sunlight.
On one day it may be cloudy and the Sun not
visible, and on another day, direct sunlight on
the thermometer would affect the reading, so
you would not be comparing the same thing.
The report should reflect what learners
have found and account for temperature,
precipitation (even recorded as zero, if
appropriate) wind speed and direction, cloud
cover, humidity, visibility, and so on. The
measurements and observations should be
presented in an appropriate way.
4
The line graph should be drawn to an
appropriate scale and accurately plotted to
show the changes in temperature over the week.
Temperature should be plotted on the vertical
axis and the date along the horizontal axis.
5
In the comparisons, there are likely to be
minor differences in the temperature readings,
due mainly to where they were taken and
how accurately they can use the thermometer.
Other observations where it is a matter of
opinion, such as cloud cover, are likely to
show greater variation. Learners should
recognise the difference between accurate
measurements and the more descriptive
assessments. They should question the
method used by each group, the timing and
whether they used the same apparatus.
6
Data should be available via the internet or
local television. Comparisons are likely to
be difficult as learners do not know exactly
where the measurements or observations were
taken and they are unlikely to be measured
in the same way or at the same time. The
measurements will be the averages of many
readings taken at different sites and times. So
the differences between the learners’ data and
national data will be down to these factors
as well as the more accurate measurements
taken by professionals and the more accurate
methods for taking the measurements and the
standardisation
of observations.
Topic 5.4 Climate and ice ages
Getting started
Most learners will be able to understand that the
body has been frozen for all that time. Some may
find it difficult to believe that any part of the Earth
has been frozen for that long. The reason why
17
her body was discovered in 1977 could lead to a
discussion about rising temperatures on Earth.
Activity: Where in the World is there ice?
1
Credit any correct country or area that can be
identified by comparing a current world map
with that in the Learner’s Book.
2
The parts of the world that are covered in ice
are all either a long way from the equator or
on the top of high mountains.
Questions
1
five
2
Yes, because an ice age is when there is
permanent ice somewhere on Earth and there
is currently permanent ice at the poles and on
some mountains and glaciers.
3
An ice age is when there is some permanent ice
somewhere on the Earth. In an ice age, there
are periods when most of the Earth is frozen,
that is a glacial period.
4
No, we are in an interglacial period with
ice only at the poles, on some mountains
and glaciers.
5
Accept any glacier locations that are correct;
answers will depend on your location.
6
Learners should provide evidence, such as
marks on the rock, U-shaped valleys as opposed
to the V-shaped valley a river would make,
deposits of large boulders and other rocks.
Topic 5.5 Atmosphere and climate
Getting started
Most learners will have some idea that an ice
age was when the Earth was frozen but many
understand this to be when the whole of the Earth
was frozen. Some discussion around an ice age
being when there is some part of the Earth that is
permanently frozen will be needed. Some learners
will be aware of fossils that indicate that parts of
the Earth were very different in the past and will
be able to recall the ideas about samples from ice
cores and cores of soil from peat bogs. This is not
about a set of correct answers but a discussion to
help the teacher to learn how much the class
have understood.
Questions
1
The early atmosphere was formed from the
gases that the many volcanoes produced.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
2
3
Any two differences, such as: there was very
little oxygen in the early atmosphere, but
today about 20% is oxygen; there is very
little carbon dioxide in the atmosphere today
(about 0.04%) but the early atmosphere was
about 80% carbon dioxide; there was very
little nitrogen in the early atmosphere (2.5%)
now there is almost 80%.
There was very little oxygen in the early
atmosphere. It was not suitable for humans or
other animals because they need oxygen
to respire.
4
Fossil fuels are those that have been formed
from plants and animals that did not rot when
they died. They have carbon locked up in them.
5
Microorganisms and plants developed
over many millions of years and they used
the carbon dioxide to produce food.
The plants produced their food by the process
of photosynthesis.
6
As a control, to see how much hotter or
cooler the ones with added carbon dioxide
or water became.
5
This will depend on the results, but the
expected temperature readings would be
highest in extra carbon dioxide and lowest in
normal air. The carbon dioxide and additional
water vapour prevent the loss of thermal
energy, so the bottle retains more of the
energy from the Sun.
6
Credit any sensible suggestions including
extending it over a longer period of time;
taking more and more accurate readings, more
accurate using digital technology; using larger
containers; finding an easier way to attach the
thermometer.
Check your progress
5.1 a
There is evidence that the oxygen levels
increased because there are rocks where iron
has combined with oxygen to form red iron
oxide. These rocks date from about 2 billion
years ago.
7
carbon and oxygen
8
calcium, carbon and oxygen
9
Limestone is formed when the shells of dead
sea creatures fall to the bottom of the ocean
and over millions of years these layers become
compressed into rock.
10 About 3500 million years ago.
Think like a scientist:
The greenhouse effect
18
4
−
neutron
proton
electron
b
i
+
+
nucleus
−
proton
ii neutron
iii electron
iv nucleus
5.2 C
5.3 Pure diamonds are colourless and
translucent, whereas those with other
elements in them are coloured.
Answers are dependent on learners’ findings.
5.4 A→2; B→5; C→4; D→3; E→1
1
Learners should consider the likely
temperature changes during the day; what
time(s) of day to take the readings, and how
often to take them.
5.5 a
2
Credit any suitable table with correct headings
and units.
3
This depends on the learners’ results. It is
likely that the bottles containing extra
carbon dioxide and water vapour will have
higher readings.
5.6 When the ice was formed, bubbles of gas from
the atmosphere were trapped in the ice. These
can be analysed. The deeper the ice that the gas
came from, the older the sample. Scientists can
also tell from the way the ice was formed what
the weather conditions were like at that time.
10 °C
b
an ice age
c
24 °C
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CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
5.7 Any two from shrinking ice caps, retreating
glaciers, rising sea levels.
5.8 a
false
b
true
c
true
d
false
e
true
c
5.9 a
Any three from solar, wind, tidal,
hydroelectric, biofuels.
b
Earth, so that less of the thermal energy
generated on Earth is dissipated into the
atmosphere.
Global warming is the term used to
describe the fact that the average global
temperature of the Earth is increasing.
This effect is caused by an increase
in the levels of gases, such as carbon
dioxide, methane and water vapour.
These gases act like a blanket around the
The carbon contained in fossil fuels
has been locked up for millions of
years. When we burn them, this carbon
combines with the oxygen in the
atmosphere to produce more carbon
dioxide. The more carbon dioxide
there is in the atmosphere, the greater
the greenhouse effect. The greater
the greenhouse effect, the more the
temperature rises, which adds to the
problem of global warming.
5.10 An analogy is the use of one structure, idea
or process to explain another. Accept any
example from any discipline; such as the idea
of the layer of greenhouse gases acting like a
blanket around the Earth.
Unit 6 Light
Topic 6.1 Reflection
3
Diagram copied with light ray coming from
the candle to the mirror; normal drawn;
reflected ray going toward the eye; arrowheads
on light rays should be in the correct direction
(from candle to mirror and from mirror to
eye); labels should be added for: the incident
ray, the normal, the reflected ray, the angle
of incidence, the angle of reflection.
(Note – the question asks only about the
reflection of light, so an image construction
is not required).
4
Mirror drawn at the end of the incident ray
that is provided; reflected ray drawn to eye
with an arrowhead pointing away from the
mirror; mirror at such an angle that angles
of incidence and reflection are approximately
correct (normal need not be included).
Getting started
1
straight lines
2
Learners could quote evidence such as the
three cards with holes activity where light can
only be seen through the holes when they are
lined up in a straight line; some may describe
shadow formation or the fact that we cannot
see around corners; some may have used ray
boxes and describe the rays produced
from these.
Questions
19
1
C
2
Ray diagram completed correctly; the normal
should be marked; the angle of incidence
should be measured and recorded; the angle
of reflection should be equal to the angle of
incidence (as judged by eye); the reflected ray
should have an arrowhead; the rays should
meet each other and the normal at the surface
but should not cross the surface (the tolerance
for these is the thickness of the pencil line).
Activity: Mirrors and reflections
Examples of uses of mirrors include: in bathrooms
for washing and grooming; in bedrooms for
dressing; in vehicles for checking behind; in shops
for security; in makeup bags for applying makeup;
at a dentist’s for seeing inside the mouth.
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Shiny surfaces that include glass, glazed tiles,
ceramics, polished metal and painted surfaces
produce reflections. Liquid surfaces such as water
also produce reflections.
2
The surfaces that produce mirror-like reflections
are all smooth, although not always flat.
All objects that do not give out their own light
and can be seen produce reflections, otherwise we
would not be able to see them.
Questions
1
2
The table should include column headers with
units; the angle of incidence should be the first
column and the values should be in ascending
order, cover a good range and be in equal
intervals; the angles of reflection should be
equal to the angles of incidence.
a
b
3
4
5
2
3
ray of light
angle of incidence
air
glass
angle of reflection
4
As the angle of incidence increases, the angle
of reflection increases; they are directly
proportional; they are equal.
a
It is difficult to mark the exact position
of the light rays as the pencil blocks the
light and the light rays are wide; any
other difficulties that are specific to their
investigation such as the presence of
bright sunlight.
Methods for improvement linked to
difficulties,such as using a narrower
slit / narrower light ray and making the
room darker.
This is an open-ended question, but most
learners should be able to offer suggestions
such as glass (solid), water (liquid) and air
(gas); some may suggest plastic for a solid
as they may have transparent rulers, etc. but
prompt whether all plastics are transparent.
angle of refraction
refracted ray
angle of
refraction
air
water
normal
refracted
ray
angle of incidence
ray of light
Activity: Refraction effects
1
The ray diagram should resemble the answer to
question 4 from the Learner’s Book, with the
light ray going from the coin toair
the water surface
closer to vertical than in the dashed
line
in the
glass or
water
diagram. The refracted ray then goes to the eye.
The possible misconception here is that light
goes from the eye to the coin.
Getting started
20
Refraction of light is when light changes
direction because of a change in speed
(accept medium).
normal
Topic 6.2 Refraction
1
Light travels faster in air than it does
in glass.
angle of incidence
Graph with angle of incidence in degrees on
the horizontal axis and angle of reflection in
degrees on the vertical axis; both axes with
linear scales starting from zero, scaled so that
plotted points cover more than half the grid;
all points plotted correctly; line of best fit
drawn through the points.
b
a
Light travels slower in water than it
does in air.
b
Think like a scientist: Measuring angles
of incidence and reflection
1
This, again, is an open-ended question
intended to find out what learners may think
about this; their responses will help you pick
up on any misconceptions about the way that
light travels; learners are not expected to know
the term refraction at this stage.
2
The ray diagram in this case should be drawn
as if looking at the glass from above. Any
indication that the light ray is refracted more
when passing from the water than passing
from the glass only is sufficient; an image
construction is not required.
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CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
3
The pencil appears broken in two places:
at the air-oil boundary and at the oil-water
boundary. An indication that the speeds
of light in oil and in water are different is
sufficient (the speed of light in cooking oil is
slower than that in water, and some learners
may be able to work this out).
Think like a scientist: Drawing accurate
ray diagrams
1
2
The angle of incidence in air is equal to
the angle of refraction in air; the angle of
refraction in glass is equal to the angle of
incidence in glass (provided a perfectly
rectangular glass block has been used).
4
As the angle of incidence increases, the angle
of refraction increases; if the learner’s graph
has been drawn as a curve then that should be
mentioned: the angle of refraction does not
increase as much as the angle of incidence.
The angle of refraction is also zero. This is
the only angle of incidence where the angle of
refraction is equal.
Topic 6.3 Making rainbows
Getting started
1
No, rainbows can only be seen in the daytime.
2
Yes, there needs to be sunshine or sunny
intervals in order to see a rainbow.
3
Yes, there need to be water droplets of some
form – a rain shower or spray from a hosepipe,
fountain or waterfall.
4
Learners may have memorised the seven
colours (red, orange, yellow, green, blue,
indigo, violet), or be able to recall some of
them, although not necessarily in the correct
order at this stage. They may refer to the
colours they see in the picture.
Questions
1
21
C (triangular glass prism)
3
a
A
b
A
c
spectrum
4
The water drops act as prisms; dispersion
happens in the water; light is refracted going
into / coming out of water.
5
Six: red, orange, yellow, green, blue and
indigo-violet.
Think like a scientist: Making a rainbow
1
Axes correctly labelled with units; linear scales
on both axes including zero; all points plotted
correctly; smooth curve or straight line drawn.
The line is not actually straight, but a slight
curve with decreasing gradient. Learners are
not expected to know this, so if they interpret
their points as being on a straight line, that
is acceptable.
3
2
dispersion
2
3
a
his varies from five to seven, depending
T
on the individual.
b
The list should include: red, orange,
yellow, green, blue, indigo and violet.
a
red
b
violet
a
The colours get closer together; the
colours get brighter.
b
The colours get further apart; the colours
get dimmer.
4
The colours get dimmer; colours get further
apart / easier to see separately.
5
Part 1 advantage: many people can view the
spectrum at once.
Part 1 disadvantage: need dark room/some
colours may not be easy to see on the screen.
6
Strength: shows the colours of the rainbow (in
the same order); shows how a rainbow forms;
models the raindrops by using a prism.
Limitations: does not show a complete,
curved, rainbow; produces the spectrum on
the screen rather than (what appears to be)
in the air; spectrum looks much smaller than a
‘real’ rainbow.
Topic 6.4 Colours of light
Getting started
This is an open-ended activity to allow learners
to begin thinking about seeing colour. Some
colours in the picture may be described differently.
For example, some may name one of the flowers
orange while others may consider it to be red.
Learners may also refer to shades of colour.
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
c
Questions
1
red, green, blue
2
a
magenta
b
yellow
c
white
a
yellow
b
orange
a
green, white
b
green, red
c
A, B, D
3
4
6
7
8
Think like a scientist: Identify the colour
The answers will depend on the pens used and the
filters used with the light source.
Topic 6.5 Galaxies
Getting started
moon, planet, star, solar system, galaxy
1
spiral, elliptical and irregular
2
planet, star and stellar gas
3
gravity
4
They are the closest to us; other galaxies are
much further away; if other galaxies can be
seen, individual stars in them cannot easily
be distinguished.
Not all of them can be seen; new stars are
forming; stars are reaching the end of their
life; some objects that look like stars may not
be stars.
Think like a scientist: Estimating large
numbers
Topic 6.6 Rocks in space
Getting started
This is an open-ended activity, but most learners
should recall stars, planets and moons; some may
know about comets or asteroids and some may
include dust and small particles that contribute
to meteors.
1
Rocky object; part of the Solar System; smaller
than a planet; can have an irregular shape.
2
They are much smaller than planets, the Sun
or moons of planets.
3
Impacts with other asteroids/impacts
with comets.
4
Formed during the formation of the Solar
System; left over as they did not come
together to form a planet.
Activity: Making a model asteroid
1
It has an irregular shape.
2
140 000
_______
3
1–3 The answers will vary according to the
samples taken.
4
5
22
Use a similar method, but estimate the
volume of the sand using the length, width
and depth of the sand on the beach.
Questions
Questions
5
Count a larger sample; measure the
mass / volume of the large sample more
accurately with equipment reading to
more decimal places.
Different groups of scientists may study
different regions of the sky; results from
different groups are brought together for an
overall result.
This will be the time taken to count the
small sample multiplied up in proportion
to how many times more grains there are in
the large sample.
This should be correctly calculated from the
answers to questions 1, 2 and 3.
a This method is quicker.
b Not all grains may have the same
mass / volume; the mass / volume of the
large sample cannot be determined to the
accuracy of a single grain.
​​= 700 times larger.
200
a A length recorded in cm or m.
​​
b
Answer to part a × 700 (units included
with answer).
Think like a scientist: What happened
at Tunguska?
1
Hypotheses 1 and 5 will probably be chosen
as supported, and the others contradicted, or
not supported; reasons should include facts
such as an alien spacecraft crashing is not
supported because no metal parts were found.
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2
a
Hypotheses 1 and 5 will probably be
chosen as the most likely, with 5 being
even more likely than 1.
b
3
6.8 a
Hypotheses 2, 3 and 4 will probably be
chosen as most unlikely.
Arrow head on refracted ray pointing
away from the surface.
Idea that there is lack of evidence to fully
support the more likely hypotheses and lack
of evidence does not mean that the less likely
hypotheses are impossible.
Angle of incidence and angle of
refraction marked between the rays
and the normal.
b
Check your progress
Arrow head on refracted ray pointing
away from the surface.
6.2 The angle of reflection is equal to the angle
of incidence.
Angle of incidence and angle of
refraction marked between the rays
and the normal.
6.3 Ray diagram with:
reflected ray at approximately the correct
angle and labelled as reflected ray
•
arrowhead on the reflected ray pointing
away from the mirror
•
angle of incidence and angle of reflection
marked and labelled between the rays and
the normal.
6.9 White light can be split into its component
colours.
This is called dispersion and can be done with
a prism.
The range of colours is called a spectrum
The range starts with red and ends
with violet.
6.4 Diagram showing:
•
mirror labelled
•
rider/eye
•
in incident ray with an arrow pointing
toward to mirror
•
a reflected ray at approximately the
correct angle going to the rider/eye
with an arrow pointing away from
the mirror.
6.10 a red
b green
c no light/none
6.11 a red
b green
c blue
6.5 refraction
d black
6.6 •
When light passes from air into glass, the
light slows down.
•
•
6.7 F
T
T
23
Normal drawn and labelled.
Refracted ray bent away from the normal
and labelled.
6.1 flat
•
Normal drawn and labelled.
Refracted ray bent toward the normal
and labelled.
6.12 a magenta
b cyan
When light passes from air into water, the
light slows down.
When light passes from glass into air, the
light speeds up.
c yellow
d white
6.13 a
stellar dust; gas; stars; planets/solar systems
b Milky Way
2
smaller; (many have) irregular shapes
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Unit 7 Diet and growth
•
•
The foods that are best for energy are ones
that contain carbohydrate and fat; in most
countries there is a staple food that contains a
lot of starch (bread, rice, potatoes, maize and
so on) which is usually the food that provides
most energy.
Learners may know that food goes into the
alimentary canal, where is it broken down so
that is can be absorbed through the walls of
the alimentary canal and get into the blood.
The blood then transports it to our cells. They
should remember that glucose is combined
with oxygen in aerobic respiration inside
mitochondria in cells, to release energy.
Think like a scientist: Testing foods
for starch
24
1
Starch from one food might get onto another
that does not contain it, so you would get an
incorrect result.
2
It makes it easier to see the colour that is
produced after iodine solution has been added
to the food.
3
The second column shows the results, and the
third (last) column shows the conclusions.
4
Learners should find starch in some foods
from plants.
5
Learners should not find starch in foods that
come only from animals.
2
Nutrient
1
Examples of
Why the body
foods that contain needs this nutrient
a lot of this
nutrient
Protein
Getting started
fish, meat, dairy
products, eggs,
milk, beans and
peas
to make new cells
for growth and
repair; to make
haemoglobin and
antibodies
Carbohydrate
Questions
cereal grains
(and foods made
from them, such
as bread and
pasta), potatoes
and sweet foods
such as biscuits,
chocolate and
cakes
for energy
Fat
Topic 7.1 Nutrients
fatty meat, dairy
products (milk,
cheese, butter),
coconut milk, oil
used in cooking
for energy;
to make cell
membranes; to
store for long-term
energy supplies
and insulation
Food refers to the things that we eat, such as
chicken and rice. Nutrients are the substances
contained in the food that the body uses,
including protein, carbohydrate, fat, vitamins,
minerals and water.
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CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
3
Nutrient
vitamin A
4
5
Examples of
Why the body
foods that
needs this
contain a lot
nutrient
of this nutrient
green
vegetables,
carrots,
squash, fruit,
dairy products,
fish
to help the
eyes to work
well, especially
in low light;
to help white
blood cells
to destroy
pathogens
vitamin C
citrus fruits,
potatoes,
berries
to keep skin
strong and able
to heal quickly;
keeps blood
vessels and
bones healthy
vitamin D
most is made
in our skin
when sunlight
falls on it; oily
fish
helps calcium
to be absorbed
from food; for
strong bones
and teeth
calcium
dairy products, for strong
seeds and nuts bones and
teeth
iron
red meat,
dark green
vegetables,
fish, shellfish,
nuts, seeds
1
8 MJ per day
2
They may be very energetic and use up a lot
of energy playing sport. They may be growing
faster than normal.
3
They might not do much exercise, either
because they cannot or because they choose
not to.
4
The boy may do more exercise, and he is
still growing. Making new cells for growth
uses energy.
5
Girls are usually smaller. It takes less energy to
move a small mass around than a larger mass.
Girls might also be less active, on average,
than boys.
6
a
I need protein for growth.
b
There is a lot of protein in fish.
c
Starch and sugar are carbohydrates.
d
I get energy from carbohydrate and fat.
a
e should not eat too many of these,
W
because they contain a lot of sugar and
fat. Too much of these foods can cause
weight gain, and increase the risk of
developing heart disease later in life.
b
They contain fibre, which helps the
digestive system to work normally and
reduces the risk of getting constipation.
They also contain vitamin A, which helps
with good vision.
c
You can eat pulses – peas, beans, and
lentils – nuts, eggs and milk.
a
protein, fat, carbohydrate, calcium, iron
b
He needs fresh fruit and vegetables, to
provide vitamins and fibre.
c
Answers should include reference to
why too much fat in the diet is harmful
to health.
7
to make
haemoglobin
(which is
found in red
blood cells
and transports
oxygen)
If they have anaemia, not enough oxygen is
transported to cells. So they cannot release
enough energy from glucose by aerobic
respiration.
8
The main nutrients are likely to be: protein
in the lentils and cheese; fat in the cheese;
Vitamin A, Vitamin D, calcium and iron in the
lentils; Vitamin A in the colourful vegetables.
Topic 7.2 A balanced diet
Getting started
The six nutrients are: protein, fat, carbohydrate,
vitamins (A, C and D), minerals (calcium, iron)
and water.
Carbohydrate, fat and protein can provide energy.
Vitamins and minerals are needed in only
small amounts.
25
Questions
Activity: Advice on a healthy diet
1
Eat a wide variety of foods...
2
Eat plenty of fresh fruit...
3
Don’t eat too much fast food.
4
Make sure you eat enough food...
5
Don’t eat too much food containing a lot of fat.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Topic 7.3 Growth, development
and health
2
Getting started
1
Possible answers include: helps the heart to
remain healthy; good for mental health; keeps
muscles and bones strong.
2
Learners may know that smoking causes lung
cancer, so not smoking reduces the risk of
getting this disease; they may not know that
it also increases the risk for most other types
of cancer; smoking also increases the risk of
heart disease and strokes.
b
Cells grow, and then divide to produce more
cells, which in turn divide, and so on.
2
Protein is needed to make new cells. If there
is not enough protein or energy, this slows
down the growth of cells, so they don’t get big
enough to divide.
Ball-and-socket joints: hip joint and
shoulder joint.
3
the radius
4
the scapula, the humerus and the ulna
5
It has three attachments at the top – one to
the scapula and two to the humerus.
6
As the muscle contracts, it exerts a pulling
force on the tendon, which transmits the force
to the bone. If the tendon stretched, the bone
would not move.
Questions
1
a
Hinge joints: elbow joint, knee joint.
Learners may also mention the wrist; this
is actually made up of many small bones
which slide over one another, and is not a
hinge joint.
Think like a scientist: Using a model
arm to investigate how the biceps
muscle works
1
The forcemeter represents the biceps muscle.
3
About 3.6%.
2
The force decreased.
4
100 − the answer to question 3, so about 96.4%.
3
5
The more a mother smokes, the more likely it
is that her baby will have a low birthweight.
Smoking 15 or more cigarettes a day increases
the chance from 3.6% to 9% – making it 2.5
times more likely.
Learners need to remember the principle
of moments. Turning forces (moments) are
found by multiplying the force by the distance
from the pivot. As the distance from the pivot
increases, less force is needed to produce the
same moment.
4
The force increased.
5
Again, learners need to think about the
principle of moments. The clockwise moment
is produced by the force pulling upwards on
the forcemeter, and the anticlockwise moment
by the masses on the hanger.
Topic 7.4 Moving the body
Getting started
1
Learners may be able to identify the cranium
(protects the brain), ribs (heart and lungs) and
pelvic girdle (abdominal organs).
2
leg and arm bones; shoulder and hip bones;
vertebral column
Questions
1
A joint is a place where two bones meet.
clockwise moment = force on forcemeter ×
distance from pivot
anticlockwise moment = force produced by
masses on hanger (weight) × distance from pivot
So, if distances do not change, and the weight
on the hanger is greater, a greater force must
be applied to the forcemeter to balance it.
Learners could show these calculations as part
of their answer.
26
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CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
6
Position 1, closest to the pivot.
7
At this position, the muscle needs to produce
the largest force to keep the radius horizontal,
so it might be thought to be better if it was
fixed at position 4. However, if it was fixed
between position 4 and the scapula, the muscle
would need to shorten by a much greater
amount than when it is fixed between position
1 and the scapula. Muscles cannot shorten by
much, so this would not work. (Learners may
also think of what their arm would be like if
the biceps was fixed between the scapula and
the wrist – answers such as ‘you would not
be able to put your shirt on’ and ‘you might
be able to fly like a bat’ show that they are
thinking.)
7.2 a
b
33 − 12 = 21 kg
c
About 9 and 13 years (the steepest part of
the graph).
d
No. The line is still sloping upwards at
this age.
7.3 a
B and C are hinge joints.
A and D are ball-and-socket joints.
b
R and S
c
P and Q
d
antagonistic
e
Idea that muscles can only contract and
pull, not push.
So one muscle is needed to pull the bone
in one direction, and another muscle is
needed to pull it back again.
f
Calcium
g
From the bones of the animals they eat.
Check your progress
7.1 a
The weightlifter uses his muscles to lift
weights. The muscles contract to make
the weights move. This uses energy. The
muscles get the energy by breaking down
glucose in a reaction called respiration.
b
Protein is needed for making new cells.
It is needed for growth. So building strong
muscles requires protein.
c
Carbohydrate is needed for energy.
The weightlifter needs energy for his
muscles to contract, to lift the weights.
d
minerals (calcium and iron); vitamins
(A, C and D); fats; water
12 kg
Unit 8 Chemical reactions
2
An exothermic reaction is one in which more
energy is given out than is put in.
3
Thermal energy is given off.
Name a product: carbon dioxide.
4
Magnesium chloride and hydrogen.
The number of atoms in a carbon dioxide particle
is 3.
5
When the fizzing stopped.
6
Sofia’s idea was correct because in their
reactions the increase in temperature is
the same.
7
Safety glasses should be worn in case the acid
spills or spits into the eyes.
Topic 8.1 Exothermic reactions
Getting started
Name a reactant: carbon or oxygen.
One of these atoms is carbon.
Suggestions might be that it gets hot.
Questions
1
27
A fuel, oxygen and energy to start off
the reaction.
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
8
Does adding more magnesium to hydrochloric
acid increase the temperature in the reaction?
Does adding a different metal to hydrochloric
acid result in a different quantity of thermal
energy being given off ?
2
Questions
Does changing the acid used in the reaction
with magnesium result in a different quantity
of heat energy being given off ?
1
Think like a scientist: Planning and
carrying out an investigation into the
reaction between acid and magnesium
2
An endothermic reaction is one where heat
energy from the environment is taken in.
3
Inside sherbet sweets there is a mixture of dry
citric acid and sodium hydrogencarbonate.
When you suck them, these substances
dissolve in the water in your saliva, and react
together. Your mouth feels cooler because this
reaction is endothermic and takes energy in
from its surroundings.
4
The ‘fizzy feeling’ is due to carbon dioxide
being given off in the reaction.
5
When the ice melts, no new products are
formed, so this is not a chemical reaction. The
ice changes state.
6
Evaporation, when a liquid changes to a gas.
7
You feel cold because the water particles on
your skin use energy from your skin to change
to a gas and evaporate. This is an endothermic
process. You lose heat energy so you feel colder.
8
When water freezes, energy from the water
is lost to the environment, so this is an
exothermic process. The particles of water in
the liquid state have enough energy to move
past one another. When ice is formed, the
particles have lost energy and can only vibrate.
9
Self-heating cans are very expensive because
they have to be made so that the chemicals used
to warm the food or drink do not come into
contact with it. Since the can and chemicals are
only used once, this also makes it expensive.
It should also include stating the variables to be
changed, measured and kept the same.
There should be an indication of repeating
experiments and how they will ensure the results
are more reliable. An outline results table is also
needed. There should be some indication of how
the results will be presented.
1
This will be based on the results obtained.
2
There should be some indication of a
comparison and/or discussion of the
other learners’ results.
3
Credit any sensible suggestions, such as
a larger range of readings, more accurate
methods of measuring the variables or
changes in the method. Suggestions should
result from the experience of the investigation.
Topic 8.2 Endothermic reactions
Getting started
The target with the most accurate arrows is B, with
the arrows at the centre. The targets B and C have
precise arrows, they are close together. C has been
precise but not accurate, arrows close together but
not at the centre.
A is neither precise nor accurate, arrows spaced out
and not at the centre. B is accurate and precise with
arrows close together and at the centre. The point
here is to discuss what the learners think and to use
this as an opportunity to assess their understanding
rather than to mark this as right or wrong.
Think like a scientist: Carrying out an
endothermic reaction
1
Credit readings from the practical they
have done.
aSodium hydrogencarbonate and
citric acid.
b
The plan should cover all the practical issues and
safety requirements, such as an equipment list.
28
Heat energy should be transferred from the
surroundings into the reaction, so a drop in
temperature should be recorded, but credit
what the students obtain in their practical.
Sodium citrate, carbon dioxide and water.
10 The can is only able to be used once because,
once the chemicals have reacted, they cannot
produce any more heat.
11 The chemical ice pack has the advantage that
it can be used when you do not have access to
a fridge or freezer. The disadvantage is that it
is more expensive and can only be used once.
The freezer ice pack has the advantage that it is
much cheaper and can be used many times. The
disadvantage of this type of ice pack is that you
must have access to a fridge or freezer.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Think like a scientist: Endothermic or
exothermic?
1
A polystyrene cup is used rather than a glass
beaker because it is a poor conductor of heat
so the contents will lose less heat energy to
the environment.
2–3 This will depend on the reactions you supply.
4
Learners may comment on the fact that some
of the changes in temperature are very small.
They may also comment that it was not
possible to take the temperature with some
of the processes, such as the steam and a cold
surface to show condensation, or the melting
ice cubes. To decide if it was an endothermic
or exothermic process without taking the
temperature, they might suggest using their
knowledge of the changes of state and what
happens. Accept any sensible suggestions.
Topic 8.3 Reactions of metals
with oxygen
Getting started
The answers will be dependent on what each
learner can remember. Use this as an opportunity
to revise the properties and to encourage cooperation between learners.
Think like a scientist:
Heating metals in air
1
2
This will depend on what was provided.
The evidence for this should involve a
practical observation.
These should cover the use of safety glasses,
holding the metal at arm’s length, not looking
directly at the metal in case it reacts in a
similar way to magnesium.
3
Learners should remember the reaction they
have seen with sodium or potassium and water
and suggest that these metals are very reactive
and it might be dangerous.
4
Learners should know that these metals are
expensive so unlikely to be provided in class.
Questions
29
1
It is soft enough to be easily cut with a knife.
2
To protect themselves because the sodium is
very reactive and may react with the moisture
on the skin.
3
sodium + oxygen → sodium oxide
4
To prevent iron from rusting it should not be
in the presence of air and water. The iron nail
in dry air does not rust.
5
The nail in test tube 2 rusted most quickly.
The conditions in this tube are water and air.
6
The same type of nail is used in all test tubes
so that it is a fair test. The only variable that
changes is the conditions.
7
The air in test tube 3 is dried by the calcium
chloride inside absorbing moisture in the air.
8
The air in test tube 4 is kept away from the
nail by having a layer of oil across the surface
of the water. The water has also been boiled so
that any air dissolved in it has been removed.
Topic 8.4 Reactions of metals
with water
Getting started
This will depend on what metals you were able
to use, and what learners have remembered and
understood. It will also encourage discussion
and co-operation. The most reactive is likely to
be magnesium but learners should base their
discussion on the metals they have used or seen
demonstrated. This is an opportunity for you to
assess the learners' understanding.
Think like a scientist: Reactions of
metals with water
1
This will depend on which metals you provide
but it is likely to be magnesium. The evidence
for this will be the speed of reaction and/or
the number of bubbles of hydrogen given off.
2
This will depend on the metals you provide.
Accept the order based on the learners’ results.
3
Some metals that did not react in cold water
may react in hot water because the particles
in the hot water have more energy than those
in cold water. The more energy particles have,
the more they move. The more they move, the
more likely they are to collide with the metal
particles and to react.
Questions
1
sodium + water → sodium hydroxide + hydrogen
2
Wear safety glasses; the metals should be
moved using tongs not hands; only small
pieces of the metals should be used; a safety
screen should be used.
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
3
These metals are stored under oil because
they are so reactive that they react with the
moisture in the air and could do so inside the
container, causing an explosion.
3
When the magnesium is placed in the acid,
bubbles of hydrogen are given off. The
temperature increases as it is an
exothermic reaction
4
Hydrogen; you could test for this gas by using
a lighted splint. If the gas is hydrogen, it
would cause a squeaky pop as it burns.
4
zinc + nitric acid → zinc nitrate + hydrogen
5
6
Measure which one produces the greater
volume of hydrogen in a given time.
The mass of calcium and magnesium used
should be the same; the volume of water used
should be the same; the temperature of the
water used should be the same.
7
calcium + water → calcium hydroxide + hydrogen
8
The particles in the steam are able to move
freely and have a lot more energy than the
particles in the liquid water. The particles in
the steam collide with the particles on the
surface of the magnesium more frequently
than the particles in the liquid water. This
means that a reaction between steam and
magnesium is more vigorous than between
liquid water and magnesium.
9
Accept any correct answers, such as copper,
gold, silver.
Think like a scientist: An investigation
into the reaction of metals in acid
1
The metals that should not be used are
potassium, sodium and calcium. This is
because they are so reactive that there would
be an explosive and dangerous reaction.
2
The measuring cylinder that should be used
is the one that is nearest in volume to the
volume needed for the test tube or beaker.
For example, if students need 25 cm3 of acid
in a beaker then to measure this volume of
acid, it would not be sensible to use a 100 cm3
measuring cylinder, as 25 cm3 is only a small
proportion of the volume of this cylinder. It
would not be very accurate to use a 10 cm3
measuring cylinder as they would have to use
it three times and there is more opportunity
for error. It is easier to get an accurate
measure of 25 cm3 by using a 25 cm3 cylinder.
Credit an appropriate response to the use of a
10 cm3 measuring cylinder, if students choose
to use a test tube for the investigation.
10 That it does not react / is chemically inactive
3–4 These depend on the results obtained.
Topic 8.5 Reactions of metals with
dilute acids
Getting started
oxygen + sodium → sodium oxide
oxygen + magnesium → magnesium oxide
oxygen + iron → iron oxide
water + potassium → potassium hydroxide + hydrogen
water + calcium → calcium hydroxide + hydrogen
magnesium + steam → magnesium oxide + hydrogen
Questions
30
1
magnesium + sulfuric → magnesium + hydrogen
sulfate
acid
2
magnesium sulfate
Activity: Reactivity order
1
This will depend on which metals they used,
but is likely to be magnesium.
2
There should be some discussion of the fact
that gold and silver are very unreactive, but
that if silver is left in the air for a long time
it goes black, as silver oxide is formed. Gold,
however, stays shiny even if it is buried in the
ground for hundreds of years.
Check your progress
8.1 a
magnesium ribbon placed in hydrochloric
acid OR burning
b
sodium hydrogencarbonate added to
citric acid
c
decreases
d
evaporation or melting ice
e
exothermic
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
8.2 a
b
c
d
8.3 a
b
he type of fuel he uses in the
T
spirit burner.
The volume of water used and the time
he heats it for.
He must take the temperature of the water
before and after he heats it.
He must do this for each of the fuels he
uses. The fuel that produces the largest
rise in temperature is the one that gives
out the most energy.
Credit comments about handling hot
equipment with care. Credit wearing
safety glasses.
carbon + oxygen → carbon dioxide
b
The temperature would increase by
about 5 °C.
c
Zara’s results, final column from top to
bottom: 1, 2, 3, 4.
Arun’s results, final column from top to
bottom: 1, 1, 3, 4
d
sodium
sodium
hydrochloric
+
→ chloride + hydrogen
hydroxide
acid
Mass of calcium Mean temperature
added in g
change in °C
e
magnesium + oxygen → magnesium oxide
d potassium + water → potassium + hydrogen
hydroxide
8.4 aThe more calcium you add, the greater
the increase in temperature.
1
1
2
1.5
3
3
4
4
iMass of calcium added in g.
c
iiTemperature increase in oC.
f
They would not be able to use these
results because the volume of water used
will affect the temperature increase.
Unit 9 Magnetism
Topic 9.1 Magnetic fields
Getting started
Learners should be able to recall some examples such as fridge magnets, holding cupboard doors closed,
holding paperclips or pins and in some toys.
Questions
1
2
The area around a magnet where the effects of the magnet can be detected.
Magnet A is stronger than magnet B.
3
S
4
N
a
b S
N
31
S
S
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Activity: Showing a magnetic
field pattern
1
2
3
a
At the poles.
b
The iron filings are clustered together
more at the poles (not ‘there are more iron
filings at the poles’, unless the idea is more
per unit area).
a
no
b
Both poles have equal strength; both poles
attract the same number of iron filings.
Some of them are piled up in vertical lines;
they are attached end to end.
Questions
1
(magnetic) compass
2
North, because the pole of the Earth’s
magnetic field close to geographic north is a
south pole; opposite poles attract.
3
The movement in that time will be so small it
can be ignored.
4
a
core
b
iron
5
a
Think like a scientist: Detecting a
magnetic field
1
Average value of d correctly worked out from
their results.
2
The stronger the magnetic field, the larger the
value of d.
3
The strength of both poles of the same
magnet is the same.
4
a
To reduce friction; make it easier for
the paperclip to slide; so the force on
the paperclip is not having to pull
against friction.
b
5
To be easier to pull (than a large
paperclip); to detect the magnetic field as
far from the magnet as possible.
Use something that does not have to
slide / is not affected by friction (so much), such
as a steel ball that can roll; another method,
such as hanging a paper clip on a string and
seeing when it starts to move/move a magnetic
compass closer until it starts to deflect.
Topic 9.2 The Earth as a
giant magnet
b
Think like a scientist: Detecting the
Earth’s magnetic field
1
To show that the direction it will point is
independent of objects in the room or position
in the room.
2
a
north
b
The Earth’s magnetic field has the south
pole closer to geographic north.
3
Getting started
1
2
32
a
Learners will refer to the pointed end or
the end with the hole depending on how
they magnetised their needle.
b
Learners should recall the north and south
poles of the Earth, but they do not need to
refer to geographic poles at this stage.
Learners should understand the idea of
navigation, although this can be expressed in
different ways.
A magnetic compass will point along the
direction of the lines; the needle will point
towards/close to geographic north.
4
The end of the needle that pointed
towards north was a north pole.
a–c Learners deduce how the needle was
magnetised in terms of the pole that
was used to stroke the needle and the
direction; they link this to the direction
their needle pointed.
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
5
b
Too fragile; easily damaged; difficult to carry;
difficult to store.
Topic 9.3 Electromagnets
Getting started
This is an open-ended activity, but learners may
suggest applications that involve lifting objects and
then dropping them again.
Questions
1
iron and steel
2
Magnetic means to be attracted to a magnet.
Magnetised means turned into a magnet.
3
An electromagnet works using electricity / flow
of current, and a permanent magnet does
not need electricity; an electromagnet can be
switched on and off, but a permanent magnet
works all the time.
4
5
Diagram showing wire coiled around a nail,
with either end of the wire connected to a
switch and a cell, which are also connected;
circuit symbols should be used for the switch
and cell.
a
xamples: lifting scrap metal, toaster,
E
controlling a fire door, electric bell.
b
Reason for each that includes the idea
of the magnet being switched on or off
as part of the function, e.g. scrap iron
and steel can be lifted using the magnet
and then dropped again as the magnet is
switched off.
Topic 9.4 Investigating
electromagnets
Getting started
These are open-ended questions, where learners
may express some different ideas, but the
electromagnet used for scrap metal will be stronger
than the one in a toaster; that used to hold open
a door will be stronger than that in a bell (it may
also be switched on for longer times).
Questions
1
More force is needed to lift the metal than to
hold the toast down.
2
Current in the coil; number of turns in the
coil; the material of the core.
3
C
4
To make an electromagnet stronger,
the current can be increased; stronger
electromagnets will have a higher current.
Think like a scientist: Investigating
electromagnet strength
1
The table should have columns headed
Number of turns and Number of paperclips.
The number of turns should be in the first
column and in ascending order.
The number of paperclips should have
columns for repeats.
Activity: Making an electromagnet
33
It would change to be the opposite pole;
reversing the cell will reverse the current;
the magnetic field will be reversed when
the current is reversed.
1
So that current does not flow through the
nail; the nail is a conductor.
2
Averages correctly calculated (can be a column
in the results table).
2
The ends of the nail are the poles; the
magnetic field around a magnet is strongest at
the poles; the magnetic field is weakest beside
the middle of a magnet.
3
Graph with axes correctly labelled, with linear
scale on both axes, scaled so points cover at
least half the grid in both directions; all points
plotted correctly; line of best fit drawn.
3
a
Either: bring a magnetic compass close to
the end; if the compass points towards the
end of the nail, it is south; if the compass
points way from the end of the nail, it
is north.
Or: bring the north pole of a bar magnet
to the end of the nail; if they attract, it is
south; if they repel, it is north.
4
As the number of turns increases, the number
of paperclips that can be lifted increases.
5
The table should have columns headed
Material of core and Number of paperclips;
number of paperclips should have columns
for repeats.
6
Averages correctly calculated (can be a column
in the results table).
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
7
Bar chart with axes correctly labelled; linear
scale on vertical axis, scaled so bars cover at
least half the grid in both directions; all bars
to correct height; bars not touching.
8
Comment on the best material and the worst;
comments on any intermediate results.
9
In Part 1, the number of turns is a continuous
variable (you can have any fraction of a turn);
the material in the core is a discontinuous
variable / discrete variable / variable with no
intermediate values.
10 Line graph because current is a
continuous variable.
b
S
S
•
Lines curving outward from the poles.
•
Arrows on lines pointing to S.
•
Lines not touching or crossing
each other.
9.4
N
11 Graph drawn according to answer in question
10; graph with axes correctly labelled; linear
scale on both axes, scaled so points cover at
least half the grid in both directions; all points
plotted correctly; line of best fit drawn.
12 Comment that links their prediction with the
trend shown in the graph.
Check your progress
9.1 B
S
9.2 N → S
•
Lines curving outward from the poles and
going around the Earth top to bottom
(ignore magnetic poles at same position as
geographic poles).
•
Arrows on lines pointing from geographic
south to geographic north.
•
Lines not touching or crossing each other
9.3 a
9.5 C
34
•
Lines connecting the poles, may curve
outward above and below the
centre line.
•
Arrows on lines all pointing N to S.
•
Lines not touching or crossing
each other.
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CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
9.6 a
b
Diagram to include:
•
9.7 a
b
35
iii
electromagnet
•
cell or power supply (does not need to
be labelled if conventional circuit
symbol used)
•
switch (does not need to be labelled if
conventional circuit symbol used)
•
coil
•
core, labelled as iron.
it will increase /double
i
the current
ii
number of paperclips held / strength
of the electromagnet
•line sloping upward
(ignore curve)
c
starting at origin
i
c urrent in the coil; number of turns in
the coil
ii
D
Science skills
Questions
1
33
2
It does not fit the pattern. It is much larger
than the other results for a distance of 40 cm.
3
Means are 28.0, 18.5, 13.0 and 9.3 for distances
of 20, 40, 60 and 80 cm.
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© Cambridge University Press 2021