CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
Learner’s Book
answers
Unit 1 Photosynthesis and the carbon cycle
Topic 1.1 Photosynthesis
Getting started
Learners should see that the plant that has light is
taller and greener than the one kept in the dark.
They may also see that leaves of the plant in the
light are broader and more numerous, and the stems
are thicker. Learners may remember that plants
make food by photosynthesis, and cannot do this
in the dark, so they do not have enough ‘food’ to
be able to grow well. They may also know that
chlorophyll is what makes plants look green, and
that this is used to absorb energy from light. With
no light, the plant does not make chlorophyll.
Think like a scientist: Investigating
how light intensity affects the rate of
photosynthesis
1
This will depend on the results that learners
obtain. They are likely to find that the mean
number of bubbles is greatest when the lamp
is closest to the test tube.
2
Check that:
• the axes are the right way round, with
distance of lamp on the x-axis and mean
number of bubbles on the y-axis
• both axes are fully labelled, including units
• there are good scales on both axes
• the points are plotted neatly as small
crosses, in exactly the right places
• a neat line has been drawn; this could be a
best fit line, or learners could use a ruler to
join each point to the next.
3
decreases
4
increases
Questions
1
carbon dioxide and water
2
glucose and oxygen
3
Photosynthesis transfers energy from sunlight
into chemical energy in glucose. The plant
can use the glucose to make other substances.
When the grasshopper eats grass, it takes in
some of this energy. The lizard gets some of
the energy when it eats the grasshopper.
4
Plants release oxygen into the air when they
photosynthesise. Animals such as lizards need
oxygen for respiration.
Activity: Words beginning with photoEasy words include: photograph, photography,
photographer, photographing, photocopier,
photocopying and photocopy. A few learners may
also know photostat and photogenic. Other less
likely words for them to think of include photon,
photophobia, photocell and photofinish.
Think like a scientist: Collecting the gas
produced in photosynthesis
1
1
So that the gas could be collected over water.
2
So that the water plant could get energy for
photosynthesis.
Activity: Photosynthesis and respiration
Similarities: They are both chemical reactions.
They both happen inside cells. They both involve
energy changes (energy transfers). They both
involve glucose, oxygen, carbon dioxide and water.
Differences: Respiration happens in all living cells,
but photosynthesis only happens in some plant cells.
(Some learners may also know that photosynthesis
can happen in the cytoplasm in bacterial cells, but
this knowledge is not expected at this level.)
Respiration happens in cytoplasm and mitochondria,
but photosynthesis happens in chloroplasts.
Photosynthesis needs sunlight, but respiration
does not.
The reactants in respiration are the products in
photosynthesis, and vice versa.
In photosynthesis, energy from sunlight is
transferred to chemical energy in glucose.
In respiration, energy in glucose is released for the
cell to use.
Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
Topic 1.2 More about
photosynthesis
Getting started
1
in the green parts/in the leaves and stem
2
because they contain chlorophyll
3
because they are not green/do not receive light
Think like a scientist: Planning an
investigation into the effect of
fertilisers on plant growth
1
The hypothesis should state a predicted effect
that changing one variable has on another
variable. For example:
The more fertiliser the duckweed plants have,
the faster they will grow.
There are many other possible hypotheses.
Check that the hypothesis is genuinely testable
by experiment.
2
Answers will depend on the hypothesis being
tested. It is advisable to have at least five
different values of the variable.
3
Learners are likely to suggest counting the
number of leaves. They could either decide to
count each set of duckweed just once, after a
set period of time, or they could count each
one at regular intervals such as every two days.
4
This will depend on which variables are being
changed; any other variables that could affect
the rate of growth, such as light intensity and
temperature, should be kept the same.
5
This will depend on the learner’s experiment.
They are likely to need Petri dishes, some
duckweed plants, some fertiliser and a way of
measuring it, and a timer.
Questions
1
The carbon dioxide particles have kinetic energy.
They are in constant, random motion. By chance,
some of them will go into the leaf through the
stomata. Some will also come out. But, overall,
more will go in than out because there are more
of them outside the leaf than inside it.
2
Some of the oxygen diffuses out of the leaf.
Some of the oxygen is used in respiration.
3
Plants get their protein by using the
carbohydrates they make in photosynthesis
and adding nitrogen to them to make proteins.
Animals get their protein by feeding on plants
and/or other animals.
4
Nitrate and magnesium are both needed for
making chlorophyll, so a shortage of either
of them makes leaves go yellow. Nitrate is
also needed for making proteins, but without
magnesium the plant cannot photosynthesise,
so it has fewer carbohydrates to make proteins
from. A lack of either nitrate or magnesium
reduces growth.
Think like a scientist: Testing a leaf for
starch
1
a
b
2
This makes it easier to see the colour change
when iodine solution is added.
Starch is stored in the chloroplasts.
Boiling breaks down the cell membranes,
so the iodine can reach the starch.
6
There are few risks in this experiment.
Fertiliser should be handled with care, as it
would not be good for it to be ingested. Clean
up any spills quickly.
3
Most learners will get a positive test result,
showing that the leaf does contain starch. This
was produced from the glucose that was made
by photosynthesis in the chloroplasts.
7
The predictions should match the hypothesis.
4
Only the green parts contained starch. The
white parts have no chlorophyll, which is
needed to absorb energy from sunlight and
without which photosynthesis cannot happen.
Answers to questions 1 and 2 in part 2 will vary
from learner to learner.
Activity: Which surface of a leaf has
most stomata?
Learners should see more bubbles emerging from
the lower surface of the leaf because this is where
most stomata are.
2
The bubbles contain air. They are likely to
contain a lot of oxygen if the leaf has been
photosynthesising.
The warm water makes the gases inside the air
spaces in the leaf expand, which makes them come
out of the leaf.
Topic 1.3 The carbon cycle
Getting started
In carbon dioxide in the air, the carbon atom is part
of a compound; in photosynthesis it becomes part
of a glucose molecule, but is still a carbon atom.
Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
Tube F: Plant photosynthesises and respires,
but photosynthesises more than it respires,
and therefore uses up carbon dioxide.
Maggots respire, giving out carbon dioxide.
The two are likely to balance out.
Questions
1
a
b
2
3
The food chain should have a correct
sequence of organisms, with one plant
and three animals. Arrows should go in
the correct direction. For example:
fig tree → wasp → spider → lizard.
Yes, the arrows could also indicate how
carbon atoms are transferred. Carbon
is contained in the food that animals
eat, in the form of compounds such as
carbohydrates and proteins.
Proteins, carbohydrates and fats. Learners
could also suggest particular compounds, such
as haemoglobin. (Note that animals do not
contain starch.)
3
There would be no (or very little) combustion
of fossil fuels.
4
They take a very long time to form. We are
using them up much faster than they are being
replenished.
6
To make sure that having a platform in place
did not cause the differences between the
results in the different tubes.
Activity: Modelling the carbon cycle
1
No, in the real carbon cycle only some carbon
atoms will move at any one point in time.
Learners could suggest having only one or two
atoms moving on each occasion.
2
Learners should find that stopping
combustion results in fewer carbon atoms
ending up in the air.
Topic 1.4 Climate change
Questions
A 3; B 1; C 3; D2
Think like a scientist: How do plants
and animals affect carbon dioxide
concentration?
Questions
1
An asteroid is a rock, smaller than a planet,
which orbits the Sun.
1
Learners will probably find these results:
Tube A: yellow, high carbon dioxide
Tube B: purple, no carbon dioxide
Tube C: yellow, high carbon dioxide
Tube D: yellow, high carbon dioxide
Tube E: yellow, high carbon dioxide
Tube F: red, some carbon dioxide
2
2
Organisms were respiring in all the tubes.
It produced a lot of heat, which killed plants
and animals close to the collision site.
It produced a huge tsunami, which killed
plants and animals on land that were swamped
by sea water.
It sent dust high into the atmosphere, so plants
died because they could not photosynthesise.
Animals then died because there was no food
for them to eat.
3
Plants were photosynthesising in tubes B and F.
3
1.3 °C
4
a
b
4
The temperature fell by 0.3 °C between 1880 and
1910. It rose by 1.6 °C between 1910 and 2016.
5
5
Tube A: No photosynthesis because no light;
plant respires, giving out carbon dioxide.
Tube B: Plant photosynthesises and respires,
but photosynthesises more than it respires;
carbon dioxide is used up.
Tube C: Maggots respire, giving out carbon
dioxide.
Tube D: Maggots respire, giving out carbon
dioxide.
Tube E: No photosynthesis because no light;
plant respires, giving out carbon dioxide.
Maggots respire, giving out carbon dioxide.
Multiply the number of years until the end of
the century by 3 mm.
6
As the mean global temperature increases,
more land ice melts and adds extra water to
the oceans. Also, higher temperatures cause
sea water to expand.
Carbon dioxide would be used up in tube B.
Carbon dioxide would be given out in
tubes A, C, D and E.
Think like a scientist: How do rising
temperatures affect sea level?
1
Learners should find that melting ice on
land and increasing water temperature both
increase the water level. Melting ice in the sea
does not increase the water level.
2
They indicate how sea level is expected to rise.
Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
Activity: The carbon cycle and
climate change
Respiration and combustion increase the level of
carbon dioxide in the atmosphere. Photosynthesis
decreases it.
Learners could suggest:
• Plant more trees, because they will
photosynthesise and take carbon dioxide out of
the air.
• Stop deforestation (same reason).
• Stop burning fossil fuels, to reduce combustion.
• Stop using so much energy, so that we do not
need to use as much fuel.
Learners may also be aware of other issues not
covered here, such as eating less meat (because
production and transport of meat uses a lot of
energy and produces a lot of carbon dioxide) or
reducing air travel.
Check your progress
1.1 a
b
c
d
e
carbon dioxide
oxygen
soil
chlorophyll
stomata
1.2 a
b
the type of seaweed
Any three from: the temperature;
the light intensity; the size of the
piece of seaweed; the time for which
the apparatus is left.
the volume of gas collected (after a set
period of time).
c
1.3 a
b
c
The wheat plants use the nitrate to make
proteins. The proteins can be used to
make new cells, some of which will be
used to produce the grains.
d In a different place, there might be a
different concentration of nitrate in the
soil before the fertiliser is added. There
might be a lack of other minerals in the
soil. The soil might be better or worse
at holding water. There might be more
shade in one place than another. The
temperature might be different.
e Magnesium is needed for making
chlorophyll.
1.4 a i D
ii B
iii A
iv C
b i 3
ii 2
iii 1
c glucose, starch, carbohydrate, protein,
fat, cellulose or chlorophyll – allow any
other correct organic compound.
1.5 a
4 tonnes per hectare
Adding more than 60 kg per ha gives
only a very small increase in yield. It is
likely that the cost of the extra fertiliser
would outweigh the small increase in
income from selling the grain.
Sea level will rise. There will be more
extreme weather events, such as
typhoons and hurricanes.
b iMany species of organisms are
completely destroyed.
ii Look for the idea of long-term
reduction in photosynthesis
because of dust thrown up into the
atmosphere, which reduces light
penetration.
This in turn reduces food for
animals.
Other reasons are the immediate
results of the impact, including
the heat and pressure wave in the
vicinity of the impact, and a
massive tsunami.
Unit 2 Properties of materials
Topic 2.1 Atomic structure and
the Periodic Table
Getting started
Answers will depend on what learners can recall.
You should use this as a form of assessment
for learning. Learners should manage to name
electrons, neutrons, protons and the nucleus. Some
4
may be able to give facts such as the charges on the
particles: protons – positive, neutrons – no charge
and electrons – negative. They may be able to
recall the relative masses of the particles: protons
and neutrons having more mass than electrons.
They may be able to recall the arrangement of the
particles as in the Rutherford model.
Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
Questions
9
1
6
2
4
10 Melting points increase as you go down
the group.
3
6
4
Diagram should have three shells, with
electrons structure 2:8:2, and a nucleus with
12p and 12n in the centre.
5
Aluminium
6
Diagram should have two shells, with electrons
structure 2,7, and a nucleus with 9p and 10n in
the centre.
7
The nucleus is made up of protons and
neutrons in both models. In the Rutherford
model, the electrons are all shown in one cloud
around the nucleus. In the model we use today,
the electrons are shown arranged in different
shells or energy levels around the nucleus. In
the model we use today, each shell can contain
up to a particular number of electrons.
Topic 2.2 Trends in groups within
the Periodic Table
Getting started
5
non-metals
11 The colour gets darker as you go down
this group.
12 Boiling points increase as you go down
the group.
13 The melting point of iodine would be higher
than −7 °C and boiling point higher than 59 °C.
14 Iodine would be less reactive than bromine.
15 7
16 The size of the atoms increases as you go
down this group.
17 The atoms are similar in that they all have 7
electrons in their outer shell.
18 Because the atoms of each element has 7
electrons in its outer shell.
19 The melting points increase as you go down
this group.
20 The size of the atoms increases as you go
down this group.
Metals in the same group as magnesium: beryllium
or calcium. (Accept other metals in this group if
you are using a full Periodic Table.)
Metals in the same period as magnesium: sodium
or aluminium.
Non-metallic solid in the same period as
magnesium: silicon, phosphorus or sulfur.
Gas in the same period as magnesium: chlorine
or argon.
21 The outer electron shells are all full and have
8 electrons (other than helium, which only has
2 electrons).
Questions
Think like a scientist: Observation of
the reactions of Group 1 metals with
water
1
The metals (except Aluminium) are found on
the left side of the table.
2
The boiling points decrease as you go down
the group.
3
It is lower than 777 °C.
4
eight more electrons
5
The size of the atoms increases as you go
down this group.
6
All have an outer shell containing one electron
and an inner shell containing two electrons.
7
This group of metals could be called Group 1
because there is one electron in the outer shell.
8
The atoms get larger and the reaction with
water gets more violent as the size of the atoms
increase.
22 The atoms of each element have 8 electrons in
their outer shell.
23 The melting- and boiling points of krypton
will be higher than those of argon.
1
These might include the use of safety glasses
and a safety screen; handling the metals with
forceps; using only a small piece of each
metal, and warning students about their
position in the room.
2
Descriptions should include any movement
across the water; change in the solid metal;
fizzing, any flame and colour of the flame.
3
lithium + water → lithium + hydrogen
hydroxide
sodium + water → sodium + hydrogen
hydroxide
potassium + water → potassium + hydrogen
hydroxide
Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
4
This might include the reaction producing
heat; a gas is released, and the metal moves
around the water surface.
5
The differences may include the amount of
movement on the water and the intensity
of the violence of the reactions. Accept any
observed differences.
6
These may include the colour; the fact that
they are soft and can be cut; they are all light
and float on water and they react to form an
hydroxide with water. Accept any observed
similarities.
7
8
The reaction increases in intensity as you
go down Group 1. This would suggest that
rubidium reacts extremely violently and would
not be safe to use in schools.
When these Group 1 metals react with water,
they produce the alkalis lithium-, sodium- and
potassium hydroxide.
from the electrostatic charges between the
electrons and the protons.
9
Diagram of calcium atom should have four
shells, with electron structure 2,8,8,2, and a
nucleus.
Diagram of calcium ion should have three
shells, with electron structure 2,8,8, and a
nucleus. (Students may or may not write 2+ to
the top right of the calcium ion diagram.)
10 2
11 CaCl2
12 CaO
13 carbon dioxide, methane, water,
hydrogen chloride and ammonia.
14
Topic 2.3 Why elements react to
form compounds
Getting started
The learners’ drawings should match those in the
Learners’ Book in Topic 2.2. The point here is to
focus the learners on getting the details correct by
discussing their drawings with their partner.
Questions
16 methane CH4; carbon dioxide CO2; nitrogen N2
Topic 2.4 Simple and giant
structures
1
2,8,1
Getting started
2
2,8
3
Cl
4
Cl−
5
Diagram should have three shells, with
electron structure 2,8,8, and a nucleus.
6
Diagram should have two shells, with electron
structure 2,8, and a nucleus.
7
Potassium can lose an electron more easily
because the outer electron is a long way from
the nucleus and the positive electrostatic
charges on the protons, so it is easier for the
electron to escape from the potassium atom.
The outer electron in the lithium atom is
closer to the positive electrostatic forces, so it
is more difficult for it to escape.
Learners should be able to describe the structure
of sodium and chlorine atoms. They might be able
to discuss the stability of the two atoms. They
should be able to describe the formation of the
ions of these two elements and the formation of
an ionic bond between them. Suitable diagrams
such as those shown in Topic 2.2 could be drawn.
This should not be used simply as a right/wrong
answer but the idea is to provoke discussion
between learners to help them improve their
understanding.
8
6
15 An ionic compound, because the compound is
formed from a metal and a non-metal.
Fluorine is more reactive than chlorine
because it can gain an electron more easily
because the outer shell of electrons is further
Questions
1
An ionic bond is formed when atoms lose or
gain an electron (or electrons) but a covalent
bond is formed when atoms share electrons.
2
ionic bond
3
A molecule is the name given to a particle
with more than one atom where the atoms
share at least one electron in a covalent bond.
Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
4
A macromolecule is a giant molecule. Examples
are silicon dioxide, diamond or graphite.
5
Ionic, because it has high melting- and boiling
points and it is a compound formed from a
metal and a non-metal.
6
A simple molecule with covalent bonds. It has
low melting- and boiling points. Also credit
the fact that it is formed from two non-metals
so must have covalent bonds.
7
A gas
8
They have high melting points because they
are ionic compounds. The electrostatic forces
between the ions in these compounds are very
strong so, in order to melt the solids, a great
deal of energy is need to break these bonds.
9
They are composed of simple molecules; the
forces within the molecules are strong, but the
forces between the molecules are weak, so less
energy is needed to melt them.
10 Copper sulfate has ionic bonds. It has formed
a giant structure of crystals and is made from
a metal and a a non-metal.
11 This substance has ionic bonds because it has
very high melting- and boiling points.
12 Silicon dioxide is hard and has a very high
melting point; these are not properties that
are expected of a substance with covalent
bonds. We know that silicon dioxide must have
covalent bonds because it is formed from two
non-metals so the only explanation can be that
silicon dioxide has a giant covalent structure.
Think like a scientist: Ionic compounds
conducting electricity
7
1
The expected answer would be yes, but credit
answers based on the learner’s findings.
2
When ionic compounds dissolve in water, the
ions are free to move about in the solution
and can carry the electric charge and so the
solution can conduct the electricity.
3
The expected answer would be no, but credit
answers where learners may have found some
conduction if they are based on their results.
4
The ions are held in a strong lattice so they
are not free to move to carry the charge and
conduct electricity. Learners should explain any
conduction they did observe, for example the
electrodes were touching or the crystal was wet.
5
If a covalent substance were used, there would
be no conduction of electricity because the
forces inside the molecules are strong and
there are no charged particles to carry the
electricity.
Check your progress
2.1 a
b
c
d
e
f
g
2.2 a
b
c
2.3 a
b
c
d
e
Below 180 °C and above 63 °C
Below 883 °C and above 688 °C
hydrogen
More bubbles of gas and more heat will
be generated than with lithium, but less
than with potassium.
Lithium 7; sodium 23; potassium 39;
rubidium 85
The number of protons plus the number
of neutrons.
Diagram should have a nucleus, three
shells, and the electron structure 2,8,1.
Diagram should be the same as in the
question, but with one additional
cross in the outer shell.
A fluorine ion is more stable than a
fluorine atom because the outer (highest
energy level) shell of electrons is full.
F−
ionic
covalent
covalent
ionic
ionic
2.4 CH4
2.5 a
b
The strong electrostatic forces between
the positive sodium ions and the
negative chlorine ions.
The melting- and boiling points of
sodium chloride will be high because
the electrostatic forces are strong.
Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
Unit 3 Forces and energy
Topic 3.1 Density
7
a
Getting started
8
The gas must be less dense than air; the gas
must have a density low enough so that the
average density of the balloon, the string and
the gas is less than that of air.
9
It is cooler at those times, so the surrounding
air will be denser; the difference in density
between the balloon and the surrounding air
will be greater; the balloon will float more
easily.
1
the (3-dimensional) space occupied by an
object / length × width × height of an object
2
1 kg feathers
3
1 cm of iron
3
Questions
1
a pine wood
b i polycarbonate
ii
The density of polycarbonate is
greater than the density of water.
2
mass
_______
a​​
b
c
3
a
b
c
volume
Activity: Densities of some
regular objects
1
Those objects with calculated densities greater
than 1.0 g/cm3 should be predictedto sink;
those that are less, to float.
2
If the balance is not at zero, then the
(recorded / measured) mass of the object will
be too large or too small.
3
a
There is material missing from the
corners, so if measured to where the
corner should be, then the calculated
volume will be too large.
b
The mass should be correct because
damage to the object will not affect the
reading on the balance.
c
If the calculated volume is too small, then
the density value will be too large / vice
versa; if the recorded mass is too small
then the density value will be too small /
vice versa.
​​
13.5
mass
​​ = ____
​​   ​​ = 2.7 g/cm3
density = _______
​​
5
volume
It will sink because its density is greater
than that of water.
4 × 3 × 6 = 72 cm3
mass
54
density = _______
​​
​​ = ___
​​   ​​ = 0.75 g/cm3
volume 72
It will float because its density is less than
that of water.
mass
10 300
density = _______
​​
​​ = ______
​​
​​ = 1030 g/cm3
10
volume
b iThe material will float because its
density is less than that of sea water.
ii
The material will sink because its density
is greater than that of pure water.
4
a
5
a
mass
density = _______
​​
​​
volume
Think like a scientist: Densities of some
irregular objects
so mass = density × volume
1
The volume is read correctly from the bottom
of the meniscus.
2
Either: place a heavier object of known
volume on top to make the less dense object
sink, measure the total volume of the two
objects by displacement, subtract the volume
of the denser object.
Or: tie a denser object with string to the less
dense object, submerge them both in water,
measure the total volume of the two objects
by displacement, subtract the volume of the
denser object and the string (that can also be
measured by displacement).
6
mass
_______
mass
_______
​​
​​ so volume = ​​
volume
density
4.5
volume = ​​ ____ ​​ = 0.50 cm3
8.96
a
78 − 50 = 28 cm3
mass
84
density = _______
​​
​​ = ___
​​   ​​ = 3 g/cm3
volume 28
Any two from: plastic is less dense than
steel / the result from part b is the average
density of all the materials / the toy is
hollow OR contains air.
b
c
8
= 8.96 × 20 = 179.2 g
b
A = kerosene; B = water; C = mercury
density = ​​
Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
3
4
Use a larger container filled to the very top,
submerge object, collect water that overflows,
measure the volume of the water collected
using several measuring cylinders.
The result is likely to be anomalous because
wood floats on water, therefore the density of
wood is expected to be less than the density of
water, which is 1.0 g/cm3.
Topic 3.2 Heat and temperature
Getting started
1
2
Any heat source, such as a flame, a hot plate
or an immersion heater; it is also acceptable
to add more water that is at a higher
temperature.
a
The water in the swimming pool.
b
The temperature increases are the same,
so the larger mass of water requires more
thermal energy.
Questions
1
a
b
J
°C
2
a
b
The temperatures are the same.
The thermal energy in the larger block,
B, is greater, so B has more heat.
a
Thermal energy contained within that
object; the total energy of all the particles
in the object.
The average energy of the particles in
an object.
3
b
4
A → B and A → C and B → C
5
The statement will be true only if the
substances are the same and have the same
mass or same number of particles. It is
possible for an object with a small mass to
have a higher temperature than an object with
larger mass, yet the object with larger mass
may have more thermal energy, so has more
heat.
Activity: The Mpemba effect
9
1
The table should have a column for starting
temperature of the water in °C (normally be
on the left). There should be a column for
time taken to freeze in minutes or seconds, or
minutes and seconds.
2
Each temperature difference correctly
calculated by subtracting −18 °C from each
temperature.
3
The greater the temperature difference, the
greater the rate of thermal energy transfer.
4
The trend in the learner’s result is correctly
described; this should be a trend rather than
only quoting results.
Think like a scientist: Measuring heat
and temperature
1
The table should have a column for energy in
joules and a column for temperature in °C.
2
The graph should be drawn with linear scales
and cover half the grid in both directions.
Ideally, the graph should be a straight line.
3
As the energy supplied to the water increases,
the temperature of the water increases.
4
Any three from: volume or mass of water
/ type of container / starting temperature
of the water / same temperature increase /
same quantity of thermal energy from the
immersion heater.
5
Any three from: transferred to the cup / to
the air above the water / to the surface below
the cup / to evaporate some of the water / to
the area around the top of the heater (if the
heater was not completely submerged).
6
Any three from: insulation around the cup /
insulation under the cup / ensure the heater is
completely submerged (if it was not) / put a lid
on the cup.
Topic 3.3 Conservation of energy
Getting started
1
Most should be able to recall at least some
from: kinetic, chemical, gravitational
potential, elastic potential, electrical, thermal.
2
For example, chemical can be changed to
electrical in a cell or battery.
3
Where energy spreads out and becomes
less useful.
Questions
1
a
2
a
b
Energy cannot be created or destroyed;
energy can be changed or transferred
(statements can be in either order).
b i false
ii false
iii true
1000 − 500 = 500 J
100 − 80 = 20 J
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c
1300 + 700 = 2000 J
3
a
b
100 − 70 = 30%
55 + 10 = 65; 100 − 65 = 35%
4
Sofia is not correct. The useful energy output
and the wasted energy cannot add up to more
than the energy input. 12 + 7 = 19 J, whereas
energy input is 18 J. So 18 − 7 = 11 J of the
electrical energy is changed to light.
Activity: Conservation of energy
1
2
3
3
The temperature will increase; the
surroundings are at a higher temperature than
the ice cream; thermal energy will move from
the surroundings to the ice cream.
4
Zara is correct; heat, or thermal energy,
moves but cold does not move, and the gloves
keep the cold air from contacting the skin;
the gloves keep the heat of the hands from
escaping to the colder surroundings.
5
a
The first bottle swings through a smaller
distance as the second bottle swings through
a greater distance. The second bottle then
swings through a smaller distance as the first
bottle swings through a greater distance. The
cycle repeats.
b
Kinetic energy from one bottle is transferred
to the other bottle. Energy cannot be gained
(as no additional energy is input), so as one
bottle swings more, the other must swing less.
Activity: Hot coffee
1
method B
Energy is used to overcome friction and air
resistance; energy is dissipated.
2
Adding the cold milk to the coffee lowers the
temperature of the coffee.
This lowers the temperature difference
between the coffee and the surroundings.
The rate of thermal energy transfer (and
therefore cooling) is lower when the
temperature difference is lower.
3
Same cups; same volume (or mass) of coffee;
same volume (or mass) of milk; same starting
temperature of coffee; same temperature of
milk; same room temperature; same exposure
to draughts / moving air.
Activity: Bottle racers
1
the (twisted) elastic band
2
elastic potential
3
kinetic
4
The bottle racer moves faster / further
(depending on their observation) as there is
more elastic potential energy to change to
kinetic energy.
Topic 3.4 Moving from hot
to cold
Think like a scientist: Temperature
change from heat dissipation
Getting started
1
Thermal energy from the room is transferred out
through the open window; cold air may enter the
room but thermal energy moves from the warm air
into the cold air.
Table should have a column for time in
seconds or minutes and a column for
temperature of water in °C.
2
Axes should be scaled in a linear way with
temperature on the y-axis.
Line graph should be drawn either with a best
fit straight line or a smooth curve.
3
The results may show a lag before temperature
starts to increase and may also show a
decrease in rate of temperature change as time
progresses. Learners should describe the trend
shown in their graph.
4
The temperature of the water will stop
increasing either when the lamp is switched
off or when the water reaches the same
temperature as the lamp.
Questions
10
The water is at lower temperature / is
colder than the engine; thermal energy
from the engine moves to the water; heat
from the engine is dissipated into the water.
Thermal energy from the water is
dissipated into the air around the radiator
(or dissipated into the radiator); the air
at the front of the radiator is at lower
temperature than the water.
1
Thermal energy moves from warmer / hotter /
higher temperature places to cooler / colder /
lower temperature places.
2
a
b
The temperature will decrease.
The food is at a higher temperature than
the surroundings; thermal energy will
move from the food to the surroundings;
heat will be dissipated from the food.
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
5
b
The temperature increase of the water will be
slower with the LED; the water will not reach
as high a temperature with the LED as it did
with the lamp.
c
Topic 3.5 Ways of transferring
thermal energy
Getting started
1
a
b
c
2
a
b
c
In a solid, the particles are regularly
arranged and in contact.
In a liquid, the particles are randomly
arranged and in contact.
In a gas, the particles are randomly
arranged and not in contact.
Particles vibrate more vigorously, taking
up more space; the solid expands.
Particles vibrate more vigorously, taking
up more space; the liquid expands.
Particles move faster and collide with each
other and the walls with more force; the
gas expands.
Think like a scientist: Conduction of
thermal energy in different materials
The risk assessment should include keeping paper
away from the flame; not touching the hot metal rod;
making sure the candle will not fall over, and allowing
everything to cool at the end of the investigation.
1
Thickness / diameter of rod; distance of rod
from flame; mass of wax; distances between
paperclips; mass of paperclips.
2
This will vary according to available
equipment and design of the investigation.
3
The paperclips closer to the heat source should
fall first, some of the more distant paperclips
may not fall within the allocated time. If
different materials have been used, then some
comparison should be made. For example,
the paperclips started to fall off faster from a
copper rod than from an iron rod.
4
The heat source makes particles in the rod
vibrate more vigorously; the vibration is
transferred to neighbouring particles by
collisions; this carries on along the rod; if
different materials have been used then a
comparison should be made – for example, the
vibrations are transfered faster in the copper
than in the iron; transferring thermal energy
along the rod, the wax is heated by conduction
from the rod and will melt when it reaches
its melting point; particles in the solid wax
vibrate more vigorously until they can move
further apart and turn to a liquid.
5
Some materials such as wood will burn; other
materials such as plastic will melt.
Questions
1
a
b
c
11
conduction, convection and radiation
conduction and convection; both of these
methods require particle movement and
there are no particles in a vacuum.
Conduction because the particles in
a solid are close together/touching to
transfer the energy from vibrations;
convection cannot occur in a solid
because the particles are not free to move.
2
The black T-shirt will absorb thermal radiation
faster, so Arun will feel hotter sooner. The
white T-shirt will reflect more thermal
radiation, so Marcus will feel cooler for longer.
3
a
b
conduction
radiation
4
a
The electric heater gets hot (changes
electrical energy to thermal energy), heat
is transferred from the heater to the water
by conduction, particles in water around
the heater vibrate more vigorously and
take up more space, water around the
heater expands and becomes less dense,
this hotter water floats to the top of the
tank, cooler water moves to the bottom
of the heater to replace the water that has
risen; this sets up a convection current
that heats all the water.
Because of convection; hotter water will
be at the top, hotter water is less dense
and will float / rise above cooler water
(which will be at the bottom).
Higher up than the first heater; because
of convection, the water below the heater
will not be heated.
Activity: Observing convection
1
The drawings should, at the very least, show
arrows for the direction of the convection
current. Arrows should point up from the heat
source (which is clearly shown at one side of
the base of the beaker), then across the upper
part of the water, then down the other side
and back across the bottom to the heat source.
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2
Explanations should refer to particles
vibrating more vigorously due to being
heated. These particles then take up more
space, expanding the liquid, decreasing the
density of the heated liquid and this heated
liquid, floating or rising through the denser
surrounding liquid.
Think like a scientist: Emitting thermal
energy by radiation
Topic 3.6 Cooling by evaporation
Getting started
1
In evaporation, some particles have sufficient
energy to leave the surface of the liquid
and enter the gas state, so evaporation
only occurs at the surface. In boiling, all
particles have sufficient energy to turn to
gas, so boiling occurs at all positions in the
liquid at once. Evaporation can occur at any
temperature whereas boiling only occurs at
one temperature.
Particles in a liquid all have different energies.
Those at the surface that have sufficient energy
can leave the liquid and enter the gas state.
1
The prediction should be that the water in the
cans will cool at different rates and that this
is linked to the colours; the black can should
cool quickest and the shiny silver can should
cool slowest. This should be linked to the
relative ability of each colour to emit thermal
radiation.
2
The table should have one column (at the
left) for time in minutes, or in minutes and
seconds. There should then be columns for the
temperature in °C for each colour.
2
3
The graph should have temperature on the
y-axis and time on the x-axis. All three (or
more) lines should be drawn on the same grid;
each line should be clearly identified using a
key for the colour of the can. The lines should
be curves if the results have been recorded
correctly.
1
4
The trend for all cans should be described as
the temperature decreasing with time. More
detail can be added, such as the decrease in
temperature was faster at the start / when the
water was hotter. A comparison should be
made between the rates of cooling of each
colour of can.
The energies of the particles in water at 25 °C
are different.
Particles with the least energy stay in the liquid.
Particles with the most energy can leave the
liquid.
When liquid water turns to gas, the water is
said to evaporate.
2
C
3
a
5
The answer should link the original prediction
with the observations.
6
Reference to the graph; any point that are
further from the line or does not appear to
fit with the others.
7
8
12
e.g., every 1 minute (details of the cans need
not be given as question asks about these cans,
i.e., the ones that were used in the first part of
the investigation).
Questions
b
4
Volume (or mass) of water in each can;
material / type of can; starting temperature
of water; location of cans; none stirred or
shaken.
Use of a radiant heat source or placing in
direct sunlight; if a radiant heater is used then
all cans to be equal distance from the heat
source; same volume of water in each; water at
same starting temperature in each; cans left for
the same time; temperature measured at equal
regular intervals which should be specified,
a
b
5
The average energy of the particles
decreases because the particles with more /
the most energy leave the liquid; slower
moving particles are left behind in the
liquid.
The temperature decreases; temperature
is the average energy of the particles in
a substance, so as the average energy
decreases, the temperature decreases.
Evaporation causes cooling; thermal
energy from skin is used to evaporate
the sweat.
There is no loss of thermal energy due to
evaporation.
When isopropanol contacts the skin, the liquid
evaporates; evaporation lowers the average
energy of the particles in the liquid, so the
temperature of the liquid decreases; thermal
energy from the skin is used to evaporate the
liquid.
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
Think like a scientist: Making an air
cooler
1
2
3
Thermal energy from your hand will affect the
thermometer reading / the thermometer will
measure the temperature of your hand rather
than the temperature of the air. (Answer
should be specific and not just refer to getting
better results.)
There should not be a significant difference
between the temperatures measured in steps
2 and 3. This is because the air has not
been heated or cooled; the only difference is
movement. The temperature from step 7 should
be lower; this is because the water from the
towel has evaporated, lowering its temperature.
Thermal energy from the air around the wet
towel is used to evaporate the water.
The three temperatures from steps 2, 3 and 7
should be the same if a dry towel is used; this
is because there is no cooling by evaporation.
3.2 B and D
60
3.3 a​​ ___ ​​= 1.2 g/cm3
50
b It will sink because its density is greater
than that of water.
3.4 a
b
3.5 a
b
°C or degrees Celsius
J or joules
3.6 a
Energy is always conserved, meaning that
energy cannot be created or destroyed.
3.7 50 − 5 = 45 J
3.8 a
Activity: Feeling the effects of
evaporation
1
To increase the rate of evaporation.
2
The alcohol should feel coldest, the water next
and the soap the least cold. Blowing makes
each of the liquids (perhaps with the exception
of the soap) feel even colder.
3
a
b
alcohol
soap
b
There are no numerical results / no measurements.
5
Either repeat the experiment using a skin
thermometer or perform an experiment
similar to that in Main Teaching Activity How
does sweating work.
Check your progress
3.1 B
The temperature of the ball decreases
because thermal energy is transferred to
the water. The temperature of the water
increases because thermal energy is
transferred from the ball.
C
3.9 conduction; thermal energy is transferred
from the tea to the spoon; metal is a good
conductor of heat
3.10 a
b
4
The average energy is the same because
the temperatures are the same.
The heat in beaker Y is greater because
there are more particles (with the same
average energy) / the total energy of all
the particles is greater.
air is heated; the air becomes less dense;
the air floats / rises
air cools; the air becomes denser; the air
sinks / falls
3.11 the black car is hotter inside; black is a
good absorber of radiation; white is a good
reflector / poor absorber of radiation
3.12 evaporation; thermal energy is removed from
the skin; the most energetic particles leave
the sweat, lowering the average energy of the
remaining particles
Unit 4 Maintaining life
4.1 Plants and water
Questions
13
1
The long extension from the cell increases its
surface area. This increases the surface across
which it can take up water and mineral salts,
so this uptake happens faster.
2
Nitrate ions are needed to make proteins.
Magnesium ions are needed to make chlorophyll.
Think like a scientist: Investigating
transport in a celery stalk
1
The drawing should show an outline of the
cut stalk, and coloured spots in the correct
positions. This will depend on the type of
stalk that has been used in the experiment.
2
xylem cells
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3
a
b
4
To make sure that the coloured areas in
the stalk had appeared because dye had
been carried up through the stalk, not
leaked in from the side.
To remove any dye from the outside of
the stalk, so we could be sure that the
coloured spots were caused only by dye
that had been carried up the stalk.
The water would move from the soil into the
root hairs, then across the root to its centre.
There it would enter the xylem vessels, which
carry it up through the stalk.
Think like a scientist:
Planning an experiment
Questions
1
The parts are identified in the diagram in
Topic 1.2.
2
The upper surface is covered with a layer of
wax that stops water passing through. The
underside has stomata, which are openings
leading to the air spaces inside a leaf. Water
vapour can diffuse out from the air spaces,
through the stomata.
Think like a scientist:
Investigating transpiration
1
Whether the leaves were exposed to the air
or not.
2
The soil was covered in both. Learners should
also have tried to keep the temperature the same
for both plants and to use two plants of the
same size. They should have ensured there was
the same quantity of water in the soil in each pot
and that the light intensity was the same.
1
The water will move up faster, because higher
temperatures give more kinetic energy to
particles.
2
As temperature increases, the speed at which
water moves up the stem increases.
3
3
The plan should include the idea of changing
the temperature, and measuring how fast
the dye moves up the stem at different
temperatures.
Answers will depend on the learners’ results.
They are likely to find that the loss of mass
was much greater in the plant that did not
have a bag covering its leaves.
4
4
The apparatus is likely to include a container,
some coloured water, several stalks, a timer and
a ruler. Learners may need other apparatus or
materials, depending on their plan.
The independent variable is temperature.
The dependent variable is the rate at which
the coloured water moves up the stalk. This
involves measuring time and distance.
Variables to keep the same include depth
of coloured water, size of the stalk and
light intensity.
Risk assessment: Cutting the stalk carries a
risk of harm from the sharp blade. Cut on
a firm, non-slip surface and move the blade
away from the body.
Water vapour was lost from the leaves of the
plant that did not have its leaves covered, by
transpiration. The water vapour that was lost
from the leaves of the other plant was trapped
inside the bag and could not escape.
4.2 Transpiration
Getting started
The particles in the liquid should be randomly
arranged, but with each particle touching at least
two other particles. The particles in the gas should
not be touching at all, and should be far apart.
When liquid water turns to a gas, the particles
move faster and spread further apart.
14
Questions
Think like a scientist: Which side of a
leaf loses most water?
1
This will depend on the learners’ results. The
most likely sequence (in increasing ability to
conserve water) is: leaf with no petroleum jelly;
with petroleum jelly on upper surface only;
with petroleum jelly on lower surface only; with
petroleum jelly on both surfaces.
2
The upper surface has few (or no) stomata, but
the underside has stomata, through which water
vapour can diffuse out from the air spaces.
3
It is unlikely that the two leaves would lose
exactly the same mass. The leaves were
probably different masses to start with and
contained different quantities of water. One
leaf may have been in a slightly draughtier
place than another. Learners may make other
suggestions, depending on what happened in
their experiment.
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4
5
Using two leaves gives more reliable results, as
you can avoid the possibility that the one leaf
you test might be unusual. Using even more
leaves would be much better, as this would
then give you the opportunity to identify
any anomalous results. It would increase the
likelihood of obtaining reliable data.
Answers will vary, depending on the desert
plants studied in Stage 8, and each learner’s own
experience. Possible suggestions could include:
small leaves with a thick layer of wax to reduce
transpiration; very deep or wide-spreading roots to
increase access to water.
4.3 Excretion in humans
Getting started
1
Yes; they both need water for transport and
cooling.
2
We also need water for getting rid of waste
materials in urine.
3
Plants use water for support and
photosynthesis.
Questions
1
renal system
2
Carbon dioxide diffuses into the blood and is
carried to the lungs. There, it diffuses from the
blood capillaries into the alveoli. It is removed
from the body in expired air.
Plants make their own proteins, using
carbohydrates that they have made in
photosynthesis and nitrates that they absorb
from the soil. So they are unlikely to have
excess proteins that they need to get rid of.
4.4 Keeping a fetus healthy
Getting started
Description of the nutrients and their functions
are detailed in Stage 8, Topic 7.1. Learners
may suggest a range of ideas about particular
requirements in the diet of a pregnant woman;
accept all at this stage, and perhaps ask learners to
revisit them when they have carried out the activity
in Topic 4.4: Display about diet during pregnancy.
15
1
oxygen and any nutrients, such as water,
glucose, vitamins, minerals
2
carbon dioxide and urea
3
Vitamin A for good vision for the mother and
the fetus, and for their white blood cells to
fight pathogens.
Vitamin C for strong skin and blood vessels
for both the mother and the fetus.
Vitamin D for strong bones and teeth for both
the mother and the fetus.
4
protein: meat, fish, pulses, milk and other
dairy products
carbohydrate: bread, rice, potatoes, pasta,
cereal grains
iron: meat, dark green vegetables, fish and
shellfish, nuts and seeds
calcium: dairy products, nuts and seeds
vitamin A: green vegetables, carrots, squash,
fruit, dairy products, fish
vitamin C: citrus fruits, potatoes, colourful
berries
vitamin D: oily fish
This will depend on the learners’ experiences as
they did their experiment. Do not give credit to
answers that involving changing another variable.
Activity: Conserving water in
the desert
3
Questions
Check your progress
4.1 a
b
c
d
e
f
kidney
ureter
urea
bladder
urethra
urine
4.2 Plants take up water from the soil into their
root hairs.
The water flows through xylem vessels which
carry it to the plant’s leaves.
In the leaves, a lot of the water changes from
liquid to gas.
It diffuses out of the leaf through the
stomata.
4.3 a
b
c
d
e
balance
3g
945 − 808 = 137 g.
137 ÷ 6 = 22.8 g
From the plant. The plant with no
covering over either the plant or the soil
lost a total of 137 g, whereas the plant
with the plant covered lost a total of 31 g.
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f
4.4 a
b
Water vapour diffused out of the leaves
of the plant, through its stomata. The
water vapour condensed to a liquid on
the inside surface of the bag.
c
There is a wide range of correct answers.
Credit any answer that includes a correct
function of that nutrient. For example:
She needs more protein because protein
is needed for growth, and the fetus is
growing.
She needs more calcium to help the fetus
form strong bones and teeth, as well as
keeping her own bones and teeth strong
and healthy.
She needs more iron so that the fetus can
produce haemoglobin for its red blood
cells, as well as increasing the number of
her own red blood cells.
d
Accept any correct responses. For
example, fish for protein; yoghurt for
calcium; meat for iron.
Most people’s diets contain more fat
than they need, so her normal diet is
likely to contain enough fat for herself
and her fetus. Too much fat can lead to
obesity and heart disease.
Any two of: Carbon monoxide from
the cigarette smoke gets into the fetus’s
blood and reduces how much oxygen
it can carry. Nicotine also gets into the
fetus’s blood; it is an addictive substance
and can damage the blood vessels.
Babies born to mothers who smoke
during pregnancy are at increased risk of
having a low birthweight.
Unit 5 Reactivity
Topic 5.1 Reactivity and
displacement reactions
5
magnesium + oxygen → magnesium oxide
6
zinc
Getting started
7
yes
The point of this task is to provoke discussion
rather than to focus on right or wrong answers.
Learners may recall colour changes, new products
such as gases being formed, changes in pH when
chemical reactions take place. They should be
able to discuss relevant examples from their
previous experience such as reactions of Group 1
metals with water, burning magnesium ribbon or
neutralisation reactions.
8
magnesium
9
no
Questions
1
a
b
2
a
b
16
Lithium should be placed below sodium
and above calcium.
Lithium reacts with water more vigorously
than calcium but less vigorously than
sodium.
Platinum should be placed below gold.
Credit a plausible position, such as near
gold.
Platinum is very unreactive, it does not
react with oxygen at all (it does not
tarnish).
3
Metal B is the most reactive. You can tell
because the most bubbles are given off.
4
zinc + sulfuric acid → zinc sulfate + hydrogen
Think like a scientist: Displacing metals
1
If there has been a change in the colour of the
solution or the metal, that would show that
one metal had displaced another.
2
This will depend on what you have been able
to provide, but it is likely to be magnesium.
3
This will depend on what you have been able
to provide, but it is likely to be copper.
Topic 5.2 Using the reactivity
series and displacement reactions
Think like a scientist: Identifying
a mystery metal – planning the
investigation
Credit: a logical plan that includes basic
observations of the metal burning in air, with
water and with dilute acid; displacement reactions;
an equipment list; safety considerations; a way
of recording results; an indication of what might
be expected in each observation/test and how this
would help to identify the metal.
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
fruits, tomato and other savoury sauces,
pickled vegetables.
Think like a scientist: Identifying a
mystery metal – carrying out the
investigation
2
hydrogen, nitrogen and oxygen
1
This will depend on which metal you provide.
3
2
Credit comments on the various reactions that
have been used to suggest a metal.
hydrogen, sulfur and oxygen; two atoms of
hydrogen, one atom of sulfur and four atoms
of oxygen.
3
This will depend on what results they found
but they may want to use different salt
solutions once they have an idea of which
metal it might be.
4
a
b
Both formulae contain chlorine, Cl.
The hydrochloric acid contains hydrogen,
H, but the sodium chloride contains
sodium, Na.
5
a
b
sodium citrate
Adding sodium citrate to foods such
as orange jam helps to maintain its
tangy taste and reduces the risk of the
product decaying. (Leaners may refer to
buffering, which appears in many articles
on the internet; only credit this if they
have explained what it means. Learners
should demonstrate engaging with the
information, not just copy and paste it.)
6
zinc chloride
7
sulfuric acid
There will be a reaction between the copper
oxide and carbon. There should be copper at the
interface of the two powders. The copper can be
identified by its distinctive colour.
8
iron + hydrochloric → iron + hydrogen
chloride
acid
9
Sodium is very reactive and the reaction
would be explosive.
2
copper + carbon → carbon + copper
oxide
dioxide
Think like a scientist: Making the salt
zinc sulfate
3
It indicates that carbon is more reactive than
copper.
1
zinc + sulfuric acid → zinc sulfate + hydrogen
2
4
Carbon should be placed below magnesium
and above zinc. The reason given should be
that carbon can displace a number of different
metals, including zinc, which is the most
reactive of the metals given in the list in the
text. Credit any ideas that involve placing
carbon above the metals iron and copper.
The solution may spit when heated, which
could cause burns.
3
Larger crystals will be produced when the
liquid is left to evaporate slowly, so that is the
better way.
4
Credit any sensible suggestions, such as using
the same mass and volume of zinc and acid for
two reactions; using two identical evaporating
basins; heating one evaporating basin with
a Bunsen burner as in the experiment in the
Learner’s Book, leaving the other evaporating
basin so that the water evaporates very slowly,
and then comparing the size of the crystals.
Questions
1
No, because iron is less reactive than
aluminium.
2
The thermite reaction can be carried out a
long way from a workshop or laboratory;
molten iron is produced so that it can be used
to join the two rails together.
3
So that the raw materials for the process, iron
ore and coal, did not have to be transported
very far. This reduced the costs of production.
Think like a scientist: Extracting metals
using carbon
1
Topic 5.3 Salts
Questions
1
a
b
17
Credit any properties of acids, such as
turning litmus red, turning universal
indicator solution yellow or red, having
a pH of less than 7, tasting sour and that
strong acids are corrosive.
Credit anything suitable, such as vinegar,
fruit juices, lemonade, fizzy drinks, citrus
Think like a scientist: Making the salt
copper sulfate
1
Safety glasses, 250 cm3 beaker, glass stirring
rod, copper oxide powder, dilute sulfuric acid,
measuring cylinder, filter funnel, filter paper,
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conical flask, evaporating basin, tripod, gauze,
pipeclay triangle, heatproof mat, Bunsen
burner, tongs.
6
Credit properties, such as soapy feel, turns
litmus blue, turns universal indicator solution
blue or purple, has a pH greater than 7.
The risk assessment should feature each
process, for example:
Step 1: Measuring acid and adding copper
oxide: risk of getting acid in your eye, so wear
safety glasses.
Step 2: Heating the copper oxide and sulfuric
acid: general risks of heating and not touching
hot items, wearing eye protection when using
acids, not boiling the mixture as harmful
fumes can be given off. Learners should
mention both the risks and how they can
attempt to overcome them.
Step 3: Allowing the mixture to cool: general
risks of heating and not touching hot items,
wearing eye protection when using acids.
Step 4: Filtering: risk of splashes of the
solution getting into the eyes, so wear safety
glasses.
Step 5: Evaporating: risk of solution spitting
and general risk of heating and not touching
hot items, using tongs to move the evaporating
basin, wearing safety glasses, taking care
about how close you get to the apparatus.
7
A base is a metal oxide. If a metal oxide
dissolves in water, it makes and alkaline solution.
8
magnesium + sulfuric → magnesium + water
oxide
acid
sulfate
9
MgO + H2SO4 → MgSO4 + H2O
3
To remove any unreacted copper oxide powder.
4
Use hydrochloric acid instead of sulfuric acid.
5
copper + hydrochloric → copper + water
oxide
acid
chloride
6
copper + nitric → copper + water
oxide
acid
nitrate
10 Iron oxide could be reacted with hydrochloric
acid to form iron chloride.
Think like a scientist: Preparing a salt
from acid and a carbonate
1
This will vary depending on what equipment
you have available but is likely to include
safety glasses, copper carbonate, hydrochloric
acid, measuring cylinder, beaker, spatula, filter
funnel, filter paper, conical flask, evaporating
basin, tripod, pipeclay triangle, Bunsen
burner, heatproof mat, tongs.
2
The risk assessment should feature each
process, for example:
Step 1: Measuring acid: risk of getting acid in
your eye, so protect yourself by wearing safety
glasses.
Step 2: Adding the copper carbonate to the
hydrochloric acid: wear eye protection when
using acids. The risk assessment should
feature each process and learners should
mention the risks and also how they can
attempt to overcome them.
Step 3: Adding excess copper carbonate: wear
eye protection when using acids.
Step 4: Filtering: risk of splashes getting into
the eyes, protection by wearing safety glasses.
Step 5: Evaporating: risk of solution spitting
and general risk of heating and not touching
hot items, using tongs to move the evaporating
basin, wearing eye protection, taking care
about how close you get to the apparatus.
Steps 6 and 7: low risk
3
Credit any sensible observations: the most
obvious will be bubbling as a gas is given off.
4
carbon dioxide
5
copper
hydrochloric
copper
carbon
+
→
+ water +
carbonate
acid
chloride
dioxide
6
Any description should include colour (pale
green) and the nature of copper chloride
(crystals/powder).
Topic 5.4 Other ways of
making salts
Questions
1
magnesium nitric
magnesium
+
→
+ water + carbon dioxide
carbonate
acid
nitrate
2
MgCO3 + H2SO4 → MgSO4 + H2O + CO2
3
By bubbling the gas through limewater, which
will go cloudy if the gas is carbon dioxide.
4
You could add an indicator such as universal
indicator solution. If the test solution is an acid,
universal indicator solution will turn yellow
or red. If the solution is an alkali, universal
indicator solution will turn blue or purple.
5
18
A neutral solution
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copper carbonate and copper chloride
8
Copper carbonate is not soluble as it is left
behind in the filter paper. Copper chloride is
soluble as it passes through the filter paper as
a solution.
9
You could add a little more alkali until the
universal indicator solution turns green.
7
sodium chloride
8
sodium
hydrochloric
sodium
carbon
+
→
+ water +
hydroxide
acid
chloride
dioxide
9
The description should include the colour
(white) and the shape of the crystals obtained
(cubic).
Think like a scientist: Preparing a salt
by neutralisation
Topic 5.5 Rearranging atoms
1
1
a
b
c
d
e
copper chloride
hydrochloric acid
water
copper carbonate
carbon dioxide
2
a
b
copper, oxygen, hydrogen and sulfur
copper 1 atom, oxygen 5 atoms, hydrogen
2 atoms, sulfur 1 atom
copper, oxygen, hydrogen and sulfur
copper 1 atom, oxygen 5 atoms, hydrogen
2 atoms, sulfur 1 atom
2
19
To make copper sulfate from copper
carbonate, the experiment could be repeated
but this time using sulfuric acid instead of
hydrochloric acid.
6
This will vary depending on what equipment
you have available but is likely to include
safety glasses; dilute hydrochloric acid, dilute
sodium hydroxide solution, universal indicator
solution, charcoal powder, burette, burette
stand, small funnel (to fill burette), measuring
cylinder, two conical flasks, beaker, glass
stirring rod, filter funnel, filter paper, tripod,
pipeclay triangle, evaporating basin, tongs,
heatproof mat.
The risk assessment should feature each
process, for example:
Step 1: Filling burette with acid: risk of
getting acid in your eye, so protect yourself by
wearing safety glasses; risk of spilling acid, so
use a small funnel and place burette at a level
lower than the bench to fill it; general risk of
breaking glassware.
Step 2: Measuring sodium hydroxide: risk of
splashing it in eyes, so wear safety glasses.
Step 3: Low risk
Step 4: Swirling acid around: risk of spilling
acid so take care, wear safety glasses.
Step 5 and 6: Low risk
Step 7: Filtering: risk of splashes of the
mixture getting into the eyes, protection by
wearing safety glasses.
Step 8: Evaporating: risk of solution spitting
and general risk of heating and not touching
hot items; using tongs to move the evaporating
basin; wearing safety glasses, taking care
about how close you get to the apparatus.
Steps 9 and 10: low risk
3
blue
4
green
5
So that they mix together and react before you
add more acid.
Questions
c
d
3
187 g
4
10 g of magnesium will be present in the
magnesium sulfate.
5
a
b
c
6
He should have used a stopper in the flask to
stop the gas escaping.
calcium carbonate
carbon dioxide and water
from the hydrochloric acid
Think like a scientist: Burning
magnesium in air
1
The mass after heating has increased. Credit
any answer that is in line with the learners’
practical findings.
2
The magnesium has reacted with the oxygen in
the air and this has added to the mass.
3
magnesium oxide
4
The safety risks are to do with the heating of
the crucible. It will get very hot and, since the
lid has to be raised during the experiment,
the tongs or spatula must be used with care.
Before re-weighing the crucible after heating,
it must be left to stand for quite a long time
before it is cool enough to touch.
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So that the air can reach the magnesium and
the oxygen in the air can react with it.
6
When you lift the lid of the crucible during the
heating, you must be careful not to allow any
of the product to escape. As you lift the lid you
should be careful not to knock the crucible
and cause the product to spill out.
Think like a scientist: The law of
conservation of mass
1
Accept any sensible observations, which
are likely to include that there were bubbles
produced showing that a gas was given off.
2
hydrochloric
calcium
carbon
calcium
+
→
+ water +
acid
chloride
dioxide
carbonate
3
calcium chloride
4
Accept any sensible answers. You should
be looking for an understanding that the
practical steps in doing this investigation may
lead to inaccuracies. The sum of the masses
of the individual items is likely to be a little
higher than the total mass at the end because
some gas is likely to be lost as there will be a
delay in getting the stopper firmly fixed in the
flask.
Check your progress
5.1 a
b
c
d
combined with the sulfate to form
aluminium sulfate, leaving copper.
zinc + lead nitrate → zinc nitrate + lead
Copper is less reactive than sodium,
so it cannot displace the sodium in the
compound sodium chloride.
5.2 a
b
Aluminium is the most reactive
There will not be a reaction as
magnesium is more reactive than lead, so
lead cannot displace magnesium.
c There will be a reaction:
iron + lead → iron + lead
nitrate
nitrate
5.3 a
b
c
d
e
5.4 a
b
c
If there has been a colour change in the
solution or the metal.
The more reactive aluminium has
‘pushed’ the less reactive copper out
of its compound. The aluminium has
hydrogen
Place a lighted splint in the neck of the
test tube; if the gas is hydrogen it will
burn with a squeaky pop.
zinc sulfate
All of the acid has reacted when the
fizzing stops.
zinc + sulfuric → zinc + hydrogen
acid
sulfate
A is a burette
hydrochloric acid
Add charcoal to remove the colour from
the universal indicator solution; filter
to remove the charcoal and then pour
the solution into an evaporating basin
and heat gently. Leave the solution to
evaporate and to form the crystals.
Unit 6 Sound and space
b
As frequency increases, pitch increases,
or As pitch increases, frequency increases.
(Can also be written in terms of both
quantities decreasing.)
2
a
b
A
C
3
a
b
B
C or D
4
a
b
c
d
e
increases
increases
decreases
stays the same
decreases
Topic 6.1 Loudness and pitch
of sound
Getting started
1
Vibration of particles; particles vibrate
backwards and forwards when the wave
moves forwards.
2
vibration
Questions
1
20
a
As amplitude increases, loudness
increases, or As loudness increases,
amplitude increases. (Can also be written
in terms of both quantities decreasing.)
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Activity: Pitch and frequency in music
1
The frequency doubles each time.
2
Pitch increases from left to right on the keyboard.
3
A5 = 880 Hz; A6 = 1760 Hz; A7 = 3520 Hz
4
a
b
decreases the amplitude
does not affect the frequency
Think like a scientist: Vibrations in a ruler
1
Table should have column headers as stated in
the Learner’s Book; units should be in column
headers; independent variable should be in the
left column with values in ascending order.
2
Frequencies and averages should be correctly
calculated from the results.
3
a
b
c
4
Graph should have linear scales, points
covering at least half the grid, axes labelled
with units, all points plotted correctly, line of
best fit or smooth curve drawn.
a
b
Taller waves should be identified as having
larger amplitude.
Waves with peaks closer together have
higher frequencies.
Questions
1
a
b
B
A
2
a
b
peak to peak
peak to trough
3
frequency 450 (Hz), amplitude 1.0 (mm)
4
a
b
0.25 mm
zero / 0 mm
Activity: Reinforcing and
cancelling waves
1
It makes it easier to get the frequency the same
for both; makes it easier to get the amplitude
the same for both.
2
a
b
3
a
b
In the areas where there is larger amplitude,
the two waves are said to reinforce.
In the areas where there is zero amplitude,
the two waves are said to cancel.
two loudspeakers (or any named device
with a loudspaker) / two tuning forks /
two musical instruments
because of sound waves reflecting off
objects / walls / furniture
5
Learners correctly describe the trend in their
own graph: ideally, as the mass increases, the
frequency decreases.
Think like a scientist: Listening to
sound waves reinforcing
6
a
1
Frequencies recorded correctly.
2
The table should have a column for frequency
in Hz at the left, and values should be
recorded in ascending order; another column
(or more if repeats have been done) for length
in mm / cm / m.
3
As the frequency increases the length decreases.
4
Longer wind instruments are capable of
producing lower pitch notes.
b
c
As the mass increases, the frequency
decreases.
As the mass increases, the pitch decreases.
The independent variable is length that is
free to vibrate. The dependent variable is
frequency. Control variables include: same
(mass of / material of) metre rule / same
mass (or no extra mass) attached each
time / masses attached to same position
on metre rule / end of metre rule pulled
down (or up) by same distance each time.
Prediction should be as length increases,
frequency decreases.
Topic 6.3 Formation of the Moon
Getting started
Topic 6.2 Interference of sound
Discussion should refer to a cloud of dust and gas
being pulled together by gravity.
Getting started
Questions
1
21
mass
frequency / number of complete
vibrations in 10 seconds / number of
complete vibrations in 1 second
Any two from: same (mass of / material of )
metre rule / same length (free to vibrate) /
masses attached to same position on metre
rule / end of metre rule pulled down (or up)
by same distance each time.
2
Learners should draw waves on plain paper.
It is assumed that the scale of each drawing is
the same.
1
A
2
C
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a
b
4
The composition of the rocks on the two
moons would be different from that of
Mars, and possibly different from each
other.
The composition of the rocks on the two
moons would be very similar to that of
Mars, and very similar to each other.
Most of the objects that were travelling in
paths close to those of planets have already
collided with planets; soon after the Solar
System was formed, there would still be
many left-over objects; the Solar System was
still developing for quite some time after the
planets were first formed; idea that the Solar
System has become more stable over time.
• The Earth and Moon formed at the same time
in the same way as the rest of the Solar System.
• The Moon formed from asteroids that were
pulled together soon after the formation of the
Solar System.
Topic 6.4 Nebulae
Getting started
1
The planets in the Solar System formed from
a disc of dust and gas. Particles attracted each
other by gravity and gradually gained mass,
so attracting more dust and gas to grow still
bigger.
2
a
Activity: Evidence for the
collision theory
Evidence that supports the collision theory
includes facts such as:
• The Moon is less dense than the Earth.
• Samples of rock from the Moon show that its
surface was once molten.
• The Moon has a small iron core, similar to the
Earth.
• There is evidence outside the Solar System of
similar collisions causing rings of rock and dust.
• The collision theory fits with the theory of how
the Solar System was formed.
• The composition of rocks on the Earth and the
Moon are the same.
Evidence that seems to contradict the collision
theory includes facts such as:
• The surface of the Earth does not appear ever
to have been molten. A collision that formed
the Moon would have caused the surface of
the Earth to melt. The surface would have later
solidified.
• Venus has no moon; collisions in the early years
of the Solar System would have been common
and scientists would have expected Venus to
have a moon formed in the same way.
• The composition of rocks on the Moon would
be expected to be more similar to rocks on Theia
than rocks on Earth. In fact, the composition of
the Moon is more similar to Earth.
Other theories for the formation of the Moon
include:
• Another passing object was captured by Earth’s
gravity.
• The Moon split away from the Earth soon after
formation.
22
b
Stars give out their own light, planets
reflect the light of stars; stars are much
bigger than planets; a star is usually at
the centre of a solar system with planets
orbiting the star.
Both objects are round / spherical / same
shape; both are formed in a similar way.
Questions
1
a
b
2
hydrogen and helium
3
a
A place in a nebula where stars are formed.
b
B
4
They are clouds of dust and gas in space.
Galaxies are larger; galaxies may contain
nebulae but not the other way around;
galaxies contain older stars and planet
systems that formed many millions of
years ago; galaxies contain other objects
such as comets and asteroids.
Dust and gas particles are pulled together
by gravity; as the object grows, the force of
gravity increases; the increasing force of
gravity attracts more material; as the object
grows larger the pressure inside increases; high
pressure inside the object can start reactions
that give out heat and light.
24
5​​ _____ ​​ = 24 000
0.001
Activity: Virtual tour of nebulae
1
Learners may find out about: planetary
nebulae, reflection nebulae, emission nebulae,
dark nebulae and supernova remnants.
2
The information sheet should contain some
facts about each type of nebula that has been
researched.
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The Hubble Space Telescope (HST) was
launched into Earth orbit in 1990. The HST
differs from other telescopes in that it is
outside the Earth’s atmosphere; being outside
the atmosphere means much higher quality
images are available (some images of nebulae
taken with the HST should be included).
Topic 6.5 Tectonics
(where new rock forms) show symmetrical
patterns of opposing alignments; this
suggests the new rock forms and pushes
the tectonic plates apart at these places.
83 000 000
5​​ _________
​​= 454 000 years
183
6
Getting started
1
The Earth consists of an inner core, an
outer core, a mantle and a crust in order of
increasing distance from the centre. This
would be best shown on a labelled diagram.
2
The crust is not just one solid layer but has
parts that move independently – these are
the tectonic plates. The tectonic plates are
supported by, and move on, the mantle.
3
Volcanoes, earthquakes and the formation of
fold mountains are all more likely at tectonic
plate boundaries.
Activity: Pangaea
1
Africa and South America, but learners may
suggest others.
2
Pangaea could have been made from one
tectonic plate that then broke up into smaller
plates, or it could have been made from the
many tectonic plates that we see today.
3
This is an open question that allows learners
to be creative within the limits of tectonic
plate theory; some learners may see that the
continents could come back together to form
another Pangaea, but in a different way.
4
5000 km × 1000 = 5 000 000 m
5 000 000 m × 100 = 500 000 000 cm
distance
speed = ________
​​
​​
time
500 000 000
= ​​ __________ ​​
140 000 000
= 3.6 cm per year
Questions
1
The mantle is heated by the core; molten
rock in contact with the core is heated (by
conduction); this expands, becomes less dense
and rises through the mantle; cooling occurs
next to the crust (which is cooler) and the
molten rock sinks again.
2
A tectonic plate is part of the Earth’s crust
that can move; it is supported on the mantle
and moves on the mantle.
3
The continents were originally one large mass
of land; this split apart, so the continental
coastlines that we see today are the lines made
by the splitting. The movement was caused by
the movement of tectonic plates; in theory, the
continents could be pushed back together to
fit again.
4
a
b
23
Some fossils of the same species are found
in continents that appear as if they could fit
together, such as South America and Africa.
This suggests that these continents were
once joined. Tectonic plate theory explains
how the continents have moved apart.
Magnetic materials in molten rocks line
up with the Earth’s magnetic field and
remain in this alignment when the rock
solidifies; the Earth’s magnetic field
reverses over periods of millions of years.
Rocks either side of mid-ocean ridges
The map supports this statement because
most of the earthquakes and volcanoes occur
at, or close to, plate boundaries, but a few
earthquakes and volcanoes have been recorded
far from plate boundaries.
Check your progress
6.1 B
6.2 a
b
c
the loudness increases
the pitch increases
the pitch increases
6.3 a
b
B
C
6.4 If squared paper is not used then apply
reasonable tolerance on measurements and
alignment.
a Two waves drawn with the peaks aligned
and the troughs aligned; two waves have
same amplitude; resulting wave shown with
same frequency and double the amplitude.
b Two waves drawn with the peaks of
one aligned to troughs of the other;
two waves have same amplitude; result
shown as a horizontal line.
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
6.5 a
b
6.6 a
Mars-sized object collided with Earth;
disc of dust and debris resulted from
collision; dust and debris came together
because of gravity to form the Moon.
Any two from:
• The Moon is less dense than the Earth.
• Samples of rock from the Moon
show that its surface was once molten.
• The Moon has a small iron core,
similar to the Earth.
• There is evidence outside the Solar
System of similar collisions causing
rings of rock and dust.
• The collision theory fits with the
theory of how the Solar System
was formed.
• The composition of rocks on the
Earth and the Moon are the same.
b
6.7 a
b
c
i A cloud of dust and gas in space.
ii
The place where stars are formed in
some nebulae.
Any two from:
• The newly formed stars are smaller.
• Newly formed stars emit less light.
• Light is (partly) blocked by dust
in nebula.
The continents look like they could fit
together because they were originally
part of one larger continent that
broke apart.
Similar / same type of fossils are found
in different continents suggesting they
were once joined.
The alignment is different in newer rocks
than older rocks / suggests that tectonic
plates are pushed apart by new rock
being pushed upward.
Unit 7 Genes and inheritance
Topic 7.1 Chromosomes, genes
and DNA
4
Getting started
Topic 7.2 Gametes and
inheritance
1
Both are in the centre of a large structure.
2
The nucleus of a cell is much, much larger
than the nucleus of an atom.
3
The nucleus of a cell controls the activities of
the cell.
Questions
1
2
3
24
Chromosomes do not usually become visible
until just before a cell divides, so unless you are
looking at a cell that is going to divide you will
not be able to see them. Also, they need to be
coloured with a stain before they are visible.
Red blood cells do not contain any
chromosomes. Chromosomes are only found
in a nucleus. (Red blood cells do have a
nucleus when they are first formed, but they
lose it as they become fully functioning red
blood cells, full of haemoglobin.)
A chromosome is a long thread of DNA.
A gene is part of a chromosome that helps
to control a particular characteristic. Each
chromosome contains many genes.
The fruit flies have different versions of the
gene for wing shape. The DNA in the different
versions of the genes is slightly different.
Getting started
1
Learners might think of red and white blood
cells, nerve cells and sex cells (gametes).
2
They all have a nucleus, a cell membrane
and cytoplasm.
3
Full descriptions can be found in Topic 1.3 in
the Stage 7 Learner’s Book.
Questions
1
A gamete is a sex cell – one of two cells that
fuse together at fertilisation to begin a new life.
2
For example:
Sperm cell
Egg cell
a male gamete
a female gamete
smaller than egg
cell
larger than sperm
cell
has a tail and can
swim
does not have a tail
and cannot move
does not contain
many food reserves
contains food
reserves
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3
Yes, the sex of a baby is determined by the
sperm cell, which can carry either an X
chromosome or a Y chromosome.
4
There are equal numbers of sperm cells with
an X chromosome and a Y chromosome. If
an X sperm fuses with an egg, the baby will
have chromosomes XX and will be a girl. If a
Y sperm fuses with an egg, the baby will have
chromosomes XY and be a boy. The chances
of these two events happening are equal.
Activity: Modelling sex inheritance
Question
1
Learners should find that there is an equal
chance of a baby being a boy or a girl.
1, 2 and 3 depend on the learners’ results.
4
All the leaves on the same tree must have the
same genes. So any differences between them
cannot be caused by genes.
Topic 7.4 Natural selection
Getting started
Accept any reasonable suggestion that describes
a feature of the frog and how this might help it
to survive. For example. the colour of its skin
helps to camouflage it, so that it can hide from
predators.
Topic 7.3 Variation
Questions
Getting started
1
The bacteria are not killed by the antibiotic.
This is an open-ended question that could elicit
many different answers. Learners should be able
to state that a species is a particular kind of
organism, but they may also be able to suggest
more focussed ideas such as a group of organisms
that are able to reproduce with each other to
produce fertile offspring.
2
When an antibiotic is used, bacteria with
varieties of genes that make it resistant to
the antibiotic are more likely to survive and
reproduce. Over many generations, this variety
of the gene becomes more common, resulting
in whole populations of bacteria that are not
killed by the antibiotic.
Questions
3
Whenever an antibiotic is used we give an
advantage to bacteria that are resistant to
it. The gene for resistance becomes more
common in the population. If we do not use
the antibiotic then there is no advantage for
the resistant bacteria, so natural selection does
not produce a resistant population. By not
using antibiotics we can help to stop resistance
developing, meaning that when we really do
need to use an antibiotic to cure a serious
infection, the antibiotic works.
4
Event 1:
Most peppered moths were pale, but some
were dark.
Event 2:
The differences in colour were caused by
having different varieties of the gene that
determines wing colour.
Event 3
Before the industrial revolution, pale moths
were most likely to survive, because they
were better camouflaged from birds. After
the industrial revolution, dark moths were
most likely to survive because the pale
lichens on the tree trunks were killed or
covered in soot.
1
For example, they all have four legs, two ears.
2
Differences include size, age, coat colour,
presence of horns, size of horns.
3
5 + 2 + 3 + 9 + 3 = 22
4
yellow
5
This will depend on the learner’s perception of
which form is easier to understand. Reasons
should be given.
6
Answers will depend on the features that
learners chose to investigate. For the examples
given in the sample table:
• natural hair colour is determined mostly by
genes; however, it can also be affected by
hair products such as hair dye
• eye colour is determined by genes alone
• shoe size is determined mostly by genes
but also partly by environment, such as
how much food the person ate as they were
growing up and how their feet were treated
• height is determined partly by genes and
partly by environment such as diet during
the growing years.
25
Think like a scientist: Investigating
variation in leaves
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
Event 4:
During the industrial revolution, dark
moths were more likely to reproduce,
passing on their genes for dark wings to the
next generation.
Event 5:
In each generation the variety of the gene
that produced dark wings became more
common and the variety of the gene
producing pale wings became rarer.
7.3 a
b
c
7.4 a
Check your progress
b
7.1 The nucleus of every cell contains several
long threads, called chromosomes.
In most cells, there are two copies of
each thread.
Each thread contains many genes.
The threads are made of a chemical
called DNA.
7.2
Description
Egg
cells
Sperm
cells
contain a nucleus
✓
✓
are gametes
✓
✓
c
in humans, contain
23 chromosomes
✓
contain either an X
chromosome or a Y
chromosome
Number of
beans in a pod
3
4
5
6
7
8
Tally
||
|||
​​||||​​ ||||
|||
|||
Number of
pods
2
3
5
3
3
4
suitable scale on x-axis; suitable scale on
y-axis; all bars correctly drawn.
A substance that kills bacteria (but does
not harm humans).
The percentage of cases of penicillinresistant pneumonia has increased.
Any two from:
• This happened because penicillin was
used to treat infections.
• Any bacteria that happened to be
resistant to penicillin survived and
reproduced.
• Their offspring inherited the genes
that made them resistant.
If penicillin continues to be used over time,
the proportion of bacteria that are resistant to
penicillin increases.
✓
can swim
Sum = 112; 112 ÷ 20 = 5.6
✓
✓
Unit 8 Rates of reaction
2
Because there is no further increase in the
volume of the gas given off after 270 seconds.
Getting started
3
The point of the first part of this task is a recap
and discussion. The examples are likely to include
colour changes, pH changes, gases being given
off or other new products being formed. The
suggestions as to how the rate of reaction could
be measured are not about the “right answer” but
rather the discussion as to what the learners think
they could do.
The syringe plunger might shoot out of the
end of the casing and break or hurt someone.
You should watch the experiment very
carefully and open the top of the flask if the
volume of gas produced gets close to 100 cm3.
You could tie the syringe plunger to the barrel
with string so that it cannot move very far if it
is forced out of the casing.
4
The result at 90 seconds is anomalous. You
can see this because it does not fit the pattern
of the graph.
Topic 8.1 Measuring the rate of
reaction
Questions
1
magnesium +
magnesium
sulfuric
+ hydrogen
→
sulfate
acid
Mg + H2SO4 → MgSO4 + H2
26
The experiment should be repeated and if you
continue to get a result that does not fit the
pattern, it might help you decide that there
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
was a change in pattern. If you get a result
that fits the pattern, you would decide that the
original result was an error.
5
copper
hydrochloric
copper
carbon
+
→
+ water +
carbonate
acid
chloride
dioxide
6
6 cm3 of carbon dioxide is produced in this 20
second period, so the average rate of reaction
is 6 ÷ 20 = 0.3 cm3/s.
This rate is less than one-third of the rate
between 10 and 30 seconds.
Think like a scientist: Measuring the
rate of reaction
1
This will depend on the method that learners
use but will include: safety glasses, calcium
carbonate, hydrochloric acid. It may include
a flask, a top pan balance, gas syringe with
tubing and a rubber bung to fit the flask, a
large beaker or trough, a beehive shelf and
water-filled measuring cylinder, delivery tube
and thistle funnel.
2
This will depend on the method used. It
should include safety measures for using
acids, such as wearing safety glasses and being
careful to avoid spills; issues relating to the
syringe and the production of large volumes
of gas that could cause the plunger to shoot
out of the casing.
3
This should allow for enough space for many
results and have two columns as shown.
Time in s Total volume of carbon
dioxide gas produced in cm3
0
slope). Credit specific time points mentioned
when referring to the rates of reaction.
5
This will depend on which method they
used and how well they were able to manage
the practical work. The likely problems are
difficulty in setting up the apparatus quickly
enough to prevent gas being lost at the start
of the reaction, and issues about being able
to read the scale quickly enough. They may
mention accuracy of results as an issue.
6
This will depend on the method used. Credit
repeating the investigation several times and
any suggestions about tightening up the
method to avoid variation in the start time
due to not getting the measuring cylinder or
syringe in place quickly at the start of the
reaction.
Topic 8.2 Surface area and the
rate of reaction
Getting started
The exact measurements are not very important,
but learners should record the surface area for all
six faces of the book in cm2 and add them together
to find the total surface area. To place two books
together with the minimum surface area, the
largest surfaces of the two books should be placed
together, thus losing these two surfaces from the
total. To put the books together with maximum
surface area, place the two smallest surfaces
together.
Think like a scientist: Burning iron
1
This will depend on what the learners see but
should include: the nail just glows as it gets
hot, the iron wool burns and pieces fly off,
whereas the iron filings burn brightly.
2
Increasing the total surface area increases the
rate of reaction.
3
For a reaction to take place the atoms of iron
must collide with the atoms of oxygen. The
larger the surface area of the iron, the more
iron atoms are in contact with the oxygen in
the air, so the faster the reaction.
30
60
90
120
4
27
This will depend on their results but credit
a graph drawn with time on the x-axis and
volume of gas on the y-axis; axes correctly
labelled; suitable scale; ruler and pencil used;
points plotted true to the results and a suitable
line of best fit drawn.
The description should fit the graph they
present but should include an indication of the
speed of the reaction at various points. The
rate should be at its fastest at the beginning of
the reaction (steepest slope) and then become
slower until the reaction is complete (no
Activity: Calculating the surface area
1
This will depend on the size of the block.
The answer should be given in cm2.
2
9
3
9 × answer to 1
4
6 × answer to 3
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5
78 × answer to 1
Large chips
6
The shape in Part 2 has a larger surface
area than the shape in Part 1, so the rate of
reaction would be greater.
Time in s Mass at
start in g
7
27 × 6 × answer to 1
30
8
The shape in Part 3 has a larger surface
area than the shape in Part 2, so the rate of
reaction would be greater.
60
9
The greater the surface area, the more atoms
are in contact with the other reactant and so
the reaction is faster.
Think like a scientist: The effect of
surface area on the rate of reaction
1
Learner’s or teacher’s choice.
2
The reaction with the smaller calcium
carbonate (marble) chips will be faster.
3
It is important to keep all these variables – the
volume, type and concentration of the acid –
the same as these factors could affect the rate
of reaction. The investigation is to see if the
surface area affects the rate of reaction, so this
is the only variable that should change.
4
The dependent variable is the time taken
for the reaction to finish. The independent
variable is the size (and therefore the surface
area) of the marble chips.
5
This will depend on the method chosen.
6
For the collection of gas method:
Small chips
Time
Volume of
gas produced in s
in cm3
0
0
30
30
60
60
90
90
Volume of
gas produced
in cm3
0
7
This will depend on the results obtained, but
is likely to be the one using the smaller chips.
8
The smaller size of marble chips reacted
more quickly.
9
As the total surface area of the chips
increases, the rate of reaction increases.
10 This will depend on the results obtained and
the prediction made in question 2. Credit an
answer that aligns with the findings and the
prediction.
11 The prediction should be that the rate
of reaction would be even faster if
powdered calcium carbonate were used
in the experiment.
Topic 8.3 Temperature and the
rate of reaction
Think like a scientist: The effect of
temperature on the rate of reaction –
Part 1: The trial run
1
The answer will depend on what the learners
found out, but it is likely to be about
organisation and being ready to start the timer
as one of them pours in the acid. There may
be issues over finding the end point.
2
This will depend on what the learners found out.
3
Small chips
Mass at
start in g
90
Think like a scientist: The effect of
temperature on the rate of reaction –
Part 2: Preliminary work
For the change in mass method:
Time
in s
Mass at
end in g
Change in
mass in g
0
Large chips
Time
in s
Mass at
end in g
Change in
mass in g
This will depend on what the learners decide
to do, but is likely to include boiling tubes
with stoppers, thermometer, timer, beaker
(to act as a water bath), sodium thiosulfate
solution, hydrochloric acid, measuring
cylinders of suitable size (10 cm3), safety
glasses, card with black cross, clamp stand.
30
60
90
28
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
4
This will depend on what the learners have
decided to do. The answer is likely to include
using two temperatures fairly close together
to see how large an interval they need to use
and may include ideas about keeping the
temperature at a set level throughout the
reaction.
5
Likely answers will include the range and / or
the interval of temperatures to use. However,
it will depend on what the learners have done
in their preliminary work.
6
7
Credit ideas, such as keeping the tube in
the water bath and some discussion of the
practical aspects of insulation of the tube
while still being able to see the end point of
the reaction.
Credit a plan that mentions what the
investigation is about; the independent and
dependent variables; indicates what must be
kept the same; has a safety comment; includes
an equipment list and outline method;
mentions the need for repeats.
Temperature
in °C
Time for mark to disappear in s
11 This will depend on the results obtained, but
credit the following points: use of pencil and
ruler; good use of the whole of the graph
paper; temperature plotted on the horizontal
axis; time taken for reaction to be completed
on the vertical axis; suitable scale used; axes
suitably labelled; points accurately plotted
using small crosses; a line of best fit should
be drawn.
12 Credit a statement to the effect that the
higher the temperature, the greater the rate of
reaction.
Questions
1
The steeper line shows the faster reaction.
2
If you did the same experiment at 50 °C, the
line on the graph would be steeper than at
40 °C.
Topic 8.4 Concentration and the
rate of reaction
Questions
1
The steeper line shows the faster reaction.
2
The line on the graph would be less steep than
for a low concentration, but it would level off
at the same volume.
Attempt Attempt Attempt Mean
1
2
3
8
This will depend on what the learners found
out, but is likely to include the range / interval
of temperatures to be used, and may involve
ideas to improve the accuracy of their results.
Answers should be specific here and based on
their findings.
Think like a scientist: The effect of
temperature on the rate of reaction –
Part 3: The investigation
9
The plan should be detailed, specific and
modified from the answers given in question 5
in light of findings in the preliminary work.
10 Credit any suitable comment that relates to
what the learners did. This is likely to include
the same volume of sodium thiosulfate used
and the same volume and type of acid used.
Do not accept repeating the experiment as
part of a fair test.
29
Think like a scientist: Investigating
the effect of concentration on the
rate of reaction – Part 1: Planning
the investigation
1
The plan should include a list of equipment
needed, what the independent variable and
dependent variables are, which variables
should be kept the same, an outline of how
the investigation should be carried out and
a risk assessment and what should be done
to avoid the risks.
Think like a scientist: Investigating
the effect of concentration on the
rate of reaction – Part 2: Carrying out
the investigation
2
Points should include using the same mass
of marble chips, the same volume of acid,
carrying out the investigation at the same
temperature. Do not credit repeating the
experiment as this does not make the
investigation fair, but more reliable.
3
This should include repeating the
investigation.
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
4
b
Credit a table with sufficient readings, at least
five different concentrations and repeated at
least three times with the mean shown. Results
should be in order, ascending or descending.
Tables should also show the correct units, and
concentration can be given as solution A to E.
Solution Time taken to collect 25 cm3
of gas in s
c
Attempt Attempt Attempt Mean
1
2
3
A
d
B
8.2 a
C
b
D
E
5
Credit:
• use of pencil and ruler
• good use of whole graph paper
• concentration along the horizontal axis
• time taken for the reaction along the
vertical axis
• suitable scales used
• axes suitably labelled
• points accurately plotted using a small cross
• points joined appropriately
• both lines labelled appropriately.
6
This will depend on the results the students
obtained but it is likely to be solution E with
50 cm3 of the acid.
7
This will depend on the results obtained but it
is likely to be the more acid that was used to
make the solution, i.e. the more concentrated
the acid, the faster the rate of reaction.
c
8.3 a
b
c
d
e
Check your progress
8.1 a
The smaller the pieces of marble are, the
larger their surface area. The powder
has more surface area exposed to the
acid and so more collisions between the
acid particles and marble particles will
happen more often. Thus, the reaction
will happen more quickly.
The test for carbon dioxide is to bubble
it through limewater. If the gas is carbon
dioxide, the limewater will turn milky.
calcium chloride
magnesium +
sulfuric
magnesium
→
+ hydrogen
acid
sulfate
To test for hydrogen he could use a
lighted splint. If the gas burns with a
squeaky pop then the gas is hydrogen.
warming the acid and stirring the
mixture
Accept answers from 85 to 90 seconds.
Accept answers from 230 to 250 seconds.
The rate of reaction is very fast up until
about 150 seconds. Then the rate of
reaction decreases between 150 and 240
seconds.. Eventually, the reaction stops
at 240 seconds (accept their answer to
question b here.).
If Zara increased the temperature of the
acid, the rate of reaction would increase.
The rate of reaction increases when
the temperature increases because the
particles of acid move faster when they
have more energy. This results in more
collisions between the particles of
acid and magnesium.
The collisions have more energy and are
more likely to result in a reaction.
C
Unit 9 Electricity
d
e
Topic 9.1 Parallel circuits
Getting started
1
a
b
c
30
Learners should draw the cell, lamp and
buzzer in series (connected end-to-end
in any order) using the correct circuit
symbols.
ammeter
2A
The lamp will no longer be lit.
The buzzer will stop making sounds.
Questions
1
C
2
A, C and D
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
3
a
currents in A2, A3 and A4 add together to give
A1, and that A2 + A3 + A4 = A1
i
Think like a scientist: Making
predictions about current
ii
1
The values of A1 and A2 should be recorded
with units; a table is not required.
2
A1 and A2 should be added to form the
prediction for the current, A3, through the cell.
3
The recorded value should be in amps and be
approximately equal to the value from 2.
4 and 5 The results and prediction should follow
the same format as 1 and 2; circuit diagrams
should be drawn with ammeters clearly labelled
with numbers that match the results.
b
Any two from: if one lamp fails / is
removed the others will continue to work;
the four lamps could be switched on and
off separately; more (identical) lamps
could be connected in parallel without
affecting the brightness.
2.0
c​​ ___ ​​ = 0.5 A
4
4
5
a
b
c
d
1 + 1 = 2A
2 + 2 = 4A
1.5 + 1.0 + 0.5 = 3(.0) A
(0 +) 1 + 0.5 = 1.5 A
a
b
c
d
6 − 3 = 3A
1.0 − 0.4 = 0.6 A
0.3 − 0.2 = 0.1 A
0.25 − 0.15 (−0) = 0.1(0) A
6 and 7 The results in this case should be the
current through the cell minus the currents in
the other branches to give the current in the
remaining branch; circuit diagrams should
be drawn with ammeters clearly labelled with
numbers that match the results.
Topic 9.2 Current and voltage in
parallel circuits
Getting started
1
electrons
2
they move faster
3
amps / A
Questions
1
An ammeter is used to measure the current
through a component.
An ammeter should be connected in series
with the component.
A voltmeter is used to measure the voltage
across a component.
A voltmeter should be connected in parallel
with the component.
2
C
3
a
b
Activity: Measuring current in parallel
circuits
The teacher should observe the readings on the
ammeters. If digital meters are used there may be
small fluctuations in the readings. This could cause
learners to think that the results differ from what
they may expect, so using less-sensitive meters or
simply advising learners to estimate the mid-point
of any fluctuations may be required.
31
1
Table can be horizontal or vertical, so values
for the current arranged in a row or in a
column; must be logical and include units in
the column / row headers.
2
Conclusion should be that the current A1
divides / splits into A2, A3 and A4, or that the
220 V
Redrawn diagram should have switch
(open or closed) in the top part above the
uppermost lamp and on either side of the
power supply.
2.4
c i​​ ___ ​​ = 0.4 A
6
ii
the current will increase / the current
will become 2.4 + 0.4 + 0.4 = 3.2 A
or 8 × 0.4 = 3.2 A
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
4
a
The rating of each lamp is 2 V / is less
than 12 V; connecting each lamp in
parallel with the battery will mean the
voltage across one lamp will be 12 V / will
exceed the rating; the lamps will be broken
/ damaged.
12
b i​​ ___ ​​= 6 lamps
2
ii
Circuit diagram with a battery (two
cells separated by a dashed line) and
six lamps in series; the circuit can
include a switch in the open or closed
position.
iii
Circuit diagram in b ii with a
voltmeter placed in parallel with any
one of the lamps..
5
a
a
b
Voltage across both buzzers = 1 + 1 = 2 V.
Voltage across both lamps = 6 − 2 = 4 V.
Voltage across one lamp = 4 ÷ 2 = 2 V.
iThe voltage of the power supply is
doubled, so the voltage across each
component will be doubled, so 2 V.
Table should have: column for number of
lamps (in ascending order); three columns for
current through the cell in A (or amps); column
for averages.
2
Graph with axes the right way around (as
specified in Learner’s Book). Linear scales
that allow points to cover at least half the grid
in both directions. Line of best fit or smooth
curve drawn, based on their points.
3
a
b
4
As the number of lamps increases, the
current through the cell increases.
When the number of lamps doubles the
current through the cell doubles (or a
comment that matches their observed
results).
Calculation should be based on the results
table or the graph. Predicted current should
be, for example, two times that with four
lamps, or four times that with two lamps.
Topic 9.3 Resistance
Getting started
1
Current is the movement of electrons;
electrons flow from negative to positive.
ii current increases
2
Activity: Measuring voltage in a
series circuit
Conductors allow the flow of electrons,
whereas insulators inhibit the flow.
3
An attempt to stop something from happening
or progressing.
1 and 2 Circuits should be correctly drawn and
should show the lamps labelled with the letter
L and a subscript number. Voltmeters should
be drawn in parallel with components; these
could be labelled with the letter V and a
subscript number.
3
4
5
32
1
9 − 2 = 7V
b i voltage decreases
ii current decreases
6
Think like a scientist: Measuring current
in a parallel circuit
Tables can show voltages for each circuit in
either rows or columns but should be logical
and contain the unit (V) in the header only.
The explanation could be (if all components
in series were identical) that the voltage across
each component is equal. The explanation
should include a statement that the voltages
across each of the components add up to the
voltage across the cell or power supply.
Any other circuits should be represented by
labelled circuit diagrams. Results should be
recorded as in 3. The conclusion should be
that similar trends are observed with other
circuits.
Questions
1
Copper wires have a very low resistance.
That makes it very easy for current to flow in
copper wires.
A resistor of 10 000 Ω has a high resistance.
2
a
ohm(s) / Ω
voltage
resistance = _______
​​
​​
current
Equation can be written in terms of
voltage or current or in letter symbols
using V, I and R.
c current
b
3
a
b
c
voltage __
6
resistance = _______
​​
​​ = ​​   ​​ = 2 Ω
current 3
voltage __
9
​​ = ​​   ​​ = 4.5 Ω
resistance = _______
​​
current 2
voltage ___
1.5
​​ = ​​   ​​ = 3 Ω
resistance = _______
​​
current 0.5
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
4
a
b
voltage =
current × resistance
= 2 × 6 = 12 V
voltage
12
current = _________
​​
​​ = ____
​​
​​ = 0.12 V
resistance 100
Activity: Working out resistance
1
Circuit should show an ammeter in series with
the component and a voltmeter in parallel
with the component.
2
Table should have the name of the component
(independent variable) in the left column, with
further columns for current and voltage. Units
for current and voltage should be in the column
headers, not in the body of the table.
voltage
a Resistance calculated as _______
​​
​​ for each
current
component.
b Another column added to the table with
resistance in ohms or resistance in Ω in the
column header.
3
4
a and b The correct components from their
list, named in both cases.
Think like a scientist: Current and
voltage in a resistor
1
2
3
Table should have columns for voltage (in
ascending order) and current. Units for
current and voltage should be in the column
headers, not in the body of the table.
Graph with axes the same way round as
specified in Learner’s Book and labelled
with units. Linear scales that allow points to
cover at least half the grid in both directions.
All points plotted correctly and line of best
fit drawn (appropriate line or curve drawn
according to their own results).
a
b
4
a
b
The trend should be that as the voltage
increases, the current increases.
Greater voltage means more energy to
drive the current, so the current can move
faster (current can be expressed in terms
of electron flow).
The line will also be straight, but have a
gradient that is less steep (the current will
be smaller for any given voltage).
The line will also be straight, but have a
gradient that is steeper (the current will be
larger for any given voltage).
Topic 9.4 Practical circuits
Getting started
1
Drawings of components using correct circuit
symbols.
2
cell – to provide electrical energy for the
circuit / to drive current
switch – to start and stop the flow of current
resistor – to slow current
ammeter – to measure current
voltmeter – to measure voltage
lamp – to emit light
buzzer – to make a sound
3
a
b
in parallel with the lamp
in series with the resistor
Questions
1
a
b
2
C
3
Circuit diagram should have a cell and a
switch close to the cell, with two identical
parallel branches, each containing a variable
resistor and a lamp.
4
a
b
Circuit diagram should have two cells, a
lamp, an ammeter and a buzzer in series,
with a voltmeter in parallel across the buzzer.
Circuit diagram should have two cells
and two parallel branches. One parallel
branch should have a lamp, a switch and
a variable resistor, the other should have a
buzzer and a switch.
Think like a scientist: Designing and
building circuits
1
Observations will be specific to the learner, or
they may state that the activity was successful
and everything worked as expected.
2
The suggestions will depend on the learner,
but should be specific. For example, ‘The tape
did not hold the wires onto the cell properly so
the current varied: it would be better to use a
cell holder or stronger tape.’
Check your progress
9.1 a
1.2 + 1.2 = 2.4 A
b i 6 ÷ 3 = 2A
ii A1 = A2 + A3 + A4
33
Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
9.2 a
b
9.3 a
b
c
decreases
decreases
decreases
9.4 a
b
increases
increases
9.5 a
resistance = voltage ÷ current
b
9.6 a
b
c
9.7 a
b
34
(ammeter) in series (with the other
components)
(voltmeter) in parallel across / in parallel
with the resistor
9.8 a
b
c
A and C
B
A
9.9 Circuit diagram should have three parallel
branches across one cell (cell or battery can
be shown). One branch to have a lamp, a
switch (can be shown open or closed) and
an ammeter; one branch to have a lamp, a
switch and a variable resistor; one branch to
have a switch and a buzzer. Branches can be
in any order.
Science Skills
ohms / Ω
resistance = voltage ÷ current
12 ÷ 2 = 6 ohms / Ω
voltage = current × resistance
0.5 × 18; = 9; volts / V
current = voltage ÷ resistance
6 ÷ 4 = 1.5 amps / A
Questions
variable resistor
Current decreases because increased
resistance makes it more difficult for
current to flow / more difficult for
electrons to flow / slows the flow of
electrons.
2
1
a
A = __
​​  F
p ​​
b
F = pA
= 50 × 3
= 150 N
a
moment
Force = _________________
​​     ​​
distance from pivot
b
500
Force = ____
​​   ​​
10
= 50 N
Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021