CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Workbook answers
Unit 1 Cells
Plant cell A comes from a leaf. This is
because it has chloroplasts, which contain
chlorophyll that absorbs energy from light for
photosynthesis. Photosynthesis takes place in
leaves. Plant cells that are not in the light do
not contain chloroplasts.
2
Topic 1.1 Plant cells
Exercise 1.1A Structure of a plant cell
sap vacuole
cell wall
Topic 1.2 Animal cells
cell membrane
chloroplast
Exercise 1.2 How to use a microscope
1
eyepiece
coarse
focusing knob
cytoplasm
mitochondrion
nucleus
fine
focusing knob
mirror
For example:
Use a ruler to draw the label lines.
2
Make sure that each line connects the label to
the part accurately.
2
cell wall
cytoplasm
cell
membrane
chloroplast
sap vacuole
nucleus
Exercise 1.1C Different plant cells
1
The most likely answers are:
•
She has not placed the part of the slide
containing cells over the hole in the stage.
•
She has not focused the microscope
correctly.
•
She has not adjusted the mirror so that
light passes through the slide.
Be prepared to accept other sensible answers.
3
There is no ‘correct’ answer to this open-ended
question. Look for:
•
Useful advice that a learner could
follow to be successful in seeing cells,
e.g. referring to the three suggestions in
the answer to question 2.
•
Advice written in a clear manner.
•
Advice provided in a sensible sequence, in
the order of the steps that Zara would take.
Plant cell A has chloroplasts, but plant cell B
does not.
Plant cell A is rectangular, but plant cell B is
hexagonal.
Plant cell A has a larger sap vacuole than
plant cell B.
1
medium-power
objective lens
low-power
objective lens
microscope stage
Exercise 1.1B Drawing and labelling a
plant cell
1
high-power
objective lens
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Topic 1.3 Specialised cells
Exercise 1.3 How cells are specialised
for their functions
1
2
3
a
ed blood cells contain a substance called
R
haemoglobin. This helps them to carry
oxygen around the body.
b
Red blood cells are smaller than most
cells. This helps them to squeeze
through the small blood vessels called
capillaries.
a
Root hair (cell)
b
It has a cell wall and a large sap vacuole.
c
Absorb water and mineral ions from the
soil.
d
It has a long extension that makes it easy
for water to move into from the soil.
a
The table should be designed so that
contrasting points are aligned with each
other. Note that the question does not
ask for comparisons of function, only
structure.
Exercise 1.4A Identifying cells, tissues,
organs and organ systems
Words
Diagrams
cell
tissue
organ
Ciliated cell
Palisade cell
does not have a cell
wall
has a cell wall
does not have
chloroplasts
has chloroplasts
has cilia
does not have cilia
has a nucleus
has a nucleus
Exercise 1.4B Human organ systems
has cytoplasm
has cytoplasm
has a cell membrane
has a cell membrane
Function
Organ
system
Some organs
in the system
does not have a sap
vacuole
has a sap vacuole
transporting
substances
around the
body
circulatory
system
e.g. heart,
arteries, veins,
capillaries
breaking down digestive
system
food and
absorbing it
into the blood
e.g. stomach,
intestines, liver
taking oxygen
into the body
and getting
rid of carbon
dioxide
e.g. lungs,
trachea
b
Look for descriptions that use different
forms of words from those in the
Learner’s Book, such as:
Ciliated cells have many tiny cilia on one
surface. These can wave in a ripple-like
movement, which moves mucus over their
surfaces. The mucus traps bacteria and dust,
and the cilia sweep this away from the lungs.
Palisade cells have many chloroplasts.
This is where photosynthesis happens,
so palisade cells are adapted to carry out
photosynthesis and make food for the plant.
2
Topic 1.4 Cells, tissues and
organs
organ
system
respiratory
system
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Function
Organ
system
Some organs
in the system
helping
different parts
of the body to
communicate
with one
another
nervous
system
e.g. brain,
nerves, spinal
cord, any
sense organs
(eye)
Exercise 1.4C Sting cells in Hydra
1
2
a
Tissue
b
Tissue
c
Cell
d
Organ
and Hydra just have a cavity inside which food
is digested.
3
Nucleus, cytoplasm, cell membrane
4
It does not have a cell wall. This is the only
genuinely distinguishing feature. The lack of a
large vacuole or lack of chloroplasts does not
mean it is definitely not a plant cell, as there
are many examples of plant cells that lack
these features.
5
Look for an explanation that relates the
structures inside the sting cell and its behaviour
to its function of trapping (and possibly
killing) prey. The answer must not replicate the
sentences in the text preceding the diagrams.
Students should use the information from here,
but present it in their own words.
No, Hydra do not have a digestive system. A
system is made up of many different organs,
Unit 2 Materials and their structure
Topic 2.1 Solids, liquids and gases
Exercise 2.1A Sorting solids, liquids
and gases
4
Yes, he is correct. Material D can flow, so it
could be a gas or a liquid. Material D keeps
the same volume, so it must be a liquid.
5
Material E keeps the same volume, so it
cannot be a gas.
6
He should test to see if material E can flow.
If it can flow (be poured), it is a liquid. If it
cannot flow, it is a solid.
1 and 2
Solids
Liquids
Gases
Flour
Milk
Butane Gas
Butter
Beaten Eggs
Air
Sugar
Water
Flame
Cooking Pan
Exercise 2.1C Properties of solids,
liquids and gases.
1
Butane Gas
Burner
Football
3
2
A
A liquid and a gas.
B
A liquid and a gas. However, since the
containers have no lid, the gas would escape.
Candle
A
Flour is a powder. Although each
individual speck of flour is solid, it is
so small that it can flow and be poured.
Exercise 2.1B Solid, liquid or gas?
B
The flour is formed of small specks
which are solid. These maintain their
shape, but there are spaces between them
as the flour is in the form of a powder,
so the specks can move past one another
to form a different shape.
C
The specks of flour have air in the spaces
between them and when the specks are
pushed together the air is forced out. This
allows the specks to be squeezed into a
smaller space.
1
A is a gas. The test shows that it can be
compressed. Only gasses can be compressed.
2
B can flow, so it could be a gas or a liquid. It
keeps the same volume, so it must be a liquid.
3
Learners should suggest testing to see if
material C can be compressed. If it can, then
C is a gas; if not, it is a liquid.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Topic 2.2 Changes of state
7
Exercise 2.2 Marcus’s water heating
investigation
1
Marcus wears safety glasses.
2
Table drawn; two columns with headings Time
in minutes and Temperature in °C.
3
After four minutes the temperature is 54 °C.
At the start, the temperature is 22 °C.
After three minutes the temperature is 46 °C.
After one minute the temperature is 30 °C.
After five minutes the temperature is 62 °C.
After two minutes the temperature is 38 °C.
4
5
Time in minutes
Temperature in °C
0
22
1
30
2
38
3
46
4
54
5
62
he point at five minutes does not fit the
T
pattern. This point should be circled.
b
Zara should ignore it on her graph.
8
Give credit for a smooth line that does not
join point-to-point and is not affected by the
point at five minutes.
9
The line goes up steeply as the temperature
increases. The slope of the curve decreases at
the eight-minutes mark and becomes almost
flat from that point on.
10 The temperatures remain about the same at
the end of the investigation because, although
there is more heat energy reaching the water,
the water is boiling and the energy is being
used for the particles of water to change to a
gas and escape as steam.
11 a
b
There is a smaller volume of liquid at the
end of the investigation because some of
the liquid water has been converted to a
gas and has escaped from the container
into the room.
Temperature in °C
60
Topic 2.3 Explaining changes
of state
50
Exercise 2.3A Change of state
40
1
Solid
2
Heading B: Particles in a solid: Particles
shown in the box should all be the same
size, similar to those shown in diagram A.
They should all be arranged in regular rows
touching one another.
3
Gas
4
Heading C: Particles in a gas: Particles shown
in the box should all be the same size, similar
to those shown in diagram A. They should all
be arranged so they are spaced far apart and
not touching one another.
5
Gain; more; strong; past; liquid
30
10
0
0
1
2
3
4
5
Time in minutes
The graph shows that the longer the water is
heated, the higher the temperature. The line
is straight, which shows that the temperature
increases regularly (by 8 °C per minute).
As long as the learner gives the idea of a
relationship between time for heating and an
increase in temperature, give them credit.
6
melting
solid
4
No. There is a smaller volume.
70
20
6
a
freezing
boiling
oiling
liquid
condensing
densing
gas
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Exercise 2.3B Particle theory and
change of state
1
2
3
In ice, water particles are in a fixed position as
it is a solid. During heating, energy transfers
to the water particles, allowing them to escape
the forces holding them in place. The particles
begin to move past each other, forming liquid
water.
The particles in the iron bar are in a fixed
position and can vibrate. As the bar is heated
the particles gain energy and can vibrate more.
As the particles vibrate they take up slightly
more space and the metal bar expands.
a
Gas
b
Condensation
c
Vibrate
d
Melting
e
Evaporation
f
Move
g
Gas
Exercise 2.3C Explaining changes of state
1
2
3
5
The particles in a liquid are touching each
other and have enough energy to be able to
slide past one another to change their positions.
They are held together by weak forces. When
the liquid is frozen, heat energy is transferred to
the freezer. The energy is lost from the particles
and they are not able to move as much. The
particles become unable to slide past one
another and become fixed in regular rows with
all the particles touching one another.
The particles in a gas are spread out, have
no forces holding them together and have so
much energy that they can move about. When
the particles touch a cold surface, some of
their heat energy is transferred to it so the
particles lose heat energy. This means that the
particles cannot move about, but can move
past one another forming a liquid with the
particles touching one another.
The particles in a liquid are touching each
other and have enough energy to be able
to slide past one another to change their
positions. They are held together by weak
forces. When a liquid is heated the particles
gain energy and are able to move more and
escape the weak forces holding them together
and change into a gas.
4
Learners may list words they have not used,
but are appropriate here. Answers depend on
the learners.
Topic 2.4 The water cycle
Exercise 2.4 The water cycle
1
2
a
Ocean
b
Clouds
c
Precipitation
d
Evaporation
e
Transpiration
f
Surface run-off
g
Ground water
3
The Sun
4
Particles of water evaporate from the ocean.
Particles have energy transferred to them and
can move more, so they can overcome the
forces holding them together. The liquid water
changes to water vapour, a gas. This gas rises
up into the atmosphere where it forms clouds.
5
It rains because the particles of water vapour
in the clouds get colder, so they lose energy,
and because the particles cannot move so
much they form drops of water that are too
heavy to stay in the clouds and fall as rain.
6
Precipitation is rain or anything else that falls
from clouds. It can take the form of liquid
water which is rain, solid lumps of ice which
is hail, or snow which is also made of ice, but
not so solid. Credit sleet, which is between
rain and snow. For hail or snow to fall it must
be colder than when rain falls.
Topic 2.5 Atoms, elements and
the Periodic Table
Exercise 2.5 Atoms, elements and the
Periodic Table
1
a
Na
b
Mg
c
B
d
Ca
e
K
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
2
3
4
a
Argon
d
Copper oxide
b
Phosphorous
e
Iron chloride
c
Carbon
a
Sodium oxide
d
Chlorine
b
Calcium carbonate
e
Lithium
c
Potassium nitrate
a
Non-metals
d
Potassium nitride
b
The vertical column containing
magnesium should be circled red.
e
Hydrogen fluoride
c
The horizontal row that contains oxygen
should be circled blue and should include
lithium and beryllium.
a
Carbon and oxygen
b
Copper, oxygen and sulfur
c
Aluminium and chlorine
d
Sodium and sulfur
e
Calcium, oxygen and chlorine
3
4
The vertical column containing aluminium
and boron should be circled green.
3b
3c
Group that
contains
magnesium
4
Period that
contains
oxygen
Group that
contains
a metal and
non-metal
H
He
hydrogen
helium
Li
Be
B
C
N
O
F
Ne
lithium
beryllium
boron
carbon
nitrogen
oxygen
fluorine
neon
Na
Mg
Al
Si
P
S
Cl
Ar
sodium
magnesium
aluminium
silicon
phosphorus
sulfur
chlorine
argon
K
Ca
potassium
calcium
5
One of nitrogen, oxygen, fluorine or neon
6
Magnesium or beryllium
7
One of silicon, phosphorous, sulfur, chlorine,
argon, potassium or calcium
8
Carbon or boron
Topic 2.6 Compounds and formulae
5
Potassium, oxygen and hydrogen
6
Answers shown in table
Chemical
name
Formula
What the
compound
contains
magnesium
oxide
MgO
sulfur dioxide
SO2
aluminium
chloride
AlCl3
calcium sulfide
CaS
magnesium
carbonate
MgCO3
one magnesium
atom bonded
to one oxygen
atom
one sulfur atom
bonded to two
oxygen atoms
one aluminium
atom bonded to
three chlorine
atoms
one calcium
atom bonded to
one sulfur atom
one magnesium
atom bonded
to one carbon
atom and three
oxygen atoms
Exercise 2.6 Compounds and formulae
1
2
6
a
True
b
False
c
True
d
False
e
False
f
7
a
NaCO3
False
b
CaCl2
g
True
c
CaCO3
a
Potassium and chlorine
d
O2
b
Potassium
e
K2CO3
c
Magnesium and oxygen
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
8
9
a
his particle is made of 12 atoms of
T
carbon, 22 atoms of hydrogen and 11
atoms of oxygen.
b
It means two particles of the sugar maltose.
a
Magnesium hydroxide
b
2
c
2
7
a
Iron sulfide is a compound. A mixture
would be iron filings mixed with sulfur
powder. Accept any other correct
example.
b
In the compound the elements are
bonded together and the new product has
different properties from the elements that
made it. In the mixture the elements are
not bonded together and no new product
is formed. The elements retain their
properties in a mixture.
c
The compound iron sulfide is not
magnetic, but iron is. Sulfur is a bright
yellow colour, but iron sulfide is not.
Accept any other correct answers.
d
In the mixture the iron is still magnetic
but in the compound it is not. The
elements retain their properties in the
mixture: the iron is still a grey colour and
the sulfur is still yellow. They are just
mixed together and can be separated. In
the compound the elements are not easily
separated.
10 Calcium hydroxide; Ca(OH)2
Topic 2.7 Compounds and
mixtures
Exercise 2.7 Compounds and mixtures
1
The correct statements are a, c, d, f, h, i.
2
A, C and D.
3
C and E
4
F
5
E
6
C
Unit 3 Forces and energy
Topic 3.1 Gravity, weight and
mass
Exercise 3.1B Values of weight and
mass
Exercise 3.1A Differences between
weight and mass
1
Mass can be measured in g or kg.
2
120 kg, 6.04 kg, 0.001 g
3
a​​ ___
10 ​​ = 25 kg or kilograms
1
Weight is measured in N.
2
Bottom row - tick force meter
weight
0.9
b
​​ ___
10 ​​ = 0.09 kg or 90 g
Changes, depending on the strength of
gravity.
c
It will be less than 10.
d
It would be the same; mass is the quantity
of matter in an object; mass is not
affected by (the strength of) gravity.
The quantity of matter in an object.
Constant, even when the strength of gravity
changes.
7
250
The force of gravity on an object.
mass
3
Top row - tick top pan balance
a
75 × 10 = 750 N or newtons
b
900 × 10 = 900 N or newtons
c
0.1 × 10 = 1 N or newtons
Exercise 3.1C Effect of gravity on
objects
1
Arrows should point towards the centre of the
Earth.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
2
3
a
Similar: attract/pull things together; they
are both non-contact forces/both act at a
distance.
b
Different: magnets can repel/gravity
cannot repel.
a
Newton meter/force meter
b
Axes labelled with the quantity and unit:
mass in kg on the x-axis and weight in
N on the y-axis. Linear scales starting at
zero on both axes and sensible use of the
grid, e.g. 1 large square to 0.1 kg and to
1
1.0 N. All points plotted to within _​​ 2 ​​ small
square.
c
Straight line ruled through points.
d
Mass is independent; weight is dependent
e
Weight of 1.0 kg is 9.8 N, so weight of
2.0 kg is 2 × 9.8 = 19.6 N
2
Scientists think the Solar System formed from
a cloud of dust and gas – hypothesis
Scientists use computers to demonstrate
the formation of the Solar System –
modelling
Scientists can see that stars are forming
in clouds of dust and gas in space – observing
Scientists know that all the planets orbit the
Sun in the same direction – evidence
Topic 3.3 Movement in space
Exercise 3.3A Travelling through space
1
Arrow should point towards the Sun
direction of
orbit
Topic 3.2 Formation of the Solar
System
Sun
Exercise 3.2A Ideas about formation of
the Solar System
Neptune
1
Jupiter
Earth
Mercury
Venus
Mars
Uranus
Saturn
2
2
b
Air resistance
a
Hypothesis
1
There is no air resistance.
b
Gravity
2
Arrow from R toward centre of planet.
c
Scientists use computers to model the
formation of the Solar System.
1
Nebula
2
Telescope
3
An observation
4
Fair tests
R
Exercise 3.3C Speeding up, slowing
down and changing direction
1
Exercise 3.2C Observing and predicting
8
Vacuum
Exercise 3.3B Are there forces in space?
Exercise 3.2B Watching stars being
born
1
a
ecause it takes millions of years/cannot be
B
completed in a person’s lifetime.
2
a
To overcome gravity and air resistance.
b
Air resistance is a force that slows things
down/acts opposite to movement.
Path curves towards, but does not touch,
Jupiter; extent of curve can be very little or
very great; path must not show start of orbit
around Jupiter.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Topic 3.4 Tides
Topic 3.5 Energy
Exercise 3.4A High and low tides
Exercise 3.5A Describing energy
1
Tidal forces from the Sun and Moon.
2
a
12 (hours)
Elastic – energy stored in an object that has
changed shape.
b
6 (hours)
Gravitational potential – energy in objects that are
lifted higher.
Electrical – energy carried by current in wires.
3
Moon Earth
Chemical – energy stored in fuel.
Sun
Sound – energy transferred from vibrations.
Thermal – energy in hot objects.
Earth
Light – energy that we can see.
Sun
Kinetic – energy of moving objects.
Moon
Exercise 3.5B Examples of energy
Earth Moon
1
Sun
Moon
Earth
1
11:00 same day
2
a
3.2 (m)
b
Any interval between 15 minutes and
60 minutes/1 hour.
2
A book lifted up onto a shelf has a store
of gravitational potential energy.
c
The Sun transfers thermal energy and light
energy to Earth (words can be in either order).
d
A musical instrument transfers sound
energy to our ears.
1
This force is called a tidal force.
2
Arrow pointing from A towards the (centre of)
the Moon.
1
Kinetic
2
A prediction
3
Two reasons from: too dangerous/unsafe;
temperature difference was too small for
them to detect; too difficult to measure the
temperature at the top and bottom at the same
time.
Topic 3.6 Changes in energy
Moon
Earth
High tide, because the gravity from the Moon
is pulling the water at A; water will be deeper
at A (than at other tide times).
20:00 or 8.00 p.m
Gravitational potential and chemical are stored.
Exercise 3.5C Energy investigations
A
9
b
Thermal and light are transferred.
Exercise 3.4C Forces and tides
4
Food is a store of chemical energy.
Sun
Exercise 3.4B Times of the tides
3
a
Exercise 3.6A Energy diagrams
1
Electrical � light
2
Electrical � sound
3
Chemical � kinetic
4
Gravitational potential � kinetic
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
1
Energy (example)
s the thermal energy transferred increases
A
the temperature of the water increases.
Cannot be decreases in both because energy is
being transferred to the water.
2
Stored
3
Useful
4
Wasted
2
10 °C
5
Recovered
3
Vertical line drawn down from a line at 70 °C
to the 25 000 J on the x-axis.
6
Dissipated
7
Light, thermal, sound
8
Destroyed
Exercise 3.6B Reading from a graph
1
Temperature of water in °C
80
70
60
50
Exercise 3.7B Energy loss
40
1
wo from: same volume/mass of water (do not
T
accept amount), same shape of beaker/same
surface area, same material of beaker, set up in
same place, take temperatures at the same times.
2
Thermal
3
Two from: (surrounding) air, container,
surface that the container is on, e.g. bench/
table.
4
Measure the temperature of the surroundings
before, during and after placing the hot
water. The temperature will have increased (if
thermal energy has gone there).
5
One from: do not touch hot beakers/hot water,
stay away from steam, use glassware/container
material that will not shatter/melt when hot
water is added.
30
20
10
0
0
5000
10000
15000
20000
25000
30000
Thermal energy transferred in joules
4
Mass of water used.
Exercise 3.6C Series of energy changes
1
Elastic energy is stored in the (compressed)
spring (when the toy is pushed down); elastic
energy is changed to kinetic energy; kinetic
energy is changed to gravitational potential
as the toy jumps up; gravitational potential is
changed back to kinetic energy as the toy falls
down.
Topic 3.7 Where does energy go?
Exercise 3.7C Wasted energy
Exercise 3.7A Energy word search
1
100 − 80 = 20%
T D E
2
a
100 − 25 = 75%
b
Two from: thermal; sound/vibration,
chemical if clearly referring to unburned
fuel/chemicals in exhaust.
c
Diesel engine is more efficient; idea that
it will be more cost-effective/cheaper in
the long-term; make more profit as less
money spent on fuel.
S
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Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Unit 4 Grouping and identifying organisms
Topic 4.1 Characteristics of living
organisms
Exercise 4.1A Matching terms and
descriptions
Nutrition – feeding – taking in materials from the
environment for energy and growth.
Exercise 4.1C Living or not?
This is a challenging activity. Learners may be able
to appreciate that deciding whether something
is alive or not is not completely straightforward.
Look for the following ideas in the learner’s
answers:
•
The characteristics of living things
are sensitivity, respiration, movement,
excretion, nutrition, reproduction and
growth.
•
Anything that shows all of these
characteristics is a living thing.
Respiration – breaking down nutrients to release
energy.
Excretion – getting rid of waste materials.
Reproduction – making new individuals of the
same kind of organism.
Growth – getting bigger.
Sensitivity – detecting changes in the
environment.
Movement – changing the position of part or all
of the body.
Exercise 4.1B Characteristics of living
organisms
11
Not all living things show these characteristics
all of the time: an elephant, for example, is alive
but does not reproduce all the time; apples do
not show sensitivity (but they are respiring, and
they contain seeds that will grow into a complete
living thing); seeds do not move (but will
eventually grow into a plant that can move parts
of its body).
1
Sensitivity
Topic 4.2 Viruses
2
Respiration
Exercise 4.2: All about viruses
3
Movement
1
4
Excretion
Viruses are very small. Viruses are not made
of cells. Viruses can only replicate when they
are inside a living cell.
5
Nutrition
2
a
They can replicate.
6
Reproduction
b
7
Growth
They can only replicate inside a living
cell and they are unable to carry out
any of the other characteristics of living
organisms.
a
earners should ensure that they use
L
trustworthy websites, such as those from
universities. They may also use Wikipedia,
although care always has to be taken
with this site, as entries are not always
correct or unbiased. If Wikipedia is used,
it is good to check that the information
it provides matches information on
academic sites.
b
The first virus to be discovered was tobacco
mosaic virus. A Russian scientist, Ivanovsky,
found that if he passed extracts from
infected leaves through a filter, bacteria
could not get through: the extract could
still infect other leaves. He concluded that
there was something in the extract that
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Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
was even smaller than bacteria and could
cause infection. But he did not use the word
‘virus’ and he thought that the ‘something’
was probably a chemical. In 1898, a Dutch
scientist called Beijerinck did further work
on this subject and decided that ‘viruses’
were a liquid. It was some years later that
an American scientist, Stanley, proved that
they were very small particles.
Look for these features in the students’ answers.
•
An appreciation of the importance of using
several specimens to study, because of
variation within a species, but that studying
too many of the frogs might endanger the
species, especially if these are not returned to
their natural habitat.
•
A clear, simple description or list of what
evidence the scientists should collect. This
could include information about observable
features, such as coloration, measurements of
body parts, behaviour and perhaps a study of
its genes, and that these should be compared
with the same features in other similar frog
species. Some students might also suggest
studying the tadpole, to see if they differ
in any way from the tadpoles of the other
species.
•
Reference to the ability of this frog to breed
with known species of frog to produce fertile
offspring.
•
Suggestions about how the scientists could
use their information to test their hypothesis
that the frog belongs to a new species, such as
investigating whether the newly-found frogs
can breed with other similar species, as well
as making a detailed comparison of their
appearance with these other species.
•
Reference to how other scientists might
evaluate this evidence, such as checking the
data that is relies on, looking at the number of
frogs that have been found and investigated,
and checking if it is possible to repeat the
findings of the first group of scientists.
•
Some students may also be able to add
information that they find on the internet.
For this, it is very important to make sure that
they have written in their own words, and not
copied sentences directly from their sources.
Note that progress was slow because
microscopes were not yet able to ‘see’ very
small things such as viruses.
Topic 4.3 What is a species?
Exercise 4.3A Different species
White rhinoceroses and Indian rhinoceroses
belong to different species. This means that they
cannot reproduce with each other to produce fertile
offspring.
White rhinoceroses and Indian rhinoceroses do
not look exactly the same as one another. Indian
rhinoceroses have one horn but white rhinoceroses
have two horns.
Exercise 4.3B Horses, donkeys and
mules
1
There is a wide range of similarities that
students could find, such as having four legs,
two ears, hair on the body and so on. Allow
any correct answers.
2
There are various answers that students might
give. For example, the donkey is smaller; it has
longer hair along its neck.
3
They have different Latin names. They cannot
breed together to produce fertile offspring.
Exercise 4.3C A new frog species
This is a very open-ended task and many students
will benefit from discussion about the issues involved
before attempting to construct their answer. This
could be done as a class discussion, or you could ask
students to discuss in pairs or small groups. They
could then either write their answers individually or
work together to construct an answer.
Some students may simply state that the
researchers should find out whether this frog
can breed with frogs of other species. You could
explain the great difficulties in determining
this, and that usually decisions about species
are made by making comparisons between the
characteristics of the organisms.
12
Topic 4.4 Using keys
Exercise 4.4A Using a key to identify a
fruit
Fruit B is sycamore.
Exercise 4.4B Using a key to identify
four fish
1
a
1a
b
Basking shark (its eye is above the front
end of its mouth)
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
2
a
1b
b
Sea bream (it has short spines on its top fin)
3
Greenland shark
4
John Dory
Exercise 4.4C Using a key to identify
tree species, using their leaves
1
Leaf A is hazel.
2
1b, 2a, 3b
3
Leaf B: 1a, rowan
Leaf E: 1b, 2b, maple
•
Edge (the proper biological term is the
margin) – smooth or jagged.
•
Veins – form a network, or run parallel to
the midrib.
•
Texture – smooth or rough.
•
Stalk – some have a leaf stalk and some
do not.
•
Size – some are larger than others.
The key should have questions that relate
to the differences identified in the answer to
question 1. Check that the key works.
3
The key should have these features:
• There should be a series of choices to
make, each time deciding between two
contrasting statements.
• Each choice should be possible to make
while looking at only one leaf, so a choice
between ‘large’ and ‘small’ is not suitable.
• The key should have no more than four
pairs of choices to make.
Topic 4.5 Writing keys
Exercise 4.5 Making a key to identify
plant species from their leaves
1
Shape – one whole shape, or divided into
three parts, or with several ‘fingers’.
2
Leaf C: 1b, 2a, 3a, 4b, cherry
Leaf D: 1b, 2a, 3a, 4a, willow
•
Answers to include:
Unit 5 Properties of materials
Topic 5.1 Metals and non-metals
Exercise 5.1 Metal properties and uses
Topic 5.2 Comparing metals and
non-metals
1
2
3
4
13
a
Iron is used for building bridges.
Exercise 5.2A Metal or non-metal?
b
Gold is used for jewellery.
1
c
Copper is used for electrical wiring.
List of
materials
Sofia's answer
Correct?
Silver
Metal
�
Oxygen
Non-metal
�
The following terms should be circled:
malleable; feels cold to the touch; makes a
ringing sound when tapped; conducts heat;
ductile; has a shiny surface.
Helium
Non-metal
�
Carbon
Metal
�
a
Sonorous
Copper
Metal
�
b
Ductile
Nitrogen
Non-metal
�
c
Malleable
Sulfur
Metal
�
d
Shiny
Iron
Metal
�
e
Magnetic
f
Conductor
2
5
g
Properties
3
3
4
3
5
5
Credit a correct named metal and any
descriptive words. Credit any appropriate
property linked to a function.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
6
circuits. Due to its toxicity, mercury is no
longer used in thermometers and barometers.
Bar chart of metals and non-metals
5
Substance B is a non-metal.
Reasons: because it is dull and brittle and only
one form (dull brittle) conducts electricity. The
shiny form does not conduct electricity.
4
It is carbon.
3
Use: In the dull, soft form it is used in pencils
for drawing, because it is so soft the carbon
wears away as it leaves marks on the paper. It
is also used in electrical motors as brushes. The
hard shiny form is diamond, which is used in
jewellery because it is shiny, rare and expensive.
Diamond is also used in drills to cut through
other substances because it is so hard.
2
1
0
metals
Substance C is a non-metal.
non-metals
Reasons: because it is a gas at room
temperature and it does not conduct electricity.
Exercise 5.2B Comparing metals and
non-metals
It is oxygen.
Use: Oxygen is used in respiration of most
living things. It is also very reactive and is used
in burning.
If the lamp goes
on, the material
conducts electricity.
1
Substance D is a non-metal.
Reasons: because it is a gas at room
temperature and it does not conduct electricity.
connect the
material you
want to test here.
2
It is helium.
a
False
Use: as it is very unreactive, but very light, it is
used in airships and to inflate balloons.
b
True
Substance E is a metal.
c
False
d
True
Reasons: because it conducts heat and
electricity well.
e
False
It is copper.
Use: for electrical wiring because it is ductile and
conducts electricity well. It is used for cooking
pans because it conducts heat very well.
Exercise 5.2C Identifying metals and
non-metals
1
Substance F is a non-metal.
Give credit for identifying any properties that
indicate metal or non-metal and for any use. If
learners are able to link the use to the properties,
this shows a good use of their knowledge.
Reasons: because it does not conduct
electricity and it is brittle.
It is sulfur.
Use: to harden rubber.
Substance A is a metal.
Reasons: because it conducts electricity.
It is mercury.
Use: It has been used in thermometers
because it is a liquid at room temperature
and it expands a lot with a small increase
in temperature. Learners may also mention
its use in barometers, dental amalgam and
as liquid contact switches in some electrical
14
Topic 5.3 Metal mixtures
Exercise 5.3 Alloys
1
An alloy is a mixture of metals.
2
Accept any correct answers, such as bronze,
nitinol (accept shape memory alloy),
duralumin, 18 carat gold, cupronickel.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
3
The atoms of iron in a solid piece of iron
are lined up in regular rows with the atoms
touching each other. The rows of atoms can
slide over one another when they are hit.
When atoms of another element, such as
carbon, are added to the iron, they disrupt
the regular pattern of the rows, so they do not
slide over one another when they alloy is hit.
This makes the alloy much stronger.
4
Answers to this question will depend which
alloy is chosen. Credit answers that address
the questions in the Workbook and not just a
copied list of information from the internet.
5
Zara must wear safety glasses and take care
when heating the evaporating basin as the
contents may spit. Zara should use tongs to
move the hot evaporating basin if it is not
possible to leave the apparatus in place to
cool. If a Bunsen burner isn’t available, an
alternative suitable heating arrangement such
as a hot plate or spirit burner could be used.
6
Marcus could carefully pick up any large pieces
of glass and sweep the rest of the mixture up
with a dustpan and brush. To keep safe, he could
wear thick gloves when he picks up the glass.
7
Marcus will use the different properties of the
glass and copper sulfate to separate them: the
glass will not dissolve in water, but the copper
sulfate will. Marcus adds water to the mixture
of glass and copper sulfate crystals and stirs
it. The copper sulfate will dissolve, the glass
will not. He should then filter the mixture.
The pieces of glass will not pass through the
filter paper. The solution of copper sulfate
and water will pass through the filter paper.
Marcus should be careful handling the small
pieces of glass in the filter paper. He should
wear gloves and dispose of it carefully.
8
Marcus should then put the solution of copper
sulfate into an evaporating basin and heat it. The
water will evaporate leaving the copper sulfate
behind in the evaporating basin. He needs to
be careful as the solution may spit as it starts to
boil. If this happens he should turn the Bunsen
burner off and leave the solution to evaporate
fully. The property he uses to separate them is
that water boils at 100 °C and changes state to
form a gas, but the copper sulfate does not.
Topic 5.4 Using the properties of
materials to separate mixtures
Exercise 5.4 Separating mixtures
1
Safety glasses, filter funnel, filter paper, conical
flask, evaporating basin, pipe clay triangle,
tripod, Bunsen burner.
2
Diagram should be drawn using a pencil
and ruler and be labelled with filter paper,
filter funnel, conical flask, beaker, clear liquid,
sandy, salty water.
beaker
filter funnel
filter paper
sandy,
salty water
conical flask
clear liquid
3
Zara should take care with the wet filter
paper as it can tear easily. If it tears, the
contents of the beaker will flow into the
conical flask.
4
Diagram should be drawn with a pencil and
ruler. All items should be labelled.
tongs
He may need to dissolve the crystals in distilled
water to wash them if they are not clean and
then reheat to remove the water (as above)
and leave the crystals so that all the water
evaporates off completely. This may take some
time, but he could speed up the process by
placing the evaporating basin in a warm oven.
water
Marcus should use tongs to move the hot
evaporating basin if it is not possible to leave
the apparatus in place to cool. If a Bunsen
burner isn’t available, an alternative suitable
heating arrangement such as a hot plate or
spirit burner could be used.
evaporating
basin
pipe clay
triangle
tripod
Bunsen burner
15
9
The condenser works to separate the
water and food dye by using the different
boiling points of the water and food dye.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Water boils at 100 °C and food dye does not.
The mixture of water and food dye is placed in
the flask and heated once the water is boiling.
The water begins to evaporate leaving the
food dye in the flask. The water vapour/steam
passes out of the flask into the condenser
where it is cooled by the flow of water in the
outer tube. The steam/water vapour condenses
back to liquid water, which is collected in
the beaker. The food dye remains in the
flask because it has a different boiling point
from the water.
5.5 Acids and alkalis
Safety point
Reason
replacing the bottle
stopper as soon as
you have finished
using the bottle
So that you are less
likely to have a spill
if you knock the
bottle over and so
that you do not mix
up which stopper
belongs on which
bottle and you do
not contaminate
the chemicals.
working in an
orderly way
So that you are less
likely to have an
accident, or mix up
what you are doing
and use the wrong
chemical.
Exercise 5.5 Acids and alkalis
1
Acid
Alkali
citric acid, corrosive,
nitric acid, sour,
lemon juice, cola,
vinegar, sharp,
harmful
sodium hydroxide,
washing powder,
harmful, corrosive,
soap, washing soda
2
Corrosive
3
Flammable
Safety point
Reason
wearing safety
glasses
To protect eyes
from sparks and
splashes.
standing up to work If you spill anything
it will not be in your
lap.
placing bottle
stoppers upside
down on the bench
16
So that you do not
get the chemical
on the work surface
or dirt into the
bottle.
5.6 Indicators and the pH scale
Exercise 5.6A Finding mistakes in a
table
Liquid
Colour with
universal
indicator
solution
pH
lemon juice
yellow
4
weakly
alkaline acid
soap
solution
blue/green
8
weakly
alkaline
water
green
57
neutral
hydrochloric blue red
acid
2
strongly acid
sodium
hydroxide
11
strongly
alkaline
blue/purple
Exercise 5.6B Indicators
1
An indicator tells you if a substance is an acid
or an alkali. Also credit any reference to pH
and information about how acidic or alkaline
a substance is, or if a substance is neutral.
2
Cut up some coloured plant material such as
red cabbage or beetroot and place it in the
mortar; crush it using the pestle; add some
ethanol and crush it some more; remove
some of the liquid using the pipette and place
it in a test tube.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
3
4
You could test your indicator solution by
placing a little acid in a test tube and adding a
few drops of the indicator. Record the colour.
Then you could place a little alkali in another
test tube and add a few drops of the indicator
solution. Record the colour change. If your
indicator works there will be different colours
in the acid and the alkali.
you will not be able to decide if it is an acid or
an alkali.
Exercise 5.6C Indicators
1
pH1
2
Universal indicator is more useful than litmus
because litmus only changes to red, blue or
purple giving the indication acid, alkali or
neutral. However, universal indicator has a
range of colour changes, which enables us to
determine the pH between 1 and 14.
If you try to use this type of indicator, you will
not be able to see the colour change because the
coffee or cola will stain it a darker colour, so
Unit 6 Earth physics
b
Topic 6.1 Sound waves
Exercise 6.1 The movement of sound
1
Particles in the air vibrate.
2
True, true, false
3
Sound does not travel though a vacuum
because there are no particles.
4
Particles in the water vibrate up and down.
5
Sound waves need particles to vibrate; there
are no particles in a vacuum.
6
Vibration of the air; idea that vibrations are
related to the music.
7
a
Arrows drawn as � and � or ↔ anywhere
on diagram.
or
or
or
17
Spring drawn with compressed and
stretched coils; does not have to be a
regular pattern; spring must be reasonably
straight.
8
Particles in a solid are closer together/
touching or particles in a gas are far apart/
not touching idea that vibrations can be
passed between particles more easily when the
particles are closer together.
9
Vibrations that are too large can damage parts
of the ear.
Topic 6.2 Reflections of sound
Exercise 6.2 Reflections of sound
1
Echo
2
A flat wall
3
Sound wave is reflected off the walls, floor and
ceiling of the tunnel; he hears the echo.
4
Tunnel; because the walls, floor and ceiling
reflect the sound.
5
a
ar graph with letters A to D on
B
horizontal axis; loudness of echo from 0
to 65 dB on vertical axis; bars of correct
height, equal width and not touching.
b
B
c
C
6
(85 × 2)
Time = ______
​​  340 ​​= 0.5 (seconds)
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
7
The submarine emits a sound. The sound
wave travels through the water and reflects off
the rock. The sound wave arrives back at the
submarine. The time between the sound wave
being emitted and received can be used to
work out the distance to the rock.
Website 2 makes a claim that the Earth is
getting bigger, which is not supported by
evidence. Claim that the Earth is getting
cooler is not supported by evidence. We
know that the plates/continents are not all
moving apart as there are fold mountains and
earthquakes that occur from plates moving
towards each other or sideways. This source
may be biased. It may use facts that are not
relevant.
water
large
rock
Topic 6.4 Changes in the Earth
Topic 6.3 Structure of the Earth
Exercise 6.4 How the Earth changes
Exercise 6.3 Continental drift
1
Plate boundary
2
Earthquake
3
a
etter E anywhere beside a black line and
L
the letter is on land.
b
Letter V anywhere beside a black line and
the letter is in water.
c
Letter M anywhere beside a black line and
the letter is on land.
a
10
b
1000
a
At plate boundaries
b
Either tsunami or idea that large
magnitude earthquake in the ocean can
cause shocks on land that is closest to the
location of the earthquake.
crust
1
2
Core
b
Crust
c
Mantle
d
Inner core
mantle
outer core
4
5
3
Slow movement of the continents
4
The shapes of the continents fit together; the
types of rocks on the different continents
match up where they fit together; the fossils on
the different continents match up where they
fit together.
5
The theory of tectonic plates
6
The Earth’s crust is made of parts called
tectonic plates; these plates are made from
solid rock and move on liquid magma which is
beneath the plates.
7
18
a
inner core
Website 1 is relevant and uses accepted science
of today that is supported by evidence.
Topic 6.5 Solar and lunar eclipses
Exercise 6.5A How eclipses happen
1
The Moon – does not give out its own light.
The Sun – gives out its own light.
The Earth – does not give out its own light.
2
Shadow
3
a
A solar eclipse happens when the Moon
comes between the Sun and the Earth.
b
A lunar eclipse happens when the Earth
comes between the Sun and the Moon.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Exercise 6.5B Diagrams of eclipses
Exercise 6.5C More detail on eclipses
In 1a and 1b positions are more important than
relative sizes.
1
1
Earth
Sun
a
Moon
Earth
total solar
eclipse seen here
Sun
Earth
b
Moon
Sun
Moon
rays of
light from
the Sun
partial solar
eclipse seen here
2
Earth
Moon
Sun
It is daytime on this side of the Earth, so the Moon in its
current position cannot be seen from here.
Unit 7 Microorganisms in the environment
and measure the dependent variable (rate
of growth of bacteria) while keeping other
variables, such as the length of time the agar is
exposed for, the same.
Topic 7.1 Microorganisms
Exercise 7.1 Microorganisms
experiment
1
3
5
1
6
19
4
Set up (at least) three Petri dishes with agar jelly
exactly as described for the previous experiment.
Put all three dishes in the same place, and take off
their lids. Leave the lids off for exactly the same
time. Put one dish in a cold place, for example
a fridge, another in the laboratory (at room
temperature) and another in a warmer place,
such as an incubator. The temperatures could be
measured with a thermometer.
To collect results, the dishes could be left for
a set amount of time, and then the sizes of
the bacterial colonies measured in each dish.
Alternatively, the sizes of the colonies could
be measured and recorded each day, for
several days.
2
2
The length of time he leaves the lid off;
the type of jelly in the dish.
3
There are more microorganisms in the air in
Classroom 203 than in Classroom 204.
4
Bacteria grow faster at a temperature of 30°C
than at 10°C.
5
Look for a description that explains how to
change the independent variable (temperature)
If the hypothesis is correct, the colonies in the
dishes kept in warm places will be larger than
those in the dishes kept in cold places.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Topic 7.2 Food chains and webs
Exercise 7.2A Arctic hares
Exercise 7.3A Decomposers in a
compost heap
Arctic wolf
Arctic fox
gyrfalcon
snowy owl
Arctic hare
Arctic willow
grasses
Circles drawn around glass, metal and
plastic.
2
These things are not organic and they will
not rot/cannot be broken down by
microorganisms.
3
Students may suggest putting the material
onto a microscope slide and looking at
it through a microscope. This should be
credited, but in practice it would be impossible
to pick out microorganisms from among the
non-living parts of the material. It would be
better to mix the material with some water
and then spread a little of the mixture onto
sterile agar jelly in a Petri dish. After some
days, microorganisms in the material will have
formed little colonies on the agar. It would
also be good to have another dish where
just water was added to the jelly as a control
experiment, so that the number of colonies
could be compared.
humans
stingrays
helmet snails
sea urchins
queen conch
pen shells
sea grass
phytoplankton
6
Sea grass and phytoplankton
7
Any two of: sea urchins, pen shells, queen
conch
8
Any two of: helmet snails, stingrays, humans
Exercise 7.3B Investigating leaf decay
1
The October result for the leaves in the 1 cm
mesh bag.
Exercise 7.2C, Constructing a food web
2
The bag with the 1 cm mesh
1
3
Microorganisms, earthworms and other small
animals.
4
Parts of the leaves disappeared because they
decayed. The results show that decay was
greatest when earthworms and other small
animals, as well as microorganisms, could
reach the leaves.
eagles
wild dogs
cheetahs
lions
birds
giraffes
impala
grass rats
locusts
acacia trees
20
1
purple saxifrage
Exercise 7.2B Building up a food web
1–5
Topic 7.3 Microorganisms and
decay
grass
2
There should be green circles around the
acacia trees and grass.
3
There should be blue circles around giraffes,
impala, grass rats and locusts.
4
There should be red circles around wild dogs,
cheetahs, lions, birds and eagles.
Exercise 7.3C Analysing data about
mould on bread
1
The best way would be to use a piece of
mesh, or some transparent paper marked off
in squares of known size, e.g. with 2 mm sides.
They could place the mesh or paper over the
mould, and count how many squares the
mould covers.
2
A circle should be drawn around the number
5, bread sample 2 in dish 4.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
3
4
16 mm2 but, strictly, this should be written as
16.0 mm2, to match the number of decimal
places given for the other means.
8
Look for:
•
An answer that relates to these particular
results, i.e. to mould growing on moist
bread at different temperatures, rather
than a general answer.
•
An explanation – that is, the answer gives
reasons why the results are as shown in
the table or graph, rather than simply
describing the results.
•
A logical explanation, which is easy to
follow sequentially, step by step.
•
An explanation that uses all of the
information provided, and that relates to
the full pattern of results across the whole
range of temperatures.
•
An answer written in the student’s own
words, with almost nothing copied wordfor-word from the information provided.
11.7 mm2
5
Mean area of mould growth in mm2
16
14
12
10
8
6
4
2
–10
6
21
10 20 30 40
Temperature in °C
50
60
There could be variables that the girls were not
able to control, for example:
•
7
0
Despite their best efforts, there may have
been more moisture on some pieces of
bread than others.
•
More mould spores might have landed on
one piece of bread than on another.
•
There might have been small variations
in the nutrient levels in different pieces of
bread, even if they came from the same slice.
•
It is really difficult to estimate the area
that the mould covers, because the patches
are irregular, so the girls’ measurements
may not have been very accurate.
The conclusion should relate to the aim of
the experiment, which was to investigate
how temperature affects the growth of
mould on moist bread. Suitable conclusions
could be:
•
Mould grows best on bread at 40 °C.
•
As temperature increases, the growth of
mould increases, until the temperature is
higher than 40 °C.
•
Mould generally grows better at higher
temperatures than at lower temperatures,
but it does not grow well at temperatures
above 40 °C.
Topic 7.4 Microorganisms in food
webs
Exercise 7.4 Microorganisms in food
webs
1
a
Microorganism
b
Food web
c
Decomposer
decomposers
2
hawks
lizards
small birds
grasshoppers
caterpillars
grass
3
They break down waste material from living
organisms, and also their dead bodies. This
returns nutrients to the soil, which plants can
use to grow. This then supplies food for all the
other organisms in the food web.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Unit 8 Changes to materials
3
If you had to use measuring cylinders of
100 cm3, your results would not be very
accurate, as you would have to change
cylinders during the reaction. This would
result in the loss of some of the gas, so the
results would not be very accurate.
The correct statements are:
4
Zinc sulfate and hydrogen
In a physical change, no new substances are
formed.
5
Magnesium chloride and hydrogen
When iron atoms bond with sulfur atoms, it is
a chemical change.
Topic 8.2 Neutralisation
Topic 8.1 Simple chemical
reactions
Exercise 8.1A Physical and chemical
reactions
1
When you cook an egg, it is a chemical
change.
2
36 cm3
b
Oxygen and hydrogen
c
Oxygen and hydrogen
D
12 cm3
E
47 cm3
Mg
O
O
Mg O
Mg O
magnesium oxide
Hydrogen
3
If a lighted splint is placed in the gas there will
be a ‘pop’ sound.
4
a
zinc +
hydrochloric
zinc
�
+ hydrogen
acid
chloride
Check that learners have drawn the level of
the liquid at these volumes:
B
20 cm3
C
35 cm3
D
15 cm3
E
5 cm3
The lines should be slightly curved, with the
bottom of the curve at the level of the scales
for these volumes.
A
16 cm3
b
sulfuric magnesium
magnesium +
�
+ hydrogen
sulfate
acid
B
23 cm3
C
40 cm3
Magnesium, hydrogen and chlorine
D
49 cm3
E
62 cm3
Exercise 8.1C Metal and acid
22
2
a and b
2
2
25 cm3
C
magnesium + oxygen
1
B
Water
Mg
5
1
a
Exercise 8.1B Atoms in chemical reactions
1
Exercise 8.2A Measuring
Graph should be plotted using a sharp pencil
and ruler. Mass of metal used on the x-axis
and volume of hydrogen on the y-axis. A
suitable scale should be used. Points should be
plotted accurately and a line of best fit drawn.
Conclusions should include the more metal
used, the larger the volume of hydrogen
produced. However, the increase in the volume
of hydrogen produced is not consistent and
varies between increases of 30 cm3 and 70 cm3
for each additional 0.5 g of metal used.
3
Exercise 8.2B Neutralising acid
For example:
I put on my safety glasses to protect my eyes in
case of spills or splashes.
I collected the chemicals from the teacher. I
used a beaker to take a small amount of acid
back to my workspace. I used 0.5 mol/dm3
hydrochloric acid and carefully filled a burette.
I made sure that the burette was secure in the
clamp stand and that the tap was closed, so that
no acid was spilt.
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
c
I collected some sodium hydroxide from the
teacher in a beaker. I measured 25 cm3 (accept any
suitable volume) of the sodium hydroxide using a
measuring cylinder and put it into a conical flask.
I added a few drops of universal indicator
solution to the sodium hydroxide in the flask.
The solution turned blue because sodium
hydroxide is an alkali. I placed the conical flask
under the burette.
Exercise 8.3C Investigating antacids
1
I slowly added acid from the burette to the conical
flask. I gently shook the flask each time I added acid.
I was careful to look at the colour of the solution.
When the solution was green, I knew I had added
enough acid to neutralise the sodium hydroxide.
Learners should be able to write this using the
method you used in class. The important points are:
The acid should be in the burette.
The sodium hydroxide should be measured using a
measuring cylinder or a pipette.
Antacid
powder
after
1g
A
2
3
4
5
6
B
2
5
7
7
7
C
2
2
2
3
3
D
2
4
6
7
7
E
2
2
3
3
4
7
2
pH of acid
3
C
Number of spatulas used to neutralise the acid.
1
2
Arun’s test:
0
Not fair because no universal indicator was
used with powder C.
Exercise 8.3B Planning investigations
1
A variable is something that can change, such
as the type of acid or the type of indigestion
powder used.
2
a
he must use the same volume of lake
S
water in each of her tests.
b
The tests are repeated to ensure the results
are consistent.
A
E
1
Zara’s test:
B
D
4
2
Not fair because a different acid (sulfuric acid)
was used with powder A than with powders B
and C (hydrochloric acid).
after
4g
5
Exercise 8.3A Indigestion investigation
Sofia’s test:
after after
2g
3g
6
Topic 8.3 Investigating acids and
alkalis
Not fair because when he tested powder B he
used less hydrochloric acid (25 cm3) than when
he tested powders A and C (50 cm3).
pH
after
0g
The safety measures and the reasons for them.
23
Lake C is the least acidic. Lake B is the
most acidic. There is a very large range in
the acidity of the lakes.
0
1
2
3
mass of antacid added in g
4
3
They kept the volume of acid and the type of
acid the same to make this a fair test.
4
B and D
5
B
6
C
7
pH 7
8
3.5 g
9
D because it reaches pH7 but it does not
neutralise the acid too fast so may not
produce a lot of uncomfortable gas quickly.
(Accept B if there is a comment about the
gas being produced quickly.)
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Topic 8.4 Detecting chemical
reactions
Exercise 8.4A Key words for material
changes
Neutralisation – this is the name of the reaction
where an acid is cancelled out by an alkali. A
neutral solution has a pH of 7.
Precipitate – this is what is formed when two
liquids react and produce a solid.
pH scale – this shows the strength of an acid or an
alkali.
Corrosive – able to dissolve or eat away other
materials.
Reactants – these are what you start with in a
chemical reaction.
Products – these are what is made in a chemical
reaction.
Alkali – pH of more than 7
Acid – pH of less than 7
Exercise 8.4B Has a reaction taken place?
Accept any sensible suggestions, such as:
Observation: Colour change; Example: copper oxide
and sulfuric acid forms copper sulfate and water.
Observation: Heat produced; Example:
potassium in water forms potassium hydroxide
and hydrogen. The heat produced ignites the
hydrogen produced.
Observation: Precipitate formed; Example: silver
nitrate and calcium chloride forms silver chloride
(solid) and calcium nitrate.
Observation: Reactant ‘disappears’; Example:
magnesium in hydrochloric acid. Forms
magnesium chloride and hydrogen. The
magnesium metal disappears as it is used to form
magnesium chloride, which is soluble.
Observation: Change in pH; Example: sodium
hydroxide and hydrochloric acid react to form
sodium chloride and water, changing the pH of
the sodium hydroxide from a pH above 7 to pH 7.
Exercise 8.4C Testing for gases.
You could place a lighted splint into each test tube.
If the gas is hydrogen it will make a ‘pop’ sound.
If the gas is oxygen, the splint will burn brightly.
If the gas is carbon dioxide, the splint will go
out. The splint will continue to burn as before in
the test tube of air. Credit ideas of testing all the
gases with a glowing splint with the appropriate
results. Any discussion of carrying out the tests for
oxygen, hydrogen and carbon dioxide on all test
tubes needs to have some comment about the need
to have more than one tube of each gas.
Unit 9 Electricity
Topic 9.1 Flow of electricity
Topic 9.2 Electrical circuits
Exercise 9.1 The movement of electrons
Exercise 9.2 Circuits and symbols
1
The electrons flow around the circuit.
1
2
a
True
2
b
False
3
Cell, lamp, ammeter, (open) switch.
a
A cell has a positive and a negative terminal.
b
In a circuit, electrons flow away from the
negative terminal and towards the positive
terminal.
4
+
3
a
–
Components can be in any order, switch
can be open or closed.
24
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 7: TEACHER’S RESOURCE
Topic 9.4 Conductors and
insulators
b
Exercise 9.4 Allowing electrons to flow
or inhibiting electrons from flowing
A
Components can be in any order, switch
can be open or closed.
4
Answers should refer to circuit Y.
1
Metal
2
Cotton
3
a
I ron is a metal; metal is a conductor; the
conductor completes the circuit (so the
lamp lights).
b
The car door is painted; paint is an
insulator; the circuit is not completed or
the car door has rusted and rust is not a
conductor.
Any three from:
Y has 2 cells and X has 1 cell / Y has an extra cell.
Y has no buzzer.
Y has an ammeter.
Y has a closed switch and X has an open switch.
Topic 9.3 Measuring the flow of
current
4
In gold, the electrons are free to move; in
glass, the electrons are not free to move.
Exercise 9.3 Measuring the flow of
current
Topic 9.5 Adding and removing
components
1
A
2
When electrons flow faster in a circuit, the
current is larger.
Exercise 9.5 Adding and removing
components
3
4
1
Cell
Anywhere in series with the cell and the lamp.
2
Another identical lamp
In series between the lamp and the positive of
the cell.
3
In series between the lamp and the negative of
the cell.
Add another cell/remove one lamp (not
remove the lamps).
4
a
Cells contain chemical energy; chemical
energy is changed to electrical energy; so
more electrical energy.
2.2 A
b
2
i​​ __2 ​​ = 1 A
ii
25
2
2
__
​​  3 ​​ = 0.67 A or __
​​  3 ​​ A
Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Workbook answers
Unit 1 Respiration
Topic 1.1 The human respiratory
system
Topic 1.2 Gas exchange
Exercise 1.1 The human respiratory
system
1
1
2
3
Name
A
diaphragm
B
intercostal muscle
C
rib
D
lung
E
air sacs
F
bronchus
G
bronchiole
H
trachea (windpipe)
J
larynx (voicebox)
Letter
Function
C
protects the lungs
D
where oxygen gets into the body
E
where oxygen goes into the blood
and carbon dioxide comes out
F
delivers air to the lungs
G
carries air from the bronchus,
deep into each lung
H
carries air from the bronchioles
to each air sac
J
makes sounds
Look for an answer that:
•
1
Letter
is written entirely in the learner’s own
words, rather than copied from the text in
the Learner’s Book or elsewhere
•
mentions each part in the correct sequence
•
gives a brief description of each part.
Exercise 1.2 Gas exchange
The entries should be arranged in order of
either decreasing or increasing body mass.
For example:
Mammal
Body mass
in g
Total surface
area of air
sacs in m2
human
80 000
70
sheep
68 000
60
fox
20 000
40
rabbit
1000
2
rat
300
0.8
mouse
20
0.1
2
The larger the body mass, the larger the
total surface area of the air sacs. Learners
might also add that the relationship is
not proportional.
3
The larger an animal is, the more oxygen it
will need, because it will contain more cells
that are all respiring and using up oxygen.
Having a larger surface area of air sacs
enables more oxygen to diffuse into the body
at the same time, which helps to supply the
demands of the respiring cells. A similar
argument could be put forward relating
to the need to get rid of carbon dioxide
produced by the respiring cells.
Topic 1.3 Breathing
Exercise 1.3A Measuring lung volumes
1
Use the measuring cylinder to measure a
known volume of water – say 50 cm3. Pour
the water into the bottle and mark its level
as representing 50 cm3. Repeat with another
known volume – say another 50 cm3 – and
mark its level as 100 cm3. Keep doing this until
they reach the top.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
2
Person Boy or Wind or
girl
string
player
Volume
displaced in
cm3
1
boy
wind
2100
2
boy
wind
1965
3
boy
wind
2005
4
girl
wind
1950
5
boy
string
1865
6
boy
string
1950
7
girl
string
1905
8
girl
string
1910
9
girl
string
1885
3
(2100 + 1965 + 2005) ÷ 3 = 2023 cm3
4
(1865 + 1950) ÷ 2 = 1908 cm3
5
(1905 + 1910 + 1885) ÷ 3 = 1900 cm3
6
2
Yes. Boys who play wind instruments have
an average of 2023 cm3, which is greater than
for boys who play stringed instruments with
a value of 1908 cm3. Similarly, the girl who
plays a wind instrument displaces 1950 cm3,
compared with the girl string players with an
average of 1900 cm3.
3
Collecting more results from more people in
the orchestra; making three measurements for
each person.
Exercise 1.3C Lung volume at
different ages
1
Measuring many samples and calculating a
mean takes account of this variation.
2030
2020
2010
2
3.9 dm3
3
5.0 dm3 (men) – 3.8 dm3 (women) = 1.2 dm3
4
The average volume of air pushed out with
one breath of women increases steadily over
time until it peaks at the age-group 30–39.
Then it steadily decreases.
5
An answer of 3.3 dm3 to 3.5 dm3 would
be acceptable.
2000
1990
1980
1970
Mean volume
displaced in cm3 1960
Topic 1.4 Respiration
1950
1940
Exercise 1.4 Respiration by yeast
1930
1920
1910
1900
boys,
wind
girls,
wind
2
1
A measuring cylinder, to measure out the
yeast and sugar solutions.
2
Make sure that her eyes are level with the
meniscus in the thermometer to read the
temperature.
3
The temperature will increase, because
respiration releases energy. Some of this
energy is given off as heat.
boys,
girls,
stringed stringed
Exercise 1.3B Looking at data on
lung volumes
1
Look for the idea that there will be a lot of
variation in the lung volumes of individual
people of the same age.
Yes. Boys who play wind instruments displace
an average of 2023 cm3, which is greater than
the one girl who plays a wind instrument
with a displacement of 1950 cm3. Boys who
play stringed instruments have an average
of 1908 cm3 while for girl string players this
is 1900 cm3.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
4
She needs to have another cup where there is
no respiration. For example, she could have a
cup containing just yeast and water with no
sugar, or a cup with just sugar solution and no
yeast. She can then compare the temperature
in the two cups.
5
Use at least three different cups, each with a
different concentration of sugar solution. The
sugar could be measured by mass, or Sofia
could put different numbers of spoonsful of
sugar into each cup.
Add the same volume of water to each cup, and
the same volume of the yeast and water mixture.
The initial temperature should be the same for
each one.
Sofia could take the temperature of the liquid
in each cup at set time intervals (for example
every two minutes). She could plot a graph
showing temperature against time, with
different lines for each cup.
Red blood cells are the most abundant cells in
the blood. Their function is to transport oxygen
from the lungs to all the cells in the body that are
respiring. To help them to do this, they contain a
red pigment called haemoglobin.
White blood cells, unlike red blood cells, contain
a nucleus. Their function is to destroy pathogens,
such as bacteria, that get into the body. Some
of them do this by producing chemicals called
antibodies, which attach themselves to the
pathogens and kill them. Other white blood cells
kill pathogens by taking them into their cytoplasm
and digesting them.
Exercise 1.5C Rats at altitude
1
The number of red blood cells might increase.
As there is less oxygen in the air, having more
red blood cells could help to get enough
oxygen to the body cells.
2
Alternatively, she can leave all the cups for
the same length of time and measure the
temperature after this set time interval.
She can then plot temperature against
concentration of sugar.
12
8
rats at sea level
6
Topic 1.5 Blood
Exercise 1.5A The components
of blood
1
plasma
2
white blood cells
3
a
red blood cells
b
white blood cells
c
plasma
Exercise 1.5B Functions of blood
components
Blood contains a pale yellow liquid, called
plasma. This liquid carries red blood cells
and white blood cells around the body. It also
transports several different substances in solution,
including nutrients and carbon dioxide.
3
rats at high altitude
10
Mean red blood
cell count
0
4
8
12
Time in days
16
3
The height above sea level (altitude).
4
The mean red blood cell count.
5
Two variables should be given. For example:
the age of the rats, the food and water
provided, how much exercise the rats did, the
volume of the rats’ blood that was tested.
6
11.5 − 6.5 = 5.0
7
5.0 ÷ 19 = 0.26 per day (Accept 5.0 ÷ 20 =
0.25)
8
Their red blood cell count would return to
normal, about 6.5 or 7.0 They would no
longer need the extra red blood cells, because
now they would be surrounded by air with a
normal concentration of oxygen.
20
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Unit 2 Properties of materials
Topic 2.1 Dissolving
Exercise 2.1A Using the correct
scientific term
Exercise 2.2B Looking at the solubility
of three solutes
1
Solute A
A
mixture
2
Solute B
B
filtrate
3
C
solute or accept solid
D
solvent
Yes, Arun’s results do agree with Zara’s: he has
the solubility of the solutes in the same order
as her.
E
solution
4
Arun used more water than Zara in his
investigation, so he was able to dissolve more
solute.
5
Marcus has not used the same volume of water
for each of his tests. He used about the same
volume of water for solute A as Zara did and
he got the same result as she did. For solute B,
he used more water than Zara and about the
same volume as Arun and got the same result
as him. For solute C, Marcus used more water
than Zara but less than Arun and his result was
different from both of theirs. Marcus should
have used the same volume of water when he
tested each of the solutes. He cannot compare
the solubility of the three solutes because he did
not make his test fair. He changed two things,
the solute he was using and the volume of water.
Exercise 2.1B What is the difference
between these terms?
1
If something is transparent, you can see
through it. For example: clear plastic or a
solution of copper sulfate is transparent
and you can see what is inside or behind it.
Something that is opaque does not allow light
through it, for example, milk or a container
made of ceramic or metal does not allow you
to see what is inside.
2
When something dissolves, such as sugar
in tea, there are two substances involved:
the sugar that dissolves and the tea that it
dissolves into. When something melts, only
that one substance is involved: ice cream on a
hot day, for example.
3
A solute is something that dissolves in a
solvent to form a solution.
Exercise 2.2C Making up a solution
1
Exercise 2.1C Explaining observations
1
120 g
2
When the salt dissolves in the water, it
does not disappear, but is still in the water,
although you can’t see it any more. You have
added 20 g of salt to 100 g of water so there
will be 120 g of solution.
2
Topic 2.2 Solutions and solubility
Exercise 2.2A Using the correct
scientific term
4
1
insoluble
2
concentrated
3
saturated solution
4
soluble
5
diluted
a
Arun should add 50 cm3 of solution X to
50 cm3 water.
b
Arun should add 25 cm3 of solution X to
75 cm3 water. (Accept Arun should add
50 cm3 of the solution produced in answer
a to 50 cm3 water.)
c
Arun should add 50 cm3 of the solution
produced in answer b to 50 cm3 water.
Credit any sensible suggestion, including
accurate measurements using a suitable
measuring cylinder (indicate which size)
and care taken to fill and read accurately
(details needed).
Topic 2.3 Planning a solubility
investigation
Exercise 2.3A Dissolving salt
1
Sofia predicted that the more water they used,
the more salt would dissolve in it.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
2
The reading taken for 20 cm3 water has been
plotted incorrectly on the graph (on the 25 cm3
line). This should be circled in red.
3
The reading taken for 60 cm3 water, 26 g,
looks too high and is the same as the reading
for 70 cm3 water. This should be circled in blue
on the graph and in the results table.
4
The line of best fit should pass through or
close to all of the plotted points, after the two
errors highlighted in question 2 has
been corrected and that in question 3 has
been ignored.
5
The graph shows that the larger the volume of
water used, the larger the mass of salt that can
be dissolved.
6
Yes, Sofia’s prediction was correct.
Exercise 2.3B Comparing the solubility
of two salts 1
1
The type of salt.
7
The solubility of salt X at 0 °C is about
55 g/100 g water. The solubility rises slowly
as the temperature increases to about 70 °C,
then the graph levels off. This shows that any
increase in temperature over 70 °C makes
no difference to the quantity of salt X that
can dissolve.
8
Salt Y has a solubility of about 30 g/100 g
water at 0 °C. The solubility of salt Y then
rises steadily up to a temperature of 100 °C, at
the same rate.
Topic 2.4 Paper chromatography
Exercise 2.4A Wordsearch
M O
L
E
N
R
O
C
E
L
O
J
F
L
B
S
O
L
U
T
E
T
S
C
G W
T
X
S
O
L
A
Y
A
L
K
A
S
L
P
I
E
N
L
C
H
R
O M
A
T
O
G
R
A
M
I
U
T
I
O
N
G
I
U
L
R
K
C
K
T
E
T
U
D
E
R
M O
R
P
A
I
M
I
L
U
T
E
B
R
A
E
P
A
T
E
S
O
L
V
E
N
T
A
T
M
H
S
E
A
2
How much of the salt dissolves
D
3
The volume of water used and the
temperature of the water.
U
N
P
R
Y
R
N
X
E
L
F
K
S
K
V
D
E
M
S
A
W
C
D
S
J
A
S
H
The account should cover all the points here
and it should be possible to follow the plan to
complete the investigation.
D
I
K
D
I
S
S
O
L
V
E
T
M
T
F
L
O
D
B
I
B
C
A
C
L
H
I
X
4
Measure a fixed volume of water in two test
tubes or beakers.
Exercise 2.4B Paper chromatography
1
So that it will be carried up as the water moves
upwards and does not move into the water at
the bottom of the beaker.
2
six
3
The third patch from the top should be
circled.
4
The scientist needs to check that she gets the
same result if she repeats the test. She also
needs to find out what the colouring is, so that
if it is harmful, the company making the drink
can be advised to stop using it.
Check the temperature is the same in both.
Add salt X to one of the test tubes or beakers
until no more can be dissolved. Mention
measuring the quantity of salt added (either
counting the number of spatulas added or
using the top pan balance to measure the
mass).
Repeat using salt Y.
If learners have drawn a diagram, credit the
use of appropriate apparatus, such as a beaker
with thermometer, water at the same level,
spatula of salt being added. The diagram
should be drawn in pencil, using a ruler where
appropriate, and should be fully labelled.
Exercise 2.3C Comparing the solubility
of two salts 2
5
5
80 °C
6
salt Y
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Exercise 2.4C Paper chromatography
with plant material
E – spot where liquid was placed at start
F – solvent
1
This happened because the dried liquid was
not soluble in water.
4
So that a small spot of liquid would be more
concentrated.
2
Sofia should now try using a different solvent
such as ethanol.
5
It is a mixture because there are several spots
of different substances.
3
A – glass rod or any sensible item, such as a
pencil or spill to support the chromatography
paper).
B – solvent front place where solvent reached.
C – beaker
D – chromatography paper
6
The liquid dissolved in the solvent. The
different substances have different solubility.
As the solvent moved up the chromatography
paper, the solutes were carried up with it. The
particles of the more soluble substances are
carried further up than the particles of the less
soluble substances.
Unit 3 Forces and energy
Topic 3.1 Forces and motion
Exercise 3.1C Changing direction
Exercise 3.1A Balanced forces
1
1
Statement
Needed for forces
to be balanced?
Two forces must be
the same size.
Two forces must be in
the same direction.
Two forces must be in
opposite directions.
3
b
Force A increases (credit can be given to
force C decreasing, although it can be
pointed out that this is less likely).
c
Force D increases; force B decreases.
2
arrow pointing to the right of the page
3
a
Arrow on the string pointing toward the
pole labelled F.
✓
b
Arrow at a tangent to the circle from the
ball in the same direction as the rotation
of the ball labelled D.
a
false
b
true
Topic 3.2 Speed
c
false
Exercise 3.2A Units of speed
Forward arrow and backward arrow of
approximately the same length; forward arrow
labelled driving force; backward arrow labelled
friction. Weight and contact force need not be
shown as they were not asked for.
Exercise 3.1B Unbalanced forces
6
ird is flying at a constant speed and at a
B
constant height.
✓
Two forces must be
different sizes.
2
a
1
Ticks by ‘a boat will slow down’, and ‘a
football will change direction’.
2
a
contact force and weight
b
driving force and friction
c
start to move forward/get faster/speed will
increase
1
a
metre
b
second
c
m/s
2
It travels a distance of 60 km every hour.
3
distance = speed × time
= 260 000 × 2
= 520 000 km
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
b
Exercise 3.2B Calculating speed
1
2
a
distance
speed = ________
​​
​​(or correct arrangement)
time
b
m/s or metres per second
a
b
3
a
distance
speed = ​​ ________
​​
time
70
= ___
​​   ​​
2
= 35 m/s
4
distance
speed = ​​ ________
​​
time
30
= ___
​​   ​​
2
= 15 m/s
b
distance
speed = ​​ ________
​​
time
450
= ____
​​
​​
300
= 1.5 m/s
His walking speed may not be constant.
distance
speed = ​​ ________
​​
time
5400
= _____
​​   ​​
6
= 900 km/h
1
the speed of an object
2
a
C
b
B
Exercise 3.3B Distance/time graphs 2
1
a
3
distance = speed × time
b
distance
​​
time = ________
​​
speed
Time
distance = speed × time
= 45 × 30
= 1350 m
b
2 minutes = 60 × 2
= 120 s
distance = speed × time
= 45 × 120
= 5400 m
distance
time = ​​ ________
​​
time
120
= ​​ ____
​​
4
= 30 s
b
Distance
a
a
Distance
a
Time
c
Distance
2
The car is likely to be travelling slower than
this or be stopped for some of the time, so
to make the average work out at 25 km/h,
there need to be some higher speeds.
Exercise 3.3A Distance/time graphs 1
Exercise 3.2C Calculating distance
and time
1
distance
speed = ________
​​
​​
time
50
= ___
​​   ​​
2
= 25 km/h
Topic 3.3 Describing movement
b
4
a
distance travelled by Sofia = speed × time
= 6 × 60
= 360 m
distance travelled by Zara = speed × time
= 4 × 60
= 240 m
difference = 360 − 240
= 120 m
Time
7
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
2
Distance from
home
Exercise 3.4B Calculating moments
1
moment = force × distance (from pivot)
2
a
b
Time
3
Distance from
the park
3
pounds foot / pounds feet / foot pounds
Exercise 3.4C Moments, force and
distance
1
a
Time
Exercise 3.3C Distance/time
graphs 3
b
a
Distance from
A in km
1
2
4000
3000
350
= ____
​​
​​
0.35
= 1000 N
1000
1
2
3
4 5 6 7 8
Time in hours
i
10 hours
i
distance
speed = ________
​​
​​
time
9 10
3
a
moment = force × distance
= 500 × 2
= 1000 Nm
b
moment = force × distance
moment
force = ​​ ________ ​​
distance
1000
= ​​ _____ ​​
400
= 2.5 m
3600
= ​​ _____ ​​
4.5
= 800 km/h
ii
distance
speed = ________
​​
​​
time
3600
= ​​ _____
​​
4
= 900 km/h
Topic 3.4 Turning forces
Exercise 3.4A Identifying turning forces
8
moment = force × distance
moment
force = ________
​​
​​
distance
40
= ___
​​   ​​
0.2
= 200 N
Increasing distance will increase the
moment using the same force.
moment
force = ​​ ________ ​​
distance
2000
0
b
moment = force × distance
= 15 000 × 5
= 75 000 (N m)
i will increase the moment
ii will decrease the moment
1
Ticks next to: pushing a door open, twisting
the top off a bottle, and pushing the hands of
a clock around.
2
Ticks next to the tap, gate and door handle.
3
moment
Topic 3.5 Pressure between solids
Exercise 3.5A Describing pressure
1
force
pressure = _____
​​  area ​​
2
tick in the box under shoes with high,
sharp heel
3
a
b
C
force
pressure = _____
​​  area ​​
It has the largest area but the force
(or weight) is the same, so the pressure
is smaller.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Exercise 3.5B Calculating pressure
1
A force of 20 N acts on each (1) cm2 of area.
2
force
pressure = _____
​​  area ​​
the inside wall of the balloon become less
frequent and occur with less force.
Exercise 3.6C Trends in pressure 3
15
___
1
Pressure inside the balloon decreases; particles
move slower at lower temperature; collisions
of particles with the inside wall of the balloon
become less frequent and occur with less
force; pressure of the air on the outside
stays the same, so the forces are not
balanced and the balloon is compressed
by atmospheric pressure.
2
a
line starting from above the origin and
sloping up (in any manner)
b
line starting from above the origin and
sloping up (in any manner)
​​
60
= 0.25 (N/cm2)
= ​​
3
force
pressure = _____
​​  area ​​
4
force = pressure × area
= 60 × 0.5
= 30 N
pounds per square inch
Exercise 3.5C Variables affecting
pressure
1
area (at end of thorn) is very small; pressure
force
on skin will be large; pressure = _____
​​  area ​​; other
parts of stem would have larger area, so
smaller pressure on skin
Topic 3.7 Particles on the move
2
area in contact with ground is larger; so
force
pressure is smaller; pressure = _____
​​  area ​​
1
3
with sharp knife, area in contact with bread is
force
smaller; so pressure is larger; pressure = _____
​​ area ​​
End A has large area to decrease pressure
on thumb when pushing, so less likely to
be painful.
Black circles and hollow circles randomly, and
roughly evenly spread throughout the whole
container; same number (10) of each type of
particle.
2
Black circles randomly, and roughly evenly
spread throughout the whole container; same
number (10) of black circles.
4
End B has small area to increase pressure on
the surface, so more likely to go into surface.
Topic 3.6 Pressure in liquids
and gases
Exercise 3.7A Diffusion in gases
and liquids
Exercise 3.7B Diffusion
1
The random movement of particles from an
area of higher concentration to an area of
lower concentration.
2
a
t he particles/the ink diffuse(s); the
particles start at high concentration and
spread out randomly to areas of lower
concentration
b
diffusion occurs faster at higher
temperature; because particles move faster
at higher temperature
Exercise 3.6A Trends in pressure 1
1
pressure increases
2
at sea level
3
pressure increases
4
pressure increases
3
Close to the container the particles/brown gas
is at high concentration; higher concentration
means the particles are closer together/there
are more particles in the space; the particles/
brown gas diffuse; further away from the
container, the particles are further apart.
4
When the green colour fills the bottle, the
movement of particles has stopped; false.
Exercise 3.6B Trends in pressure 2
9
1
The pressure is equal in all directions.
2
Pressure increases with depth in a liquid.
3
a
pressure decreases
b
Particles move slower at lower
temperature; collisions of particles with
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
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CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
When the green colour fills the bottle, diffusion
has stopped; true.
2
Diffusion happens faster at higher
temperature; particles move faster at higher
temperature; the particles from the hot coffee
will change from being a liquid to being a
gas faster/will evaporate faster; there will be
a higher concentration of coffee particles in
the air just above the hot coffee than the cold;
particles from the hot coffee will take less time
to travel from the cups to Zara’s nose.
3
The concentration of particles causing the
smell will be higher closer to the food; if the
animal moves closer to the food, the smell will
get stronger; if the animal moves away from
the food, the smell will get less/weaker.
4
If all the Gila woodpeckers and gilded flickers
died out, there would be no holes made in the
saguaro cacti, so other animals that use these
holes would not be able to use them. This
could mean that the population of birds such
as elf owls might decrease.
Exercise 3.7C Variables affecting
diffusion
1
a
b
he particles are closer together when the
T
crystal first dissolves; the particles are in
high concentration; the particles have not
yet started to diffuse; particles randomly
spread out to areas of lower concentration;
when fully spread out, the particles are
further apart.
Any two from: increasing the temperature;
using more purple crystals; using a
smaller volume of water.
Unit 4 Ecosystems
Topic 4.1 The Sonoran Desert
Exercise 4.1 The Sonoran Desert
ecosystem
10
1
The Sonoran Desert, which is very dry, and
the temperature never goes below 0 °C
2
It has wide-spreading, shallow roots to absorb
water when it rains. It has no leaves to reduce
water loss by evaporation. It has spines to stop
animals eating it.
3
It is too cold. They die if the temperature falls
below 0 °C, because their cells are killed if
they freeze.
If all the saguaro cacti died out, all the birds
that use them for nesting (Gila woodpeckers,
gilded flickers, elf owls, Harris hawks) would
not be able to breed, so their populations
would decrease. Bats would not have a source
of pollen and nectar from the cacti, so,
unless they could switch to feeding on other
plants, their population might also decrease.
Animals that eat the cactus fruits could also
die out.
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
5
The cacti are probably unable to compete with
other plants that are specifically adapted to
survive in wetter places. For example, other
plants are likely to be able to grow faster than
saguaro cacti, and produce a lot of leaves.
They would overshadow the cacti, reducing
the light falling onto them, so that they would
not be able to photosynthesise.
3
The masses for all species are lower where there
are no mangroves. The biggest difference is for
yellowtail, where the mass is less than half of
that where there are mangroves on the shore.
4
When no mangroves are present, there is no
habitat for the baby fish to develop safely from
predators, so fewer baby fish grow to become
adults, and there are fewer adult fish on
the coral reef.
Topic 4.2 Different ecosystems
Exercise 4.2A A tropical rainforest
ecosystem
Topic 4.3 Intruders in an ecosystem
Tropical rainforests grow where the temperature is
always high and there is plenty of rainfall. Many
different species of plant grow in the rainforest.
Exercise 4.3A Beavers in South America
1
streams and rivers in North America
The rainforest provides habitats and food for many
different species of animal.
2
They make dams, which cause deep pools to
form. They cut down trees.
On the forest floor, fungi break down dead
leaves and waste from the animals. These fungi
are decomposers.
3
The bears would almost certainly harm other
native species (including humans) as well as
killing beavers.
The fungi release nutrients from the dead leaves
and waste, which help the plants to grow.
All of the plants, animals and fungi interact with
one another. They also interact with the non-living
parts of their environment.
Exercise 4.3B Water hyacinth
1
invasive species: a species that has been
introduced into an ecosystem where it is not
native, and that has spread widely and in
large numbers
This network of interactions makes up the tropical
rainforest ecosystem.
Exercise 4.2B Hydrothermal vents
1
There is no light, so they cannot
photosynthesise.
2
For example: bacteria ➔ zooplankton ➔ sea
anemones ➔ crabs
3
bacteria
4
From chemicals dissolved in the hot water that
comes out of the vent.
5
For example: inside a tube worm; in the hot
water around the vent; on the sea floor.
Exercise 4.2C Mangroves and fish
1
aquatic: living in water
2
Water hyacinths are native to South America,
and there are several herbivores in the
ecosystems there that eat water hyacinth and
keep its numbers under control.
3
The water hyacinths stop oxygen getting into
the water, so native plants and fish are killed.
They make it difficult for fishermen to make
a living, because the boats cannot move easily
through the water hyacinth and the nets
cannot catch fish.
Exercise 4.3C Cane toads in Australia
1
There will be other species in their native
country that keep cane toad numbers under
control – for example, predators that can eat
them without being poisoned. In Australia, no
species can eat them safely.
2
The researchers should obtain a large number
of quolls, and keep them all in the same
conditions. They should feed cane toad
sausages to half of them, and sausages that do
habitat – the place where an organism lives
ecosystem – a network of interactions between
living and non-living things
predator – an animal that kills and eats
other animals
2
11
yellowtail
herbivore: an animal that eats (only) plants
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not contain cane toad to the other half. (This
is the independent variable.)
They should then give each quoll the chance
to eat a cane toad, and record whether or
not the quoll tries to eat it. (This is the
dependent variable.)
If the hypothesis is correct, the results should
show that the quolls that have eaten cane toad
sausages try to eat fewer cane toads, than the
quolls that have only eaten sausages that do
not contain cane toad.
7
Exercise 4.4B Bias
1
The company wants to make money by selling
its product, so it might try to make the risk
posed by using the spray seem less important
than it really is.
2
Yes. Once again, the company that sells the
predators wants to make money, so it might
play down the risk (represent it as lower than
it really is) to other species posed by using the
predators.
3
No damage is done to organisms that live in
the area.
4
This could reduce the populations of other
insects and, in some cases, could make them
become extinct. Some of these could be useful:
they could be pollinators, for example. This
could, in turn, affect the populations of plants
that rely on pollinators.
5
The chemicals in the spray build up in each
organism that is exposed to it. The further up
the food chain an animal is, the more of the
chemicals it will take in over its lifetime, as it
eats many animals that contain the chemicals.
6
No, they cannot be absolutely sure, but they
can certainly trust this information more than
the information from the companies.
7
Checking for bias is difficult, but it could
involve looking at the results of any tests
that have been done, so that they can see
for themselves whether the results match
the statements made by the agriculture
department.
Topic 4.4 Bioaccumulation
Exercise 4.4A Microplastics
1
tiny pieces of plastic less than 5 mm long
2
Some come from large pieces of plastic
that break up into small pieces. Others are
manufactured as microplastics, used in
products such as face creams and toothpaste.
3
Some sink to the bottom because they are
denser than water. Some go into the bodies
of animals and may be carried to the bottom
when the animal dies.
4
a
54
b
5
6
12
156 − 54 = 102
As they feed, they take in microplastics that
are floating in the water. There may also
be some microplastics in the bodies of
the zooplankton that they eat.
Bioaccumulation is the build-up of substances
in an organism’s body over its lifetime,
because the substance does not break down in
its body.
Seals eat many fish in their lifetimes, and all
of the microplastics in the fish that they eat
gradually build up in their bodies.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Unit 5 Materials and cycles on Earth
2
Topic 5.1 The structure of
the atom
Exercise 5.1A Labelling the structure of
the atom
Topic 5.2 Purity
1 and 2
Exercise 5.2 Purity
1
It means that all the atoms in the element are
the same. So pure silver has only silver atoms.
2
Diamonds are made of carbon atoms. When
diamonds are coloured, they have atoms of
different elements mixed in with the carbon
atoms. When they have boron atoms the
diamonds will be a blue colour. If diamonds
have nitrogen atoms mixed with the carbon
atoms, the diamond will be a yellow colour.
The rarest colour of diamond is green. Green
diamonds have nitrogen, nickel or hydrogen
mixed in with the carbon atoms.
Neutrons have more mass than electrons.
3
92.5%
Exercise 5.1B Models of the structure
of the atom
4
a
37.5%
b
91.7%
c
58.3%
electron
neutron nucleus of
proton the atom
++
empty space
3
The following statements should be ticked
Electrons have less mass than protons.
Electrons have a negative electrical charge.
1
−
−
positively
charged
matter
−
−
−
J. J. Thompson
2
3
−
−
−
−
electrons
−
−
positively
charged
matter
++
+++++ −
5
−
−
electrons
Rutherford
In J. J. Thompson’s model, the particles he knew
about, electrons and positively charged particles,
are scattered randomly throughout the atom
and there is no nucleus. In Rutherford’s model,
there is a nucleus and the electrons are
randomly scattered throughout the rest of the
space in the atom.
Credit any of the scientists named, such as
James Chadwick or Niels Bohr.
1
The diagram should be completed by drawing
most particle pathways passing straight
through the foil. A few should be shown
being reflected back or deflected from the
gold foil.
Purity of
gold alloy in
carats
Purity of
gold alloy in
percentage
Hardness
in arbitrary
units
9
37.5
80
14
58.3
90
18
75.0
120
22
91.7
40
24
100.0
30
6
Credit: a suitable scale on the horizontal axis;
the points plotted accurately and neatly; a
best-fit line drawn.
7
The assistant gave an opinion. The science
shows that 18 carat gold is much harder than
pure gold. Although the other samples are
harder than pure gold, they are not harder
than 18 carat gold, so it is mostly not in line
with the science.
8
The description should state that the hardness
of the gold increases up to 18 carat gold and
then decreases at values greater than 18 carat.
Exercise 5.1C Rutherford’s gold foil
experiment
13
The results of Rutherford’s experiment told
him that the atom was mostly empty space,
but with a dense/solid nucleus.
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CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
9
This may be due to the fact that the other
metal used in the alloys is not the same.
Exercise 5.3C Weather data
1
Data should be plotted as instructed with the
date and time along the horizontal axis and
the temperature up the vertical axis. Credit a
suitable scale, labelled axes, accurately plotted
points and the points joined ‘temperature style’,
that is point-to-point.
2
It is difficult to see any pattern in these results
but learners may spot that generally the
temperature at 00:00 is lower than that for the
rest of the day. The temperature often rises
during the day and falls a little over night.
They should give examples. They may be able
to link the small fall in temperature to the fact
that Iceland has a very long day length. If they
fail to see a pattern, give them credit if they
give examples.
meteorology ➔ the study of weather
3
The only ‘pattern’ in the week is that the
temperatures are fairly constant.
Exercise 5.3B Weather or climate?
4
The temperature on this day remained
constant from 06.00 to 18.00 and that was not
typical of other days during the week.
5
The description of this climate zone is cold
and dry.
6
This week the weather in Iceland was not very
cold and there was rain, which is not typical
of this climate zone.
7
Credit ideas about Iceland being an island in
the middle of an ocean and a long way from
any other land. They may also realise or find
out that the winds and weather systems move
quickly in this area and are influenced by the
Gulf Stream.
Both silver or copper can be used. The data do
not say which is used in each case.
Topic 5.3 Weather and climate
Exercise 5.3A Words and meanings
temperature ➔ how hot it is
humidity ➔ how much water vapour there is in the
atmosphere
precipitation ➔ rain, hail or snow which falls from
clouds
visibility ➔ how far you can see; it depends on the
atmospheric conditions or darkness
atmosphere ➔ the layer of gases around the Earth
1
2
14
The weather is the atmospheric conditions over
the short term, from minute to minute, hour to
hour or day to day.
Climate is the average weather of an area over
a much longer time, usually at least 30 years.
Credit approximate areas, such as Antarctica,
northern Canada, Greenland and northern
Russia, but both Poles must be included and
labelled.
3
The climate in the polar zone is very cold and
dry all year.
4
Credit approximate areas, such as central
America, south America (east of the Andes)
central Africa, south-east Asia, the north-east
tip and south-east coastal strip of Australia,
but tropical zone in more than one continent
must be shown and labelled.
5
The climate in the tropical zone is hot and wet
all year.
6
Meteorologists record the weather in so much
detail because they are looking for patterns to
see if they can predict what will happen in the
future. Knowing what the weather will be like
has a big effect on the agriculture, transport,
health and other industries.
Topic 5.4 Climate and ice ages
Exercise 5.4A Wordsearch
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Exercise 5.4B Soil cores
1
a
he oldest peat is from the bottom of
T
the bog.
6
b
The plant material has not rotted because
the conditions in the bog slow down
decay. There is not enough oxygen and the
conditions are acidic.
Topic 5.5 Atmosphere and climate
c
2
Scientists hope to find out which plants
were growing in that area thousands of
years ago. If they can identify the plants
from their pollen, they can then work out
what the climate was like at that time.
a
These periods are the glacial periods.
b
These periods are called
interglacial periods.
Exercise 5.4C Climate cycles
1
The graph should be labelled with the peaks
as interglacial periods and the troughs as
glacial periods.
2
About 75 000 years ago. It lasted from about
75 000 years ago until about 25 000 years ago,
so it lasted about 50 000 years.
3
In an interglacial period the average
temperatures are generally above freezing
reaching as high as 20 °C.
4
When the temperatures are well below freezing
for a long time, most living organisms cannot
survive.
5
There have been four glacial and five
interglacial periods over the past 450 000 years.
The first interglacial period was 85 000 years
long and was followed by 25 000 years of
a glacial period. The second glacial period
lasted 70 000 years the second interglacial
period was warmer and lasted longer than
the first.
The third glacial period lasted 20 000 years so
the glacial periods seem to be getting shorter.
During the third interglacial period (about
225 000 years ago) there was a short, sharp dip
in the average temperatures. The next glacial
period was longer and the next interglacial
period had very high average temperatures, the
highest of all the interglacial periods in this
time span, and lasted until about 75 000 years
ago. The most recent glacial period lasted
about 50 000 years and we have been in
15
the current interglacial period for about
25 000 years.
The evidence we have comes from core soil
samples from peat bogs and from the evidence
in the landscape from the effect of glaciers.
Exercise 5.5A
In the first billion years after the Earth formed
there were lots of volcanoes. These produced
gases, which made up the atmosphere. The
water vapour that was produced condensed, to
form lakes and oceans. The early atmosphere
was mainly made up of carbon dioxide gas.
There was little or no oxygen gas. This is like the
atmosphere of the planet Venus today.
As plants began to grow on Earth, they used
up the carbon dioxide gas and produced food
by the process of photosynthesis. Over billions
of years the carbon in the carbon dioxide gas
became locked up as fossil fuels, such as oil and
coal and as carbonates in sedimentary rocks such
as limestone. This caused the levels of carbon
dioxide in the atmosphere to fall.
Exercise 5.5B
1
80%
2
10%
3
0.038%
4
It decreased very quickly at the start and then
continued to decrease, but at a much slower
rate.
5
The level of carbon dioxide has increased
quite dramatically over the past 200 years.
This is because, as industry developed, more
fossil fuels were burnt to provide energy for
factories and transport. More forests have
been cut down to use the wood and make
room for people, crops and farm animals,
so this means less carbon dioxide from the
atmosphere is being used up.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Exercise 5.5C
1
The answers will depend on what learners have
found out, but as a minimum should include
the following:
There is evidence that iron oxide was formed
in rocks after the period 2.1 to 2.0 billion
years ago, not before. There is evidence from
the pockets of air trapped in the ice cores
from Greenland and Antarctica. We have
measurements of the percentage of gases in
the atmosphere over the past 100 or so years.
2
There is evidence from the ice cores about the
way the ice was formed over time.
There is evidence of an increase in the rate
at which the polar ice caps and glaciers
are melting. There is evidence of the sea
levels increasing.
3
The answers will depend on what learners have
found out, but as a minimum should include
the following:
The evidence from a long time ago is not
direct evidence, but has been inferred from
other things, whereas the records over the
past 100 years were taken directly and there
are lots of records. However, even with the
more recent records we cannot be sure of the
way in which they were taken unless they were
taken and recorded by professionals that we
can trust.
Unit 6 Light
c incident ray
Topic 6.1 Reflection
Exercise 6.1A Making reflections
1
flat mirror
2
bouncing
3
a
incident ray
b
reflected ray
c
normal
i r
2
Exercise 6.1B Ray diagrams
1
a
plane mirror
normal
normal
incident ray
i
i r
normal
reflected
ray
plane mirror
a
line drawn at 90° to the mirror surface at
the point where the light ray meets the
surface; line can be dashed or solid and
may pass through the mirror surface
b
angle of incidence = 50°
reflected
ray
r
plane mirror
b
incident ray
normal
plane mirror
i
r
reflected
ray
16
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Exercise 6.1C Accurate ray diagrams
1
a
plane mirror
incident ray
When light changes direction, the change in
direction can be caused by a change in speed.
When light changes direction passing from air
into glass, this is called refraction.
Exercise 6.2B Predicting refraction
i
normal
r
reflected ray
1
When light changes speed (caused by) passing
from one transparent substance/medium
to another.
2
a
diamond
b
air and diamond
c
corn oil and glycerol
3
r i
When light passes into a medium where
it slows down, the light bends towards
the normal.
normal
When light passes into a medium where it speeds
up, the light bends away from the normal.
plane mirror
b
incident ray
reflected ray
2
3
First angle of incidence in range 20–23°. First
angle of reflection should be equal to this.
Second angle of incidence should be smaller
than first. Second angle of reflection should be
equal to second angle of incidence.
4
Raindrops refract light; raindrops are curved;
raindrops refract light in different directions.
Exercise 6.2C Refraction ray diagrams
1
a
ray of light
normal
plane mirror
angle of incidence
incident ray
air
glass
angle of refraction
refracted ray
plane mirror
Topic 6.2 Refraction
Exercise 6.2A Causes of refraction
17
1
medium
2
a
hen light passes from air into water,
W
the light slows down.
b
When light passes from glass into air, the
light speeds up.
c
When light passes from water into glass,
the light slows down.
b
angle of
refraction
air
water
normal
refracted
ray
angle of incidence
incident ray
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Topic 6.4 Colours of light
c
Exercise 6.4A Adding primary colours
i
r
air
air
Colours of light that cannot be made by
adding other colours.
2
a
Adding red light and green light makes
yellow light.
r
i
2
1
glass
air
glass
refracted ray
3
normal
b
Adding green light and blue light makes
cyan light.
c
Adding red light, green light and blue
light makes white light.
All seven colours are given out together; all
seven colours are of (approximately) equal
brightness; all seven colours mix to give
white light.
Exercise 6.4B Subtracting colours of light
incident ray
1
Topic 6.3 Making rainbows
a
a ny one from orange, yellow, blue,
indigo, violet
b
The green light has been absorbed by the
red filter. Red light passes through the
filter because red light is transmitted by
the filter.
Exercise 6.3A Colours of the rainbow
1
spectrum
2
red, orange, yellow, green, blue, indigo, violet
3
a
white
b
dispersion
c
Each colour merges into the next one with
no space.
2
b
3
Exercise 6.3B Making a spectrum 1
1
a
triangular prism
b
violet; because violet bends through the
largest angle
c
i
Move the screen closer to the prism.
ii
The colours get closer together /
merge together more.
Exercise 6.3C Making a spectrum 2
1
18
a
blue
All other colours except blue are
subtracted/absorbed/removed from the
white light, so only blue remains.
Violet light slows the most when passing from
air into plastic; violet is refracted the most;
violet travels slowest in plastic; red light travels
fastest in plastic and is refracted the least;
other 5 colours listed in order of speed, either
increasing or decreasing (increasing speed starts
with violet, decreasing speed starts with red).
The remaining blue light will be absorbed
by the green filter.
A yellow filter is used; all other colours except
yellow are subtracted/absorbed/removed from
the white light, so only yellow is transmitted.
Exercise 6.4C Seeing colours
1
a
The green T-shirt reflects only green light.
The green T-shirt absorbs all the other
colours of light.
2
3
b
black
a
red or white
b
blue
c
red or blue
a
Black does not reflect light of any colour /
black is the absence of light.
b
White reflects all colours equally / white
light contains all colours.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Topic 6.5 Galaxies
Topic 6.6 Rocks in space
Exercise 6.5A Our own galaxy
Exercise 6.6A Describing asteroids
1
1
Asteroids are made from rock. Asteroids can
have irregular shapes.
2
Between the orbits of Mars and Jupiter.
3
orbit
2
3
a
Milky Way
b
tick under first picture (spiral)
a
the Sun
b
more than 1 000 000
There is a small quantity of dust between the
stars in our galaxy; true.
Exercise 6.6B Asteroids and planets
1
Any two from: asteroids are smaller than
Earth; asteroids have no atmosphere; asteroids
have no oceans; (many) asteroids have an
irregular shape.
2
There are too many asteroids/not all have been
discovered/difficulty telling them apart by
appearance.
There is a small quantity of gas between the
stars in our galaxy; true.
Exercise 6.5B Galaxies in space 1
1
a
Universe
b
They contain stars; stars give out their
own light.
2
spiral, elliptical, irregular
3
Scientists have made an estimate of how many
galaxies there are in total. This number may
not be accurate/exact.
Exercise 6.5C Galaxies in space 2
1
2
a
gas, stars, planets/solar systems
b
Each particle of dust causes a small force
of gravity; there are very many particles
of dust; the gravity from all of them adds
up to a large force.
a
stars
b
Any two from: they do not reflect light; they
absorb light; they do not give out light.
3
Any two from: fewer will be seen; they will be
dimmer; they will appear smaller.
4
aCount the number of grains in a small
volume / volume given, for example
0.1 cubic centimetre; then estimate the
volume of sand on the whole beach by
multiplying length × width × depth;
convert both volumes to the same unit;
divide the volume of the sand on the
whole beach by the volume of the small
sample; multiply the counted number of
grains by the result of this calculation.
b
19
3
5000
_____
​​ = 500 km
​​
10
Exercise 6.6C Asteroids and planets
1
Any two from: both orbit the Sun; both are
part of the Solar System; both contain rock.
2
Asteroids are too small/gravity from asteroids
is too low to attract/hold a moon.
3
There was not enough gravity between them
to form a planet; there were not enough of
them to form a planet.
4
Answer can refer to: poor quality/low
resolution of the photograph; lack of evidence
that aliens exist; desire to attract attention to
the website/make a sensational claim; light
reflecting off a crater is more likely/more
realistic; alien building is exciting but not
realistic explanation; universities will have
experts looking at the picture; independent
website may not have experts contributing;
opinions can vary on interpreting
photographs; reference to opinion or fact.
he total number cannot be counted
T
accurately; the method for both estimates
is the same; both methods assume the
spacing of objects is uniform.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Unit 7 Diet and growth
Topic 7.1 Nutrients
Exercise 7.1A Nutrients and their
functions
Exercise 7.1B Analysing information
about nutrients
1
chicken
protein ➔ for growth (making new cells)
2
orange
vitamin A ➔ to help with night vision
3
8g
4
Sofia is right. Brazil nuts contain 60 g of fat,
but only 16.18 g of other nutrients.
5
Brazil nuts, because they contain the
most calcium.
calcium ➔ for strong bones and teeth
carbohydrate ➔ to use in respiration to release
energy
iron ➔ to make haemoglobin
vitamin D ➔ to help us to absorb calcium, for
strong bones and teeth
Alternatively, learners may suggest milk. This
has the second highest quantity of calcium,
but learners may think it is easier to digest
than brazil nuts. It also has less fat and oil,
which they may think makes it a better choice.
fat and oil ➔ to use in respiration to release
energy, and to make an energy store under the skin
vitamin C ➔ to keep skin strong and able to heal
quickly
Exercise 7.1C Summarising functions and sources of different nutrients
Accept any one or two functions and sources.
Nutrient
Function in the body
protein
growth; making new cells; repairing damaged meat, fish, pulses
tissues; making haemoglobin and antibodies
Some good sources
fat and oil
for energy; as a layer under the skin, it forms
an energy store and provides insulation
carbohydrate for energy, which is released by respiration
grains (e.g. rice, wheat, oats, corn),
potatoes, sweet potatoes, pasta,
bread
vitamin A
for good vision, especially at night; helping
white blood cells to fight pathogens
green vegetables, carrots, dairy
products (foods made from milk)
vitamin C
keeps skin strong
citrus fruits, potatoes, berries
vitamin D
helps us to absorb calcium
sunlight on skin
calcium
strong teeth and bones
dairy products, seeds
iron
making haemoglobin
meat, dark green vegetables, fish,
shellfish, nuts and seeds
water
a solvent for many different chemicals
any drink that contains water
Topic 7.2 A balanced diet
3
200 g of chicken contains no fibre. 200 g of
rice contains 2 × 3 = 6 g. 100 g of spinach
contains 6 g.
Total = 6 + 6 = 12 g.
4
Bar charts will vary according to the ten foods
and bar widths chosen.
Exercise 7.2A Fibre in food
1
2
20
butter, margarine, cooking oils, fried
foods, meat, eggs
Fibre helps to keep food moving easily
through the alimentary canal.
Chicken, eggs, fish and mutton – that is, foods
from animal sources.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
•The names of the foods should be written
beneath the bars.
•The bars should be carefully drawn using
a ruler. They should be drawn accurately
They should all be of equal width. It is
preferable if they do not touch.
•The sequence of foods in the chart should
have some logic behind it – for example,
from lowest to highest fibre content, or
from highest to lowest fibre content, or all
animal foods grouped together and then
plant foods.
Topic 7.3 Growth, development
and health
Exercise 7.3A Interpreting data about
smoking
1
respiratory diseases
b
diseases of the digestive system
2
39%
3
2 × 39 (or answer to question 2) = 78
4
21%
Exercise 7.2B Energy requirements
5
5 × 21 (or answer to question 4) = 105
1
carbohydrate and fat
6
2
His weight will increase. The excess nutrients
will be turned into fat, and stored in his body
3
a
2.8 MJ
The bar chart shows that the percentages of
deaths due to smoking were greater for men
than for women OR smaller for women than
for men.
b
2.8 MJ (the answer is the same as a)
7
c
Both boys are likely to use a lot of energy
each day, especially for movement and
growth. However, an eight-year-old boy
has fewer cells in his body than a teenage
boy – his body mass is smaller. It is the
cells that use energy, so if you have fewer
of them, you use less energy. If less energy
is used, then less energy needs to be
taken in.
Accept any explanation that suggests that
more men than women are smokers, or that
men smoke more than women, or that men are
more susceptible to those diseases.
d
Exercise 7.3B Smoking statistics
1
Answers will depend on the country that
learners choose.
2
The bar chart should have:
Learners do not have any specific
knowledge to enable them to answer
this, so any reasonable suggestion should
be accepted. For example: women, on
average, have a lower body mass than
men; women may be less active than men.
Exercise 7.2C Planning a diet
Look for:
•
21
a
foods that contain all six nutrients (including
vitamins A, C and D, calcium and iron) and
some fibre – with the nutrients contained in at
least some of the foods described
•
interesting, balanced meals that would appeal
to an eight-year-old
•
attention given to the quantity of energy in
the diet
•
not too much fat or oil
3
•
‘Country’ on the horizontal axis, with
individual bars labelled with the name of
the country
•
different style bars for men and women,
indicated with a key
•
women and men for the same country
shown as bars close together, or touching
•
bars for different countries a little further
apart, not touching
•
each bar drawn with a ruler, all the same
width and correctly plotted.
•
‘Percentage of people who smoked’ on the
vertical axis
•
a scale on the vertical axis running from
0 to at least 65 in sensible steps (e.g. in
fives or tens)
a
Chile
a
Indonesia
b
Indonesia
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Exercise 7.3C Looking at data on giving
up smoking
1
Learners could choose to display any of these
sets of data:
•
•
•
2
Exercise 7.4A The skeleton and forces
1
Sofia, 28 N
2
Force in N
Right hand
Left hand
thumb
27
25
the reasons for successfully giving
up smoking
first finger
28
25
second finger
22
19
the reasons for failing to give up smoking.
third finger
21
16
little finger
19
17
Look for:
•
a neatly drawn chart with ruled columns
and rows
•
clear headings with units
•
correct entries, with no units included in
the body of the chart.
Exercise 7.4B Antagonistic muscles in
the leg
1 and 3
pelvis
3
The chosen method of display should be
clearly presented and labelled, so that it is easy
to understand.
femur
4
The answer should include some of the
following points:
tibia
•
•
•
22
the percentages of men and women who
have given up smoking already, and the
percentages of those who are trying to
give up smoking
Topic 7.4 Moving the body
ball and
socket joint
reference to the fact that people find
giving up smoking difficult because nicotine
is addictive
2
hinge joint
4
The leg will bend at the knee.
reference to the percentage of people whose
reasons for smoking appear to be related to
addiction (learners should refer directly to
the data here, for example, 54% of people
say they went back to smoking because they
could not manage without cigarettes)
5
It will straighten – the lower leg will be pulled
forward.
6
A and B; C and D
the idea that e-cigarettes supply users
with nicotine, so they will still get the
drug to which they are addicted, but can
gradually reduce the amount of nicotine
in the e-cigarettes until they are ‘smoking’
nicotine-free e-cigarettes.
Exercise 7.4C Choosing a hypothesis
about bones to investigate
1
Thick bones are stronger than thin bones.
Long bones break more easily than short
bones.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
2
a
here should be a clear statement of
T
either the thickness or length of the straw
(depending on the chosen question).
b
The force needed to bend the straw.
c
Look for at least two correct answers.
They should be things that would actually
affect the results if they were altered, for
example: the length of the straw (if testing
the thickness); the thickness of the straw
(if testing the length); the position of the
hook on the straw; the angle at which the
force meter is pulled; the material from
which the straw is made.
d
The description should state clearly
what the learner would do, in a suitable
sequence. A good measure of success is
whether someone else could follow these
instructions without having to ask for
further guidance.
e
f
The results chart should be drawn with
a ruler and a pencil. The first column (or
row) should be headed with the variable
that will be changed (either the thickness
or length of the straw) with the appropriate
unit. The second column (or row) should
be headed Force needed to bend the straw
in newtons. Some learners may decide to
make repeat measurements, in which case
they will need to include columns (or rows)
for each of the force measurements, and
another column (or row) for the calculated
mean.
g
Accept any prediction that relates to the
stated hypothesis. It does not have to be a
‘correct’ prediction. For example, for the
first question, any of these predictions
would be appropriate:
This is a low risk experiment. Care
should be taken not to pull suddenly
on the forcemeter/newton meter, which
could become detached from the straw
and suddenly fly upwards.
•
Thick bones are stronger than
thin bones.
•
Thick bones are not stronger than
thin bones.
•
Thin bones are stronger than
thick bones.
•
There is no difference in the strength
of thick bones and thin bones.
Unit 8 Chemical reactions
Topic 8.1 Exothermic reactions
Exercise 8.1A Investigating an exothermic reaction
1
the length of the magnesium ribbon
2
the change in temperature
3
the type of acid used; the volume of acid used; credit any other sensible control variables
4
5
23
Length of
ribbon in cm
Start temperature
in °C
End temperature
in °C
Temperature
change in °C
0.5
19.0
36.0
17.0
1.0
19.0
36.0
17.0
1.5
19.0
36.5
17.5
The results show that changing the length of
magnesium used makes very little difference to
the end temperature.
6
No. They have only used a very small range of
lengths of magnesium.
7
0.5 cm
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
8
A larger interval in length. Because then any
differences in the temperature rise will be
more obvious.
9
Accept any sensible number from 5 upwards.
10 Credit any sensible suggestion to reduce heat
loss to the room. Ideas such as wrapping the
test tube in some sort of a jacket are the most
likely, but there should be some comment
about still being able to read the thermometer.
Exercise 8.1C Exothermic reactions
with metals
1
potassium + water → potassium + hydrogen
hydroxide
2
thermal, light and sound energy
3
Wear safety glasses and carry out the reaction
behind a safety screen.
4
Measure any increase in the temperature
of the water. Learners should make some
comment about it being difficult to measure
the amount of light and/or sound energy.
5
Learners should include the following points:
11 They can repeat the investigation with each
length of magnesium ribbon at least twice.
Exercise 8.1B Investigating exothermic
reactions between metals and acid
•
1
magnesium + sulfuric → magnesium + hydrogen
acid
sulfate
Use the same acid, use the same volume
of acid.
•
Use the same mass of the different metals.
2
a
hey needed to change the metal they
T
place into the acid.
•
b
The variables they have kept the same are
the type of acid used, the volume of acid
used and the method they used.
The measured volume of acid should be
placed in a test tube, the temperature
taken and recorded and then the
metal added.
•
The temperature is taken again after the
reaction has finished. (Mention could be
made that the rise in temperature is what
is required, so if there are slightly different
starting temperatures, it is not significant.)
•
Safety aspects such as wearing
safety glasses.
c
The variable they should have kept the
same is the mass of the metal used (X is
described as ‘small’, but Y is not).
d
You cannot form a reliable conclusion
with these results because they have not
used the same mass of each metal.
e
They could improve their investigation
and make the results more reliable by
using the same mass of each metal.
Repeating their experiments several times,
so that they allow for any errors, would
also improve the reliability of the results.
6
The results should be presented as a bar chart,
because the temperature rises are for four
different metals (the type of metal is a discrete
variable) so it is best not to use a line graph.
Topic 8.2 Endothermic reactions
Exercise 8.2A Energy changes
1
24
Reaction
Start
temperature
in °C
Final
temperature
in °C
Exothermic or
endothermic
A
21
45
exothermic
B
18
22
exothermic
C
19
16
endothermic
D
18
20
exothermic
2
endothermic
3
exothermic
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Exercise 8.2B Exothermic or
endothermic?
1
a
b
c
he reaction between sodium
T
hydrogencarbonate and citric acid is
endothermic. The reactions between
sodium hydroxide and sulfuric acid,
between hydrochloric acid and zinc, and
between copper sulfate and magnesium
powder are exothermic.
Exercise 8.3 Why does iron rust?
1
iron oxide
It was sensible to use polystyrene cups
rather than test tubes or glass beakers
because polystyrene is a good insulator,
so that less of the heat energy produced in
the reaction was lost to the environment.
There would be a more accurate
temperature reading taken.
2
The nail in tube B will go rusty.
3
The water has been boiled to remove any
dissolved air and the layer of oil on the top of
the water prevents any more air from entering.
4
a
No, this is not an expected result.
b
The nail in the dry air may have gone
rusty because Zara has not put the
stopper into the tube firmly enough and
some moisture from the air has entered.
Credit any useful product, such as self-heating
food or drink cans. Credit any sensible
original ideas.
3
Credit any ideas, such as ‘chemical ice-packs’
or self-cooling drinks.
Exercise 8.2C Endothermic reactions
and processes
2
25
Topic 8.3 Metals and their
reactions with oxygen
The reaction between copper sulfate
solution and magnesium powder has the
largest temperature change.
2
1
energy transferred from the surroundings, they
escape the forces holding them together in
the liquid and change into gas and evaporate.
Since the energy to do this comes from the
surrounding water in the bowl, this water
cools down and keeps the bottles of soda cool.
In an endothermic reaction, a chemical
reaction takes place with new products being
formed. Energy is taken from the environment,
so there is a decrease in temperature. An
example is the reaction of sodium hydrogen
carbonate with citric acid to produce sodium
citrate, water and carbon dioxide. In an
endothermic process, energy is also taken in
from the environment, but there are no new
products formed. For example, ice melting
takes in energy from the environment, so it
is endothermic, but since no new products
are formed (water merely changes state) it is
an endothermic process. (Credit any other
suitable examples such as potassium chloride
dissolving in water as an endothermic process.)
The water in the bowl soaks into the cloth
over the soda bottles. The liquid water
evaporates as it heats up in the hot weather.
The particles in the liquid water move all the
time and can slide past each other as they only
have weak forces holding them in place. The
more energy the particles have, the more they
can move. When the particles have enough
5
Credit any two sensible ideas, such as painting,
galvanising or coating with any other suitable
material, such as plastic or grease.
6
The plan for the investigation should clearly
state the variable the learner will change, the
temperature of the nail. This can be done in a
variety of ways. As long as the method is clear
and workable, credit it. A suggestion may be
to place new shiny nails of the same shape, size
and composition into test tubes containing
water at different temperatures. Credit learners
if they give a suitable range of temperatures.
Learners may decide to keep the test tubes
in a water bath to maintain the different
temperatures.
There must be a clear indication of the
variables to be controlled, such as the type and
size of the nail, the volume of water used and
the time for the experiment. There should also
be a clear indication of the dependent variable
(rusting) and how they will measure it. This
will probably be by eye and a comparison of
the rust on the nails after a given time.
Credit should be given to a plan that considers
the practicality of the approach.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Topic 8.4 Reactions of metals
with water
Exercise 8.4 Reactions with water
and steam
1
In order starting with the most reactive:
potassium; magnesium; zinc; copper.
2
potassium + water → potassium + hydrogen
hydroxide
sodium or lithium
3
4
5
6
Copper can be used for roofs because it does
not react with water. Magnesium reacts slowly
with water, so would not be used for a roof, as
it would react when there is rain or snow.
11 Copper does not react with water. This is why
it is used for pipes carrying water. Iron does not
react with water either but it does react with
oxygen if it is in the presence of water. So the
iron in the pipes would react with any dissolved
oxygen in the water and rust. Iron oxide would
form. This would result in the water being
coloured reddish brown with the iron oxide,
and the pipes would eventually collapse.
Topic 8.5 Reactions of metals with
dilute acids
Exercise 8.5A Investigating reactivity
1
The test tube with metal C has less acid than
the others, so it is not a fair test. All the test
tubes should have the same volume of acid.
The volume of acid must be one of the
control variables.
2
They have put on safety glasses.
3
Because the tube with metal A contains a
different acid, nitric acid; the others have
hydrochloric acid. The type of acid must be
one of the control variables.
4
No, because the piece of metal B is larger
than the pieces of the other metals. The size
of the pieces of metal must be one of the
control variables.
5
how reactive different metals are with
dilute acids
calcium + water → calcium + hydrogen
hydroxide
rubber
bung
boiling
tube
steam
ceramic
wool
piece of
metal
7
hydrogen
6
the type of metal used
8
The test for hydrogen gas is to place a lighted
splint in the gas to see whether it makes a
squeaky pop sound when it burns.
7
the amount of bubbling/number of bubbles
there are when the metal reacts with the acid
8
9
magnesium + steam → magnesium + hydrogen
oxide
The volume of acid used, the type of acid
used, the mass of metal used. Credit also
‘the same temperature’, and any mention
of the form the metal is in, i.e. powder, lump
or ribbon, which would show a high degree
of understanding.
10
test tube
bubbles of gas
Exercise 8.5B Reactions of metals with
dilute acids
1
They can tell that a reaction has taken
place if there is a colour change, bubbles
of gas are given off or if there is a change
in temperature.
2
They can tell which metal is more reactive by
comparing the number of bubbles given off
in a given time or comparing the temperature
changes. Colour change is not a reliable or
practical way to compare reactions.
beaker
water
funnel
metal
26
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© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
3
4
They cannot use their observations to
compare copper, aluminium, zinc and lead
because the two boys have used different acids.
The acids are also of different concentrations
and different volumes.
The plan should use the concept that the only
variable to be changed is the type of metal.
The type, volume and concentration of the
acid used should be the same in each test. The
mass of metal used should be the same. There
should be an indication of how these variables
will be measured to ensure they are the same in
each case. For example, the use of a measuring
cylinder to measure the volume of the acid.
There should be some indication of how the
number or volume of bubbles of hydrogen given
off will be compared. This could be by doing
the tests at the same time and comparing by eye.
There should be an equipment list or indication
of what equipment will be required. Safety
information, such as wearing safety glasses and
how to use reagent bottles, replacing stoppers
and so on, should be included. The plan should
be presented in a logical sequence and manner.
Exercise 8.5C How reactive are these
metals?
1
The mass of metal used; the volume of acid
used; the type of acid and its concentration.
Also, the inverted test tube must always be
completely full of water at the start of the
investigation; the timer must be started at
the same point in the investigation: when the
delivery tube is back in place, for example; the
test tube of gas must be completely full when
timing is stopped.
2
Copper does not react in dilute acid.
3
Learners should draw a bar chart, with the bars
in order of height, the tallest bar furthest left.
4
Accept any sensible suggestions, for example:
she might have misread the timer, or not
stopped it at exactly the right time; she might
have got the mass of metal wrong, or mixed
up which metal she was using.
5
Learners could mention the difficulties of
keeping the delivery tube in place so that no
hydrogen is lost; getting the delivery tube
back in place in the conical flask after adding
the metal; being exactly sure when the tube is
completely full of gas.
6
Accept sensible suggestions to improve
accuracy; do not accept repeating the
experiments with each metal, as this improves
the reliability, not the accuracy. Suggestions
that might be expected and which would
provide evidence that learners have thought
carefully about the practical aspects of the
investigation are: one person adding the metal
and another person putting the delivery tube
back; using a graduated tube or measuring
cylinder or marking the test tube so that it
is easier to see when the gas reaches a
particular level.
Unit 9 Magnetism
Topic 9.1 Magnetic fields
Exercise 9.1A Magnetic field patterns
1
b
a
S
X in either of the positions shown.
N
X
27
X
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
c
W in any of the positions shown.
W
Exercise 9.1C Interaction of magnetic
fields
1
W
W
The magnetic field lines between the two poles
are in the same directions; attract.
2
W
2
The magnetic field lines between the two poles
are in opposite directions; repel.
Place two magnets on a surface with the two
south poles facing; place a piece of paper over
both magnets; sprinkle iron filings on the paper.
Topic 9.2 The Earth as a
giant magnet
a
Exercise 9.2A The Earth’s magnetic field
N
S
1
The Earth’s magnetic poles have not always
been in the same positions.
The Earth’s magnetic poles are similar to the
poles of a bar magnet.
2
The Earth’s magnetic field occurs all around
the Earth.
3
a
core
b
iron and nickel
b
N
N
1
toward geographic north
2
south
3
a
The area around a magnet where the
effect of the magnet can be detected.
a
Stroke the needle with the magnet; use
the same pole of the magnet; stroke
several times; stroke in the same direction
each time.
b
A magnetic compass will turn according
to the position of a magnetic object;
the needle will point in the direction of
magnetic field lines.
b
a
gets weaker
b
gets weaker (to the middle of the magnet)
then gets stronger again
Exercise 9.1B Magnetic fields
1
2
28
Exercise 9.2B Direction of the Earth’s
magnetic field
4
Any method that will allow the needle to
rotate freely, such as float on a cork in
water or suspend horizontally using
a thread.
Attach the string to the middle of the magnet
using the adhesive tape; hang the bar magnet
so it is horizontal and supported from the
wooden clamp stand; allow the magnet to
turn. The magnet will align close to the
geographic north-south direction; the north
pole of the magnet will point closely to
geographic north.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Exercise 9.2C Strength of the Earth’s
magnetic field
1
2
The strength of the magnetic field 1 cm from
the end of a bar magnet. Reason: the Earth’s
magnetic field will not make a paperclip move,
but when 1 cm from the end of a bar magnet,
a paperclip will move.
a
4
b
2500
c
Exercise 9.3B Electromagnets 2
1
Any two from: lifting/sorting scrap metal;
toaster; electric bell; electric motor; holding
doors open.
2
a
hen current flows, the nail is magnetised;
W
the pins are magnetic and will be attracted
to the nail.
b
When current stops flowing, the nail is no
longer magnetised; the pins will no longer
be attracted to the nail.
c
Either: bring a magnetic compass close to
the end; if the compass points towards the
end of the nail, it is south; if the compass
points away from the end of the nail, it is
north; OR bring the north pole of a bar
magnet to the end of the nail; if it attracts
it is south; if it repels, it is north.
50 000
65 000
X
Exercise 9.3C Electromagnets 3
d
30 000
1
a
It could be a south pole.
b
Bring the north pole of a bar magnet
toward the end of the nail; if they repel,
then the end of the nail is a north; if they
attract, then the end of the nail is a south
(accept explanation using south pole with
opposite effects).
c
Reverse the current in the coil/reverse the
cell in the circuit; remove the nail from the
coil and insert the other way round / wind
the coil in the opposite direction.
W
30 000
e
The learner’s position should be correctly
identified; if the learner’s location is
between two lines then any value between
the values of those lines can be given.
Topic 9.3 Electromagnets
Exercise 9.3A Electromagnets 1
1
29
Topic 9.4 Investigating
electromagnets
a
wire to make the coil; iron or steel rod/nail
for the core
Exercise 9.4A Strength of
electromagnets 1
b
1
steel paperclips
2
steel and iron
3
The electromagnet uses electricity/current to
work; the electromagnet can be switched on
and off.
a
As the number of turns on the coil
increases, the number of paperclips lifted
increases. This means the electromagnet
gets stronger as the number of turns on
the coil increases.
b
20 turns/5 paperclips
c
repeat it/do it again (not check it)
d
size of the paperclips; current in the coil;
material in the core
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE
Exercise 9.4B Strength of
electromagnets 2
1
a
material in the core; number of turns in
the coil; same size paper clips
b
c
i
ii
ells can run out/run low, whereas the
C
power supply will not/power supply
is more reliable; easier to change the
current with the power supply than
connecting/disconnecting cells.
The wire in the coil gets too hot.
i
ii
50 pins
12 or 13 pins (not 12.5)
Exercise 9.4C Strength of
electromagnets 3
1
30
a
current in the coil and material in the core
2
b
small paperclips; a better range of
values can be measured/measurement is
in smaller intervals/can detect smaller
changes in electromagnetic strength
a
he reading on the balance will decrease;
T
the iron block will be attracted up to the
electromagnet; the force of attraction on
the block is in the opposite direction to
the weight of the block; the force down on
the balance is less.
b
As the current in the electromagnet
increases, the reading on the balance will
get smaller/decrease.
c
No, this is not correct; if the connection is
reversed, then the current will be reversed;
the poles on the electromagnet will be
reversed; whichever pole is close to the iron
block will still attract the block equally.
Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth
© Cambridge University Press 2021
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CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE
Workbook answers
Unit 1 Photosynthesis and the carbon cycle
Mean number of bubbles
per minute
5
Topic 1.1 Photosynthesis
Exercise 1.1A How light level affects
photosynthesis
1
The type of plant; the mass of the plant; the
temperature
2
3
Apparatus
Amount of
light
Volume of gas
collected in cm3
A
high
18.3
B
low
7.2
C
none
0.5
6
Plants photosynthesise faster when they have
more light.
The colour of the light / cellophane.
2
The number of bubbles produced in one
minute.
3
Any three from: the light intensity (strength);
the type of water the water plant was in; the
quantity of water plant; the type of water
plant; the temperature.
4
For example:
Colour of light Number of bubbles per minute
1st try 2nd try 3rd try mean
white
1
12
10
8
6
4
2
red
green blue
Colour of light
white
Accept any valid conclusion that can be
made from these results, for example: plants
photosynthesise fastest in white light;
photosynthesis happens faster in blue light
than in green light.
Exercise 1.1C Turning an idea into a
hypothesis that can be tested
Exercise 1.1B The effect of different
colours of light on the rate of
photosynthesis
1
14
11
13
12
12
red
10
12
11
11
green
4
5
6
5
blue
8
12
10
10
1
Accept any answer that:
• is in the form of a clearly phrased hypothesis
• relates to the effect of carbon dioxide on
the rate of photosynthesis of an aquatic
plant
• can be tested by experiment.
For example, a possible hypothesis could be:
Water plants give off more bubbles per minute
when they are given more carbon dioxide.
2
Look for:
• a clear statement of the independent
variable and dependent variable
• at least two other variables that will be
controlled
• a clearly explained method, with enough
detail that someone else could follow
it, including a labelled diagram of the
apparatus
• a clear description of how the independent
variable will be changed
• a clear description of how and when results
will be collected
• a results chart, with headings and units (but
no results)
• a prediction based on scientific
understanding.
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Topic 1.2 More about
photosynthesis
Exercise 1.2B Testing a variegated leaf
for starch
Exercise 1.2A Duckweed experiment
1
A 0, B 1, C 2, D 3, E 4
2
quantity of fertiliser
3
number of duckweed plants, volume of water,
temperature, light intensity
4
Dish
Number of
grains of
fertiliser
Number of
plants at end
of experiment
A
0
5
B
1
9
C
2
10
D
3
8
E
4
0
5
Number of plants at end of experiment
7
2
chlorophyll
2
Chlorophyll absorbs energy from sunlight.
Without chlorophyll, the leaf cells will not
be able to photosynthesise and make glucose.
Without glucose, they will not be able to make
starch.
3
This is to break down the cell membranes in
the leaf, allowing the iodine solution to get to
the starch.
4
This is to remove the chlorophyll from the
leaf, making it easier to see any colour changes
when iodine solution is added.
5
dish C
10
dish B
blue-black
dish D
8
6
6
4
2
1
oxygen
2
The stomata (little holes in the epidermis)
are on the underside of leaves. The oxygen is
made by the cells inside the leaf, from where it
diffuses out through the stomata.
3
The more bubbles of oxygen produced, the
more quickly the leaf disc will rise; the bubbles
of gas collecting under the leaf make it float
upwards. A mention of the gas bubbles
attached to the leaf making it less dense would
show a very good level of understanding.
4
For example: Leaves photosynthesise more
quickly in bright light than in dim light or
leaves make more oxygen in bright light than
in dim light.
5
Light intensity/brightness
6
3 (bright light) and 44 (dim light) should
be circled.
7
Mean for bright light = 12.75, 12.8 or 13.
Mean for dim light = 70.75, 70.8 or 71.
dish E
0
starch
Exercise 1.2C Floating discs
experiment
dish A
0
6
1
1
2
3
4
Number of grains of fertiliser
Duckweed plants grew and reproduced faster
in the dishes with 1 or 2 grains of fertiliser
than with no fertiliser.
This shows that adding fertiliser causes the
duckweed plants to grow and reproduce faster.
However, fewer plants grew and reproduced
when 3 grains of fertiliser were added than
when 2 were added, and all the plants died
when 4 grains were added.
Use three sets of dishes for each quantity of
fertiliser.
(The other two choices would be different
experiments and would not test Sofia’s original
idea, which was that giving duckweed plants
extra nitrate fertiliser helps them to grow and
reproduce faster.)
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8
9
There were a lot of variables that the girls
could not control, however hard they tried.
For example: the bubbles of oxygen might not
come out of every part of each leaf evenly, so
some of the leaf discs would tip over and rise
to the surface more quickly or more slowly;
some of the discs might hit the sides of the
beaker, which would make them rise more
slowly; it would be difficult to decide exactly
when to start the timer, and when to stop it.
The conclusion should be a response to
the hypothesis that the learner stated in the
answer to question 4. For example: Leaf discs
photosynthesise more quickly in bright light
than in dim light.
4
D
carbohydrates
in animals
2
3
3
P
carbon compounds
in fossil fuels e.g. oil
and coal
R
D
F
carbohydrates
in green plants
C
So that the gases in the tube could not mix
with the air. This allowed Arun to see how the
processes happening inside the tubes changed
the concentration of carbon dioxide in
the tube.
plant and
animal
red
red
B
animal only
red
yellow
C
plant only
red
purple
D
nothing
red
red
Look for these ideas:
• The only process that removes carbon dioxide
from the atmosphere is photosynthesis.
• Respiration and combustion add carbon
dioxide to the atmosphere.
• If there was no photosynthesis, then carbon
dioxide would build up in the atmosphere.
carbon dioxide
in the air
carbohydrates
in decomposers
A
6
Exercise 1.3 Completing a carbon cycle
diagram
R
Colour of
indicator
after two
hours
In tube A, the plant photosynthesised and
respired, but it photosynthesised more than it
respired. The animal respired. Overall, about
the same quantity of carbon dioxide was
taken in for photosynthesis as was given out
by respiration. The quantity of carbon dioxide
in the tube did not change.
In tube B, the animal respired, giving
out carbon dioxide. There was a high
concentration of carbon dioxide in the tube.
In tube C, the plant photosynthesised and
respired, but it photosynthesised more than
it respired. More carbon dioxide was taken in
than was given out. So there was almost no
carbon dioxide left in the tube.
In tube D, there was no respiration or
photosynthesis. The quantity of carbon
dioxide in the tube did not change.
Topic 1.3 The carbon cycle
R
Colour of
indicator
at start
5
10 Leaves use light as their energy source for
photosynthesis, so they photosynthesise more
quickly in bright light than in dim light. This
means that they make oxygen more quickly.
Oxygen bubbles collect more quickly on the
undersides of the leaf discs in bright light, so
the discs rise to the surface more quickly.
1
Tube Contents
Topic 1.4 Climate change
Exercise 1.4 Interpreting graphs about
climate change
1
There is more carbon dioxide in the atmosphere
now than there used to be: Graph C.
Sea level is steadily rising: Graph A.
Sea ice in the Arctic is present for fewer months
in the year now, and there is less of it: Graph B.
2
Sea level is rising. Sea level has risen by 230
mm since 1880.
3
Sea ice covered a smaller area in 2017–2018
than between 1979 and 2016.
Sea ice appeared later and disappeared earlier
in 2017–2018.
Any two from: temperature, volume of
indicator, time the apparatus was left for.
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4
You would need to collect data for more years
after 2017–2018 to see if this is a trend or just
a one-off result for this period.
5
For example: We can correlate an increase
in burning fossil fuels with the rise in carbon
dioxide concentration.
6
In the northern hemisphere there is more
light and higher temperatures in summer
than in winter. Plants photosynthesise more
in summer, using more carbon dioxide. So
carbon dioxide concentration falls in summer
and rises in winter when plants cannot
photosynthesise as much.
Unit 2 Properties of materials
Topic 2.1 Atomic structure and the Periodic Table
6
Exercise 2.1 Atomic structure
1
12
2
14
3
aluminium
4
neon
5
Atomic number = 5; Mass number = 11;
Number of protons = 5; Number of neutrons
= 6; Number of electrons = 5
7
Element
Atomic
number
Mass
number
Protons
beryllium
4
9
phosphorus
15
calcium
20
8
9
6
6
6
6p6n
Neutrons
Electrons
Electronic
structure
4
5
4
2,2
31
15
16
15
2,8,5
40
20
20
20
2,8,8
The atomic number increases by 1 every time
you move along to the next element in the
Periodic Table.
The mass number increases in most cases
(except between argon and potassium where
the mass number decreases by 1) but the
increase is not by a fixed number each time.
calcium and argon
10 Accept helium, nitrogen, oxygen or neon.
4
a
b
c
d
11
Element
Potassium
atomic number
19
mass number
39
number of protons
19
number of neutrons
20
number of electrons
19
electronic structure
2, 8, 8, 1
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Topic 2.2 Trends in groups within
the Periodic Table
Exercise 2.2A Elements in the same
group
1
The number of protons increases.
2
The mass number increases.
3
Atomic number = 11; Mass number =
23; Number of protons = 11; Number of
neutrons = 12; Number of electrons = 11
d
e
Exercise 2.2C Comparing the trends in
Groups 1 and 7
4
2, 8, 1
1
The melting point decreases.
5
They have the same number of electrons
(one) in the outer shell and both have 2 in
the inner shell and both have 2 in the inner
shell.
2
The melting point increases. This is the
opposite of what happens in Group 1. (Watch
out for any confusion in understanding that
−7 °C is a higher temperature than −220 °C.)
6
Atomic number = 19; Mass number =
39; Number of protons = 19; Number of
neutrons = 20; Number of electrons = 19
3
7
2, 8, 8, 1
In Group 1, the boiling point decreases as the
atomic number increases, whereas in Group
7, the boiling point increases as the atomic
number increases.
8
All three atoms have one electron in the outer
shell, and two in the inner shell.
4
9
The atoms get larger / there are more electron
shells as you go down the group. The atoms
have a larger mass / more protons and
neutrons as you go down the group.
In Group 1, the least reactive element is the
one with the smallest atom; the most reactive
is the one with the largest atom. In Group 7,
the least reactive element is the one with the
largest atom; the most reactive is the one with
the smallest atom.
5
Rubidium, Group 1: Students should predict
that:
Exercise 2.2B Trends in groups in the
Periodic Table
1
A group in the Periodic Table is a column of
elements.
2
a
b
c
5
The melting point of bromine is −7 °C
so the melting point of iodine would be
expected to be much higher than that.
Iodine would have a much lower boiling
point than astatine. (The trend in the
group is that the further down you go, the
more the boiling point increases.)
Astatine is less reactive than iodine as it is
below iodine in Group 7.
• it will be more reactive than the other
elements shown (as it has a larger atom)
• it will have a lower melting point
Watch out for any confusion in
understanding that −7 °C is a higher
temperature than −220 °C.
The trends are:
• the melting points increase as you go
down the group
• the boiling points increase as you go
down the group
• the elements become less reactive as
you go down the group.
The melting point of iodine will be higher
than that of bromine.
Iodine is a solid at room temperature.
This is because the melting point of
iodine is likely to be more greater than
room temperature (around 22 °C). The
table shows very large changes in melting
points between the elements in the group.
• it will have a lower boiling point
Iodine, Group 7: Students should predict that:
• it will be less reactive than the other
elements shown (as it has a larger atom)
• it will have a higher melting point
• it will have a higher boiling point.
Topic 2.3 Why elements react to
form compounds
Exercise 2.3A Atoms and ions
1
The outer shell of the atom should be labelled
as the highest energy level.
2
Diagram should have a nucleus, and one shell
with two electrons.
3
Li+
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Diagram should have two shells, with electron
structure 2,8 and a nucleus.
5
F−
b
Exercise 2.3B Why do ions form?
1
sodium:
atomic number 11
mass number 23
sodium atom:
chlorine:
atomic number 17
mass number 35
chlorine atom:
The learners must place
the electron crosses in
the correct shells but
they can be anywhere
in those shells.
The learners must place
the electron crosses in
the correct shells but
they can be anywhere
in those shells.
sodium ion:
chlorine ion:
c
Calcium ion diagram should have a
nucleus, three shells, with electron
structure 2,8,8.
Chlorine ion diagram should have
a nucleus, three shells, with electron
structure 2,8,8.
Diagrams must be labelled; learners
may mark the chlorine ion as negatively
charged and the calcium ion as positively
charged.
The calcium atom has two electrons in its
highest energy shell. For the calcium atom
to become more stable these two electrons
must be lost. Chlorine has seven electrons
in its highest energy level so only needs
one electron to fill this shell. Two atoms
of chlorine are needed to use the two
electrons lost from the calcium atom so
the formula for calcium chloride is CaCl2
because two atoms of chlorine are needed
for every one atom of calcium.
Topic 2.4 Simple and giant
structures
Exercise 2.4A Ionic or covalent bonds
1
Ionic bonding, because the particles are
packed closely together in a lattice pattern.
2
The learners must place
the electron crosses in
The learners must place
the correct shells but
the electron crosses in
they can be anywhere
the correct shells but
in those shells.
they can be anywhere
in those shells.
Arrows should indicate the points where the
large atom and the four small atoms in each
molecule join. The label should read ‘strong
forces within each molecule’.
3
Substance B
4
Substance A
5
Ionic
2
6
covalent
7
Any correct example, such as graphite or
silicon dioxide.
3
The electrons are held in place by the electrostatic
forces between the protons and the electrons.
Ions are formed because the outer shells of the
atoms are not full and that makes the atom
less stable. The atoms can form full shells by
losing or gaining electrons.
Exercise 2.3C Forming ionic
compounds
1
6
a
Calcium atom diagram should have a
nucleus, four shells, with electron structure
2,8,8,2.
Chlorine atom diagram should have
a nucleus, three shells, with electron
structure 2,8,7.
Diagrams must be labelled.
Exercise 2.4B Properties of ionic and
covalent substances
1
Its melting and boiling points are high.
2
a gas
3
potassium chloride, calcium chloride and
magnesium oxide
4
ammonia and bromine
5
Water; because it has a boiling point of 100 °C
and a melting point of 0 °C.
6
bromine
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8
Magnesium oxide has high melting and
boiling points because it is an ionic
compound. The ions have strong forces
holding them together in a lattice pattern.
This means that a lot of energy is needed
to overcome these forces and make the
magnesium oxide melt or boil.
Ammonia has low melting and boiling
points because, although the forces inside the
molecules are strong, the forces between the
molecules are weak and less energy is needed
to overcome these intermolecular forces and
make the ammonia melt or boil.
Exercise 2.4C Giant structures of carbon
1
diamond (left) and graphite (right)
2
The atoms of carbon in graphite are arranged
in layers. The bonds between the carbon atoms
in the layers are strong (each carbon atom
bonds with three other atoms) but the bonds
between the layers are weak. This means that
the layers can slide over one another and the
surface is soft and comes away. For example,
when you write with a graphite pencil.
3
The atoms of carbon in diamond are arranged
in a rigid, giant three-dimensional structure or
lattice. This means that there are strong bonds
throughout the whole structure and this is
what makes diamond so hard.
Unit 3 Forces and energy
2
Topic 3.1 Density
Exercise 3.1A Comparing densities
1
gas
2
B
3
R
4
The density of the material should be less than
that of water / less than 1.0 g/cm3.
3
Exercise 3.1B Understanding and
calculating density
1
2
3
4
the mass of a certain volume of substance
mass
(density =) _______
volume
mass
10
a density = _______ = ___ = 1(.0) (g/cm3)
volume 10
mass
170
b density = _______ = ____ = 8.5 (g/cm3)
20
volume
mass
56
c density = _______ = ____ = 0.56 (g/cm3)
volume 100
a 2 × 2 × 2 = 8 cm3
mass
71.2
b density = _______ = ____ = 8.9 (g/cm3)
8
volume
Exercise 3.1C Density, floating and
sinking
1
7
a
polyethylene
b
polypropylene
c
cellulose acetate / polyvinyl chloride
mass
density = _______, so mass = density × volume
volume
= 1.0 × 250 = 250 g; so, the mass of the boat
must be less than 250 g (accept values such as
249 g or 249.9 g)
The shape of the mild steel is designed so
the ship is hollow / contains air; the average
density of the mild steel and the air (and other
materials) is less than 1.03 g/cm3.
Topic 3.2 Heat and temperature
Exercise 3.2A Heat or temperature
1
a
b
c
100 °C is the temperature at which water
boils.
25 000 J is the quantity of heat needed to
make cold water warmer.
22 °C is often described as
room temperature.
2
The temperature of the coffee in each cup is
different; the heat in the coffee in each cup is
different.
3
The temperature of the soup in each bowl is
the same; the heat in the soup in each bowl is
different.
Exercise 3.2B Heat or temperature
1
a
b
°C or degrees Celsius
J or joules
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3
4
heat – the total energy of particles in a
substance.
temperature – the average energy of particles
in a substance.
In a solid, the particles vibrate about fixed
positions.
When a solid is heated, the particles vibrate
faster / more vigorously.
When the temperature of a solid decreases, the
particles vibrate more slowly / less vigorously.
Heat: the block with more mass has more
particles, so it has more heat.
Temperature: the temperature of the two
blocks is the same.
1
1000 − 850 = 150 J
2
1000 + 600 = 1600 J; 2400 − 1600 = 800 J
3
a
b
100 − 50 − 30 = 20%
Diagram should have the input labelled
(on the left) as 100% electrical energy.
There should be three output arrows
labelled 50% thermal, 30% light, 20%
sound. The thickness of each output
arrow should be approximately in
proportion to these percentages.
Topic 3.4 Moving from hot to cold
Exercise 3.2C Measuring heat and
temperature
Exercise 3.4A Direction of thermal
energy transfer 1
1
a
b
thermometer
joule meter
1
Thermal energy is transferred from a place
of higher temperature to a place of lower
temperature.
2
a
i 3000 J or 15 °C
ii repeat the experiment (not just repeat
that reading as it cannot be done in
isolation)
i 4500 J
ii 10 000 J
2
a
b
arrow pointing from flame to cooking pot
arrow pointing from heater towards air in
room (arrow can point up or down, but
must go from the heater to the air)
c
arrow pointing from foot to ice pack
b
Topic 3.3 Conservation of energy
Exercise 3.3A What does conservation
of energy mean?
1
The quantity of energy will stay the same.
2
Energy input to the lamp equals energy output
from the lamp.
3
100 J
4
3500 J
Exercise 3.3B The law of conservation
of energy
1
2
3
4
8
Exercise 3.3C Calculating energy
changes
Energy cannot be created or destroyed; energy
can be changed from one form to another,
(Statements can be in either order.)
Exercise 3.4B Direction of thermal
energy transfer 2
1
Thermal energy will move from the object
at higher temperature to the object at lower
temperature.
2
Two arrows pointing into the centre block
(10 °C): one from the left (20 °C) and one from
the right (30 °C).
3
Curved line from top dashed line, starting
at time 0, down to lower dashed line, then
levelling off on the lower dashed line.
Exercise 3.4C Direction of thermal
energy transfer 3
1
The total of the light and thermal energy
output must be equal to the quantity of
electrical energy input.
She uses more energy for running and being
active than when resting, so this extra energy
must be supplied in her food.
100 − 65 = 35%
a
b
2
Thermal energy moves from her body to
the air because her body is at a higher
temperature than the air / surroundings.
Thermal energy moves from the air /
surroundings into her body; the air is at a
higher temperature than her body.
The temperature of the water will decrease;
the ice is at a lower temperature than the
water; thermal energy will move from the
water to the ice.
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The temperature of the coffee decreases;
the temperature of the milk increases; the
temperature of the coffee and the milk
eventually become the same; the coffee is
initially at a higher temperature than the
milk; thermal energy flows from the coffee to
the milk; the (overall) flow of thermal energy
stops when the temperatures of the milk and
the coffee are the same.
Topic 3.5 Ways of transferring
thermal energy
2
White is a good reflector of thermal radiation /
white is a poor absorber of thermal radiation;
the house will stay cool inside during hot
sunny weather.
3
Wool is a poor conductor of heat / wool is a
good thermal insulator; thermal energy will be
transferred from the body to the surroundings
more slowly through the wool.
4
The shiny metal reflects thermal radiation
back to the food; plastic is a poor conductor
of heat / plastic is a good thermal insulator;
thermal energy will be transferred from the
food in the box to the surroundings more
slowly through the plastic.
Exercise 3.5A Describing thermal
energy transfers
1
a
b
c
d
2
Thermal energy is transferred from the
Sun to Earth by radiation.
Thermal energy is transferred within
metals by conduction.
When warm air rises through cold air,
this is called convection.
Neither conduction nor convection can
occur in a vacuum.
Conduction – particles vibrate more, collide
with particles beside them, making these
particles also vibrate more.
Convection – particles vibrate more, take up
more space and decrease the density of the
substance.
Radiation – type of wave that does not require
particles to transfer thermal energy.
Topic 3.6 Cooling by evaporation
Exercise 3.6A How evaporation works
1
when a liquid changes to a gas
2
(they can escape from the liquid and
become gas).
3
Zara is correct; an example such as rain water
evaporates from the ground, but the ground
is not at 100 °C, or sweat evaporates from the
skin, but the skin is not at 100 °C.
Exercise 3.6B Evaporation and
cooling 1
1
Sweat evaporates, removing thermal energy
from skin.
2
a
Exercise 3.5B Comparing thermal
energy transfers
1
2
3
The particles in a solid are closer together;
vibration of particles can be transferred to
neighbouring particles more easily in a solid.
Convection requires particles to move;
particles in liquids and gases can move;
particles in solids are not free to move.
There are no particles in a vacuum; radiation
does not require particles; conduction and
convection both require particles.
Exercise 3.5C Variables affecting
thermal energy transfer
1
a
b
9
Metal is a good conductor of heat;
thermal energy is transferred to the
contents quickly / easily.
Wood is a poor conductor of heat / wood
is a good thermal insulator; the handle
will not get hot / will not cause burns
when held.
b
3
The average energy decreases; this is
because the particles with the highest
energy leave the liquid during the
evaporation process.
The temperature decreases; this is because
the average energy of the particles
decreases and temperature is the average
energy of the particles.
The fan makes air move; moving air speeds
up evaporation; evaporation of sweat removes
thermal energy from the skin; speeding up the
evaporation speeds up the removal of thermal
energy.
Exercise 3.6C Evaporation and
cooling 2
1
The perfume feels colder; evaporation of a
liquid removes thermal energy from the skin;
speeding up the evaporation speeds up the
removal of thermal energy.
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2
Evaporation of sweat removes thermal
energy from the skin; when evaporation stops
(because of high humidity) then the removal
of thermal energy stops / the cooling effect
stops.
3
The water evaporates into the moving air;
the water cools as it evaporates, lowering the
temperature of the sponge; the air is now
moving through a cooler sponge and thermal
energy from the air is removed to the sponge /
removed to the water to make it evaporate.
3
As temperature increases, the rate of transport
of water in celery stalks increases.
Unit 4 Maintaining life
Topic 4.1 Plants and water
Exercise 4.1A Water uptake by orange
plant seedlings
2
3
Add up the total number of root hairs on all
ten plants, then divide the total by 10.
Variety A plants had more root hairs per plant
(920 compared with 800, i.e., 120 more root
hairs per plant).
The mean length of the root hairs was greater
than variety B (0.03 compared with 0.02,
i.e. 0.01 mm longer).
The root hairs, therefore, had a greater surface
area, so they could take up more water.
1
They want to be able to compare the ability
of different varieties to take up water. The
quantity of water taken up may also be
affected by the size of the plants, and the
plants might be different sizes. Calculating
the volume taken up per gram makes it
easier to compare the varieties; it controls a
variable (the mass of the plant) and makes the
comparison fair.
2
A bar chart is the best way to display these
data.
It moves across to the centre of the root into
the xylem vessels. It then goes up the xylem
into the leaves.
Volume of water taken up per g of
wheat plant in cm3
1
Exercise 4.1C Interpreting data about
water uptake
Exercise 4.1B Celery experiment
1
3.2 at 50 °C is the anomalous result.
2
9
8
7
160
120
80
40
0
Distance the dye travels in cm
Key
6
C
after 6 weeks at 2 °C
3
After two weeks, variety A took up the most
water, with variety C next and variety B taking
up the lowest volume. Learners could also
calculate the differences between the volumes.
4
All the plants had taken up a greater volume
of water after six weeks. Now, instead of
variety A taking up the most, it is variety C.
5
Variety C, because it takes up the most water
over the longer period. This suggests that it
might grow better and faster than the other
varieties in the cold climate of Canada.
4
ignore this point
3
2
1
10
B
Variety of wheat
after 2 weeks at 2 °C
5
0
A
0
10
20
30
40
Temperature in °C
50
60
70
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Topic 4.2 Transpiration
6
Exercise 4.2 How temperature affects
water loss
1
She wanted to make sure that any water that
was lost came from the plants and not from
the soil.
2
The results table should have:
• clearly ruled columns and rows
• headings for the mass in the three different
pots (either rows or columns), with the unit g
• headings for the 8 days, such as Day 1, Day
2 and so on; or Time in days
• the correct reading written in each cell in
the table.
3
The anomalous result of 861 g for plant B
should be circled.
4
The line graph should have:
• time in days on the x-axis and mass in
grams on the y-axis
• suitable scales on both axes, using most
of the graph paper and going up in even,
sensible intervals
• each point plotted accurately, for each of
the three pots
• three lines carefully drawn, either joined
point-to-point or as a line of best fit, one
for each pot
• each line labelled to show which pot it
represents.
5
11
Plant B:
mass on day 1 = 893 g
mass on day 8 = 761 g
loss of mass over 7 days was 893 − 761 = 132 g
the mean loss of mass per day was
132 ÷ 7 = 19 g per day
Plant C:
mass on day 1 = 842 g
mass on day 8 = 618 g
loss of mass over 7 days was 842 − 618 = 224 g
the mean loss of mass per day was
224 ÷ 7 = 32 g per day
The results show that higher temperatures
increase the rate of loss of mass. The loss in
mass is due to water loss. Higher temperatures
increase the rate at which water evaporates
into the air spaces in the leaf. They also
increase the rate at which water vapour
diffuses out of the leaves into the air.
Topic 4.3 Excretion in humans
Exercise 4.3 Structure and function of
the excretory system
1
The kidneys are part of the excretory system.
This is also known as the renal system.
In the excretory system, a waste substance
called urea is filtered out of the blood.
It dissolves in water, forming a liquid called
urine.
2 and 3
artery bringing
blood to the kidney
right kidney
left kidney
ureter
vein taking blood
away from the kidney
urethra
bladder
4
kidney: filters the blood, removing urea from
it, and mixing the urea with water to produce
urine
ureter: carries urine from the kidney to the
bladder
bladder: stores urine
urethra: carries urine from the bladder to the
outside of the body
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in proportion to the interval widths. This is
entirely correct.
Topic 4.4 Keeping a fetus healthy
Exercise 4.4A Length of pregnancy
1
Species
1
33
goat
15
150
wolf
40
64
chimpanzee
40
227
llama
113
330
lion
150
108
moose (elk)
550
245
elephant
5000
640
There is no correlation.
Credit any use of figures that illustrates this
answer. For example, wolves and chimpanzees
both have a mean mass of 40 kg, but the length
of pregnancy of a chimpanzee is more than three
times longer than that of a wolf. Goats are much
smaller than wolves, but have a longer pregnancy.
Also credit arguments that there is some degree
of correlation. For example, the largest animal
(elephant) has the longest pregnancy, and the
smallest animal (rabbit) has the shortest.
There will be a lot of variation in the mass of
the female animals in a species. Many different
females would have been weighed and their
masses recorded so that a mean could be
calculated. Similarly, lengths of pregnancy will
vary between individuals.
Exercise 4.4B Does caffeine affect
birthweight?
1
12
Caffeine intake has no effect on mean
birthweight.
Credit any use of supporting figures. Learners
should also be encouraged to recognise that a
difference of just a few grams is not significant
when the total mass is more than 3000 g.
3
They could have actually measured the mother’s
intake of coffee, rather than asking them to fill
in questionnaires (which the mothers might not
have done correctly or accurately).
They could have used more mothers in
their study.
They could have used a wider range of
caffeine intake.
They could have split the levels of caffeine intake
into smaller intervals, for example less than 49,
from 50 to 99, from 100 to 149 and so on.
Mean mass of Mean length of
a female in kg pregnancy in days
rabbit
2
2
The animals could be arranged in order of
increasing or decreasing mean mass.
For example:
The bar chart should have:
• full labels on each axis, using the full
column headings from the table, i.e.,
‘caffeine intake per day in mg’ on the x-axis
and ‘mean birthweight in g’ on the y-axis
• a suitable, evenly spaced scale on the y-axis,
with a range that allows the bars to be
plotted with some accuracy (e.g. from 3500
to 3700, in divisions of 25 or 50)
• each bar plotted reasonably accurately.
Some learners may appreciate that the intervals
are not equal and may, therefore, construct a
histogram in which the widths of the bars are
Exercise 4.4C Smoking and birthweight
1
2609 + 23 713 = 26 322
2
No, the number of babies born to mothers
who did not smoke was 23 713, but the
number born to mothers who smoked was
2609. This means that the number of mothers
who smoked was much smaller than the
number who did not smoke.
3
Yes, the evidence suggests that it did. The
percentage of babies with low birthweight
in 2004 to 2005 was 14.0 for mothers who
smoked, and only 9.6 for mothers who did
not smoke. So, although there were quite a
lot of low birthweight babies born to mothers
who did not smoke, the risk was less than for
mothers who smoked.
4
In 2004 to 2005 there were 2609 babies born
to mothers who smoked, but in 2006 to 2007
there were only 2109. This suggests that fewer
mothers smoked during pregnancy.
These figures could also mean that fewer women
had babies overall in 2006 to 2007, but the figures
for mothers who did not smoke shows that this
was not so, because these numbers increased.
The total number of babies born in 2006 to 2007
is slightly greater than the number born in 2004
to 2005 (27 064 and 23 713 respectively).
Some learners might like to calculate the
percentage of babies born to women who
smoked and who did not smoke in each row:
For 2004 to 2005: Total number of babies =
26 322
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Percentage of babies born to mothers who
smoked = (2609 ÷ 26 322) × 100 = 9.9%
For 2006 to 2007: Total number of babies =
27 064
Percentage of babies born to mothers who
smoked = (2109 ÷ 27 064) × 100 = 7.8%
5
having a baby with low birthweight. The data
do support the idea that smoking increases the
risk of low birthweight. However, they do not
prove that smoking actually causes this effect.
To be certain that it is smoking that causes
the increased risk, we would need a lot more
evidence from other studies. (That evidence
does, of course, exist.)
Overall, there is correlation between smoking
during pregnancy and an increased risk of
Unit 5 Reactivity
copper sulfate she will know that the
metal is more reactive than copper. If
there is no reaction with zinc sulfate she
will know that it is less reactive than zinc.
By observing the reactions in all four of
the solutions she will be able to work out
which metal she has.
Topic 5.1 Reactivity and
displacement reactions
Exercise 5.1A Using the reactivity series
1
less vigorously
2
It does not react at all; give credit for silver
reacts less / is less reactive than copper.
3
Zinc will react more quickly than iron with
dilute acid.
4
No; there will be not be a displacement
reaction because copper is less reactive than
iron.
5
Silver or gold; give credit if another unreactive
metal such as platinum is named.
6
iron, lead or copper
7
a
b
c
d
e
1
13
Metal
A
B
C
D
E
F
A
7
3
7
3
3
3
B
7
7
7
7
3
7
C
3
3
7
3
3
3
D
7
3
7
7
3
7
It tells you that zinc is more reactive than
copper.
E
7
7
7
7
7
7
b
zinc + copper → zinc + copper
sulfate
sulfate
F
7
3
7
3
3
7
c
It tells you that zinc is less reactive than
magnesium.
magnesium (most reactive), iron, copper
(least reactive).
yes
no
no
yes
yes
magnesium +
a
d
2
Metal E is the most reactive because it has the
most displacement reactions.
2
zinc → magnesium + zinc
chloride
chloride
Exercise 5.1B Displacement reactions
1
To distinguish between iron and zinc you
could place a piece of each of the two
metals in a solution of iron sulfate. The
zinc would react but the iron would not.
Credit the use of any iron salt.
Exercise 5.1C Displacing metals
Metal salt
8
b
a
Sofia could place a small piece of the
metal in each of the solutions. She will
be able to observe the reactions with the
solutions and if there is a reaction with
3
The metals that are more reactive than C,
copper, and less reactive than D, zinc, are lead
and iron. Iron is more reactive than lead, so
A is lead and F is iron. The metals that are
more reactive than D, zinc, are magnesium
and aluminium. B is less reactive than E, so
B is aluminium and E is magnesium. Learners
should not suggest an alkali metal as these are
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too reactive in water to use in displacement
reactions.
4
5
a
copper + iron → iron + copper
sulfate
sulfate
b
magnesium chloride + zinc → no reaction
c
iron + magnesium → magnesium + iron
sulfate
sulfate
d
e
zinc chloride + silver → no reaction
zinc chloride + iron → no reaction
b
c
4
Potassium is very reactive in water and if
used in solutions of salts it would be very
dangerous.
Topic 5.2 Using the reactivity
series and displacement reactions
c
d
Exercise 5.2 Using the reactivity series
1
a
b
c
2
a
14
Zinc is more reactive than iron so the zinc
combines with the chlorine in the iron
chloride and forms zinc chloride and
leaves iron metal.
iron → zinc + iron
chloride
chloride
b
zinc +
c
Iron can be displaced by zinc because
zinc is more reactive. Copper is even less
reactive than iron so zinc will displace
copper from a solution of copper
chloride.
Zinc is less reactive than magnesium so
it cannot displace magnesium from a
solution of magnesium chloride.
d
3
The metal is more reactive than iron and
copper but less reactive than magnesium.
aluminium or zinc
Accept any metal above copper in the
reactivity series such as iron, zinc or
magnesium.
Accept any metal above zinc such as
magnesium.
a
Aluminium and iron oxide are mixed in
a container over the rail that needs to be
welded. This reaction produces so much
heat energy that the displaced iron melts.
The molten iron produced can be shaped
and used to join the rails together. For the
iron oxide and aluminium to react they
have to be ignited and this is done using
another exothermic reaction. (Credit
naming the reaction between magnesium
powder and barium nitrate, but it is the
a
b
idea of using an exothermic reaction to
start the main reaction that is needed here,
rather than the details.)
This method is used because it produces
enough energy to melt the iron, and is
possible to do when the work has to be
done away from an electricity supply.
aluminium + iron → aluminium + iron
oxide
oxide
carbon
Iron ore is heated in the blast furnace with
carbon in the form of coke. The carbon
displaces the iron from the iron oxide and
molten iron is produced.
iron oxide + carbon → iron + carbon
dioxide
It is above iron in the reactivity series.
(Accept any more specific suggestion
provided it is not above aluminium.)
Topic 5.3 Salts
Exercise 5.3A Which acid is used to
make which salt?
1
Hydrochloric acid — HCl — chlorides
Sulfuric acid — H2SO4 — sulfates
Nitric acid — HNO3 — nitrates
2
magnesium chloride: hydrochloric acid;
magnesium nitrate: nitric acid;
magnesium sulfate: sulfuric acid.
3
NaCl: sodium chloride;
CuSO4: copper sulfate;
CuCl2: copper chloride;
KNO3: potassium nitrate
4
citrates
Exercise 5.3B Making salts
1
Place some zinc metal into dilute nitric acid.
When it has stopped reacting, put your
solution into an evaporating basin and heat it
gently to evaporate off the water and produce
crystals of zinc nitrate.
2
zinc + nitric acid → zinc nitrate + hydrogen
3
Silver is much less reactive than zinc and will
not react with dilute sulfuric acid.
4
Potassium is far too reactive; there would be
an explosive reaction if potassium metal were
placed in dilute sulfuric acid.
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5
6
a
It is important because harmful fumes
will be given off from the acid.
b
copper + sulfuric → copper + water
oxide
acid
sulfate
a
magnesium +
b
copper oxide + nitric → copper + water
acid
nitrate
c
zinc + hydrochloric → zinc + hydrogen
acid
chloride
d
zinc + sulfuric → zinc + hydrogen
acid
sulfate
nitric → magnesium + hydrogen
acid
nitrate
Exercise 5.3C Practical steps for
making salts
1
Copper chloride cannot be made by reacting
copper with dilute sulfuric acid because,
to make a chloride, you would need to use
hydrochloric acid and copper is unreactive and
does not react with any dilute acid.
2
The first step is to react copper oxide with
sulfuric acid. Excess copper oxide is added to
sulfuric acid in a beaker. This is heated gently
and stirred constantly. When a colour change
(to blue) is seen, you should stop heating.
Safety precautions: wear safety glasses, as you
are using acid; do not boil the acid mixture, as
harmful fumes are given off.
The second step is to filter the mixture. The
excess copper oxide is left in the filter paper and
the filtrate is a solution of copper sulfate. No
additional safety precautions need to be taken.
The third step is to evaporate the water from the
copper sulfate solution by heating it gently in an
evaporating basin. When small crystals form, or
the solution starts to spit, stop heating and allow
the rest of the water to evaporate slowly. Safety
precautions: wear safety glasses and take care as
the hot solution may spit and burn you.
Credit labelled diagrams that help to explain
the above method.
Topic 5.4 Other ways of making salts
Exercise 5.4A Preparing copper chloride
1
The copper carbonate reacts with the acid and carbon dioxide gas is given off. Credit any mention of
the formation of copper chloride or water.
2
(unreacted) copper carbonate
3
A solution of copper chloride: credit `a mixture of water and copper chloride’. (Learners should
recognise that water and the salt are present.)
4
Place the filtrate in an evaporating basin and heat it to evaporate off the water and leave the crystals.
5
When the solution is being heated it tends to spit, and this can burn.
6
They should wear safety glasses to prevent damage to their eyes; take special care when close to the
evaporating dish; turn off the heat when the solution begins spitting.
7
copper + hydrochloric → copper + water + carbon
carbonate
acid
chloride
dioxide
Exercise 5.4B Preparing potassium chloride
15
1
hydrochloric acid
2
The list should include: measuring cylinder, beaker (credit conical flask), hydrochloric acid, burette,
stand, universal indicator solution, safety glasses.
3
Put on safety glasses. First add a drop of universal indicator solution to the potassium hydroxide in
the beaker, which turns blue. Set up the burette and fill with acid. Add acid, a little at a time, to the
potassium hydroxide, and swirl the beaker to mix the contents.
4
When they see the universal indicator solution turn from blue to green.
5
Add charcoal to the neutral solution to remove the colour. Then the solution should be filtered to
remove the pieces of charcoal.
6
potassium + hydrochloric → potassium + water
hydroxide
acid
chloride
7
KOH + HCl → KCl + H2O
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Exercise 5.4C Mystery substances
6
1
carbon dioxide
2
hydrogen
3
salts
Exercise 5.5B Before and after
the reaction
4
sulfuric acid
1
5
a solution of copper chloride (accept any
chloride of a metal below iron on the
reactivity series)
calcium, chlorine, hydrogen, oxygen and
carbon
2
The particle diagram should show a molecule
of sulfur dioxide: a light circle representing
the sulfur atom, touching two dark circles
representing the oxygen atoms.
sulfur + oxygen → sulfur dioxide;
S + O2 → SO2
3
a
b
c
d
4
45 g
5
25 g of magnesium will be present in the
magnesium sulfate
6
The term conservation of mass means that all
of the atoms present at the start of a reaction
are still there at the end. No elements are
destroyed and no elements are created, so the
mass of the products is the same as the mass
of the reactants.
7
250 g
8
zinc + sulfuric acid → zinc sulfate + hydrogen
9
a
No, he has not made a mistake.
b
One of the products is hydrogen gas. Since
Arun used a beaker without a lid, this gas
has escaped into the air. This accounts for
the apparent loss of mass.
6
hydrochloric acid
7
zinc carbonate
8
iron
9
magnesium
10
zinc + sulfuric → zinc + carbon + water
sulfate
acid
sulfate dioxide
11 iron + copper → iron + copper
chloride
chloride
(Accept another chloride as the reactant,
provided it is below iron on the reactivity
series.)
12 magnesium +
hydrochloric
magnesium
→
+ hydrogen
acid
chloride
Topic 5.5 Rearranging atoms
Exercise 5.5A What happens to
the atoms and the mass when
chemicals react?
1
The magnesium atoms should be coloured
green and oxygen atoms red.
2
a
b
3
a
b
4
a
b
c
5
16
80 g (Accept a figure less than 80 g with an
explanation that some carbon dioxide will be
lost to the atmosphere.)
The magnesium atoms should be coloured
green, chlorine atoms yellow and
hydrogen atoms left blank.
magnesium chloride
The answer to each of the four questions
is 2.
yes
Oxygen atoms should be coloured red and
the hydrogen atoms left blank.
The number of hydrogen atoms in the
reactants is the same as the number of
hydrogen atoms in the products.
The number of oxygen atoms in the
reactants is the same as the number of
oxygen atoms in the products.
magnesium, carbon and oxygen
carbon and oxygen
from the hydrochloric acid
from the hydrochloric acid
10 When scientists get an unexpected result in an
experiment they should repeat the experiment
several times to ensure the unexpected result is
not a mistake.
Exercise 5.5C Investigating burning
magnesium
1
The volume of oxygen used, the time taken to
transfer the deflagrating spoon, the time taken
to light the magnesium.
2
magnesium + oxygen → magnesium oxide
24 g
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3
Credit: axes the correct way round and
correctly labelled, including units; suitable
choice of scale; points plotted accurately and
joined appropriately.
magnesium up to 2.0 g; above this the mass of
the product does not change.
5
The mass of the product formed stays the
same at these masses because the magnesium
has used up all the (limited supply of ) oxygen
available. Some of the magnesium may not
have been burnt.
6
a
Mass of compound formed in g
4
3
2
1
0
4
0
1
2
3
Mass of magnesium burned in g
The greater the mass of magnesium burned,
the greater the mass of product formed.
However, this is only true of masses of
b
There are a number of movements of things
into and out of the gas jar, and so chances
to spill magnesium or the product. Also,
there is a good chance that some oxygen will
be lost from the gas jar as the deflagrating
spoon is transferred. The lighting of the
magnesium would need to be done quickly.
If some magnesium had not burned it would
need to be separated from the product.
The burning magnesium should not be
looked at directly. The deflagrating spoon
will get hot so will need to cool down before
the mass of the product can be measured.
Unit 6 Sound and space
6.1 Loudness and pitch of sound
3
Exercise 6.1A Comparing sound waves
b
sound is higher pitched (accept one octave
higher)
double the frequency / twice as fast / twice
as many in the same period of time
double the frequency / twice as fast / twice
as many in the same period of time
1
A
2
A
3
D
4
C
Topic 6.2 Interference of sound
5
B
Exercise 6.2A Reinforcing sound
6
C
1
The sound becomes louder.
2
D
Wave spacing should be the same; height of
the peaks and the depth of the troughs should
increase equal and opposite about the mid-line.
3
The sound waves reinforce.
2
Wave spacing should decrease so there are
more waves (still evenly spread) on the grid;
height and depth should stay the same.
1
3
Wave spacing should increase so there are
fewer waves (still evenly spread) on the grid;
height and depth should decrease equal and
opposite about the mid-line.
c
Exercise 6.1B Drawing sound waves
1
Exercise 6.1C
Understanding sound waves
17
a
1
a
b
2
loudness decreases, pitch increases
0.5 mm
250; unit Hz
Exercise 6.2B Cancelling and
reinforcing
a
b
2
a
b
The pitch stays the same.
The loudness increases.
Arun hears nothing / no sound.
A wave drawn with peaks aligned with
the original wave; it must cross the
mid-line at the same points as the
original wave; it need not be the same
amplitude as the original.
A wave drawn with peaks aligned to the
troughs of the original wave; it must
cross the mid-line at the same points as
the original wave; it must be the same
amplitude as the original.
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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 different to
rocks on Earth. In fact, the composition of
the Moon is more similar to Earth.
Exercise 6.2C Interfering sound waves
1
a
b
2
a
b
i They are equal.
ii They are equal.
iii They are equal.
Amplitudes are equal.
Frequencies are equal.
i 2500 Hz
ii 2 mm
frequency 2500 Hz; amplitude 1 mm
3
The composition of rocks on the Moon is very
similar to that on Earth.
4
a
Topic 6.3 Formation of the Moon
b
Exercise 6.3A How was the
Moon formed?
1
D, B, A, C
2
A newly formed planet.
Topic 6.4 Nebulae
3
Both the Earth and the Moon.
Exercise 6.4A What are nebulae?
Exercise 6.3B Describing the
collision theory
1
A
2
An object of a similar size to Mars collided
with Earth; the object has been called Theia.
The impact caused a disc of dust and rock
to form around Earth; the dust and rock
eventually came together under gravity to form
the Moon.
Exercise 6.3C Evidence for the
collision theory
1
2
18
The composition of rocks on the Earth
and the Moon are very similar.
A captured object would have formed
separately from Earth / far away from
Earth / at a different time than Earth; the
composition of a captured object would
probably be different from that of Earth.
Any three 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.
Any one from:
• 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
1
asteroid, moon, star, nebula
2
All nebulae contain dust and gas. All nebulae
are different shapes.
3
hydrogen
Exercise 6.4B Types of nebula
1
emission nebula / supernova remnant
2
Horsehead (nebula) / Pleiades
3
a
b
emission nebula / supernova remnant
Newly formed stars would emit light; this
type of nebula emits its own light.
Exercise 6.4C Stellar nurseries
1
A nebula / part of a nebula where stars are
formed.
2
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.
3
No stars were being formed at the very
beginning of the universe; stars started
being formed at a low rate when the universe
was very young. The rate of star formation
increased rapidly until about 2000 million
years, then slowed until about 6000 million
years, then the rate started to decrease; the
rate is still decreasing today.
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Topic 6.5 Tectonics
2
a
Lack of evidence for movement /
movement was too slow for people to see;
no knowledge of what forces could drive
the movement; people are slow to accept
new ideas.
b
i
Exercise 6.5A Movement of
tectonic plates
1
a
b
c
2
3
(labels from top to bottom): crust, mantle,
outer core, inner core
curved arrows drawn in the mantle, coming
up from the outer core toward the crust and
curving down again toward the inner core.
crust
Slowly moved apart / moved into different
positions due to the movement of tectonic
plates; continental drift.
23
23 mm = ________ = 0.000 023 km
1 000 000
speed is 0.000 023 km / year
The following should be ticked: The same
types of fossils have been found in different
continents.
distance
time = ________
speed
Volcanoes and earthquakes are more likely to
happen in particular places.
1
= _________
0.000 023
= 43 500 years (or other methods
using direct proportion to
reach the same answer)
The alignment of magnetic materials in rocks
varies with the age of the rock.
Exercise 6.5B Tectonic plates
1
2
a
b
a
b
inner core, outer core, mantle, crust
i mantle
ii Molten rock in the mantle gets heated
from the core; heated material expands
and becomes less dense and rises.
Close to the crust, this material cools,
becomes more dense and sinks again.
iii Movement of molten rock across the
top of the mantle pulls the tectonic
plates along with it.
New rock forming in the middle of
the ocean takes up more space; pushes
the tectonic plates either side of the
ridge away from the ridge, causing the
continents to separate.
The ridge is a boundary between two
tectonic plates. Volcanoes occur because
magma / molten rock is being pushed
up. Earthquakes occur because of the
movement between the two adjacent
tectonic plates.
The North American continent is on
a tectonic plate. The movement of
the plate causes the movement of the
continent. The movement is measured
relative to surrounding plates /
continents that move differently.
ii 1 000 000 mm = 1 km
3
a
b
Small mammals could not swim between
these continents (at their separation
today) so the continents must have been
joined / part of the same land mass /
larger continent in the past; the continents
have separated due to movement of
tectonic plates.
The Earth’s magnetic poles have reversed
several times in the past. Newer rock is
forming in the middle and the magnetite
there will align with the current magnetic
field direction. Rock is pushed outward, so
older rocks are found further away from
the middle. This shows that the tectonic
plates are moving slowly apart, pushed by
the newly forming rock and this has been
continuing for millions of years.
Exercise 6.5C Evidence for
tectonic plates
1
a
b
19
Irregularly shaped parts of the Earth’s
crust that can move relative to each other.
Convection currents in the mantle, caused
by heating from the Earth’s core, pull the
tectonic plates from below.
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Unit 7 Genes and inheritance
Topic 7.1 Chromosomes, genes
and DNA
2
Exercise 7.1 Chromosomes, genes and
DNA
1
A: nucleus; B: cytoplasm
2
X written in the nucleus of each cell.
3
Look for a sentence that includes correct
information about each term. Example
sentences are:
Chromosomes are found in the nucleus of
every cell / Chromosomes are made of DNA.
Genes are found on chromosomes / Genes
contain information that is inherited from an
organism’s parents.
DNA is the substance that chromosomes and
genes are made of.
4
For example:
Egg cell
Sperm cell
has food reserves in
the cytoplasm
does not have food
reserves in the
cytoplasm
round in shape
elongated
no tail
has a tail
has an extra layer
does not have layer
round the outside of round the outside of
the cell
the cell
larger
smaller
has a cell membrane has a cell membrane
3
The DNA in a cell contains instructions for
making a cell and a whole organism. If any
of these instructions are missing or damaged
then the cell or the organism cannot be
correctly formed. So when a cell divides it is
essential that each of the new cells gets a full
set of all the DNA in the parent cell.
has a nucleus
has a nucleus
has cytoplasm
has cytoplasm
Accept any statement that makes clear what
the difference is and that states a sensible
reason for the difference. For example:
Sperm cells have a tail to swim to the egg cell,
but egg cells do not need to swim.
Sperm cells are elongated to make it easier for
them to swim, but egg cells do not move so
they can just be round.
Topic 7.2 Gametes and
inheritance
Topic 7.3 Variation
Exercise 7.2 Egg cells and sperm cells
1
number of plants: 6, 3, 4, 7
1
2
20
3
7
6
5
Number of plants
Egg cells and sperm cells are specialised cells
called gametes.
Egg cells are female and sperm cells are male.
All sperm cells contain one X chromosome,
but egg cells can contain an X chromosome or
a Y chromosome.
A sperm cell can join with an egg cell in a
process called fertilisation.
Exercise 7.3A Recording variation
4
3
2
1
0
4
20
yellow
white
red
Flower colour
orange
variation
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Exercise 7.3B Variation in holly leaves
1
As some of the prickles are very small, allow
some leeway in learners’ answers. The
numbers are:
3 and 4 There are different possibilities for the
choices of categories into which to group the
results, so accept other groupings.
Number
6 to 7 8 to 9 10 to 11 12 to 13
of peas
17, 15, 14, 17, 15, 17, 17, 15, 16, 13, 14, 11, 14,
12, 17, 20, 15, 17
||||
|||| ||||
||||
||
Number
of pods
4
10
4
2
276 ÷ 18 = 15.3 prickles
3
Number
of prickles
11
12
13
14
15
Tally
|
|
|
|||
||||
Number
of leaves
The frequency diagrams that learners draw
will depend on the feature they have chosen,
and the way that they have grouped the data.
1
1
1
3
4
Look for:
Number
of prickles
16
17
Tally
|
|||| |
Number
of leaves
1
6
4
18
19
5
• the chosen feature on the x-axis, with a
clearly labelled scale including units
• the number of pods on the y-axis, with a
scale with equal intervals
• at least half of the graph grid used,
preferably more
• bars carefully and neatly drawn (and
touching if a histogram is drawn instead of
a bar chart).
20
|
0
0
1
6
Topic 7.4 Natural selection
Number of leaves
5
Exercise 7.4A Blue-tailed lizards
4
3
1
nucleus
2
inheritance
3
When the lizard sheds its tail the snake is more
likely to be attracted to a blue tail than to a
brown tail. So the blue tails are more likely to
distract the snake from eating the lizard itself.
4
More parent lizards with blue tails survive, so
they are the ones that reproduce. They pass on
their genes for blue tails to their offspring.
2
1
0
5
11 12 13 14 15 16 17 18 19 20
Number of prickles
Exercise 7.4B Camouflaged caterpillars
For example, length, width.
Exercise 7.3C Variation in pea pods
21
Tally
2
1
Number of peas, length, width.
2
Number of peas: 9, 9, 9, 11, 8, 7, 10, 6, 13, 7,
9, 12, 9, 10, 9, 9, 7, 11, 9, 8
1
How many green caterpillars and how many
yellow caterpillars Marcus picks up.
2
Repeat the experiment five times with the
same caterpillars, using five different students
to collect them.
3
D1, B2, A3, E4, C5
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Exercise 7.4C Woolly mammoths
Look for the following ideas somewhere in the answer:
• variation in the steppe mammoths – some have
longer fur and longer tusks
• these were better adapted to survive when the
climate got colder
• steppe mammoths with short fur and short
tusks were less likely to survive
• most reproduction was done by individuals with
long fur and long tusks
• genes for these characteristics were passed on to
offspring
• over time, more mammoths in the population
came to have long fur and long tusks.
Unit 8 Rates of reaction
Exercise 8.1C Explaining observations
Topic 8.1 Measuring the rate
of reaction
Exercise 8.1A Showing the change in
rate of reaction on a graph
1
2
3
4
1
Mg + 2HCl → MgCl2 + H2
Credit the equation if it is not balanced.
2
Suggestions could include: the difficulty of
assembling the apparatus, adding the acid
and starting the stop clock all the same time;
difficulty in reading the measuring cylinder
accurately as bubbles are being given off;
difficulty of reading the volume quickly and
accurately at 30 second intervals. Accept any
sensible suggestions. Ideas for overcoming
these could be: to have one person in charge
of the timing and one in charge of the
assembling of the apparatus; being very
organised with everything ready and then
assembling as quickly as possible; one person
watching the measuring cylinder and another
calling out when a reading is needed.
between 0 and 100 seconds
between 250 and 350 seconds
35 cm3 (allow 36 cm3)
(66 − 53) cm3 = 13 cm3
Exercise 8.1B Changes in the rate of
reaction
hydrochloric
magnesium
→
+ hydrogen
acid
chloride
1
magnesium +
2
She did this to ensure her results were reliable.
3
4
22
Volume of gas collected in cm3
Attempt
1
Attempt
2
Attempt Mean
3
0
0
0
0
0
20
28
31
31
30
40
39
48
42
43
60
56
53
57
55
80
60
59
61
60
100
60
59
61
60
Credit:
• use of pencil and ruler
• good use of whole graph paper grid
• suitable scales used
• points accurately plotted using small crosses
• appropriate line of best fit drawn.
5
The reaction ended after 80 seconds. We know
this because no more hydrogen was produced
after this time.
6
The reaction is fastest between zero seconds
and twenty seconds.
3
Volume of hydrogen collected in cm3
Time
in s
50
40
30
20
10
0
0
50
100
150
200
250
Time in s
300
350
400
Credit:
• use of pencil and ruler
• good use of whole grid
• suitable scales used
• points accurately plotted using small crosses
• appropriate line of best fit drawn.
4
The graph shows that the volume of hydrogen
gas collected increases over the time of
the experiment. However, more hydrogen
is collected in the first 30 seconds than in
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all subsequent 30-second periods. The rate
of reaction decreases over the time of the
experiment and by 270 seconds the reaction is
complete, as there is no further increase in the
volume of hydrogen collected.
5
16 cm3 per minute or 0.27 cm3/s. Allow slight
variations in this answer if the learners have
read it correctly off their own graph.
6
6 cm3 per minute or 0.1 cm3/s. Allow slight
variations in this answer if the learners have
read it correctly off their own graph.
7
At the start of the reaction there are many
particles of magnesium and hydrochloric
acid. These must collide with each other with
enough energy to react. As the particles react
there are fewer left that are unreacted, so the
chance of them colliding decreases and the
rate of reaction decreases. When there are no
more unreacted particles left, the reaction is
complete.
8
The line should be to the left of the other
lines. It should be steeper and reach the end of
the reaction more rapidly. The final volume of
gas produced should be the same as for the flat
piece of zinc.
9
The zinc powder has a much greater surface
area than the flat piece of zinc. There are
more particles (on the surface of the zinc
powder) exposed to the hydrochloric acid,
so the reaction can take place more quickly.
The reaction again slows as there are fewer
particles left to react. The reaction is complete
more quickly than with the flat piece of zinc.
But because the masses of the flat piece of
zinc and the zinc powder are the same, the
total volume of hydrogen produced is the
same.
Topic 8.2 Surface area and the
rate of reaction
Topic 8.3 Temperature and the
rate of reaction
Exercise 8.2 Surface area and the rate
of reaction
Exercise 8.3A Explaining changes in the
rate of reaction
1
hydrogen
2
zinc + hydrochloric → zinc + hydrogen
acid
chloride
3
It is difficult to read the volume of gas on the
measuring cylinder, especially if the changes
are very small. You have to read it carefully
as the cylinder is upside down. Credit other
comments about the difficulty of getting the
reactants mixed together and the apparatus
assembled all at the same time.
4
the same
5
There should be a statement to the effect that
the reaction starts off fairly quickly, then slows
down. At 420 seconds, the reaction has not yet
finished.
6
The line for the flat piece of zinc is steeper than
the one for the lump of zinc and the line flattens
out sooner than the one for the lump of zinc.
7
23
react with the acid as they are the only ones in
contact with it. So the flat piece of zinc reacts
more quickly.
There is the same mass of zinc in both
experiments but the reaction using the flat
piece of zinc is faster than the one using the
lump of zinc. This is because the flat piece of
zinc has a larger surface area than the lump
of zinc. When the reaction takes place, only
the particles on the surface of the zinc can
1
a
b
2
At the start of the reaction there are a lot
of reactant particles. They move about
and a large number of them are likely
to collide with one another with enough
energy to react.
As the reaction continues, some of the
particles have reacted so there are fewer
reactant particles left. There are fewer
available particles to collide and react so
the rate of reaction decreases.
When the temperature increases, some of the
thermal energy is transferred to the particles.
The particles with more energy move more
quickly. This means that there will be more
collisions in a period of time, so the rate of
reaction will increase.
Exercise 8.3B Temperature and the rate
of reaction
1
a
Credit any suitable metal such as
magnesium or zinc and acids such as
hydrochloric, sulfuric or nitric acid. Very
reactive metals, such as potassium or
sodium, should not be credited.
b
Wear safety glasses and there should be
some comment about taking care when
using hot acids.
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c
d
e
The mass, surface area and type of metal;
the volume, concentration and type of acid.
Because there will be no more bubbles of
gas given off.
Table with these headers
Temperature Time in s
in °C
Attempt Attempt Attempt Mean
1
2
3
Exercise 8.4A Concentration and the
rate of reaction
Time for reaction to take place in s
a and c
2
using
powdered
metal
a
c
b
c
3
4
Temperature in °C
24
Topic 8.4 Concentration and the
rate of reaction
1
Challenge
2
On the graph, credit any line that shows
the results will be faster than those shown
in answer a on the graph above. The line
should be to the left of the line shown
above. The line should be to the left of the
line in part a and labelled
For a reaction to take place, the particles
of the reactants must collide with
enough energy. The particles of the acid
are constantly moving. The higher the
temperature, the more energy the particles
have and they move more quickly. This
means that there are likely to be more
collisions that result in a reaction. The higher
the temperature, the faster the reaction.
See graph in a above. The results would
show that the reaction times at all
temperatures would be lower than when the
first experiment was done. This is because
the powdered metal has a greater surface
area so more particles are available to react
in a given time.
5
There should be an explanation of mixing the
acid with different volumes of water. Some
reference to accuracy should be included, such
as how to read the measuring cylinder correctly
using the bottom of the meniscus and ensuring
it is at eye level, and the use of safety glasses. For
example, dilutions could be: 10 cm3 acid with
40 cm3 water; 20 cm3 acid with 30 cm3 water;
30 cm3 acid with 20 cm3 water; 40 cm3 of acid with
10 cm3 of water and 50 cm3 acid with 0 cm3 water.
The girls measure the time taken for the
reaction to end. They can see this when no
more bubbles of gas are given off.
Measuring cylinders, test tubes or beakers, test
tube rack, safety glasses, stopwatch.
You would expect them to find the more
concentrated the acid, the faster the reaction.
This would happen because there are more acid
particles in the more concentrated acid than in
the less concentrated acid. The same volume
of acid has been used so that there are more
acid particles in the same volume. The acid
particles move around and collide with the zinc
particles and this is when a reaction happens.
Since there are more acid particles in the higher
concentration acid, there will be more collisions
and so a faster reaction.
Exercise 8.4B Which results are which?
1
Concentration ×0 was not used because there
is no acid present in it, and zinc does not react
with water.
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2
×5 concentration
60
Volume of hydrogen produced in cm3
×4 concentration
50
×3 concentration
40
×2 concentration
30
20
10
0
0
30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570
Time in s
3
4
5
At all three concentrations of acid, the
reaction rate follows the same pattern. The
reaction starts off quickly and slows over time.
The ×4 concentration, the most concentrated,
completed the reaction in the fastest time. The
least concentrated acid, ×2, took the longest
to complete the reaction. All three reactions
produced the same volume of hydrogen but
took different times to reach that final volume.
Learners’ answers should cover the following
ideas. The ×4 acid had the most acid particles
available in the volume of acid solution
used, the ×3 acid had fewer and the ×2 acid
had the least. This meant that, for the ×4
concentration, there were more particles in
contact with the zinc so more collisions took
place in each given time period until all the
zinc particles had reacted with acid particles.
The reaction was completed more quickly
than with the ×3 and ×2 acid because the rate
of collisions was always greater.
See graph in question 2. Credit a smooth
curve to the left of the ×4 line. The curve
should reach the same volume of hydrogen
sooner than the other concentrations. This
need only be a sketch and does not need to be
exactly as in the graph shown.
Exercise 8.4C As fast as possible
1
25
Learners’ diagrams should show any sensible
method of carrying this out – either by
collecting the gas over water, in a trough, in a
beaker or in a syringe. Examples are shown in
diagrams in the Learner’s Book, but learners’
own diagrams will be clearer if drawn in 2D,
with the apparatus ‘cut through’. Diagrams
should be drawn in pencil, with apparatus to a
suitable scale and labelled using straight lines
and horizontal labels. In 2D diagrams, tubes
in rubber bungs should be shown continuing
through the bung.
2
Depending on what learners have shown in
their diagram in answer to question 1, the list
could include: top pan balance, measuring
cylinder for acid, timing device of some kind,
pestle and mortar, a water bath (or some
other way of increasing the temperature of
the acid) and thermometer for monitoring the
temperature.
3
The mass of marble chips and the volume of
dilute hydrochloric acid (credit also the type
and concentration of acid used).
4
The surface area of the marble chips. The
temperature of the acid.
5
Surface area: If they crush the marble chips
to a powder there will be a greater surface
area of reactant. This means that there will be
more particles of the marble chips in contact
with the acid particles so there will be more
collisions between the particles and thus the
reaction will be faster.
Temperature: If they warm the acid the
particles will have more energy and will move
more rapidly. This will mean more frequent
collisions of the particles, so the reaction will
be quicker. It will also mean that more of the
collisions will happen with enough energy for
the reaction to take place.
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6
This will depend on the method chosen. Points
covered could be:
• 20 g marble chips measured, crushed in
a pestle and mortar and placed in a filter
paper
• 50 cm3 dilute hydrochloric acid measured
and placed in a flask
• apparatus assembled, details depending on
method
• marble chips added carefully and timer
started; then 100 cm3 carbon dioxide
collected and timer stopped.
7
Ideas could include:
• it is difficult to add the crushed marble
chips quickly without losing any
• it is difficult to get the stopper back on the
flask quickly
• some of the gas produced may be lost, the
top of the tubes cannot easily be made
airtight, or gas lost into water trough
• it is difficult to do the above and start the
timer at the correct moment, for example,
should it be when the chips are added,
when the stopper is back in place or when
the reaction starts?
2
a
b
Unit 9 Electricity
Topic 9.1 Parallel circuits
Exercise 9.1A Current flow in
parallel circuits
1
a
b
Parallel circuit, because there is a branch
in the circuit / because current can follow
more than one path / because both lamps
are connected directly across the cell (and
switch).
C
2
3 + 3 = 6 (A)
3
4
__
2
2
a
b
c
d
a
b
volts
The energy that the battery can supply.
2
a
b
c
1.5 V
1.5 V
voltmeter
3
3; 3 (top row)
A4
A3
A2 or A3
A1 or A4
a
Circuit copied and an ammeter anywhere
in series with the other components and
with a voltmeter in parallel with the
buzzer.
b
The voltages across each of the lamps and
across the buzzer add up to the voltage
across the cell.
i decreases
ii decreases
c
The reading on A1 must be the largest of all
four ammeters.
The reading on A2 must be smaller than that
on A1.
Exercise 9.1C Understanding current in
parallel circuits
26
1
1
There is more than one path for current to
flow in a parallel circuit.
Current divides through different parts of a
parallel circuit.
1
Exercise 9.2A Voltage
Exercise 9.2B Current and voltage
1
3
Topic 9.2 Current and voltage in
parallel circuits
= 2; P = 2 (A); R = 2 (A)
Exercise 9.1B Facts about
parallel circuits
no change
decreases
a
A1 and A2 are equal; A1 and A2 are greater
than A3
b
A4 = A1 + A2 + A3
2
a
b
The voltage across each lamp is 4 V. Each
lamp will not be at full brightness when
the voltage across it is less than 12 V.
Circuit diagram should show battery (two
cells separated by a dashed line) and three
lamps, each in parallel with the battery.
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Exercise 9.2C Changes in current and
voltage
1
2
a
b
decrease
ii decrease
Increase, because there are two lamps
connected directly across the battery /
because the same current will flow
through both lamps.
ii Stay the same, because L1 will still be
connected directly across the terminals
of the cell / because the voltage across
each branch of a parallel circuit is
equal to that of the cell.
1
a
b
current
As R increases and I stays the same,
V increases.
As R increases and V stays the same,
I decreases.
2
a
b
drops by half / becomes 0.5 A
doubling the resistance will halve the
current
i
i
a
VC
VL = ___
N
b
VL = VC
3. 0.001 Ω
Topic 9.4 Practical circuits
Exercise 9.4A Variable resistors
1
Topic 9.3 Resistance
2
1 − 50 Ω
Exercise 9.3A Describing resistance
3
a
b
1
ohms
2
current will decrease
brightness will decrease
Exercise 9.4B Uses of variable resistors
3
current decreases
4
12
___
4
1
The resistance of a variable resistor can be
changed. The resistance of a fixed resistor
cannot be changed. (Descriptions can be given
in terms of values in ohms.)
2
Circuit diagram should have a cell, a lamp and
a variable resistor in series.
3
Circuit diagram should have a cell, two lamps
and a variable resistor in series.
4
Circuit diagram should have a cell, a variable
resistor close to the cell, and two lamps in
parallel (variable resistor in unbranched part).
= 3 (Ω)
Exercise 9.3B Calculating resistance,
voltage and current
1
voltage
resistance = _______
current
2
a
voltage 6
resistance = _______ = __ = 3Ω
current 2
b
voltage 12
resistance = _______ = ___ = 12Ω
current
1
c
voltage
6
resistance = _______ = ___ = 30Ω
current 0.2
1
C
2
B
voltage = current × resistance
= 3 × 10 = 30 V
voltage = current × resistance
= 2 × 12 = 24 V
voltage = current × resistance
= 0.1 × 0.5 = 0.05 V
3
D
4
B
5
A, C and D
6
B and D
3
a
b
c
4
27
Exercise 9.3C Ohm’s law
a
voltage
30
current = _________ = ___ = 2 A
resistance 15
b
voltage
4
current = _________ = ___ = 10 A
resistance 0.4
c
voltage
0.5
current = _________ = ___ = 5 A
resistance 0.1
Exercise 9.4C Comparing circuits
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