Question 1
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B13.1 — Coordination and response (Part (a), (b) & (c))
▶️ Answer/Explanation
(a)
(b)(i) Pupil reflex
The pupil becomes smaller in bright sunshine than in normal light, as shown in Fig. 1.2.
This automatic narrowing of the pupil is called the pupil reflex.
(b)(ii) Stimulus: change in light intensity; Effector: circular (iris) muscles
The stimulus detected is a change in light intensity (an increase in brightness).
The effector that responds is the circular muscles of the iris, which contract to constrict the pupil.
(c)
Involuntary actions occur automatically without conscious control.
Heart beating and sneezing are reflex/automatic actions, unlike drinking, running and talking, which are voluntary.
Question 2
State the names of two of these properties.
In the complete combustion of methane, methane reacts with oxygen, \( \text{O}_2 \).
Carbon dioxide and water are made.
Construct the balanced symbol equation for the complete combustion of methane.
State what is meant by the term exothermic.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C11.1 — Formulas and terminology, hydrocarbons (Part (a))
• Topic C11.3 — Fuels, fractional distillation of petroleum (Part (b))
• Topic C11.3 — Fuels, combustion (Part (c))
• Topic C5.1 — Exothermic and endothermic reactions (Part (d))
▶️ Answer/Explanation
(a) A compound containing carbon and hydrogen atoms only
A hydrocarbon is a compound made up only of carbon and hydrogen atoms.
No other elements may be present.
(b)(i)
The coolest part of a fractionating column is at the top, since the column is hottest at the bottom.
X should therefore be marked inside the column, either inside the central pipe or anywhere above the top dotted line shown on Fig. 2.1.
(b)(ii) Any two from: boiling point, volatility, viscosity, flammability, density
Fractional distillation separates petroleum based on differences in boiling point.
Substances collected in the same fraction therefore share similar boiling points, and consequently similar volatility, viscosity, flammability, and density.
(c) \( \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \)
One mole of methane reacts with two moles of oxygen.
This produces one mole of carbon dioxide and two moles of water, with all atoms balanced on both sides.
(d) Idea of thermal energy given out
An exothermic reaction is one in which thermal (heat) energy is transferred to the surroundings.
This usually causes the temperature of the surroundings to rise.
Question 3
Calculate the wavelength of this light in air.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.2 — Motion, speed–time graphs (Part (a)(i)–(ii))
• Topic P1.6.1 — Energy, kinetic energy (Part (a)(iii))
• Topic P3.3 — Electromagnetic spectrum, wave equation (Part (b))
▶️ Answer/Explanation
(a)(i) 240 m
The distance travelled equals the area under the speed–time graph.
Distance \(= \frac{1}{2} \times 40 \times 12 = 240\,\text{m}\).
(a)(ii) rate of change of velocity
Acceleration is defined as the rate of change of velocity.
It can also be expressed as the change in velocity divided by the time taken.
(a)(iii) 1500 kg
The maximum speed from the graph is \(12\,\text{m/s}\).
Using \(E_k = \frac{1}{2}mv^2\), \(m = \dfrac{2 \times 108\,000}{12^2} = 1500\,\text{kg}\).
(b) \(5.4 \times 10^{-7}\,\text{m}\)
The speed of light in air is \(3.0 \times 10^8\,\text{m/s}\).
Using \(\lambda = \dfrac{v}{f} = \dfrac{3.0 \times 10^8}{5.6 \times 10^{14}} = 5.4 \times 10^{-7}\,\text{m}\).
Question 4
State two factors which increase the rate of diffusion during gas exchange.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B6.2 — Leaf structure (Part (a))
• Topic B8.4 — Translocation (Part (b))
• Topic B3.1 — Diffusion (Part (c))
▶️ Answer/Explanation
(a)(i) D
D identifies the guard cells in Fig. 4.1.
Guard cells control the opening and closing of the stomata, regulating water vapour loss.
(a)(ii) A – (upper) epidermis; B – cuticle
A is the upper epidermis, the outer protective layer of cells.
B is the waxy cuticle that covers the epidermis and reduces water loss.
(a)(iii) any two from: contains lots of chloroplasts; located at the top of the leaf; tightly packed/column shaped
The palisade mesophyll (G) contains many chloroplasts to absorb light efficiently.
The cells are positioned near the top of the leaf and are tightly packed and column-shaped, maximising light capture for photosynthesis.
(b)(i) as sucrose, by translocation, in the phloem
Carbohydrates are converted to sucrose for transport.
They are moved through the phloem tissue by the process of translocation, from the source (leaf) to the sinks.
(b)(ii) any two from: storage; respiration; growth
Carbohydrates delivered to sinks may be used for respiration to release energy.
They may also be used for growth or converted to starch for storage.
(c) any two from: increased surface area; increased temperature; steeper concentration gradient; shorter diffusion distance
A larger surface area or a steeper concentration gradient increases the rate of diffusion.
A higher temperature and a shorter diffusion distance also speed up the diffusion of carbon dioxide into the leaf.
Question 5
Use Fig. 5.1 to explain why sodium is in Period 3.
Use ideas about the particles in an atom.
Sodium has the electronic structure 2.8.1.
Chlorine has the electronic structure 2.8.7.
Draw a dot-and-cross diagram to show the ions in sodium chloride.
Show outer-shell electrons only. Include the charges on the ions.
Put a tick (✓) next to the statement that describes this lattice structure.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C8.3 — Group VII properties (Part (a))
• Topic C2.2 — Atomic structure and the Periodic Table (Part (b))
• Topic C2.4 — Ions and ionic bonds (Part (c))
• Topic C2.4 — Ions and ionic bonds (Part (d))
▶️ Answer/Explanation
(a)(i) red-brown
Bromine is a red-brown liquid at room temperature.
(a)(ii) gas
Chlorine has a boiling point of \(-35\,^{\circ}\text{C}\), below room temperature.
This means chlorine exists as a gas at room temperature.
(a)(iii) in the range \(-189\) to \(-272\,^{\circ}\text{C}\)
Melting and boiling points decrease going up Group VII.
Since chlorine melts at \(-101\,^{\circ}\text{C}\), fluorine (above chlorine) must melt at a lower temperature than this.
(b)(i) sodium has three occupied electron shells
Fig. 5.1 shows the sodium atom has three electron shells in use.
The period number corresponds to the number of occupied electron shells, so sodium is in Period 3.
(b)(ii) protons are positive and electrons are negative; equal numbers of each
A sodium atom contains protons, which carry a positive charge, and electrons, which carry a negative charge.
Since the number of protons equals the number of electrons, the charges cancel out and the atom is neutral.
(c) 
Sodium loses one electron to form Na\(^{+}\), leaving a full outer shell from the shell below.
This electron is transferred to chlorine, giving Cl\(^{-}\) a full outer shell of 8 electrons.
(d) regular arrangement of alternating positive and negative ions
Solid sodium chloride forms a giant ionic lattice.
The positive sodium ions and negative chloride ions are arranged in a regular, alternating pattern.
Question 6
The mass of the jellyfish is 0.15 kg.
There are no horizontal forces acting on the jellyfish.
Describe and explain the motion of the jellyfish.
The gravitational field strength \(g = 10\,\text{N/kg}\).
The circular lens has a radius of 0.035 m.
Calculate the force exerted by the water on the lens of the camera.
Complete Fig. 6.3 to show how a thin converging lens forms an image.
Draw two rays to locate the image and draw an arrow to represent the image.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.5.1 — Effects of forces Exam (Part (a))
• Topic P1.7 — Pressure (Part (b)(i))
• Topic P3.2.3 — Thin converging lens (Part (b)(ii))
▶️ Answer/Explanation
(a) accelerates upwards
Weight \(= mg = 0.15 \times 10 = 1.5\,\text{N}\).
Resultant force \(= 2.1 – 1.5 = 0.6\,\text{N}\) upwards, so by Newton’s second law the jellyfish accelerates upwards.
(b)(i) 690 N
Area of the lens \(= \pi r^2 = \pi \times 0.035^2 = 3.85 \times 10^{-3}\,\text{m}^2\).
Force \(= P \times A = 180\,000 \times 3.85 \times 10^{-3} \approx 690\,\text{N}\).
(b)(ii) two rays drawn to locate the image, with the image arrow correctly drawn
One ray is drawn parallel to the axis from the object, refracting through the far principal focus.
A second ray is drawn through the centre of the lens undeviated; where the two rays cross marks the position of the image, which is drawn as an inverted arrow.
Question 7
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B7.3 — Digestion (Part (a)–(d))
• Topic B7.1 — Diet (Part (e))
▶️ Answer/Explanation
(a) kills bacteria/microorganisms; provides the optimum pH for protease
Organ Y is the stomach, with a strongly acidic pH of 2.0.
This acidic environment kills harmful bacteria taken in with food and provides the optimum pH for the enzyme protease (pepsin) to work effectively.
(b) bile
Bile is released into the small intestine and is alkaline.
It neutralises the acidic contents leaving the stomach, raising the pH from 2.0 towards 7.3.
(c) the breakdown of food into smaller pieces without chemical change
Mechanical digestion involves physically breaking food into smaller pieces, for example by chewing.
No chemical change occurs to the food molecules themselves during this process.
(d)(i) bacteria in the mouth respire sugars from food, producing acid
Bacteria present in the mouth feed on sugars left from eating.
As these bacteria respire the sugars, they produce acid as a waste product, lowering the pH.
(d)(ii) the acid dissolves the enamel or dentine of the teeth
The acid produced by bacteria gradually dissolves the protective enamel and underlying dentine.
This leads to tooth/dental decay over time.
(e)(i) any two from: carbohydrates, fats, protein, fibre, water
A balanced diet requires several nutrient groups in addition to vitamins and minerals.
These include carbohydrates and fats (or protein, fibre, water), each providing energy or supporting body functions.
(e)(ii) scurvy
A deficiency of vitamin C causes the disease scurvy.
Symptoms include bleeding gums and slow wound healing due to weakened connective tissue.
Question 8
During the electrolysis, hydrogen ions, \(\text{H}^+\), gain electrons.
Hydrogen gas, \(\text{H}_2\), is made.
Construct the ionic half-equation for this reaction.
Use \(e^-\) to represent an electron.
Calculate the volume occupied by 40 g of oxygen gas at r.t.p.
The volume of one mole of any gas is 24 dm\(^3\) at room temperature and pressure (r.t.p.).
[\(A_r\): H, 1; O, 16]
Explain why these covalent molecules have low melting and boiling points.
Fig. 8.2 shows part of the structure of silicon dioxide.
Silicon dioxide is an acidic oxide.
Draw a line to classify each of the oxides in the diagram. One has been done for you.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C4.1 — Electrolysis, half-equations (Part (a))
• Topic C3.3 — The mole and the Avogadro constant, gas volumes (Part (b))
• Topic C2.5 — Simple molecules and covalent bonds (Part (c))
• Topic C2.6 — Giant covalent structures (Part (d))
• Topic C7.2 — Oxides (Part (e))
▶️ Answer/Explanation
(a)(i) \(2\text{H}^+ + 2e^- \rightarrow \text{H}_2\)
Two hydrogen ions each gain one electron at the cathode.
This forms one molecule of hydrogen gas, balancing both charge and atoms.
(a)(ii) loss of electrons
In the half-equation, hydroxide ions lose electrons to form water and oxygen.
Since oxidation is defined as the loss of electrons, this reaction is an oxidation.
(b) 30 dm\(^3\)
\(M_r\) of \(\text{O}_2 = 32\).
Moles of \(\text{O}_2 = 40 \div 32 = 1.25\); volume \(= 1.25 \times 24 = 30\,\text{dm}^3\).
(c) weak intermolecular forces between molecules, which require little energy to break
Hydrogen, oxygen and water exist as simple covalent molecules.
Only the weak forces between molecules need to be overcome on melting/boiling, not the strong covalent bonds, so little energy is required.
(d) giant covalent (covalent lattice) structure
Silicon dioxide forms a giant covalent lattice.
Each silicon atom forms strong covalent bonds with 4 oxygen atoms, while each oxygen atom bonds to 2 silicon atoms.
(e) 
Aluminium oxide reacts with both acids and bases, so it is classified as amphoteric.
Carbon monoxide is a neutral oxide, while sodium oxide, a metal oxide, is classified as basic.
Question 9
Calculate the value of the current \(I_1\).
State the unit for your answer.
State and explain what the student observes on the ammeter and voltmeter.
Compare the arrangement and motion of molecules in a solid to the arrangement and motion of molecules in a liquid.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P4.3.2 — Series and parallel circuits (Part (a))
• Topic P4.2.4 — Resistance (Part (b)(i))
• Topic P2.1.2 — Particle model (Part (b)(ii))
▶️ Answer/Explanation
(a)(i) \(I_1 = I_2\)
The resistors are connected in series in a single loop.
In a series circuit the current is the same at every point, so \(I_1\) equals \(I_2\).
(a)(ii) \(V = V_1 + V_2 + V_3\)
In a series circuit, the supply voltage is shared between the components.
The total voltage equals the sum of the potential differences across each resistor.
(a)(iii) 7.5 \(\Omega\)
In series, resistances simply add together.
Total resistance \(= 2.5 + 2.5 + 2.5 = 7.5\,\Omega\).
(a)(iv) 0.20 A
Using \(I = \dfrac{V}{R} = \dfrac{1.5}{7.5} = 0.20\).
The unit of current is the ampere (A).
(b)(i) ammeter reading decreases; voltmeter reading stays the same
As the thermistor cools in the ice, its resistance increases, which decreases the current shown on the ammeter.
The voltmeter reading stays the same because it is connected across the supply and receives the full voltage regardless of resistance.
(b)(ii) arrangement: solid is regular, liquid is random; motion: solid molecules vibrate about a fixed point, liquid molecules can move/slide past each other
In the solid, molecules are arranged in a regular, fixed pattern and only vibrate about fixed positions.
In the liquid, molecules are arranged randomly and are free to move and slide past one another.
Question 10
Falcons are observed and selected for their ……… .
These falcons breed together.
This passes on their alleles to their ……… .
This process is ……… over many generations.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B18.2 — Food chains and food webs (Part (a))
• Topic B17.2 — Selection (Part (b))
▶️ Answer/Explanation
(a)(i) cactus → kangaroo rat → spider → snake → falcon
A quaternary consumer feeds at the fourth consumer level, so the chain needs five organisms.
Following the arrows in Fig. 10.1 gives cactus → kangaroo rat → spider → snake → falcon.
(a)(ii) 5
The longest path through the food web (producer to quaternary consumer) has five organisms.
This corresponds to a maximum of 5 trophic levels.
(a)(iii) cactus
Trophic level 1 is occupied by producers.
The cactus is the only producer in the food web, so it occupies trophic level 1.
(b)(i) speed/desirable features … offspring … repeated
Falcons are selected for desirable features such as speed.
The selected falcons breed, passing on their alleles to their offspring, and this process is repeated over many generations.
(b)(ii) changes are not caused by natural selection; the population is not more suited to its environment
Selective breeding involves humans choosing which organisms breed, not natural selection.
As a result, the population becomes better suited to human purposes rather than more adapted to survive in its natural environment.
Question 11
Calcium chloride, water and carbon dioxide are made.
Explain why. Use ideas about collisions between reacting particles.
Calcium carbonate (limestone) is added to the blast furnace to remove impurities in the iron ore.
Complete the symbol equations to show the reactions to remove the impurities.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C6.2 — Rate of reaction, collision theory (Part (a)–(b))
• Topic C3.3 — The mole and the Avogadro constant, reacting masses (Part (c))
• Topic C9.6 — Extraction of metals (Part (d))
• Topic C9.5 — Corrosion of metals (Part (e))
▶️ Answer/Explanation
(a) gas syringe / measuring cylinder over water
A gas syringe can be connected to the reaction vessel to directly measure the volume of gas produced.
Alternatively, the gas can be collected over water in an inverted measuring cylinder.
(b) any three from: particles have more kinetic energy/move faster; more particles have energy ≥ activation energy; more frequent collisions; more successful collisions
Increasing temperature gives reacting particles more kinetic energy, so they move faster.
This results in more frequent collisions, with a greater proportion having energy equal to or above the activation energy, so more collisions are successful and the rate increases.
(c) 22.2 g
\(M_r\) of \(\text{CaCO}_3 = 100\) and \(M_r\) of \(\text{CaCl}_2 = 111\).
Mass of \(\text{CaCl}_2 = \dfrac{111}{100} \times 20 = 22.2\,\text{g}\).
(d)(i) carbon is more reactive than iron
A more reactive element can displace a less reactive one from its compound.
Since carbon is more reactive than iron, it can reduce iron oxide to extract the metal.
(d)(ii) aluminium
Aluminium is more reactive than carbon, so carbon cannot displace it from its ore.
Aluminium must instead be extracted by electrolysis.
(d)(iii) \(\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2\); \(\text{CaO} + \text{SiO}_2 \rightarrow \text{CaSiO}_3\)
Limestone decomposes on heating to form calcium oxide and carbon dioxide.
The calcium oxide then reacts with silicon dioxide impurities to form molten slag (calcium silicate).
(e) zinc loses electrons more readily than iron
Zinc is more reactive than iron, so it loses electrons more readily.
Zinc is oxidised in preference to iron, sacrificially protecting the iron from rusting.
Question 12
Calculate the useful energy output from the power station in one year.
Fig. 12.2 shows a diagram of a simple a.c. generator.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P5.2.2 — The three types of nuclear emission (Part (a))
• Topic P1.6.3 — Energy resources (Part (b)(i)–(ii))
• Topic P4.5.2 — The a.c. generator (Part (b)(iii))
▶️ Answer/Explanation
(a)(i) beta curves towards the negative plate (less than alpha); gamma travels straight through
The beta particle is negatively charged and much lighter than the alpha particle, so it curves more sharply towards the positive plate.
The gamma ray has no charge, so it passes straight through the field undeflected.
(a)(ii) relative mass of 4; relative charge of +2; high ionising ability; low penetrating ability
An alpha particle consists of 2 protons and 2 neutrons, giving it a relative mass of 4 and a charge of +2.
Because of its larger mass and charge, it has a high ionising ability but, correspondingly, a low penetrating ability.
(b)(i) \(2.2 \times 10^{9}\,\text{J}\)
Useful energy output per day \(= 0.89 \times 6.7 \times 10^{6} = 5.96 \times 10^{6}\,\text{J}\).
Useful energy output in one year \(= 5.96 \times 10^{6} \times 365 \approx 2.2 \times 10^{9}\,\text{J}\).
(b)(ii) does not release carbon dioxide/does not contribute to global warming or climate change
Unlike fossil fuels, nuclear fission does not involve burning carbon-based fuel.
This means it does not release carbon dioxide, so it does not contribute to climate change in the same way.
(b)(iii) coil rotates; coil cuts/experiences a changing magnetic field; emf/current is induced in the coil; slip rings maintain electrical contact and prevent the wires from tangling
As the coil rotates within the magnetic field, it continuously cuts through magnetic field lines, experiencing a changing flux.
This changing flux induces an emf (and hence a current) in the coil, which alternates direction every half turn; the slip rings rotate with the coil and maintain continuous electrical contact with the fixed brushes, transferring this alternating output to the external circuit without the wires becoming tangled.