Question 1
Place ticks (✓) in the boxes to show the term(s) used to describe each organism.
Add this information to the food web in Fig. 1.1.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B18.2 — Food chains and food webs (Parts (a), (b))
• Topic B18.1 — Energy flow (Part (c))
• Topic B6.1 — Photosynthesis (Part (d))
▶️ Answer/Explanation
(a)
Arctic cod: primary consumer and secondary consumer (it eats phytoplankton and krill).
Krill: herbivore and primary consumer (it feeds on phytoplankton).
Phytoplankton: producer (it makes its own food by photosynthesis).
Leopard seal: secondary consumer (it eats krill, a primary consumer).
1 mark is awarded for each correctly completed row.
(b) Arrows drawn from arctic cod and leopard seal to orca
A food web arrow always points from the organism being eaten to the organism that eats it.
Since the orca eats both arctic cod and leopard seal, two new arrows must be added.
One arrow goes from arctic cod to orca, and another from leopard seal to orca.
(c) The Sun
Sunlight provides the energy that producers, such as phytoplankton, capture during photosynthesis.
This light energy is converted into chemical energy stored in glucose.
All other organisms in the food chain ultimately depend on this transferred energy.
(d)(i) carbon dioxide + water \(\rightarrow\) glucose + oxygen
Photosynthesis uses light energy to convert carbon dioxide and water into glucose.
Oxygen is released as a by-product of this reaction.
Both reactant names and both product names are required for full marks.
(d)(ii) Chloroplast
The chloroplast contains chlorophyll, the pigment that absorbs light energy.
This light energy drives the reactions of photosynthesis inside the organelle.
Only plant and algal cells (not animal cells) contain chloroplasts.
Question 2
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 C4.1 — Electrolysis (Part (c))
• Topic C10.1 — Water (Part (d))
▶️ Answer/Explanation
(a)
The correct statements are “the halogens are elements” and “the halogens exist as diatomic molecules”.
Halogens do not form covalent molecules with metals; they form ionic compounds with metals.
Reactivity of the halogens actually decreases down the group, not increases.
(b)(i) Protons = 17, Neutrons = 20
The number of protons equals the number of electrons in a neutral atom, so protons \(= 17\).
The number of neutrons is found from the nucleon number minus the proton number.
Neutrons \(= 37 – 17 = 20\).
(b)(ii) Nucleus
The nucleus is the dense central part of the atom.
It contains all the protons and neutrons of the atom.
Electrons orbit around the nucleus in shells.
(c)(i) Anode (positive electrode)
During electrolysis, negatively charged chloride ions are attracted to the positive electrode.
At the anode, chloride ions lose electrons (are oxidised) to form chlorine gas.
This is why chlorine forms at the anode.
(c)(ii) Hydrogen
At the cathode, positively charged hydrogen ions gain electrons (are reduced).
This produces hydrogen gas at the negative electrode.
Sodium hydroxide solution is also formed, but this is not a gas.
(c)(iii) Graphite is inert / does not react / is a good electrical conductor
Graphite does not react with the products of electrolysis, such as chlorine.
It conducts electricity well, allowing current to pass through the solution.
This makes it a suitable, unreactive electrode material.
(c)(iv) New substances are formed and the change cannot be reversed
In electrolysis, sodium chloride solution is converted into new substances: chlorine, hydrogen and sodium hydroxide.
This shows that a chemical reaction has taken place.
Physical changes do not produce new substances and are usually reversible.
(d) Chlorine kills microbes / sterilises the water
Chlorine is added to drinking water to kill harmful microorganisms and bacteria present in the water.
This prevents the spread of waterborne diseases.
It makes the water safe for human consumption.
Question 3
State the two quantities needed to calculate the pressure exerted by the car on the road.
Describe a simple test to show that a wheel is not made from steel.
He puts a spanner on a wheel nut as shown in Fig. 3.2.
Calculate the moment of the force about the centre of the wheel nut.
The turning effect of an electric motor can be increased by increasing the number of turns on the coil in the motor.
State one other way to increase the turning effect of a d.c. motor.
The force that causes the build-up of electrostatic charges on the car is …………………………. .
The charged particles that are added or removed during the build-up of charge are called …………………………. .
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.7 — Pressure (Part (a))
• Topic C9.3 — Alloys and their properties (Part (b)(i))
• Topic P1.5.2 — Turning effect of forces (Part (b)(ii))
• Topic P4.5.5 — The d.c. motor (Part (b)(iii))
• Topic P4.2.1 — Electrical charge (Part (c))
▶️ Answer/Explanation
(a) Weight of the car; surface area of tyres in contact with the road
Pressure is calculated using \(\text{pressure} = \dfrac{\text{force}}{\text{area}}\).
The force here is the weight of the car pressing down on the road.
The area is the total contact area of all the tyres touching the road surface.
(b)(i) Use a magnet — the wheel is not attracted to it
Steel is magnetic, so a magnet will be attracted to a steel wheel.
An aluminium alloy wheel is not magnetic, so a magnet held near it will show no attraction.
This simple test distinguishes between the two materials.
(b)(ii) 100 N m
Moment is calculated using \(\text{moment} = \text{force} \times \text{perpendicular distance}\).
Moment \(= 250\,\text{N} \times 0.4\,\text{m}\).
Moment \(= 100\,\text{N m}\).
(b)(iii) Increase the current, increase the voltage, or increase the strength of the magnetic field
A stronger magnetic force is produced by increasing the current flowing through the coil.
Using a stronger magnet also increases the turning effect (torque) on the coil.
Either of these changes increases the force on the current-carrying coil.
(c) Friction; electrons
Friction between the tyres and the road (or the car and the air) causes electrons to be transferred.
This transfer of electrons results in a build-up of electrostatic charge on the car.
The charged particles involved in this process are electrons.
Question 4
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B16.3 — Monohybrid inheritance (Parts (a), (b))
• Topic B16.1 — Chromosomes and genes (Part (c))
▶️ Answer/Explanation
(a) 5 people with polydactyly; 4 people with a heterozygous genotype
Polydactyly is caused by the dominant allele \(D\), so any genotype containing \(D\) (i.e. \(Dd\) or \(DD\)) shows polydactyly.
From Table 4.1, parent A \((Dd)\), parent B \((Dd)\), offspring Q \((Dd)\), offspring S \((Dd)\) and offspring U \((DD)\) all show polydactyly, giving \(5\) people.
A heterozygous genotype is \(Dd\): parent A, parent B, offspring Q and offspring S, giving \(4\) people.
(b) 25%
Both parent A and parent B have genotype \(Dd\), so each produces gametes \(D\) and \(d\).
The Punnett square gives offspring genotypes \(DD\), \(Dd\), \(Dd\), \(dd\).
Only \(dd\) does not show polydactyly, giving \(\frac{1}{4} \times 100 = 25\%\).
(c)(i) A gene is a length of DNA that codes for a protein
A gene is a section (or length) of the DNA molecule.
Each gene codes for the production of one specific protein.
(c)(ii) XY
Human body cells contain 23 pairs of chromosomes, one pair being the sex chromosomes.
In males, the sex chromosomes are one X chromosome and one Y chromosome \((XY)\).
(c)(iii) Nucleus
The nucleus is the structure within a cell that contains the chromosomes.
Chromosomes are made of DNA, which carries the genetic material of the organism.
Question 5
- the same mass of calcium carbonate
- different sizes of calcium carbonate pieces
- a different concentration of hydrochloric acid.
Suggest the piece of apparatus the student uses to measure a time of \(100 \, \text{s}\).
Only show the outer shell electrons.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C6.2 — Rate of reaction (Part (a))
• Topic C7.1 — The characteristic properties of acids and bases (Part (b))
• Topic C2.5 — Simple molecules and covalent bonds (Part (c))
• Topic C1.1 — Solids, liquids and gases (Part (d))
▶️ Answer/Explanation
(a)(i) Experiment D
Experiment D uses small pieces of calcium carbonate (greater surface area) with concentrated hydrochloric acid.
Both factors increase the frequency of collisions, giving the fastest rate of reaction.
(a)(ii) Stopwatch
A stopwatch is the appropriate apparatus for accurately timing an interval such as \(100 \, \text{s}\).
(b)(i) Check colour against a pH chart
The colour of the indicator paper is compared to a standard pH colour chart.
A red colour corresponds to pH 1–3 (very acidic), while orange/yellow corresponds to pH 4–6 (weakly acidic).
(b)(ii) Any value between pH 1 and 6
Dilute hydrochloric acid is acidic, so any pH value in the acidic range (below 7) is acceptable.
(c)(i) 
Hydrogen contributes one electron and chlorine contributes one electron to form a single shared pair.
The remaining outer shell electrons on chlorine (three lone pairs) are shown unshared.
(c)(ii) Covalent bonding
This type of bonding, involving a shared pair of electrons, is called covalent bonding.
(d) Particle separation and motion
Particle separation: particles in a liquid are close together, whereas particles in a gas are far apart.
Motion: particles in a liquid move around and slide past each other (slower), whereas particles in a gas move randomly and freely at higher speed.
Question 6
The television is designed to transfer …………….. energy to …………….. energy and …………….. energy. …………….. energy is wasted by the television.
Calculate the mass of the television.
The gravitational field strength, \(g\), is \(10 \, \text{N/kg}\).
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.6.1 — Energy (Part (a)(i)–(ii))
• Topic P1.3 — Mass and weight (Part (a)(iii))
• Topic P4.4 — Electrical safety (Part (b))
• Topic P3.2.1 — Reflection of light (Part (c))
▶️ Answer/Explanation
(a)(i) 5 J
From Fig. 6.1, total energy supplied \(= 100 \, \text{J}\), with \(65 \, \text{J}\) as light and \(30 \, \text{J}\) as thermal energy.
Energy as sound \(= 100 – 65 – 30 = 5 \, \text{J}\).
(a)(ii) electrical → light and sound; thermal is wasted
The television is designed to transfer electrical energy into light energy and sound energy (its useful output).
Thermal energy is the wasted output, since it does not contribute to the television’s purpose.
(a)(iii) 12 kg
Weight = mass × \(g\), so mass = weight ÷ \(g\).
Mass \(= \dfrac{120}{10} = 12 \, \text{kg}\).
(b)(i) Frayed cables
Fig. 6.2 shows the cable insulation is worn away/frayed, exposing the wires underneath.
(b)(ii) Danger of electrocution or short circuit
Exposed wires from frayed cables can be touched directly, risking electric shock.
Exposed wires may also touch each other and cause a short circuit, which can start a fire.
(c)(i) The normal
Line XY is drawn perpendicular to the mirror at the point where the ray strikes it.
This line is called the normal, and angles of incidence/reflection are measured from it.
(c)(ii) Angle b
The angle of incidence is the angle between the incident ray and the normal, on the side of the incoming ray.
This corresponds to angle b in Fig. 6.3.
(c)(iii) The angle of incidence equals the angle of reflection
This is the law of reflection, which applies to all reflecting surfaces including plane mirrors.
Question 7
where egestion occurs ………………………….
where most absorption of food molecules occurs ………………………….
that releases food into the small intestine ………………………….
Assimilation is the movement of digested/insoluble food molecules into the cells/genes of the body where they are used.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B7.3 — Digestion (Parts (a), (b))
• Topic B7.1 — Diet (Part (c))
▶️ Answer/Explanation
(a)(i) F (egestion); D (absorption); B (releases food into small intestine)
Egestion (removal of undigested waste) occurs at the anus/rectum, labelled F.
Most absorption occurs in the small intestine, labelled D.
The stomach, labelled B, releases food into the small intestine.
(a)(ii) A – liver; C – pancreas
Part A is the liver, which produces bile.
Part C is the pancreas, which produces digestive enzymes.
(b) digested and cells
Assimilation is the movement of digested food molecules (not insoluble ones) into the cells of the body, where they are used.
(c)(i) 
Butter is a fatty food, so it links to fat.
Rice is a starchy food, so it links to carbohydrate.
Tuna fish is a protein-rich food, so it links to protein.
(c)(ii) Carbon, hydrogen, oxygen
Carbohydrates are made up of only these three elements, in the ratio typically seen in sugars and starches.
(c)(iii) Calcium strengthens bones and teeth
Calcium is an important mineral required for building strong bones and teeth.
A deficiency can lead to weak or brittle bones.
Question 8
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C9.2 — Uses of metals (Parts (a), (b))
• Topic C9.3 — Alloys and their properties (Part (c))
▶️ Answer/Explanation
(a)(i) A finite resource is one that is no longer being made, or is made extremely slowly
This means the resource will eventually run out, since it cannot be replenished at the rate it is used.
(a)(ii) Bauxite
Bauxite is the ore from which aluminium metal is extracted, usually by electrolysis.
(b) Unreactive/resists corrosion; low density
Aluminium is unreactive and resists corrosion, so food stored in it stays safe and uncontaminated.
Aluminium has a low density, so containers made from it are lightweight and easy to transport.
Aluminium is also malleable, allowing it to be shaped easily into thin sheets for containers.
(c)(i) An alloy is a mixture of two or more metals, or a metal and other elements
Mixing elements in this way often improves the properties of the pure metal, such as its strength.
(c)(ii) 83.8 g
Total mass of alloy \(= 100 \, \text{g}\).
Mass of aluminium \(= 100 – (1.3 + 0.6 + 1.1 + 2.3 + 10.9) = 100 – 16.2 = 83.8 \, \text{g}\).
(c)(iii) Copper, iron, nickel
These three elements listed in Table 8.1 are transition elements, found in the central block of the Periodic Table.
Aluminium, magnesium and silicon are not transition elements.
Question 9
State the range of frequencies emitted by a bat that a healthy human ear can hear.
Calculate the time taken by the bat to travel \(200 \, \text{m}\).
State one other disadvantage of using wind turbines to generate electrical energy.
State one other renewable energy source.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B13.1 — Coordination and response (Part (a))
• Topic P1.2 — Motion (Part (b)(i))
• Topic P1.6.3 — Energy resources (Part (b)(ii)–(iii))
• Topic P3.3 — Electromagnetic spectrum (Part (c))
▶️ Answer/Explanation
(a)(i) Bat and dolphin
The rat’s highest frequency is \(76\,000 \, \text{Hz}\).
Pitch is determined by frequency, so any animal with a higher highest-frequency value can hear a higher pitch.
Bat \((200\,000 \, \text{Hz})\) and dolphin \((130\,000 \, \text{Hz})\) both exceed this value.
(a)(ii) Highest frequency 20,000 Hz; lowest frequency 2,000 Hz
Bats emit sound from \(2000\,\text{Hz}\) to \(200\,000\,\text{Hz}\).
The human ear can only detect up to about \(20\,000\,\text{Hz}\), so the audible range of the bat’s sound to humans is \(2000\,\text{Hz}\) to \(20\,000\,\text{Hz}\).
(b)(i) 5 s
Time = distance ÷ speed.
Time \(= \dfrac{200}{40} = 5 \, \text{s}\).
(b)(ii) Unreliable, as it depends on the wind blowing
Wind turbines cannot generate electricity when there is no wind, making supply inconsistent.
(b)(iii) HEP / solar / tidal / wave / geothermal
Any renewable energy source other than wind is acceptable, such as hydroelectric power or solar energy.
(c)(i) Ultraviolet sits between X-rays and visible light
The electromagnetic spectrum in order of decreasing frequency is: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, radio waves.
Ultraviolet radiation is placed directly between X-rays and visible light.
(c)(ii) Skin cancer or sunburn
Excessive exposure to ultraviolet radiation damages skin cells, which can cause sunburn and increase the risk of skin cancer.
Question 10
Place ticks (✓) next to all the statements that correctly describe diffusion.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B11.1 — Gas exchange in humans (Parts (a)–(c))
• Topic B8.3 — Transpiration (Part (d))
▶️ Answer/Explanation
(a) A – trachea; B – bronchus; C – alveoli
The trachea (windpipe) leads into the bronchi, which branch into smaller tubes ending in the alveoli.
Gas exchange with the blood takes place at the alveoli.
(b) Expired air contains more carbon dioxide, less oxygen, and more water vapour
Oxygen is used up by the body during respiration, so expired air contains less of it than inspired air.
Carbon dioxide is produced by respiration, so expired air contains more of it.
Water vapour is added to the air as it passes through the moist respiratory passages, so expired air contains more water vapour.
(c) 
Diffusion is the net movement of any particles (not only water) due to their random motion.
It occurs down a concentration gradient (from high to low concentration), not against it, and does not require energy from respiration.
It can occur across a cell membrane, such as at the alveoli or in plant leaves.
(d)(i) Stoma / stomata
Water vapour exits the leaf through small pores called stomata, usually located on the underside of the leaf.
(d)(ii) Transpiration
Transpiration is the term for the evaporation of water from inside the leaf followed by its diffusion out through the stomata.
(d)(iii) Increase in temperature; decrease in humidity
Higher temperature increases the rate of evaporation of water from leaf cells, speeding up transpiration.
Lower humidity increases the concentration gradient between the leaf and the air, speeding up diffusion of water vapour out of the leaf.
Question 11
Balance the symbol equation for this reaction.
Describe what is observed during an exothermic reaction.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C11.3 — Fuels (Part (a))
• Topic C11.1 — Formulas and terminology (Part (b))
• Topic C11.3 — Fuels (Part (c)(i)); Topic C5.1 — Exothermic and endothermic reactions (Part (c)(ii))
• Topic C11.6 — Alcohols; Topic C11.5 — Alkenes (Part (d))
▶️ Answer/Explanation
(a)(i) Natural gas
Methane is the main constituent of natural gas, a fossil fuel formed from the remains of ancient marine organisms.
(a)(ii) Coal or petroleum
Coal and petroleum (crude oil) are the other two main fossil fuels, alongside natural gas.
(a)(iii) Carbon dioxide
Carbon dioxide is another common greenhouse gas, alongside methane and water vapour.
(b) 
Methane \(\text{CH}_4\) has one carbon atom bonded to four hydrogen atoms, arranged symmetrically around the central carbon.
Each C–H bond is a single covalent bond.
(c)(i) \(\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}\)
There are 4 hydrogen atoms in methane, requiring \(2\text{H}_2\text{O}\) on the product side to balance them.
This gives 4 oxygen atoms needed on the product side (2 from \(\text{CO}_2\) and 2 from \(2\text{H}_2\text{O}\)), so \(2\text{O}_2\) is needed as reactant.
(c)(ii) Temperature rise
An exothermic reaction releases heat energy to the surroundings.
This is observed as an increase in temperature during the reaction.
(d)(i) C
Diagram C contains an –O–H group attached to the carbon chain, which is the functional group of an alcohol.
Diagrams A, B and D do not contain this group.
(d)(ii) Test: add aqueous bromine
Aqueous bromine is added to both A and B.
Result for A: no change, the solution stays orange, since A is a saturated compound with no C=C double bond.
Result for B: the solution decolorises (changes from orange to colourless), since B contains a C=C double bond typical of an alkene.
Question 12
- power the electric motor which operates the cooler
- light the lamp inside the refrigerator.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P4.3.2 — Series and parallel circuits (Part (a))
• Topic P5.2.1 — Detection of radioactivity (Part (b))
• Topic P1.4 — Density (Part (c))
• Topic P2.2.1 — Thermal expansion of solids, liquids and gases (Part (d))
▶️ Answer/Explanation
(a)(i) Correct symbol for lamp; lamp and motor in parallel
The lamp should be drawn using the standard circle-with-cross circuit symbol.
The lamp and motor branches should each connect separately across the supply, forming a parallel arrangement.
(a)(ii) Fuse
Component X, shown in series in the main circuit, is a fuse.
(a)(iii) Protects the circuit
The fuse melts and breaks the circuit if the current becomes too large.
This prevents damage to the circuit components and reduces the risk of fire.
(b) Alpha, beta or X-rays
Any of these three types of radiation are also classified as ionising radiation, alongside gamma radiation.
(c) 320 g
Mass = density × volume.
Mass \(= 1.28 \times 0.25 = 0.32 \, \text{kg}\).
Converting to grams: \(0.32 \times 1000 = 320 \, \text{g}\).
(d)(i) Ethanol, mercury and methanol
A suitable thermometer liquid must remain liquid at \(-18\,^\circ\text{C}\), meaning its melting point must be below this temperature.
Ethanol \((-114\,^\circ\text{C})\), mercury \((-39\,^\circ\text{C})\) and methanol \((-98\,^\circ\text{C})\) all satisfy this, but water \((0\,^\circ\text{C})\) does not, since it would be frozen solid.
(d)(ii) Density (or volume)
As temperature increases, the liquid expands, changing its volume (and therefore its density).
This physical change is what allows the thermometer to indicate a temperature reading.