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Question 1

(a) Fig. 1.1 is a diagram of a single-celled organism called a euglena.
(i) Table 1.1 shows some of the cell components of animal, euglena and plant cells.
Complete Table 1.1 by placing ticks (✓) to show the correct cell components of each type of cell.
Use the information in Fig. 1.1 and your knowledge to answer the question.
(ii) State evidence from Fig. 1.1 for and against euglena being a plant cell.
(b) State the function of the nucleus.
(c) The length of a palisade cell is 0.08 mm.
The length of a red blood cell is 0.007 mm.
Calculate how many times bigger a palisade cell is than a red blood cell.
Give your answer to the nearest whole number.
(d) Fig. 1.2 shows a type of nerve cell (neurone).
(i) Name the type of neurone shown in Fig. 1.2.
(ii) The type of neurone shown in Fig. 1.2 can be 1.5 m in length.
Suggest why these cells need to be very long.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B2.1 — Cell structure (Parts (a), (b))
• Topic B2.2 — Size of specimens (Part (c))
• Topic B2.1 — Cell structure (Part (d))

▶️ Answer/Explanation

(a)(i)

(a)(ii) For: has chloroplasts. Against: no cell wall/vacuole

Chloroplasts are normally only found in plant cells, supporting the “for” case.
A true plant cell would also have a rigid cell wall and a large vacuole, both absent in Fig. 1.1.

(b) Controls the cell’s activities / contains genetic material (DNA)

The nucleus stores DNA, which carries the instructions for making proteins.
It therefore directs and controls all the activities of the cell.

(c) 11

Number of times bigger \( = \dfrac{0.08}{0.007} \).
\[ \dfrac{0.08}{0.007} = 11.43 \]
Rounded to the nearest whole number \( = 11 \).

(d)(i) Sensory neurone

The cell shown has a long axon with a cell body positioned partway along it, a feature typical of a sensory neurone.

(d)(ii) To transmit impulses over large distances/areas

Nerve impulses must travel from receptors at the body’s extremities to the central nervous system.
A single long cell allows the impulse to travel this distance quickly, without needing multiple synapses (which would slow transmission).

Question 2

(a) Table 2.1 shows the melting points and reactivity with water of three Group I metals.
Complete Table 2.1 to predict
  • the melting point of potassium
  • the reactivity of lithium with water.
(b) Name the gas made when a Group I metal reacts with water.
(c) When sodium reacts with chlorine, an orange flame is seen and the sodium melts.
Sodium chloride is formed.
(i) State if the reaction is exothermic or endothermic.
Explain your answer.
(ii) Sodium chloride contains chloride ions.
Describe a test for chloride ions and the positive result.
(iii) State the type of bonding present in sodium chloride.
Explain your answer.
(d) Concentrated aqueous sodium chloride is electrolysed.
State the products at the electrodes.
(e) A student separates a mixture of sand and aqueous sodium chloride.
(i) State the method of separation used to separate the sand from the aqueous sodium chloride.
(ii) Describe how solid sodium chloride can be obtained from aqueous sodium chloride.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C8.2 — Group I properties (Parts (a), (b))
• Topic C5.1 — Exothermic and endothermic reactions (Part (c)(i))
• Topic C12.5 — Qualitative analysis (Part (c)(ii))
• Topic C2.4 — Ions and ionic bonds (Part (c)(iii))
• Topic C4.1 — Electrolysis (Part (d))
• Topic C12.4 — Separation and purification (Part (e))

▶️ Answer/Explanation

(a) Potassium melting point: below 90°C. Lithium: reacts slowly

Melting point decreases going down Group I, so potassium melts below sodium’s 98°C.
Reactivity increases going down Group I, so lithium (above sodium) reacts more slowly than sodium.

(b) Hydrogen

Group I metal + water → metal hydroxide + hydrogen gas.
The bubbles of gas observed are hydrogen escaping.

(c)(i) Exothermic

Thermal energy is released to the surroundings, seen as the orange flame and the melting of sodium.
This release of energy is the defining feature of an exothermic reaction.

(c)(ii) Aqueous silver nitrate; white precipitate

Add aqueous silver nitrate to a solution of the sample.
A white precipitate of silver chloride, \( \text{AgCl} \), forms if chloride ions are present.

(c)(iii) Ionic bonding

Bonding occurs between a metal (sodium) and a non-metal (chlorine).
Sodium transfers an electron to chlorine, forming \( \text{Na}^+ \) and \( \text{Cl}^- \) ions held together by electrostatic attraction.

(d) Hydrogen and chlorine

At the cathode, \( \text{H}^+ \) ions are reduced to form hydrogen gas.
At the anode, \( \text{Cl}^- \) ions are oxidised to form chlorine gas.

(e)(i) Filtration

Sand is insoluble, so filtration separates the solid sand from the aqueous sodium chloride solution.

(e)(ii) Evaporation/crystallisation

Heating the solution evaporates the water, leaving solid sodium chloride behind.

Question 3

(a) An astronomer on Earth is able to see the Moon even though the Moon does not emit visible light.
State one property of visible light that enables observation of the Moon.
(b) Visible light is part of the electromagnetic spectrum.
Place visible light in the correct place in the incomplete electromagnetic spectrum in Fig. 3.1.
(c)
(i) Light rays from the Moon travel at \(3 \times 10^5 \, \text{km/s}\) to reach the astronomer on Earth.
The distance travelled is 400 000 km.
Calculate the time taken for the light rays to travel from the Moon to the Earth.
(ii) Explain why sound waves are unable to travel from the Moon to the Earth.
(d) The astronomer uses lenses in a telescope to look at the Moon.
Fig. 3.2 shows rays of light passing through a lens.
(i) On Fig. 3.2 label the focal length of the lens with a double headed arrow (↔).
(ii) On Fig. 3.2 label the principal focus of the lens with the letter F.
(e) An astronaut on the Moon is exposed to ionising background radiation.
(i) State one effect of ionising radiation on the human body.
(ii) Suggest one source of background radiation on the Moon.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P3.2.1 — Reflection of light (Part (a))
• Topic P3.3 — Electromagnetic spectrum (Part (b))
• Topic P1.2 — Motion (Part (c)(i))
• Topic P3.4 — Sound (Part (c)(ii))
• Topic P3.2.3 — Thin converging lens (Part (d))
• Topic P5.2.5 — Applications and safety precautions (Part (e))

▶️ Answer/Explanation

(a) Reflection

The Moon does not produce its own visible light.
Sunlight reflects off the Moon’s surface and travels to the astronomer’s eye, allowing it to be seen.

(b) Visible light placed between ultraviolet and infrared

The electromagnetic spectrum is ordered by wavelength: gamma, X-ray, ultraviolet, visible light, infrared, microwave, radio.
Visible light therefore sits between ultraviolet and the (missing) infrared box, just before microwaves.

(c)(i) 1.33 s

\( \text{time} = \dfrac{\text{distance}}{\text{speed}} = \dfrac{400\,000}{3 \times 10^5} \)
\( \text{time} = 1.33 \, \text{s} \)

(c)(ii) Sound needs a medium; space is a vacuum

Sound waves are mechanical waves and require particles of a medium to vibrate and transfer energy.
The space between the Moon and Earth is a vacuum, so sound cannot travel through it.

(d)(i)/(ii) Arrow from lens centre to F; F marked at convergence point

The focal length is the distance from the centre of the lens to the point where parallel rays converge.
This convergence point is labelled F, the principal focus.

(e)(i) Cancer/mutation

Ionising radiation can damage DNA within cells.
This can cause mutations, potentially leading to cancer.

(e)(ii) Cosmic radiation

The Moon has no atmosphere to shield against radiation from space.
Cosmic radiation therefore reaches the lunar surface directly.

Question 4

Fig. 4.1 is a diagram of a cross-section through skin tissue.
(a)  Identify the parts labelled A, B and C in Fig. 4.1.
(b) Complete the sentences to describe how the body responds in cold conditions using words from the list.
Each word may be used once, more than once or not at all.
blood     energy      muscles      skin
When the internal body temperature decreases, the brain detects the low temperature of the ………………….. .
To increase the body temperature ………………….. contract and relax rapidly. This is called shivering.
This increases the rate of respiration which releases ………………….. in the form of heat.
(c) The boxes on the left show some sentence beginnings.
The boxes on the right show some sentence endings.
Draw one line to link one box on the left to one box on the right to show the correct definition of homeostasis.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B13.3 — Homeostasis/thermoregulation (Parts (a), (b), (c))

▶️ Answer/Explanation

(a) A: sweat gland; B: fat(ty tissue); C: (hair) erector muscle

A coiled structure near the skin surface is the sweat gland, producing sweat for cooling.
B is the fatty tissue layer beneath the dermis, providing insulation.
C is the erector muscle attached to the hair follicle, causing hairs to stand up.

(b) blood; muscles; energy

The brain detects a fall in blood temperature.
Muscles contract and relax rapidly (shivering) to generate heat.
This raises the rate of respiration, releasing energy as heat.

(c) Homeostasis is the maintenance of a constant internal environment

Homeostasis keeps internal conditions (temperature, water balance, glucose, etc.) stable.
This stability is maintained despite changes in the external environment.

Question 5

(a)
(i) State the percentage of oxygen and of nitrogen in a sample of clean air.
  • Oxygen: …….%
  • Nitrogen: …….%
(ii) A sample of air collected near a busy road contains carbon monoxide.
Carbon monoxide is made by car engines.
Describe how carbon monoxide is made by car engines.
(iii) State one harmful effect of carbon monoxide on the health of a human.
(b) The atmosphere contains small quantities of sulfur dioxide.
Sulfur dioxide causes acid rain.
(i) Suggest a pH for acid rain.
(ii) Suggest one adverse effect of acid rain on buildings.
(iii) Sulfur dioxide is made when sulfur is burned in oxygen.
This reaction is called an oxidation reaction.
State the meaning of the term oxidation.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C10.2 — Air quality and climate (Parts (a), (b)(i), (b)(ii))
• Topic C6.3 — Redox (Part (b)(iii))

▶️ Answer/Explanation

(a)(i) Oxygen 21%; nitrogen 78%

Clean, dry air is approximately 78% nitrogen and 21% oxygen by volume.
The remainder is made up of argon, carbon dioxide, and other trace gases.

(a)(ii) Incomplete combustion of hydrocarbon fuel

Car engines burn hydrocarbon fuel in a limited supply of oxygen.
This incomplete combustion produces carbon monoxide instead of carbon dioxide.

(a)(iii) Carboxyhaemoglobin formation / poisoning / unconsciousness / death

Carbon monoxide binds strongly to haemoglobin, forming carboxyhaemoglobin.
This reduces the blood’s oxygen-carrying capacity, causing oxygen deprivation.

(b)(i) Any value less than 7

Acid rain has a pH lower than that of pure water (pH 7) due to dissolved acidic gases.

(b)(ii) Corrosion of building materials

Acid rain reacts with materials such as limestone, gradually dissolving and weakening them.

(b)(iii) Gain of oxygen

Oxidation is defined as the gain of oxygen (or loss of electrons) by a substance.
Sulfur gains oxygen when it burns to form sulfur dioxide, \( \text{S} + \text{O}_2 \rightarrow \text{SO}_2 \).

Question 6

(a) Fig. 6.1 shows an electric heater containing two heating elements.
(i) The two heating elements are connected in series.
Each heating element has a resistance of \(8\,\Omega\).
Calculate the combined resistance of the two heating elements.
(ii) A different heater has the two heating elements connected in parallel.
State which value could be the combined resistance of the two heating elements connected in parallel.
Explain your answer.
\(4\,\Omega\) \(8\,\Omega\) \(16\,\Omega\) \(32\,\Omega\)
(iii) Complete the circuit diagram for the two heating elements (resistors) connected in parallel to an a.c. power supply.
The circuit should contain one switch to operate both heating elements.
The symbol for a heating element is
(b) Fig. 6.2 shows the heater on a wall in a room.
When the heater is switched on, the air around the heater is warmed.
(i) On Fig. 6.2 draw four arrows to show how the warm air circulates around the room.
(ii) Name the process which circulates the warm air.
(c) A man walks on the floor in the room.
As he walks he gains a negative charge.
Describe how the man gains this charge.
Use ideas about charged particles in your answer.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P4.3.2 — Series and parallel circuits (Part (a))
• Topic P2.3.2 — Convection (Part (b))
• Topic P4.2.1 — Electrical charge (Part (c))

▶️ Answer/Explanation

(a)(i) 16 Ω

In series, resistances add: \( R_{total} = R_1 + R_2 \).
\[ R_{total} = 8 + 8 = 16\,\Omega \]

(a)(ii) 4 Ω

In parallel, \( \dfrac{1}{R_{total}} = \dfrac{1}{8} + \dfrac{1}{8} = \dfrac{1}{4} \), so \( R_{total} = 4\,\Omega \).
The combined resistance in parallel is always less than either individual resistance.

(a)(iii) Two heaters in parallel, one switch in the main line

Both heating elements are drawn as separate parallel branches connected across the a.c. supply.
A single switch is placed in the main circuit line so it controls current to both elements together.

(b)(i) Arrows showing rising air near heater, falling air elsewhere, forming a loop

Warm air rises above the heater; two arrows near the ceiling move away from the heater; two arrows show air falling back down and returning to the heater at floor level.

(b)(ii) Convection

Convection is heat transfer through the bulk movement of a fluid.
Warm air is less dense and rises, while cooler, denser air sinks, creating a convection current.

(c) Friction transfers electrons from the floor to the man

As the man’s shoes rub against the floor, friction causes electrons to be transferred.
Electrons move from the floor onto the man, giving him an excess of negative charge.

Question 7

(a) State the word equation for photosynthesis.
(b) Fig. 7.1 is a diagram of a cross-section of a leaf.
(i) Identify the area in Fig. 7.1, A, B, C or D, where most photosynthesis takes place.
Give one reason for your answer using evidence from Fig. 7.1.
(ii) On Fig. 7.1, draw one arrow to show the pathway of water during transpiration.
(iii) State the name of part X shown in Fig. 7.1.
(c) A group of pea plants is grown with standard fertiliser and another group is grown with fertiliser containing additional magnesium.
The height of the plants is measured and an average calculated.
Table 7.1 shows the results.
Carbohydrates are needed for plant growth.
Explain the results shown in Table 7.1.
Include ideas about carbohydrates and photosynthesis in your answer.
(d) Fertilisers contain nitrate ions.
Describe the importance of nitrate ions to plants.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B6.1 — Photosynthesis (Part (a))
• Topic B6.2 — Leaf structure (Part (b)(i))
• Topic B8.3 — Transpiration (Part (b)(ii))
• Topic B6.2 — Leaf structure (Part (b)(iii))
• Topic B6.1 — Photosynthesis (Part (c))
• Topic B4.1 — Biological molecules (Part (d))

▶️ Answer/Explanation

(a) Carbon dioxide + water → glucose + oxygen

Photosynthesis uses light energy absorbed by chlorophyll to convert carbon dioxide and water into glucose, releasing oxygen as a by-product.

(b)(i) Area B; has the most chloroplasts

B is the palisade mesophyll layer, shown with the densest packing of chloroplasts in the diagram.
More chloroplasts means more chlorophyll available to absorb light for photosynthesis.

(b)(ii) Arrow from a mesophyll cell surface to/through a stoma

Water vapour diffuses out of the leaf’s air spaces and exits through the stomata into the atmosphere.

(b)(iii) Cuticle

The waxy cuticle covers the upper epidermis, reducing water loss from the leaf surface.

(c) Extra Mg → more chlorophyll → more photosynthesis → more carbohydrate → more growth

Magnesium is required to make chlorophyll, the pigment needed for photosynthesis.
More chlorophyll allows more photosynthesis, producing more carbohydrates for growth.
This explains the greater average height (33.0 cm vs 27.4 cm) with added magnesium.

(d) Needed to make amino acids/proteins

Nitrate ions are absorbed by roots and combined with sugars to form amino acids.
Amino acids are then used to build proteins, essential for plant growth.

Question 8

(a) An atom of aluminium has a proton number of 13 and nucleon number of 27.
(i) State what is meant by the term nucleon number.
(ii) Describe the electronic structure of an atom of aluminium.
You may wish to draw a diagram to help your answer.
(b) Aluminium is extracted from its ore by electrolysis.
(i) Name one ore from which aluminium is extracted.
(ii) Electrolysis results in a chemical change.
Explain what is meant by a chemical change.
(c) Aluminium alloys are used in aircraft parts.
(i) State what is meant by the term alloy.
(ii) State why aluminium alloys are used in aircraft parts.
(iii) State why aluminium is used in the form of alloys rather than as pure aluminium.
(iv) Describe and explain one other use of aluminium.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C2.2 — Atomic structure and the Periodic Table (Part (a))
• Topic C9.6 — Extraction of metals (Part (b)(i))
• Topic C6.1 — Physical and chemical changes (Part (b)(ii))
• Topic C9.3 — Alloys and their properties (Part (c)(i)–(iii))
• Topic C9.2 — Uses of metals (Part (c)(iv))

▶️ Answer/Explanation

(a)(i) Total number of protons and neutrons in the nucleus

Nucleon number = protons + neutrons.
For aluminium: 13 protons + 14 neutrons = 27.

(a)(ii) 13 electrons; arrangement 2.8.3

Aluminium has 13 electrons, matching its proton number.
These fill shells in the order 2, then 8, then the remaining 3: \( 2.8.3 \).

(b)(i) Bauxite

Bauxite is the ore that contains aluminium oxide, \( \text{Al}_2\text{O}_3 \), from which aluminium metal is extracted.

(b)(ii) New substance(s) produced

A chemical change forms one or more new substances with different properties from the starting materials.
In electrolysis, aluminium oxide is broken down into aluminium metal and oxygen gas.

(c)(i) A mixture of a metal with one or more other elements

Alloys are usually mixtures of a metal with other metals (or sometimes non-metals) to alter its properties.

(c)(ii) Low density

Aluminium alloys are lightweight yet strong, reducing overall aircraft weight and improving fuel efficiency.

(c)(iii) Stronger

Pure aluminium is relatively soft; alloying increases its strength for structural use.

(c)(iv) Food containers/drink cans; resistant to corrosion

Aluminium forms a protective oxide layer that resists further corrosion.
This makes it safe and durable for storing food and drinks.

Question 9

(a) Choose words from the list below to complete the sentences that describe the energy changes occurring when a wind turbine is used.
Each word may be used once, more than once or not at all.
electrical kinetic light potential thermal sound
The kinetic energy of the wind is transferred to the ………………….. energy of the moving rotor blades of the wind turbine.
The useful output energy from the wind turbine is ………………….. energy.
The wind turbine makes sound energy which is unwanted. Another unwanted form of energy made by wind turbines is ………………….. energy.
(b) State one advantage of using wind rather than coal to generate electricity.
(c) One disadvantage of wind turbines is they give out very low frequency sound waves.
(i) State what is meant by the frequency of a wave.
(ii) The frequency of the sound waves produced is very low.
A healthy human ear can only just hear this sound.
Suggest a value for this frequency.
(d) Magnets are used in the generators of wind turbines.
Fig. 9.1 shows a bar magnet.
On Fig. 9.1, draw the pattern and direction of the magnetic field lines around the magnet.
(e) Another method of generating electricity is to use nuclear fission in a nuclear power station.
During nuclear fission, α-particles, β-particles and γ-rays may be released from atoms.
(i) Complete Table 9.1 to show the properties of α-particles, β-particles and γ-rays.
(ii) Describe what happens to the nucleus of an atom during nuclear fission.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P1.6.1 — Energy (Part (a))
• Topic P1.6.3 — Energy resources (Part (b))
• Topic P3.4 — Sound (Part (c))
• Topic P4.1 — Simple phenomena of magnetism (Part (d))
• Topic P5.2.2 — The three types of nuclear emission (Part (e)(i))
• Topic P5.1 — The nucleus (Part (e)(ii))

▶️ Answer/Explanation

(a) kinetic; electrical; thermal

Wind’s kinetic energy transfers to the rotor blades’ kinetic energy.
The generator converts this to useful electrical energy.
Friction in moving parts wastes energy as unwanted thermal energy.

(b) Does not use fossil fuel / does not produce CO₂ / renewable

Wind is a renewable resource that does not deplete, and it produces no greenhouse gas emissions during operation, unlike coal.

(c)(i) Number of waves produced/passing a point per second

Frequency, measured in hertz (Hz), counts how many complete wave cycles occur each second.

(c)(ii) 20 Hz

The typical lower limit of human hearing is about 20 Hz, making this the threshold value a healthy ear can just detect.

(d) Field lines from N to S, forming closed curved loops

Magnetic field lines emerge from the north pole and curve round to enter the south pole.
Lines are denser near the poles, showing where the field is strongest.

(e)(i) α: low penetrating ability; β: electron, medium penetrating ability; γ: low ionising ability, high penetrating ability

Alpha particles are large and easily stopped (low penetration) but highly ionising.
Beta particles (fast electrons) are moderately ionising and moderately penetrating.
Gamma rays are electromagnetic waves — weakly ionising but highly penetrating.

(e)(ii) Nucleus splits into two smaller nuclei

During fission, a large unstable nucleus splits into two smaller nuclei, releasing energy and radiation, along with neutrons.

Question 10

(a) A student writes a definition of an enzyme. The definition is not correct.
‘Enzymes are fats that function as chemical catalysts.’
Circle the two words in the student’s definition that are not correct.
(b) Enzymes are used to break down large molecules into smaller molecules.
Table 10.1 shows some large molecules and the smaller molecules they are made from.
Complete Table 10.1.
(c) List the three chemical elements that make up fats.
(d) Fig. 10.1 is a graph showing the enzyme activity at different temperatures of four different enzymes, A, B, C and D.
Table 10.2 shows average temperatures in different environments.
(i) Describe the effect of temperature on the enzyme activity of enzyme B. Use data to support your answer.
(ii) Use Fig. 10.1 and Table 10.2 to identify the enzyme, A, B, C or D, found in bacteria that can survive in:
hydrothermal vent regions ……………………………………
arctic seas ……………………………………
the same environment as enzyme C. ……………………………………

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B5.1 — Enzymes (Parts (a), (d))
• Topic B4.1 — Biological molecules (Parts (b), (c))

▶️ Answer/Explanation

(a) “fats” and “chemical”

Enzymes are proteins, not fats.
They act as biological catalysts, not chemical catalysts, though both terms relate to speeding up reactions.

(b) glycogen; protein; glycerol

Starch and glycogen both break down to glucose.
Proteins break down to amino acids.
Fats break down to fatty acids and glycerol.

(c) Carbon, hydrogen, oxygen

Fats (lipids) are composed only of these three elements, arranged as glycerol and fatty acid chains.

(d)(i) Activity increases then decreases; peak/optimum at 33°C

As temperature rises towards the optimum, enzyme activity increases.
Enzyme B peaks at around 33°C, after which activity falls sharply as the enzyme denatures.

(d)(ii) Hydrothermal vent: D; Arctic seas: A; same environment as C: D

D has the highest optimum temperature (~95°C), matching the hydrothermal vent region (95°C).
A has the lowest optimum, matching the arctic sea (–2°C).
C’s optimum (~65-75°C, volcano sediment) is closest to D’s high-temperature environment.

Question 11

(a) Methane is a greenhouse gas.
Name one other greenhouse gas.
(b) Methane is completely combusted in oxygen.
Carbon dioxide and water are made. Balance the symbol equation for this reaction.
(c) Complete Fig. 11.1 to show the structural formula of methane.
(d) Methane is the main constituent of a fossil fuel.
(i) Name this fossil fuel.
(ii) Name one other fossil fuel.
(e) Methane is an alkane. Ethene is an alkene.
(i) State the difference in structure between an alkane and an alkene.
(ii) A student uses a chemical reagent to show the difference between an alkane and an alkene.
Tick (✓) the correct box to show the chemical reagent used.
(f) Ethene, \(\text{C}_2\text{H}_4\), reacts with steam to produce ethanol, \(\text{C}_2\text{H}_5\text{OH}\).
Ethene is a hydrocarbon.
Explain why ethanol is not a hydrocarbon.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C10.2 — Air quality and climate (Part (a))
• Topic C3.1 — Formulas (Part (b))
• Topic C11.1 — Formulas and terminology (Part (c))
• Topic C11.3 — Fuels (Part (d))
• Topic C11.5 — Alkenes (Part (e))
• Topic C11.6 — Alcohols (Part (f))

▶️ Answer/Explanation

(a) Carbon dioxide

Carbon dioxide, water vapour, and nitrous oxide are other common greenhouse gases besides methane.

(b) \( \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \)

Balancing carbon: 1 on each side.
Balancing hydrogen: 4 H atoms need \(2\text{H}_2\text{O}\).
Balancing oxygen: \(2\text{O}_2\) supplies the 4 oxygen atoms needed for \(\text{CO}_2 + 2\text{H}_2\text{O}\).

(c) Four hydrogen atoms bonded singly around the central carbon

Methane has one carbon atom bonded by four single covalent bonds to four separate hydrogen atoms.

(d)(i) Natural gas

Natural gas is composed mainly of methane.

(d)(ii) Coal (or petroleum)

Coal and petroleum (crude oil) are the other two main fossil fuels alongside natural gas.

(e)(i) Alkanes have only single C–C bonds; alkenes have at least one C=C double bond

This makes alkanes saturated hydrocarbons and alkenes unsaturated hydrocarbons.

(e)(ii) Aqueous bromine

Alkenes decolourise aqueous bromine rapidly (orange-brown to colourless) due to the double bond; alkanes do not react.

(f) Ethanol contains oxygen

Hydrocarbons contain only hydrogen and carbon.
Ethanol contains an oxygen atom in addition to carbon and hydrogen, so it cannot be classified as a hydrocarbon.

Question 12

(a) Fig. 12.1 shows the horizontal forces acting on a motorcyclist and his motorcycle.
(i) Calculate the resultant horizontal force acting on the motorcyclist and motorcycle.
(ii) Describe how this resultant force changes the speed of the motorcycle.
(b) Fig. 12.2 shows a speed-time graph for the motorcycle’s journey over 80 s.
(i) State a time when the motorcycle is not moving.
(ii) On Fig. 12.2 label with the letter C a point when the motorcycle is moving at a constant speed.
(iii) On Fig. 12.2 label with the letter S a point when the speed of the motorcycle is increasing.
(c) The motorcycle produces a loud sound with a high frequency when moving.
Describe the pitch and amplitude of the sound waves produced.
(d) As the motorcycle moves along the road, the temperature of the air in the tyres increases.
Explain why the pressure of the air in the tyres increases.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P1.5.1 — Forces and resultant force (Part (a))
• Topic P1.2 — Speed-time graphs (Part (b))
• Topic P3.4 — Sound: pitch and amplitude (Part (c))
• Topic P2.1.3 — Kinetic theory/gas pressure (Part (d))

▶️ Answer/Explanation

(a)(i) 300 N

Resultant force = forward force − backward force.
\( 400\,\text{N} – 100\,\text{N} = 300\,\text{N} \)

(a)(ii) Slows the motorcycle down

The 100 N backward force is greater relative to direction of travel context in this case the net force opposes motion, decelerating the motorcycle.

(b)(i) 0 s, 40–45 s, or 80 s

These are the intervals where the speed-time graph reads zero, meaning the motorcycle is stationary.

(b)(ii) Point between 15–30 s or 60–70 s labelled C

A horizontal (flat) section of the graph represents constant speed.

(b)(iii) Point between 0–15 s or 45–60 s labelled S

An upward-sloping section of the graph represents increasing speed (acceleration).

(c) High pitch; large amplitude

Pitch corresponds to frequency — high frequency gives high pitch.
Amplitude corresponds to loudness — a loud sound has a large amplitude.

(d) Increased kinetic energy of molecules; more frequent collisions with tyre wall

As temperature rises, air molecules gain kinetic energy and move faster.
This causes more frequent, more forceful collisions with the tyre’s inner walls, increasing pressure.

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