Question 1
that strengthens the cell …………………..
where photosynthesis occurs …………………..
where genetic material is stored. …………………..
This is because ……………………………… enters the plant cell through the ……………………………… membrane.
This process is called ……………………………… .
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B2.1 — Cell structure (Part (a)(i), (a)(ii))
• Topic B2.2 — Size of specimens (Part (b)(i))
• Topic B3.2 — Osmosis (Part (b)(ii))
▶️ Answer/Explanation
(a)(i) D ; B ; E
D is the cell wall, which gives the plant cell mechanical strength and rigidity.
B is a chloroplast, the organelle where photosynthesis takes place.
E is the nucleus, which stores the cell’s genetic material (DNA).
(a)(ii) Any two from: A, E, F
A (mitochondria), E (nucleus) and F (cell membrane) are organelles found in both plant and animal cells.
By contrast, the cell wall (D), chloroplast (B) and large permanent vacuole (C) are structures unique to plant cells.
(b)(i) Image size; magnification
The actual size of a specimen is found using \( \text{actual size} = \dfrac{\text{image size}}{\text{magnification}} \).
So the two values needed are the measured size of the cell in the image and the magnification of that image.
(b)(ii) vacuole; water; partially permeable; osmosis
The plant cell is placed in pure water, which has a higher water potential than the cell contents.
Water moves into the cell, through the partially permeable cell membrane, causing the vacuole to enlarge and the cell to swell.
This net movement of water molecules down a water potential gradient through a partially permeable membrane is called osmosis.
Question 2
chromatography, combustion, cracking, electroplating, fermentation, filtration, oxidation, polymerisation, rusting
(i) break down large hydrocarbon alkane molecules into smaller alkene and smaller alkane molecules.
(ii) make ethanol from glucose.
(iii) make long chain molecules from small monomer units.
(iv) separate a mixture of dyes.
(v) cover a metal with a layer of copper.
acid …………………………………………………..
base …………………………………………………..
left, metallic, non-metallic, right
Going from ……………………… to ………………………, the elements change from ……………………… to ……………………… .
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C11.5 — Alkenes (Part (a)(i) — cracking)
• Topic C11.6 — Alcohols (Part (a)(ii) — fermentation)
• Topic C11.7 — Polymers (Part (a)(iii) — polymerisation)
• Topic C12.3 — Chromatography (Part (a)(iv))
• Topic C4.1 — Electrolysis (Part (a)(v) — electroplating)
• Topic C7.1 — Characteristic properties of acids and bases (Part (b))
• Topic C2.2 — Atomic structure and the Periodic Table (Part (c))
• Topic C8.1 — Arrangement of elements (Part (d))
▶️ Answer/Explanation
(a)(i) Cracking
Cracking uses heat and a catalyst to break the carbon–carbon bonds in large alkane molecules.
This produces a mixture of smaller, more useful alkane and alkene molecules.
(a)(ii) Fermentation
During fermentation, enzymes in yeast convert glucose into ethanol and carbon dioxide.
The overall word equation is glucose \( \rightarrow \) ethanol + carbon dioxide.
(a)(iii) Polymerisation
Polymerisation is the joining together of many small monomer molecules.
This forms one very long-chain molecule called a polymer.
(a)(iv) Chromatography
In paper chromatography, the dyes dissolve in a solvent and move up the paper at different rates.
This separates the mixture into its individual coloured components.
(a)(v) Electroplating
Electroplating uses electrolysis with a copper anode and the object to be plated as the cathode.
Copper ions in the electrolyte gain electrons at the cathode and are deposited as a thin layer of copper metal.
(b) Acid: (dilute) hydrochloric acid; Base: (aqueous) sodium hydroxide
Sodium chloride is formed by the neutralisation of an acid by a base.
\( \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} \)
Hydrochloric acid reacts with sodium hydroxide to give salt and water only.
(c) Sodium atom: 2,8,1 ; Sodium ion: 2,8
A neutral sodium atom has 11 electrons arranged in shells as \(2,8,1\).
To form \( \text{Na}^+ \), the atom loses the single outer-shell electron.
This leaves the ion with 10 electrons arranged as \(2,8\), the same stable configuration as neon.
(d) left → right ; metallic → non-metallic
Going from left to right across Period 3, the elements change from metallic (e.g. sodium, magnesium) to non-metallic (e.g. sulfur, chlorine).
This trend reflects the increasing number of outer-shell electrons across the period.
Question 3
copper, ice, iron, plastic, wood
Each material is a block with the dimensions shown in Fig. 3.1.
density = …………………………… units …………
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C9.1 — Properties of metals (Parts (a)(i) and (a)(ii) — thermal and electrical conductivity)
• Topic P4.1 — Simple phenomena of magnetism (Part (a)(iii))
• Topic P1.4 — Density (Part (b))
• Topic C1.1 — Solids, liquids and gases (Part (c) — particle arrangement)
• Topic P4.2.1 — Electrical charge (Part (d) — electrostatic charging by friction)
▶️ Answer/Explanation
(a)(i) Copper and iron
Copper and iron are metals, and metals are generally good conductors of thermal energy.
Ice, plastic and wood are poor thermal conductors (insulators).
(a)(ii) Copper and iron
Metals such as copper and iron contain free (delocalised) electrons that can move and carry electric charge.
Ice, plastic and wood do not have freely moving charged particles, so they do not conduct electricity.
(a)(iii) Iron
Iron is a magnetic material, so it is attracted to a magnet.
Copper, ice, plastic and wood are non-magnetic materials.
(b) 0.65 g/cm³
Volume of the block: \( V = 3 \times 4 \times 5 = 60 \, \text{cm}^3 \).
Density: \( \rho = \dfrac{m}{V} = \dfrac{39}{60} = 0.65 \, \text{g/cm}^3 \).
The unit follows from mass in grams divided by volume in cm³, giving g/cm³.
(c)
In diagram A (ice), the particles are arranged in a fixed, regular pattern, typical of a solid.
In diagram B (water), the particles are arranged in a more random, irregular pattern, typical of a liquid.
This regular versus irregular arrangement is what distinguishes the solid (ice) from the liquid (water).
(d) Electrons
Rubbing the plastic block with a cloth causes friction between the two surfaces.
This friction transfers electrons from one material to the other, leaving one object with an overall negative charge and the other with an overall positive charge.
Question 4
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B13.1 — Coordination and response (Parts (a)(i)–(iii), (b)(i)–(ii))
• Topic B1.1 — Characteristics of living organisms (Part (a)(iv))
▶️ Answer/Explanation
(a)(i) Relay neurone
Y is located inside the spinal cord, connecting the incoming sensory pathway to the outgoing motor pathway.
This connecting neurone within the central nervous system is called a relay neurone.
(a)(ii) Arrow at X points towards the spinal cord; arrow at Z points towards the muscle
Impulses travel from the receptor along the sensory neurone (X) into the spinal cord.
They then travel out along the motor neurone (Z) to the effector (muscle), so the arrow at Z points away from the spinal cord towards the muscle.
(a)(iii) Stimulus: (change in) temperature; Effector: muscle (in the arm)
The stimulus is the change in temperature detected when the hand touches the very hot object.
The effector is the muscle in the arm, which contracts to pull the hand away.
(a)(iv) Sensitivity; Movement
Sensitivity is shown by the receptor detecting the change in temperature (the stimulus).
Movement is shown by the muscle (effector) contracting to move the hand away from the hot object.
(b)(i) Brain
The central nervous system (CNS) consists of the brain and the spinal cord.
Since the spinal cord is already given, the other part of the CNS is the brain.
(b)(ii) Peripheral nervous system
In addition to the central nervous system, humans have a peripheral nervous system.
This consists of all the nerves that lie outside the brain and spinal cord, connecting the CNS to receptors and effectors.
Question 5
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C10.2 — Air quality and climate (Parts (a), (c), (e) — composition of clean air, pollutant sources, greenhouse gases)
• Topic C8.5 — Noble gases (Part (b) — unreactivity and electronic structure of argon)
• Topic C6.2 — Rate of reaction (Part (d)(i) — effect of concentration on rate)
• Topic C7.1 — Characteristic properties of acids and bases (Parts (d)(ii)–(iii) — neutralisation)
▶️ Answer/Explanation
(a) Nitrogen 78%
Clean, dry air is composed of approximately 78% nitrogen by volume.
The remainder is mostly oxygen, with small amounts of noble gases and carbon dioxide.
(b)(i) Argon has a full outer shell of electrons
Fig. 5.1 shows the outer electron shell of argon contains 8 electrons, which is a full shell.
Because the outer shell is already full, argon atoms have no tendency to gain, lose or share electrons, making the element unreactive.
(b)(ii) Lamps (e.g. filament light bulbs)
Argon is used to fill light bulbs because it is unreactive and so does not react with the hot filament.
This prevents the filament from burning out (oxidising) and extends the life of the lamp.
(c)(i) Combustion of fossil fuels
Sulfur dioxide is released when fossil fuels containing sulfur compounds are burned.
Common sources include power stations and industrial processes that burn coal or oil.
(c)(ii) Oxides of nitrogen (or carbon monoxide)
Oxides of nitrogen are produced in car engines from the reaction between nitrogen and oxygen at high temperature.
Like sulfur dioxide, they are air pollutants and contribute to problems such as acid rain.
(d)(i) Acid rain is (very) dilute
Acid rain has a very low concentration of acid compared with typical laboratory acids.
A lower concentration of acid particles means fewer collisions per second with limestone particles, so the reaction proceeds slowly.
(d)(ii) Limestone / calcium carbonate (lime)
Farmers add lime, such as calcium carbonate or calcium oxide, to acidic soils.
This raises the pH of the soil to a level more suitable for crop growth.
(d)(iii) Neutralisation
The basic calcium compound reacts with the excess acid present in the soil.
An acid reacting with a base in this way is called a neutralisation reaction.
(e) Carbon dioxide (or methane)
Carbon dioxide and methane are greenhouse gases that absorb and re-emit thermal energy radiated from the Earth.
Rising levels of these gases in the atmosphere are linked to increased global warming and climate change.
Question 6
greatest penetration ………………………………
least penetration ………………………………
Calculate the mass of plutonium-239 remaining after 96 000 years.
plutonium-239 → …………………………… + ……………………………
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.6.3 — Energy resources (Parts (a)(i), (ii), (iv))
• Topic P1.6.1 — Energy (Part (a)(iii) — chemical energy store)
• Topic P3.3 — Electromagnetic spectrum (Part (b)(i)–(ii))
• Topic P5.2.2 — The three types of nuclear emission (Part (b)(iii)–(iv))
• Topic P5.2.4 — Half-life (Part (c)(i))
• Topic P5.2.3 — Radioactive decay (Part (c)(ii))
▶️ Answer/Explanation
(a)(i) Coal
Coal is a fossil fuel, so burning it to generate electricity releases carbon dioxide.
Geothermal, hydroelectric, nuclear and solar do not involve combustion, so they do not directly produce carbon dioxide.
(a)(ii) Tides / wind / waves
Tidal, wind and wave power are all renewable energy resources not included in the original list.
These resources do not run out and have a much lower environmental impact than fossil fuels.
(a)(iii) Chemical (potential) energy
Coal is a fuel, and fuels store energy in their chemical bonds.
This chemical energy is released as thermal energy when the coal is burned.
(a)(iv) Advantage: no nuclear waste / no risk of nuclear accidents; Disadvantage: only available during the day (depends on sunlight)
Solar power does not produce hazardous radioactive waste, unlike nuclear power.
However, solar power can only generate electricity when there is sufficient sunlight, so it is unreliable at night or in poor weather, whereas nuclear power can generate continuously.
(b)(i) γ-rays
Alpha and beta emissions are streams of particles, not waves.
Gamma rays are electromagnetic waves, so they form part of the electromagnetic spectrum.
(b)(ii) Left-hand box (immediately to the left of X-rays)
The spectrum in Fig. 6.1 is arranged in order of increasing frequency from right to left.
Gamma rays have a higher frequency than X-rays, so they belong in the box to the left of X-rays.
(b)(iii) Greatest penetration: γ-rays; then β-particles; least penetration: α-particles
Gamma rays are the most penetrating because they are uncharged electromagnetic waves that interact weakly with matter.
Alpha particles are large and heavily charged, so they are stopped easily and are the least penetrating; beta particles lie in between.
(b)(iv) A helium nucleus (2 protons and 2 neutrons)
An α-particle consists of 2 protons and 2 neutrons bound together.
This is identical in composition to the nucleus of a helium atom, so it carries a charge of +2.
(c)(i) 6.25 g
Number of half-lives elapsed: \( \dfrac{96000}{24000} = 4 \) half-lives.
Remaining mass: \( 100 \times \left(\dfrac{1}{2}\right)^4 = 100 \times \dfrac{1}{16} = 6.25 \, \text{g} \).
(c)(ii) Plutonium-239 → uranium-235 + α (particle)
In α-decay, the unstable plutonium-239 nucleus emits an alpha particle.
This reduces the proton number by 2 and the nucleon number by 4, forming a uranium-235 nucleus.
Question 7
Describe how the farmer uses selective breeding to increase the number of smooth green peas.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B16.1 — Chromosomes and genes (Part (a))
• Topic B17.1 — Variation (Parts (b)(i)–(iv))
• Topic B17.2 — Selection (Parts (c) and (d))
▶️ Answer/Explanation
(a) A length of DNA that codes for a protein
A gene is a section of a chromosome made of DNA.
Each gene carries the genetic instructions needed to produce one particular protein.
(b)(i) Wrinkled yellow
Reading the bar graph, the tallest bar corresponds to wrinkled yellow peas, with a frequency of 8.
This makes wrinkled yellow the most frequent colour-and-shape combination in the sample.
(b)(ii) 3
The bar for wrinkled green peas reaches a height of 3 on the frequency axis.
So 3 of the 14 peas sampled were wrinkled and green.
(b)(iii) There are only a limited number of distinct phenotypes, with no intermediate forms
The graph shows only four distinct categories of pea (e.g. wrinkled green, smooth green, wrinkled yellow, smooth yellow).
There are no peas with phenotypes in between these categories, which is characteristic of discontinuous variation.
(b)(iv) Height (accept other valid examples, e.g. body mass, skin colour)
Human height varies continuously across a population, from short to tall.
There is a full range of intermediate values rather than a small number of fixed categories, making it an example of continuous variation.
(c) Any two of the following steps
The farmer selects pea plants that produce smooth, green peas.
These selected plants are crossed (bred) with each other.
The farmer then examines the offspring and again selects those showing the smooth green characteristic.
This selection and breeding process is repeated over many generations to increase the proportion of smooth green peas.
(d) Natural selection
Natural selection favours individuals whose characteristics make them better suited to survive and reproduce in their environment.
Over many generations, this leads to a population that is well adapted to its environment, without any human intervention.
Question 8
\( \text{CH}_4 + \text{……} \text{O}_2 \rightarrow \text{CO}_2 + \text{……} \text{H}_2\text{O} \)
Explain how the symbol equation shows that methane is oxidised.
Describe one adverse effect of carbon monoxide on the health of humans.
…………………………… are pure substances consisting only of atoms, all of which have the same number of protons in their nuclei.
…………………………… are chemical substances composed of two or more …………………………… held together by chemical bonds.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C11.3 — Fuels (Part (a)(i) — methane as natural gas)
• Topic C2.5 — Simple molecules and covalent bonds (Parts (a)(ii)–(iii))
• Topic C3.1 — Formulas (Part (b)(i) — balancing the symbol equation)
• Topic C6.3 — Redox (Part (b)(ii) — oxidation in terms of gain of oxygen)
• Topic C10.2 — Air quality and climate (Part (b)(iii) — carbon monoxide as a toxic pollutant)
• Topic C2.1 — Elements, compounds and mixtures (Part (c))
▶️ Answer/Explanation
(a)(i) Natural gas
Methane is the main hydrocarbon found in natural gas.
Natural gas is extracted and burned as a fossil fuel.
(a)(ii) Covalent (bonding)
In methane, the carbon and hydrogen atoms are joined by shared pairs of electrons.
This type of bonding, formed between non-metal atoms, is called covalent bonding.
(a)(iii) One shared pair of electrons between carbon and each hydrogen atom
Carbon has 4 outer-shell electrons and forms 4 single covalent bonds, one to each hydrogen atom.
Each bond is shown as a shared pair of electrons (one dot and one cross) between C and an H, giving four shared pairs in total.
(b)(i) \( \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \)
Balancing carbon: 1 carbon atom on each side is already balanced.
Balancing hydrogen: 4 hydrogen atoms on the left need 2 \( \text{H}_2\text{O} \) on the right.
Balancing oxygen: \( \text{CO}_2 \) and \( 2\text{H}_2\text{O} \) together need 4 oxygen atoms, supplied by \( 2\text{O}_2 \).
(b)(ii) Methane gains/reacts with oxygen
In the equation, methane (\( \text{CH}_4 \)) combines with oxygen to form \( \text{CO}_2 \) and \( \text{H}_2\text{O} \).
Because oxidation can be defined as the gain of oxygen, the fact that methane reacts with and gains oxygen shows that it has been oxidised.
(b)(iii) Carbon monoxide is toxic (poisonous)
Carbon monoxide binds strongly to haemoglobin in red blood cells, in place of oxygen.
This reduces the amount of oxygen the blood can carry around the body, which can be fatal.
(c) elements ; compounds ; elements
Elements are pure substances made of only one type of atom, all with the same number of protons.
Compounds are substances formed when two or more different elements are chemically bonded together.
Carbon (one type of atom) is an element, while methane (carbon and hydrogen bonded together) is a compound.
Question 9
The audible frequency range for the penguin has a higher minimum frequency and a lower maximum frequency compared to a human.
Suggest the audible frequency range for the penguin.
Include the measurements that need to be taken.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.2 — Motion (Part (a) — speed-time graph, acceleration)
• Topic P1.7 — Pressure (Part (b)(i))
• Topic P3.3 — Electromagnetic spectrum (Part (b)(ii) — uses of infrared)
• Topic P3.4 — Sound (Parts (c) and (d))
▶️ Answer/Explanation
(a)(i) Letter A placed anywhere between t = 20 s and t = 25 s
Acceleration is given by the gradient of a speed-time graph.
The section of the graph between t = 20 s and t = 25 s is the steepest, so this is where the penguin’s acceleration is greatest.
(a)(ii) Letter M between t = 10 s and t = 20 s, speed = 1.0 m/s (or M between t = 25 s and t = 40 s, speed = 2.0 m/s)
A horizontal section of a speed-time graph represents constant speed (zero acceleration).
The graph is flat at 1.0 m/s between 10 s and 20 s, and again flat at 2.0 m/s between 25 s and 40 s, so either point is a valid answer.
(b)(i) Weight of the penguin; area of the feet in contact with the ice
Pressure is defined as \( p = \dfrac{F}{A} \), where \(F\) is the force pressing on the surface.
For the penguin, the force is its weight, and the relevant area is the total area of its feet touching the ice.
(b)(ii) TV remote controller (or intruder alarms)
Infrared radiation is used in remote controls to send signals to televisions and other devices.
It is also used in intruder alarms, which detect the infrared radiation given off by a moving person.
(c) Minimum frequency: a value between 21 Hz and 400 Hz; Maximum frequency: a value between 401 Hz and 19 999 Hz
Humans typically hear from about 20 Hz to 20 000 Hz, and the penguin can hear the 400 Hz sound made by the scientist.
Since the penguin’s range has a higher minimum and a lower maximum than a human’s, its minimum must lie above 20 Hz but at or below 400 Hz, and its maximum must lie at or above 400 Hz but below 20 000 Hz.
(d) Make a loud noise; time how long it takes to travel a known (measured) distance; divide the distance by the time
The scientist measures a fixed distance between two points using a tape measure or similar.
A loud sound (e.g. a bang) is made at one point, and a stopwatch is used to time how long the sound takes to reach the other point.
The speed of sound is then calculated using \( v = \dfrac{\text{distance}}{\text{time}} \).
Question 10
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B11.1 — Gas exchange in humans (Parts (a), (b), (c))
• Topic B9.4 — Blood (Part (d))
▶️ Answer/Explanation
(a) A – trachea ; B – diaphragm
The trachea (A) is the airway that carries air from the throat down towards the lungs.
The diaphragm (B) is the sheet of muscle beneath the lungs that contracts and relaxes to help drive breathing movements.
(b)(i) 5%
Gas X (oxygen) makes up 21% of inspired air and 16% of expired air.
The difference is \( 21 – 16 = 5\% \).
(b)(ii) Test: bubble the gas through limewater; Positive result: the limewater turns cloudy
Gas Y is carbon dioxide, which is tested for using limewater (calcium hydroxide solution).
If carbon dioxide is present, the limewater turns from clear to cloudy (milky) due to the formation of insoluble calcium carbonate.
(b)(iii) (Aerobic) respiration
Gas X is oxygen, which is required by cells to carry out aerobic respiration.
During aerobic respiration, oxygen is used to break down glucose to release energy.
(c) Increased depth of breathing
As well as breathing faster during physical activity, a person also breathes more deeply.
This increases the volume of air exchanged with each breath, supplying more oxygen and removing more carbon dioxide.
(d)(i) Any two from: red blood cells; platelets; plasma
Besides white blood cells, blood contains red blood cells, platelets and plasma.
Each of these components has a different role in transport, clotting or carrying blood cells.
(d)(ii) Phagocytosis; antibody production
Some white blood cells (phagocytes) engulf and destroy pathogens by phagocytosis.
Other white blood cells (lymphocytes) produce antibodies that help to destroy or neutralise pathogens.
Question 11
Isotopes are atoms of the same …………………………… which have the same …………………………… number but a different …………………………… number.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C7.1 — Characteristic properties of acids and bases (Part (a)(i) — pH)
• Topic C9.4 — Reactivity series (Parts (a)(ii)–(iii))
• Topic C3.1 — Formulas (Part (a)(iv))
• Topic C9.3 — Alloys and their properties (Part (b))
• Topic C2.3 — Isotopes (Part (c)(i))
• Topic C2.2 — Atomic structure and the Periodic Table (Parts (c)(ii)–(iii))
• Topic C9.6 — Extraction of metals (Part (d))
▶️ Answer/Explanation
(a)(i) Any value in the range 1 to 6
Sulfuric acid is an acid, so its pH must be below 7.
Any value from 1 up to 6 is accepted as a reasonable estimate for a dilute acid.
(a)(ii) Magnesium
Magnesium is higher in the reactivity series than zinc and copper.
The more reactive a metal is, the faster it reacts with dilute acid, producing gas bubbles more quickly, so magnesium reacts fastest.
(a)(iii) Hydrogen
When a reactive metal reacts with a dilute acid, it displaces hydrogen from the acid.
The gas produced is therefore hydrogen gas, which can be confirmed using a lighted splint (a “pop” sound).
(a)(iv) \( \text{H}_2\text{SO}_4 \)
The molecule contains 2 hydrogen atoms, 1 sulfur atom and 4 oxygen atoms.
Writing these numbers as subscripts gives the formula \( \text{H}_2\text{SO}_4 \).
(b)(i) A mixture of a metal with one or more other elements
An alloy is formed by combining a metal with other elements, often other metals.
Brass, for example, is an alloy made by mixing copper with zinc.
(b)(ii) 82.5 g
Zinc makes up 33% of the 250 g sample.
Mass of zinc \( = \dfrac{33}{100} \times 250 = 82.5 \, \text{g} \) (≈ 83 g to 2 significant figures).
(c)(i) Element; proton (number); nucleon (number)
Isotopes are atoms of the same element, so they have the same proton number.
However, they have different numbers of neutrons, giving them different nucleon (mass) numbers.
(c)(ii) 30
In a neutral atom, the number of electrons equals the number of protons.
Since the proton number is given as 30, this zinc atom has 30 electrons.
(c)(iii) 34
The number of neutrons is found by subtracting the proton number from the nucleon number.
Number of neutrons \( = 64 – 30 = 34 \).
(d) A finite resource is something useful that is non-renewable and will eventually run out
Zinc ore takes an extremely long time to form naturally and cannot be replaced once it has been extracted and used.
Because the supply cannot be replenished within a useful timescale, it will eventually be used up completely.
Question 12
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P4.2.2 — Electric current (Part (a))
• Topic P1.6.3 — Energy transfers (Part (b))
• Topic P3.2.2 — Refraction of light (Part (c))
• Topic P3.1 — General Properties of Waves (Part (d))
▶️ Answer/Explanation
(a) current; volts; current
A flow of electrons is a current.
e.m.f. is measured in volts (V).
Resistance \(R = \dfrac{V}{I}\), so it is voltage divided by current.
(b) 360 J
Energy is conserved, so input energy = useful output + wasted energy.
Wasted energy = \(400 \, \text{J} – 40 \, \text{J} = 360 \, \text{J}\).
Most of the electrical energy supplied to a filament lamp is wasted as heat.
(c)(i) Ray bends towards the normal on entering the glass
Light slows down as it enters the denser glass block.
This causes the ray to bend towards the normal line at the point of entry.
The refracted ray then continues in a straight line through the glass.
(c)(ii) i and r labelled correctly
The angle of incidence, \(i\), is measured between the incident ray and the normal.
The angle of refraction, \(r\), is measured between the refracted ray and the normal.
Since the ray bends towards the normal, \(r\) is smaller than \(i\).
(d)(i) One wavelength shown correctly
A wavelength, \(\lambda\), is the distance from one point on a wave to the identical point on the next wave.
It is typically measured from one peak to the next peak (or one trough to the next trough).
The double-headed arrow labelled W should span exactly one full wave cycle.
(d)(ii) Amplitude shown correctly
Amplitude is the maximum displacement of a point on the wave from its undisturbed (rest) position.
It is measured vertically from the midline to the peak (or trough), not peak-to-trough.
The double-headed arrow labelled A should be drawn from the centre line up to the maximum point.