Question 1
Most-appropriate topic code (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B15.4 — Sexual reproduction in humans (Parts (a)–(d))
▶️ Answer/Explanation
(a) female gametes released: E; fertilisation: A; implantation: D; meiosis: E
The ovary (E) is where egg cells are produced and released, and where meiosis occurs during their formation.
The oviduct/fallopian tube (A) is the usual site of fertilisation.
The uterus (D) is where the fertilised egg implants into the lining.
(b) sperm
The male gamete in humans is called the sperm (spermatozoon).
It is produced in the testes and is adapted for motility to reach the egg cell.
(c)
Sperm are small and produced in millions so that a few reach and fertilise the much larger, single egg cell.
Sperm are motile (swim using a flagellum) while the egg cell is non-motile, relying on cilia in the oviduct for movement.
(d) energy; jelly
The egg cell contains energy stores (cytoplasm/yolk reserves) to nourish the early embryo before implantation.
It also has a jelly coating (zona pellucida) that hardens/changes after fertilisation to prevent entry of further sperm (polyspermy).
Question 2
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C11.3 — Fuels (Parts (a), (b))
• Topic C11.1 — Formulas and terminology (Part (c))
• Topic C6.1 — Physical and chemical changes (Parts (d), (e))
▶️ Answer/Explanation
(a)(i) fractions have different boiling points
Each fraction contains hydrocarbons of similar chain length, and different chain lengths have different boiling points.
As vapour rises up the column it cools and each fraction condenses out at the height matching its own boiling point.
(a)(ii) X marked at the top of the column
Temperature decreases going up the fractionating column.
X should be placed at the very top, above the highest fraction outlet, since this is the coolest region.
(b)
(c) straight-chain propane structure
Propane, \(\text{C}_3\text{H}_8\), has three carbon atoms joined by single covalent bonds in a chain.
Each carbon atom is fully saturated, bonded to enough hydrogen atoms to give four bonds in total.
(d) \(2\text{C}_4\text{H}_{10} + 13\text{O}_2 \rightarrow 8\text{CO}_2 + 10\text{H}_2\text{O}\)
Carbon and hydrogen atoms are balanced first, giving 4 \(\text{CO}_2\) and 5 \(\text{H}_2\text{O}\) per butane molecule.
This requires \(6.5\,\text{O}_2\) per butane molecule, so all coefficients are doubled to give whole numbers.
(e) a chemical change forms a new substance
In a chemical change (like burning butane) new substances with different properties are formed, and the change is usually not easily reversed.
In a physical change, no new substance is made — only the state or appearance changes, and it is usually reversible.
Question 3
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.4 — Density (Part (a))
• Topic P1.5.1 — Effects of forces (Part (b)(i))
• Topic P1.6.4 — Power (Part (b)(ii))
• Topic P4.2.5 — Electrical energy and electrical power (Part (b)(iii))
▶️ Answer/Explanation
(a)(i) displacement method
Submerge the graphite fully in a measuring cylinder partly filled with water.
The volume of water displaced (rise in water level) equals the volume of the graphite.
(a)(ii) 2.2 g/cm³
Density is calculated using \(\rho = \dfrac{m}{V}\).
\(\rho = \dfrac{33}{15} = 2.2 \, \text{g/cm}^3\).
(b)(i) reduces friction, increasing useful energy transfer
Lubricants reduce the friction between moving parts of the machine.
This means less heat energy is wasted, so a greater proportion of the input energy is transferred to useful kinetic energy.
(b)(ii) 75%
Efficiency is calculated using \(\text{efficiency} = \dfrac{\text{useful output energy}}{\text{total input energy}} \times 100\%\).
\(\text{efficiency} = \dfrac{900}{1200} \times 100\% = 75\%\).
(b)(iii) 450 W
Electrical power is calculated using \(P = I \times V\).
\(P = 25 \times 18 = 450 \, \text{W}\).
Question 4
He repeats this investigation, changing the temperature of the water each time.
The number of oxygen bubbles produced per minute is equivalent to the rate of photosynthesis.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B6.1 — Photosynthesis (Parts (a), (d))
• Topic B5 — Enzymes (Part (b))
• Topic B8.4 — Translocation (Part (c)(i))
• Topic B4 — Biological molecules (Part (c)(ii))
▶️ Answer/Explanation
(a) 30 °C
The highest bubble count in the table (19 bubbles per minute) occurs at 30 °C.
This indicates the maximum measured rate of photosynthesis in this experiment.
(b)(i) rising temperature increases enzyme activity up to this range
As temperature increases, particles gain more kinetic energy and move faster.
This increases the frequency of successful collisions between enzyme and substrate.
More enzyme-substrate complexes form per second, so the rate of photosynthesis (bubble count) increases.
(b)(ii) 40 °C
At 40 °C, no bubbles are produced, meaning photosynthesis has stopped completely.
This shows all the enzymes controlling photosynthesis have been denatured and can no longer function.
(c)(i) sucrose transported through the phloem by translocation
Glucose is converted to sucrose, a more soluble and stable form for transport.
Sucrose is carried in the phloem tissue from sources (e.g. leaves) to sinks (e.g. roots, fruits) by translocation.
(c)(ii) starch
Glucose molecules are joined together to form starch, an insoluble polysaccharide.
Being insoluble, starch does not affect the water potential of cells, making it ideal for storage.
(d) light energy \(\rightarrow\) chemical energy
Chlorophyll absorbs light energy during photosynthesis.
This light energy is transferred into chemical energy, stored in the bonds of glucose molecules.
Question 5
\(\text{H}^+\)
\(\text{H}_2\text{O}\)
\(\text{SO}_4^{2-}\)
\(\text{OH}^-\)
Describe how impure copper is purified by electrolysis.
Include ionic half-equations in your answer.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C4.1 — Electrolysis (Parts (a), (b), (c))
• Topic C6.3 — Redox (Part (d))
▶️ Answer/Explanation
(a) \(\text{Cu}^{2+}\) (or \(\text{H}^+\))
The cathode is the negative electrode, so it attracts positively charged ions.
From the list, \(\text{Cu}^{2+}\) and \(\text{H}^+\) are cations and are attracted to it.
(b) contains ions that are free to move
Aqueous copper(II) sulfate contains free-moving ions such as \(\text{Cu}^{2+}\) and \(\text{SO}_4^{2-}\).
These mobile charged particles act as charge carriers, allowing the solution to conduct electricity.
(c)(i) anode
In electrolysis, the positive electrode is always called the anode.
Oxidation occurs at the anode, and negative ions (anions) are attracted to it.
(c)(ii) impure anode dissolves, pure copper deposits at cathode
Impure copper is used as the anode and a strip of pure copper as the cathode, in copper(II) sulfate solution.
At the anode, copper atoms lose electrons and dissolve into solution: \(\text{Cu} \rightarrow \text{Cu}^{2+} + 2\text{e}^-\).
At the cathode, \(\text{Cu}^{2+}\) ions gain electrons and deposit as pure copper: \(\text{Cu}^{2+} + 2\text{e}^- \rightarrow \text{Cu}\).
Insoluble impurities fall to the bottom as anode sludge.
(d) reduction
The \(\text{Al}^{3+}\) ion is gaining electrons to form \(\text{Al}\) atoms.
Reduction is defined as the gain of electrons, so this half-equation represents reduction.
Question 6
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.2 — Motion (Parts (a), (b))
• Topic P1.6.1 — Energy (Part (c))
• Topic P2.2.2 — Melting, boiling and evaporation (Part (d))
▶️ Answer/Explanation
(a) velocity has a direction, speed does not
Speed is a scalar quantity, measuring only how fast an object moves.
Velocity is a vector quantity, so it also specifies the direction of motion.
(b) accelerates, then moves at constant speed
The cheetah initially accelerates, shown by the steep, rising part of the graph.
The rate of acceleration decreases over time (the curve becomes less steep).
Eventually the cheetah reaches a constant maximum speed, shown by the flat, horizontal part of the graph (zero acceleration).
(c) 18 900 J
Kinetic energy is calculated using \(KE = \dfrac{1}{2}mv^2\).
\(KE = \dfrac{1}{2} \times 42 \times 30^2 = \dfrac{1}{2} \times 42 \times 900 = 18\,900 \, \text{J}\).
(d)(i) evaporation occurs at any temperature, boiling only at the boiling point
Evaporation happens only at the surface of a liquid and can occur at any temperature.
Boiling happens throughout the liquid and only occurs at the liquid’s specific boiling point.
(d)(ii) increase temperature; increase surface area (or increase air movement)
Increasing the temperature of the water gives particles more kinetic energy, so more escape the surface.
Increasing the surface area of the puddle (spreading the water out) exposes more particles to the air, increasing evaporation.
Increasing air movement (draught) over the puddle also removes water vapour faster, maintaining a low concentration of vapour above the surface.
Question 7
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B13.2 — Hormones (Part (a))
• Topic B13.1 — Coordination and response (Parts (b), (d))
• Topic B13.3 — Homeostasis (Part (c))
▶️ Answer/Explanation
(a)(i) 65 beats per minute
Before the injection (before 1 minute), the graph shows a steady pulse rate of 65 beats per minute.
(a)(ii) sharp/steep increase
Immediately after the injection, pulse rate rises sharply.
It increases from 65 to about 98 beats per minute, a rise of roughly 33 beats per minute, before gradually falling back down.
(b)(i) pupils dilate (widen)
Adrenaline causes the pupils in the eye to widen (dilate), improving vision in a “fight or flight” response.
(b)(ii) optic nerve
The optic nerve carries electrical impulses from the retina of the eye to the brain for processing.
(c)(i) insulin
Insulin is the hormone that lowers blood glucose concentration.
(c)(ii) pancreas
Insulin is produced and secreted by the pancreas.
(c)(iii) liver
Excess glucose is converted to glycogen and stored mainly in the liver (also in muscles).
(d) hormonal actions are slower and longer-lasting
Hormonal responses act more slowly than nervous responses, since hormones travel in the blood rather than as fast electrical impulses.
Hormonal effects also tend to last longer than the brief, short-lived effects of nervous impulses.
Question 8
He uses the same volume of hydrochloric acid and the same mass of magnesium.
This time he increases the temperature of the hydrochloric acid.
All of the magnesium reacts with the acid.
On Fig. 8.3, sketch the shape of the graph you would expect this time.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C1.1 — Solids, liquids and gases (Parts (a), (b))
• Topic C6.2 — Rate of reaction (Parts (c), (d))
• Topic C2.4 — Ions and ionic bonds (Part (e))
▶️ Answer/Explanation
(a) arrangement becomes random; ions move around each other
On melting, the regular, ordered arrangement of magnesium ions becomes random/irregular.
The ions change from vibrating about fixed positions to moving freely around each other.
(b) widely spaced, randomly arranged particles
At 1800 °C magnesium is above its boiling point, so it exists as a gas.
The box should show particles drawn far apart and randomly arranged, not touching each other.
(c)(i) 48 cm³
Reading the graph at \(t = 40\,\text{s}\) gives a volume of hydrogen gas of \(48\,\text{cm}^3\).
(c)(ii) acid concentration and magnesium surface area are highest at the start
At the start, the acid is at its most concentrated and the magnesium ribbon has its full surface area exposed.
This gives the highest frequency of collisions between particles, so the reaction proceeds fastest.
(c)(iii) steeper initial slope, same final volume
A higher acid temperature gives particles more kinetic energy, increasing the frequency and energy of collisions.
The new graph should rise more steeply at first, reaching completion sooner, but should still level off at \(58\,\text{cm}^3\) since the same amounts of reactants are used.
(d) more particles per unit volume increases collision frequency
A more concentrated acid has more acid particles in the same volume.
This increases the frequency of collisions between acid and magnesium particles, increasing the number of successful collisions per second and so the rate of reaction.
(e) \(\text{MgCl}_2\)
\(\text{Mg}^{2+}\) has a charge of \(+2\), and \(\text{Cl}^-\) has a charge of \(-1\).
Two \(\text{Cl}^-\) ions are needed to balance the charge of one \(\text{Mg}^{2+}\) ion, giving the formula \(\text{MgCl}_2\).
Question 9
Calculate the charge flowing through the LDR in 1 minute when 3 glass slides are used.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P4.2.4 — Resistance (Part (a)(i))
• Topic P4.2.1 — Electrical charge (Part (a)(ii))
• Topic P3.1 — General properties of waves (Part (b)(i), (ii))
• Topic P3.3 — Electromagnetic spectrum (Part (b)(iii))
▶️ Answer/Explanation
(a)(i) resistance increases as light intensity decreases
As more glass slides are added, less light reaches the LDR, so its resistance increases.
The increase is not linear — resistance rises steeply at first, then more gradually as further slides are added.
(a)(ii) 0.0012 C
From the graph, resistance at 3 slides is \(R \approx 700\,\text{k}\Omega = 700\,000\,\Omega\).
Current: \(I = \dfrac{V}{R} = \dfrac{14}{700\,000} = 2 \times 10^{-5}\,\text{A}\).
Charge: \(Q = I \times t = 2\times10^{-5} \times 60 = 0.0012\,\text{C}\).
(b)(i) number of waves passing a point per second
Frequency is the number of complete wave oscillations (cycles) passing a fixed point in one second, measured in hertz (Hz).
(b)(ii) \(6.0 \times 10^{-7}\,\text{m}\)
The wave equation \(c = f\lambda\) is rearranged to \(\lambda = \dfrac{c}{f}\), using \(c = 3\times10^8\,\text{m/s}\).
\(\lambda = \dfrac{3\times10^8}{5.0\times10^{14}} = 6.0\times10^{-7}\,\text{m}\).
(b)(iii) ultraviolet (or X-rays / gamma rays)
Ultraviolet radiation has a higher frequency than visible light in the electromagnetic spectrum.
Question 10
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B9.4 — Blood (Part (a)(i), (ii))
• Topic B17.1 — Variation (Part (a)(iii))
• Topic B16.1 — Chromosomes and genes (Part (a)(iv))
• Topic B17.2 — Selection (Part (b))
• Topic B15.2 — Sexual reproduction (Part (c))
▶️ Answer/Explanation
(a)(i) AB
The bar chart shows blood groups A, B and O labelled; the fourth, unlabelled bar represents blood group AB.
(a)(ii) O
Blood group O has the tallest bar (highest frequency, 16 patients), making it the most common group shown.
(a)(iii) limited, distinct phenotypes with no intermediates
There are only a small number of distinct blood group categories (A, B, AB, O).
There are no intermediate values between these categories, which is characteristic of discontinuous variation.
(a)(iv) genes/alleles
Blood group is determined entirely by the genes/alleles a person inherits from their parents, with no environmental influence.
(b)
Both processes pass alleles to offspring and occur over many generations.
Only selective breeding is deliberately used to improve domesticated animals; only natural selection keeps features best suited to the (natural) environment.
(c) takes time/energy to find a mate; can produce unfavourable gene combinations
Sexual reproduction requires an organism to spend time and energy finding a mate, which is not needed in asexual reproduction.
It can also produce offspring with unfavourable combinations of alleles, which may reduce their chance of survival.
Question 11
- 450°C
- atmospheric pressure
- a catalyst.
Use ideas about:
- the percentage of sulfur trioxide made
- the rate of reaction.
Complete the labels on Fig. 11.1.
Choose the labels from the list.
energy taken in
products
reactants
reactants have less energy
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C6.2 — Rate of reaction (Parts (a), (b))
• Topic C5.1 — Exothermic and endothermic reactions (Part (c))
• Topic C3.3 — The mole and the Avogadro constant (Part (d))
▶️ Answer/Explanation
(a) sulfur + oxygen
In stage 1, sulfur is burned in oxygen (from the air) to form sulfur dioxide.
(b)(i) vanadium(V) oxide
Vanadium(V) oxide (\(\text{V}_2\text{O}_5\)) is the catalyst used to speed up stage 2 of the Contact process.
(b)(ii) — question removed from paper (no mark scheme content)
For reference, the catalyst increases the rate of reaction without affecting the equilibrium percentage yield, while 450°C is a compromise temperature giving an acceptable rate without lowering the equilibrium yield too much (the forward reaction is exothermic).
(c) reactants (top), energy given out (arrow), products (bottom)
In an exothermic reaction, the reactants start at a higher energy level than the products.
The vertical drop between them, labelled “energy given out,” represents energy released to the surroundings.
(d) 60 dm³
Moles of \(\text{SO}_3\): \(n = \dfrac{200}{80} = 2.5\,\text{mol}\).
Volume at r.t.p.: \(V = 2.5 \times 24 = 60\,\text{dm}^3\).
Question 12
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.6.2 — Work (Part (a))
• Topic P1.5.3 — Centre of gravity (Part (b))
• Topic P4.5.4 — Force on a current-carrying conductor (Part (c))
• Topic P5.2.2 — The three types of nuclear emission (Part (d))
▶️ Answer/Explanation
(a) 125 kg
Work done against gravity is \(W = mgh\), so \(m = \dfrac{W}{gh}\).
\(m = \dfrac{2750}{10 \times 2.2} = \dfrac{2750}{22} = 125\,\text{kg}\).
(b) lower centre of mass
Lowering the crate lowers the overall centre of mass of the forklift truck system.
A lower centre of mass increases stability, since a larger tilt is needed before the line of action of weight moves outside the base, reducing the tendency to topple.
(c)(i) X: force upwards; Z: force downwards
Using Fleming’s left-hand rule with current and the magnetic field direction shown, the force on X acts upwards and the force on Z acts downwards.
These opposite forces on either side of the coil create the turning effect (torque) that rotates the motor.
(c)(ii) current is parallel to the magnetic field at Y
A force is only produced when current flows at an angle to the magnetic field.
At point Y, the current direction is parallel to the field lines, so no force acts on it.
(d)(i) it is a charged particle
A β-particle is a fast-moving electron and therefore carries a (negative) electric charge.
A charged particle moving through a magnetic field experiences a force (the motor effect), which deflects its path.
(d)(ii) opposite direction, smaller deflection
An α-particle carries a positive charge, opposite to the negative charge of a β-particle, so it deflects in the opposite direction.
Because an α-particle has a much greater mass than a β-particle, it deflects less for the same force.