Question 1
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B15.4 — Sexual reproduction in humans (Parts (a), (b), (c))
• Topic B2.1 — Cell structure (Part (d))
▶️ Answer/Explanation
(a) organism
Reproduction is a characteristic of all living organisms.
It is defined as the process by which organisms produce new individuals of the same species.
This ensures the continuation of the species over generations.
(b)
A links to “produces sperm” — this is the testis.
B links to “secretes fluid for sperm to swim in” — this is a gland such as the seminal vesicle.
C links to “carries semen and urine out of the body” — this is the urethra.
(c) nucleus
The head of the sperm cell contains the nucleus.
The nucleus houses the chromosomes, which carry the genetic material (DNA).
This genetic material is passed on to the offspring during fertilisation.
(d) chloroplast; cell wall; (permanent) vacuole (any two)
Plant cells have a rigid cellulose cell wall that animal cells lack.
Plant cells also contain chloroplasts, used for photosynthesis, and a large permanent vacuole for storage and support.
Animal cells do not possess any of these three structures.
Question 2
For example, when molten lead bromide is electrolysed, lead and bromine are made.
Complete the sentences about the electrolysis of lead bromide using words from the list.
Each word may be used once, more than once or not at all.
The …………………………………………….. electrode is called the cathode and the …………………………………………….. electrode is called the anode.
…………………………………………….. forms at the anode and …………………………………………….. forms at the cathode.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C12.4 — Separation and purification (Part (a))
• Topic C10.1 — Water (Part (b))
• Topic C4.1 — Electrolysis (Part (c))
▶️ Answer/Explanation
(a)(i)
Chromatography separates the blue dye from black ink.
Crystallisation separates copper sulfate from aqueous copper sulfate.
Fractional distillation separates bitumen from petroleum, since it is based on different boiling points.
(a)(ii) water
In aqueous copper sulfate, water is the liquid that dissolves the solute.
Copper sulfate is the solute dissolved within it.
(a)(iii) road surfaces
Bitumen is a thick, sticky, waterproof substance obtained from fractional distillation of petroleum.
It is commonly used to surface roads.
(b) filtration – removes solid particles; chlorination – kills microbes
Filtration physically removes insoluble solid particles from the water.
Chlorination adds chlorine to kill harmful microorganisms, making the water safe to drink.
(c) electrolyte; ions; negative; positive; bromine; lead
Molten lead bromide is called the electrolyte because it contains ions free to move.
The negative electrode is the cathode, and the positive electrode is the anode.
Bromine (a non-metal) forms at the anode, and lead (a metal) forms at the cathode.
Question 3
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P3.3 — Electromagnetic spectrum (Part (a))
• Topic P1.7 — Pressure (Part (b))
• Topic P1.3 — Mass and weight (Part (c))
• Topic P3.1 — General properties of waves (Part (d))
• Topic P3.2.3 — Thin converging lens (Part (e)(i))
• Topic P1.4 — Density (Part (e)(ii))
▶️ Answer/Explanation
(a)(i) ultraviolet
Ultraviolet (UV) radiation from the Sun damages skin cells.
This damage causes the reddening and pain known as sunburn.
(a)(ii) UV placed to the right of X-rays
The electromagnetic spectrum is arranged in order of increasing frequency from radio waves to gamma rays.
Ultraviolet has a higher frequency than visible light but lower than X-rays, so it sits immediately to the right of X-rays.
(b) surface area of feet; weight of man
Pressure is calculated using the formula \( \text{pressure} = \dfrac{\text{force}}{\text{area}} \).
Here, the force is the man’s weight, and the area is the surface area of his feet in contact with the sand.
(c) \(g = 9.8 \, \text{N/kg}\)
Gravitational field strength is calculated as \( g = \dfrac{\text{weight}}{\text{mass}} \).
\( g = \dfrac{4.9}{0.50} = 9.8 \, \text{N/kg} \).
The unit can also be expressed as \(\text{N/kg}\), equivalent to \(\text{m/s}^2\).
(d)(i) wavelength = 4.0 m
The wavelength is the distance between two consecutive identical points on the wave, such as two crests.
From the graph, one complete wave cycle spans 4 m (e.g. from 1 m to 5 m).
(d)(ii) amplitude = 1.0 m
The amplitude is the maximum displacement from the undisturbed (zero) position.
From the graph, the displacement reaches a maximum of 1.0 m.
(e)(i) three rays converging at X
A convex lens refracts parallel incoming rays of light so that they converge at a single focal point.
All three rays should be drawn bending toward and meeting at point X on the paper.
(e)(ii) density = 2.5 g/cm³
Density is calculated using \( \text{density} = \dfrac{\text{mass}}{\text{volume}} \).
\( \text{density} = \dfrac{5.0}{2.0} = 2.5 \, \text{g/cm}^3 \).
Question 4
Give your answer to the nearest whole number.
Use ideas about the carbon cycle to explain why.
List three other undesirable effects of deforestation on the environment.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B19.1 — Habitat destruction (Part (a)(iii))
• Topic B18.3 — Carbon cycle (Parts (a)(ii), (b))
• Mathematical skills — Data handling (Part (a)(i))
▶️ Answer/Explanation
(a)(i) 2004 = 27000 km², 2007 = 11000 km², percentage change ≈ 59%
Reading the bar chart gives values of \(27000 \, \text{km}^2\) in 2004 and \(11000 \, \text{km}^2\) in 2007.
Percentage decrease \( = \dfrac{27000 – 11000}{27000} \times 100 = 59.3\% \).
Rounded to the nearest whole number, this is \(59\%\).
(a)(ii) increase in carbon dioxide; less photosynthesis
Between 1997 and 2004, the area cleared by deforestation increased.
Fewer trees means less photosynthesis occurring, so less carbon dioxide is removed from the atmosphere.
This causes carbon dioxide concentration in the atmosphere to increase.
(a)(iii) habitat destruction; extinction; soil erosion; flooding (any three)
Removing trees destroys habitats, which can lead to species extinction.
Without tree roots to bind the soil, soil erosion increases.
Loss of trees can also increase the risk of flooding, since less water is absorbed by roots.
(b) feeding; respiration (any two)
Animals transfer carbon by feeding, since carbon compounds pass along the food chain when animals eat plants or other animals.
Animals also transfer carbon through respiration, releasing carbon dioxide back into the atmosphere.
Question 5
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C8.3 — Group VII properties (Parts (a), (b), (d))
• Topic C2.2 — Atomic structure and the Periodic Table (Part (c))
• Topic C1.1 — Solids, liquids and gases (diffusion) (Part (e))
▶️ Answer/Explanation
(a)
Bromine has the formula \(\text{Br}_2\) and is a non-metal.
Chlorine has the formula \(\text{Cl}_2\), is pale green in colour, and is also a non-metal.
Iodine is a non-metal, matching the pattern shown by the other Group VII elements.
(b) halogens
Group VII elements are collectively known as the halogens.
They are all non-metals with seven electrons in their outer shell.
(c) “All iodine atoms contain 53 electrons” and “The protons are found in the nucleus” and “The neutrons are found in the nucleus” (correct statements)
An atom is neutral, so the number of electrons equals the number of protons, which is 53.
Protons and neutrons are both located in the nucleus of the atom.
The statement about molecules containing 148 neutrons is incorrect, since not all iodine atoms are necessarily the same isotope.
(d) potassium chloride – white precipitate; potassium bromide – cream/off-white precipitate
Silver nitrate reacts with halide ions to form insoluble silver halide precipitates.
Silver chloride is white in colour, while silver bromide is cream or off-white.
(e) diffusion; random molecular movement
Bromine molecules and air molecules are in constant, random motion.
This causes bromine molecules to move from a region of high concentration to a region of low concentration.
This process, called diffusion, continues until the bromine is evenly spread throughout the air.
Question 6
Only the water molecules with the greatest …………………………………………….. escape.
State the boiling point of water.
State what happens to the temperature of the water when it is boiling.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P4.3.2 — Series and parallel circuits (Part (a))
• Topic P2.3.4 — Consequences of thermal energy transfer (Part (b)(i)–(ii))
• Topic P2.2.2 — Melting, boiling and evaporation (Part (b)(iii)–(v))
▶️ Answer/Explanation
(a)(i) 6 A
Current is calculated using \( I = \dfrac{V}{R} \).
\( I = \dfrac{240}{40} = 6 \, \text{A} \).
(a)(ii) parallel
Fig. 6.2 shows both hotplates connected across the same two points of the supply.
This is the arrangement known as a parallel circuit.
(a)(iii) 20 Ω
For resistors in parallel, the combined resistance is always less than the smallest individual resistance.
Since both hotplates have equal resistance of \(40 \, \Omega\), the combined resistance is \(20 \, \Omega\).
(b)(i) conduction
Thermal energy passes through the solid metal base of the saucepan by conduction.
This occurs as vibrating particles pass on energy to neighbouring particles.
(b)(ii) arrows circulating upward then outward and down
Water heated at the bottom becomes less dense and rises.
Cooler, denser water then sinks to take its place, creating a circulating convection current.
(b)(iii) surface; energy
Evaporation occurs only at the surface of the liquid.
Only the water molecules with the greatest energy have enough energy to escape into the air.
(b)(iv) 100 °C
Water boils at \(100\,^\circ\text{C}\) at standard atmospheric pressure.
(b)(v) no change in temperature
While boiling, the extra thermal energy supplied is used to change state rather than raise temperature.
So the temperature of the water remains constant at \(100\,^\circ\text{C}\) throughout boiling.
Question 7
active over the widest range of pH values ……………………………………………..
active at pH 8. ……………………………………………..
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B5.1 — Enzymes (Parts (a), (b), (c))
• Topic B4.1 — Biological molecules (Part (d))
• Topic B7.3 — Digestion (absorption) (Part (e))
▶️ Answer/Explanation
(a) A and D; C; B and C
A (pH 1–5) and D (pH 2–3) are active only within acidic pH ranges.
C has the widest active range, from pH 7 to 12.
Both B (pH 5–9) and C (pH 7–12) are active at pH 8.
(b) temperature
Enzyme activity is also affected by temperature.
At high temperatures, enzymes become denatured and lose their activity.
(c) carbon, hydrogen, oxygen, nitrogen
Enzymes are proteins made up of amino acids.
All amino acids contain the elements carbon, hydrogen, oxygen, and nitrogen.
(d) 
Fats and oils are made from fatty acids and glycerol.
Proteins are made from amino acids.
Both starch and glycogen are made up of smaller glucose molecules.
(e) 
Absorption is the movement of small, soluble, digested food molecules into the bloodstream.
This process occurs across the wall of the small intestine, which is adapted with a large surface area for absorption.
Question 8
The other product is aqueous magnesium chloride.
The observations are shown in Table 8.1.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C6.2 — Rate of reaction (Parts (a)(i), (ii)); Topic C5.1 — Exothermic and endothermic reactions (Part (a)(iii))
• Topic C9.4 — Reactivity series (Part (a)(iv))
• Topic C9.3 — Alloys and their properties (Part (b))
▶️ Answer/Explanation
(a)(i) magnesium + hydrochloric acid → magnesium chloride + hydrogen
Magnesium reacts with hydrochloric acid to form a salt and hydrogen gas.
The salt formed is magnesium chloride, and hydrogen is released and collected in the cylinder.
(a)(ii) increase temperature; increase concentration (any two)
Increasing the temperature of the acid gives particles more kinetic energy, increasing collision frequency.
Increasing the concentration of the acid, or decreasing the particle size of magnesium, also increases the rate of reaction.
(a)(iii) releases thermal energy
An exothermic reaction is one that releases thermal energy to the surroundings.
This is why the temperature of the reaction mixture increases during the reaction.
(a)(iv) calcium, magnesium, iron, copper
Calcium reacts most rapidly, so it is the most reactive of the four metals.
Copper does not react at all, making it the least reactive.
Magnesium and iron fall in between, with magnesium reacting faster than iron.
(b)(i) 89%
The percentages of aluminium, manganese, and zinc total \(9.0 + 1.0 + 1.0 = 11.0\%\).
Since all percentages must sum to 100%, magnesium makes up \(100 – 11 = 89\%\).
(b)(ii) 1.8 kg
Aluminium makes up 9.0% of the alloy.
Mass of aluminium \( = \dfrac{9.0}{100} \times 20 = 1.8 \, \text{kg}\).
(b)(iii) stronger
Pure metals have layers of identical-sized atoms that can slide over each other easily.
Adding other elements to form an alloy disrupts this regular arrangement, making the alloy stronger and harder than the pure metal.
Question 9
State the name of the process by which a nuclear fuel produces heat.
Plutonium-239 has the nuclide notation \(^{239}_{94}\text{Pu}\).
The decay product is uranium-235.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.6.3 — Energy resources (Part (a))
• Topic P5.1 — The nucleus (Part (c)); Topic P5.2.3 — Radioactive decay (Part (b), (d))
• Topic P5.2.2 — The three types of nuclear emission (Part (e))
▶️ Answer/Explanation
(a)
Geothermal energy uses energy from inside the Earth.
Hydroelectric (HEP) uses energy from falling water.
Nuclear energy produces dangerous waste, and wind energy is unreliable since it depends on wind conditions.
(b) (nuclear) fission
In a nuclear power station, heat is produced by nuclear fission.
This is the splitting of large, unstable nuclei into smaller nuclei, releasing energy.
(c) 145
The nucleon (mass) number is 239, and the proton (atomic) number is 94.
Number of neutrons \( = 239 – 94 = 145\).
(d)(i) plutonium-239 → uranium-235 + alpha particle
During alpha decay, the nucleus emits an alpha particle.
This causes the mass number to decrease by 4 and the atomic number by 2, forming uranium-235 from plutonium-239.
(d)(ii) helium nucleus / 2 protons and 2 neutrons
An alpha particle consists of 2 protons and 2 neutrons.
This is identical in composition to the nucleus of a helium atom.
(e) alpha, beta, gamma (most to least ionising)
Alpha particles are the most strongly ionising due to their larger mass and charge.
Gamma radiation is the least ionising, as it has no mass or charge and interacts weakly with matter.
Question 10
- including axis labels
- drawing a line to show the trend.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B6.2 — Leaf structure (Parts (a), (b))
• Topic B8.2 — Water uptake (Part (c))
• Topic B8.1 — Xylem and phloem (Part (d))
• Topic B8.2 — Water uptake (Part (e))
• Topic B9.4 — Blood (Part (f))
▶️ Answer/Explanation
(a)(i) X – (upper) epidermis; Y – spongy mesophyll
X is the outer layer of cells covering the leaf, called the (upper) epidermis.
Y is a loosely packed cell type located below the palisade layer, called spongy mesophyll.
(a)(ii) arrow from inside the leaf out through a stoma
Water vapour diffuses out of the air spaces inside the leaf.
It exits the leaf through a stoma, typically found on the lower epidermis.
(b) axis labels; negative correlation
The x-axis should be labelled humidity, and the y-axis labelled rate of transpiration.
As humidity increases, the rate of transpiration decreases, so the line should show a negative correlation.
(c) root hair cell
Root hair cells have long, thin extensions that increase the surface area for water absorption.
This adaptation allows efficient uptake of water from the soil.
(d) xylem
Xylem tissue is responsible for transporting water and dissolved mineral ions.
It carries this from the roots up through the stem to the leaves.
(e) used in photosynthesis / used for support
Not all absorbed water is lost through transpiration.
Some of the water is used in photosynthesis, and some provides turgor pressure for support of the plant.
(f)(i) phagocytosis / production of antibodies
White blood cells help defend the body against disease.
They do this through phagocytosis, engulfing pathogens, or by producing antibodies.
(f)(ii) red blood cells; plasma; platelets (any two)
Besides white blood cells, blood also contains red blood cells, which transport oxygen.
It also contains plasma, the liquid component, and platelets, which help blood clotting.
Question 11
Describe the differences between a solid and a gas using ideas about particle separation and particle motion.
Sodium reacts violently with water.
Describe the reaction of lithium with water.
Describe the trend in the reactivity of Group I elements as shown by sodium and lithium.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C7.2 — Oxides (Part (a))
• Topic C1.1 — Solids, liquids and gases (Part (b))
• Topic C2.6 — Giant covalent structures (Part (c))
• Topic C2.4 — Ions and ionic bonds (Part (d)(i), (ii))
• Topic C8.2 — Group I properties (Part (d)(iii))
▶️ Answer/Explanation
(a) non-metals form acidic oxides; metals form basic oxides
Sodium is a metal, and metals typically form basic oxides.
Carbon is a non-metal, and non-metals typically form acidic oxides.
(b) particle separation: solid closer together, gas further apart; particle motion: solid vibrates about a fixed point, gas moves freely and faster
In a solid, particles are packed closely together and only vibrate about fixed positions.
In a gas, particles are far apart and move freely and rapidly in random directions.
(c) giant; covalent
Diamond consists of a giant covalent (macromolecular) structure.
Each carbon atom forms four strong covalent bonds with neighbouring carbon atoms.
(d)(i) \(2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl}\)
The equation must be balanced so the number of atoms of each element is equal on both sides.
Using a coefficient of 2 for both sodium and sodium chloride balances the equation.
(d)(ii) sodium atom: 2,8,1; chlorine atom: 2,8,7
A sodium atom has the electronic structure 2,8,1, with one electron in its outer shell.
A chlorine atom has the electronic structure 2,8,7, with seven electrons in its outer shell.
During the reaction, sodium loses its outer electron to chlorine, forming ions with full outer shells.
(d)(iii) reaction: lithium reacts less rapidly/vigorously than sodium; explanation: reactivity increases down Group I
Lithium reacts with water, but less vigorously and more slowly than sodium.
This shows that as you go down Group I, the reactivity of the metals increases.
Question 12
Each word or phrase may be used once, more than once or not at all.
Describe the change in the motion of the air molecules.
Fig. 12.3 shows the wheel nut that must be unscrewed.
Explain why spanner X will unscrew the wheel nut more easily than spanner Y.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P1.2 — Motion (Part (a))
• Topic P1.6.1 — Energy (Part (b)(i)); Topic P2.1.2 — Particle model (Part (b)(ii))
• Topic P1.5.2 — Turning effect of forces (Part (c))
▶️ Answer/Explanation
(a)(i) 20 s
From the graph, cyclist A reaches \(1000 \, \text{m}\) at \(100 \, \text{s}\), and cyclist B reaches it at \(120 \, \text{s}\).
Time difference \( = 120 – 100 = 20 \, \text{s}\).
(a)(ii) 8.3 m/s
Speed is calculated using \( \text{speed} = \dfrac{\text{distance}}{\text{time}} \).
\( \text{speed} = \dfrac{1000}{120} = 8.3 \, \text{m/s} \) (or \(8.33 \, \text{m/s}\)).
(a)(iii) constant gradient
The line for cyclist B on the distance–time graph is a straight line.
A straight line has a constant gradient, which indicates the cyclist is moving at a constant speed.
(b)(i) chemical (potential); kinetic
The cyclist’s body stores energy as chemical potential energy.
As the cyclist speeds up, this chemical potential energy is converted into kinetic energy.
(b)(ii) molecules move faster
As temperature increases, the air molecules inside the tyre gain kinetic energy.
This causes the molecules to move faster.
(c) X is longer, so provides a greater moment
The moment (turning effect) of a force is calculated as \( \text{moment} = \text{force} \times \text{perpendicular distance} \).
Since spanner X is longer than spanner Y, the same applied force produces a greater moment.
This greater moment makes it easier to unscrew the wheel nut.