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Question 1

(a) Fig. 1.1 is a diagram of the human gas exchange system.
(i) Identify the parts labelled A and B in Fig. 1.1.
(ii) List three structures inspired air passes through on its way to the alveoli.
(iii) Place a tick (✓) in the box to show the blood vessel that brings blood to the lungs.
(b) Expired air contains a higher percentage of carbon dioxide than inspired air.
(i) State one other way that the composition of expired air is different from inspired air.
(ii) State the test for carbon dioxide gas and give the observation for a positive result.
(c) A student records their breathing rate while walking and while running. The results are shown in Fig. 1.2.
(i) State the breathing rate of the student while walking.
(ii) The student repeats the investigation and records the breathing rate while at rest. Describe the expected changes to the pattern of breathing while at rest when compared to running.

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

• Topic B11.1 — Gas exchange in humans (Parts (a)(i), (a)(ii), (b), (c))
• Topic B9.3 — Blood vessels (Part (a)(iii))
• Topic C12.5 — Identification of ions and gases (Part (b)(ii), CO2 test)

▶️ Answer/Explanation

(a)(i) A: rib; B: diaphragm

Structure A sits around the ribcage and is labelled as the rib.
Structure B lies beneath the lungs and is the diaphragm.
Both are muscles/bones involved in the mechanism of breathing.

(a)(ii) nose/mouth, trachea, bronchus (any three)

Inspired air travels: nose or mouth → larynx → trachea.
It then passes into a bronchus, then bronchioles.
Any three of these structures in the correct order are accepted.

(a)(iii) pulmonary artery

The pulmonary artery carries deoxygenated blood from the heart to the lungs.
This is the only vessel of the four listed that brings blood \(to\) the lungs.
The pulmonary vein does the opposite — it carries oxygenated blood away from the lungs.

(b)(i) less oxygen / more water vapour

During gas exchange, oxygen is absorbed into the blood from inspired air.
Water vapour is also added to expired air as it passes over moist airway surfaces.
So expired air contains less oxygen and more water vapour than inspired air.

(b)(ii) test: limewater; observation: turns cloudy/milky

Carbon dioxide is bubbled through or shaken with limewater.
A positive result is shown by the limewater turning cloudy (milky) white.
This occurs because \(\text{CO}_2\) reacts with the calcium hydroxide in limewater to form insoluble calcium carbonate.

(c)(i) 20 breaths per minute

This is read directly from the bar chart in Fig. 1.2.
The “walking” bar reaches the 20 mark on the y-axis.

(c)(ii) breathing rate decreases; depth of breathing decreases

At rest, the body needs less oxygen and produces less carbon dioxide than during running.
So both the rate of breathing and the depth of each breath decrease compared to running.

Question 2

(a) Table 2.1 shows information about three Group VII elements.
(i) Complete Table 2.1.
(ii) State the name given to the Group VII elements in the Periodic Table.
(b) Bromine reacts with hydrogen to make hydrogen bromide. Construct the word equation for this reaction.
(c) Aqueous bromine is orange. Predict the colour change, if any, when aqueous bromine is mixed with ethene gas. Explain your answer.
(d) An aqueous solution is tested to see if bromide ions are present. State the test for aqueous bromide ions and give the observation for a positive result.
(e) Fig. 2.1 shows the electrolysis of molten lead(II) bromide using inert electrodes.
Identify the substances formed at the cathode and the anode.

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

• Topic C8.3 — Group VII properties (Part (a))
• Topic C3.1 — Formulas (word equation, Part (b))
• Topic C11.5 — Alkenes (bromine/ethene test, Part (c))
• Topic C12.5 — Identification of ions and gases (bromide ion test, Part (d))
• Topic C4.1 — Electrolysis (Part (e))

▶️ Answer/Explanation

(a)(i)

ElementFormulaColourPhysical state at 20 °C
ChlorineCl2Pale greenGas
BromineBr2OrangeLiquid
IodineI2GreySolid

Chlorine is a pale green gas at room temperature.
Bromine is one of the few elements that is liquid at room temperature.
Iodine is a grey solid at room temperature.

(a)(ii) halogens

Group VII elements are collectively known as the halogens.
They all have 7 electrons in their outer shell.

(b) hydrogen + bromine → hydrogen bromide

The reactants, hydrogen and bromine, combine directly.
They form a single product, hydrogen bromide.

(c) colour change: orange to colourless

Ethene, \(\text{C}_2\text{H}_4\), is an unsaturated hydrocarbon containing a carbon–carbon double bond.
This double bond reacts with bromine in an addition reaction to form colourless 1,2-dibromoethane.
As the bromine is used up, the orange colour disappears.

(d) test: add aqueous silver nitrate (acidified with dilute nitric acid); observation: cream-coloured precipitate

Aqueous silver nitrate is added to the solution being tested.
Silver ions react with bromide ions to form insoluble silver bromide.
A cream-coloured precipitate confirms the presence of bromide ions.

(e) at cathode: lead; at anode: bromine

During electrolysis, positive lead ions, \(\text{Pb}^{2+}\), migrate to the negative cathode and gain electrons to form lead metal.
Negative bromide ions, \(\text{Br}^-\), migrate to the positive anode and lose electrons to form bromine.
This follows the rule that metals form at the cathode and non-metals form at the anode.

Question 3

(a) A cyclist starts from rest and accelerates for 20 s. The cyclist then travels at a constant speed of 5 m/s for 90 s. Finally, the cyclist slows down and stops after a further 5 s.
(i) On the grid in Fig. 3.1, draw a speed-time graph for the cyclist’s journey.
(ii) Calculate the distance travelled when the cyclist is travelling at constant speed.
(b) Energy from the Sun heats the black saddle of the bicycle.
(i) State the method of energy transfer between the Sun and the Earth.
(ii) Name the part of the Sun’s electromagnetic spectrum that is responsible for heating the saddle.
(iii) The Sun also heats up the air in the bicycle tyres. This causes the pressure of the air in the tyres to increase. Describe, in terms of the motion of the air molecules, why the pressure of the air in the tyres increases as the temperature of the air increases.
(c) Fig. 3.2 shows a metal nut on the bicycle which is difficult to unscrew.
Fig. 3.3 shows two spanners A and B.
Explain why it is easier to use spanner B to unscrew the nut rather than spanner A.
(d) The cyclist uses a plane mirror placed on his bicycle to see behind him. State two characteristics of an image seen in a plane mirror.

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

• Topic P1.2 — Motion (Part (a))
• Topic P2.3.3 — Radiation (Part (b)(i))
• Topic P3.3 — Electromagnetic spectrum (Part (b)(ii))
• Topic P2.1.3 — Pressure changes (Part (b)(iii))
• Topic P1.5.2 — Turning effect of forces (Part (c))
• Topic P3.2.1 — Reflection of light (Part (d))

▶️ Answer/Explanation

(a)(i) speed-time graph with three sections

A straight line rises from (0, 0) to (20, 5) representing constant acceleration.
A horizontal line runs from (20, 5) to (110, 5) representing constant speed.
A straight line falls from (110, 5) to (115, 0) representing constant deceleration.

(a)(ii) 450 m

Distance = speed × time.
Distance \(= 5 \, \text{m/s} \times 90 \, \text{s} = 450 \, \text{m}\).

(b)(i) radiation

Thermal energy from the Sun reaches the Earth as radiation.
Radiation is the only method of thermal transfer that does not need a medium, which is why it can cross the vacuum of space.

(b)(ii) infrared

Infrared radiation from the Sun is responsible for heating dark surfaces such as the saddle.
Black surfaces are good absorbers of infrared radiation.

(b)(iii) molecules move faster and collide more often with the tyre walls

As temperature increases, the air molecules gain kinetic energy and move faster.
This causes them to collide with the walls of the tyre more frequently.
More frequent (and more forceful) collisions increase the pressure of the air in the tyre.

(c) spanner B has a longer handle, giving a greater moment for the same force

Moment = force × perpendicular distance from the pivot.
Spanner B is longer, so it gives a greater distance from the pivot (the nut).
A greater distance means a smaller force is needed to produce the same turning effect, making it easier to loosen the nut.

(d) upright; laterally inverted

The image formed in a plane mirror is upright, the same way up as the object.
It is laterally inverted, meaning left and right appear reversed.
The image is also the same size as the object and appears the same distance behind the mirror as the object is in front.

Question 4

(a) The list below shows some information about feeding relationships in a national park.
(i) Use the information to construct a food chain containing all the organisms.
(ii) Use the information to identify the: producer; secondary consumer.
(b) State the principal source of energy for all food chains.
(c) Table 4.1 shows the number and types of teeth for goats and humans.
(i) Goats have a greater total number of premolar and molar teeth than humans. Describe two other differences between the types and number of teeth in goats and humans.
(ii) Goats are herbivores. Humans are able to gain their energy by eating both animals and plants. Suggest reasons why goats have a greater total number of premolar and molar teeth than humans.
(iii) Circle the top two layers in a human tooth.
cement      dentine      enamel
gum      pulp    nerve

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

• Topic B18.2 — Food chains and food webs (Part (a))
• Topic B18.1 — Energy flow (Part (b))
• Topic B7.3 — Digestion (closest surviving match, Part (c)) — see flag below

▶️ Answer/Explanation

(a)(i) grass → goat → jackal → lion

Grass is the producer, so it starts the chain.
Goats eat grass, jackals eat goats, and lions eat jackals.
Each arrow points from the organism eaten to the organism that eats it.

(a)(ii) producer: grass; secondary consumer: jackal

The producer makes its own food by photosynthesis — this is the grass.
The primary consumer (goat) eats the producer.
The secondary consumer eats the primary consumer, so this is the jackal.

(b) the Sun

The Sun provides the light energy that producers convert into chemical energy through photosynthesis.
This energy then passes along the food chain as organisms feed on one another.

(c)(i) goats have no canine teeth (humans have 4); goats have more premolars (12 vs 8)

Goats lack canine teeth entirely, while humans have four.
Goats also have a greater number of premolar teeth than humans.
These differences reflect the different diets of the two species.

(c)(ii) goats need more grinding teeth to break down tough plant material

Goats rely entirely on plant material, which is fibrous and tough to break down.
More premolars and molars provide a greater grinding surface area for this task.
Humans eat a more varied, softer diet, so fewer grinding teeth are needed.

(c)(iii) enamel and dentine

Enamel is the hard, outer protective layer of a tooth.
Dentine lies directly beneath the enamel and is the second layer.
These are the top two layers, above the pulp and nerve at the tooth’s core.

Question 5

(a) Table 5.1 shows information about four metallic elements.
(i) State the names of the two metals in Table 5.1 that are transition elements.
(ii) Suggest the name of the gas produced when an alkali metal reacts with water.
(iii) Place the four metals in order of reactivity from the most reactive to the least reactive.
(b) Copper is extracted by heating copper oxide with carbon. The word equation for the reaction is shown.
copper oxide + carbon → copper + carbon dioxide
(i) Balance the symbol equation for this reaction:
(ii) Identify which substance is reduced during this reaction. Explain your answer.
(c) During the extraction of copper, carbon dioxide is released into the air. Carbon dioxide is found in small quantities in clean air.
(i) State the names of the two gases which are found in large quantities in clean air.
(ii) Carbon dioxide is a greenhouse gas.
State the name of one other greenhouse gas.
(iii) Carbon dioxide is released into the air during the combustion of fossil fuels.
State the names of two fossil fuels.

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

• Topic C8.4 — Transition elements (Part (a)(i))
• Topic C9.1 — Properties of metals (Part (a)(ii))
• Topic C9.4 — Reactivity series (Part (a)(iii))
• Topic C3.1 — Formulas (Part (b)(i))
• Topic C6.3 — Redox (Part (b)(ii))
• Topic C10.2 — Air quality and climate (Part (c)(i), (c)(ii))
• Topic C11.3 — Fuels (Part (c)(iii))

▶️ Answer/Explanation

(a)(i) copper and iron

Transition elements are metals with high density, high melting points, and coloured compounds, positioned in the central block of the Periodic Table.
Of the four metals listed, copper and iron are transition elements.
Lithium and sodium are Group I (alkali) metals instead.

(a)(ii) hydrogen

Alkali metals react with water to form a metal hydroxide and hydrogen gas.
For example: sodium + water → sodium hydroxide + hydrogen.

(a)(iii) sodium, lithium, iron, copper (most to least reactive)

Reactivity with water increases down this list based on how vigorously each metal reacts.
Sodium reacts most violently, followed by lithium, then iron (very slowly), then copper (not at all).

(b)(i) 2CuO + C → 2Cu + CO₂

Balancing requires 2 copper oxide units to supply enough oxygen for one \(\text{CO}_2\).
This gives 2 copper atoms and one carbon atom on each side, so the equation balances.

(b)(ii) copper oxide is reduced

Copper oxide loses oxygen during the reaction, forming copper metal.
Loss of oxygen is the definition of reduction.
Carbon, meanwhile, gains oxygen and is oxidised to carbon dioxide.

(c)(i) oxygen and nitrogen

Clean, dry air is approximately 78% nitrogen and 21% oxygen.
These two gases make up the vast majority of clean air by volume.

(c)(ii) methane

Methane is released from the decomposition of vegetation and from digestion in animals.
Like carbon dioxide, it traps heat in the atmosphere, making it a greenhouse gas.

(c)(iii) coal and petroleum (natural gas also accepted)

Fossil fuels form from the remains of ancient organisms over millions of years.
Coal, petroleum (oil), and natural gas are the three main fossil fuels; any two are acceptable here.

Question 6

(a) A car has two identical headlamps. The lamps are connected in parallel across a 12 V battery.
A single switch is used to turn on both lamps.
(i) Draw a circuit diagram for this circuit using standard electrical symbols.
(ii) The resistance of each lamp is 3.0 Ω.
Calculate the current in each lamp when lit.
(iii) State one reason why the lamps are connected in parallel and not in series.
(b) A lamp consists of a glass bulb, which contains a thin metal filament attached to a metal base.
The glass bulb is filled with nitrogen gas.
When electricity passes through the lamp, the filament is at a very high temperature.
Thermal energy is transferred from the hot filament through the nitrogen gas and through the glass bulb.
(i) State the method by which thermal energy is transferred by the nitrogen gas to the glass bulb.
(ii) State the method by which thermal energy is transferred through the glass bulb.
(c) On a journey, a car becomes electrostatically charged.
Describe what happens to cause the car to become charged.
(d) Fig. 6.2 shows how damage to a steel door of the car has been repaired with a plastic filler. The filler has been painted over and cannot be seen.
Suggest how the owner of the car uses a magnet to detect the repair to the bodywork.

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)(i))
• Topic P2.3.1 — Conduction (Part (b)(ii))
• Topic P4.2.1 — Electrical charge (Part (c))
• Topic P4.1 — Simple phenomena of magnetism (Part (d))

▶️ Answer/Explanation

(a)(i) circuit with two lamps in parallel, both controlled by one switch

The circuit shows a 12 V battery as the power source.
Both lamps are drawn side by side in parallel branches.
A single switch is placed in the main circuit so it controls both lamps together.

(a)(ii) 4 A

Using Ohm’s law, \(I = \dfrac{V}{R}\).
Each lamp has the full 12 V across it since they are in parallel.
\(I = \dfrac{12\,\text{V}}{3.0\,\Omega} = 4\,\text{A}\).

(a)(iii) if one lamp fails, the other still lights

In a parallel circuit, each lamp has its own independent path connected across the battery.
If one lamp fails or is removed, the circuit for the other lamp remains complete.
In series, one broken lamp would break the whole circuit and switch off both lamps.

(b)(i) convection

The nitrogen gas near the hot filament heats up and becomes less dense.
It rises and carries thermal energy to the glass bulb through convection currents.

(b)(ii) conduction

Heat passes through the solid glass bulb by conduction.
Vibrations are passed from particle to particle through the glass lattice.

(c) friction between the car and air/road transfers electrons

As the car moves, friction occurs between its surface and the air (or the tyres and the road).
This friction causes electrons to be transferred from one surface to another.
This leaves the car with an overall imbalance of charge, making it electrostatically charged.

(d) a magnet will not stick to the plastic filler

Steel is a magnetic material, so a magnet will be attracted to and stick to the normal steel bodywork.
The plastic filler is non-magnetic, so the magnet will not stick over the repaired area.
Moving the magnet over the door and noting where it fails to stick reveals the location of the repair.

Question 7

(a) Table 7.1 shows some of the functions of the main components of blood.
Complete Table 7.1 with the name of the component of blood for each function.
(b) Some of the substances transported by the blood need to be excreted.
The boxes contain the beginnings and the endings of some sentences.
Join one sentence beginning to one sentence ending to define the term excretion.
(c) Excretion, respiration and nutrition are three characteristics of living organisms.
Name two other characteristics of living organisms.

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

• Topic B9.4 — Blood (Part (a))
• Topic B1.1 — Characteristics of living organisms (Part (b), (c))

▶️ Answer/Explanation

(a) platelets; red blood cells; white blood cells; plasma

Platelets are cell fragments responsible for blood clotting.
Red blood cells contain haemoglobin, which binds oxygen for transport.
White blood cells carry out phagocytosis and produce antibodies.
Plasma is the liquid component of blood, and it carries dissolved substances such as hormones.

(b) excretion is the removal from organisms of toxic materials and substances in excess of requirements

Excretion specifically refers to waste removal, not intake or digestion of substances.
It covers both toxic materials and substances the body simply has too much of.
This distinguishes excretion from egestion, which is the removal of undigested food.

(c) movement; growth (any two of: movement, sensitivity, growth, reproduction)

Living organisms share a set of characteristic life processes.
Alongside excretion, respiration and nutrition, these include movement, sensitivity, growth and reproduction.
Any two of these (other than the three already given) are accepted.

Question 8

(a) Fig. 8.1 shows three molecules A, B and C.
State the formula of the substance that reacts with molecule C to make molecule A.
(b) Molecule B, CH4, is methane which is a compound. Methane contains the elements carbon and hydrogen.
Use this information to explain the difference between an element and a compound.
(c) State the two products made when methane undergoes complete combustion in oxygen.
(d) The combustion of methane is an exothermic reaction. State what is meant by exothermic.
(e) An atom of carbon has a nucleon number (mass number) of 12 and a proton number (atomic number) of 6.
An atom of hydrogen has a nucleon number (mass number) of 1 and a proton number (atomic number) of 1.
(i) State the number of electrons in an atom of carbon and in an atom of hydrogen.
(ii) State the number of neutrons in this atom of hydrogen.
(f) Complete the dot-and-cross diagram in Fig. 8.2 to show the bonding in a methane, CH4, molecule.

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

• Topic C11.5 — Alkenes (Part (a))
• Topic C2.1 — Elements, compounds and mixtures (Part (b))
• Topic C11.4 — Alkanes (Part (c))
• Topic C5.1 — Exothermic and endothermic reactions (Part (d))
• Topic C2.2 — Atomic structure and the Periodic Table (Part (e))
• Topic C2.5 — Simple molecules and covalent bonds (Part (f))

▶️ Answer/Explanation

(a) H₂O

Molecule C is ethene, \(\text{C}_2\text{H}_4\), shown by its carbon–carbon double bond.
Molecule A is ethanol, \(\text{C}_2\text{H}_5\text{OH}\), formed by adding water across the double bond.
This addition reaction (hydration of an alkene) requires the substance \(\text{H}_2\text{O}\).

(b) an element has one type of atom; a compound has two or more elements chemically combined

Carbon and hydrogen are each elements, made of only one type of atom.
Methane, \(\text{CH}_4\), is a compound because carbon and hydrogen atoms are chemically bonded together.
A compound has different chemical properties from the elements that make it up.

(c) carbon dioxide and water

Complete combustion of a hydrocarbon in plenty of oxygen produces carbon dioxide and water.
\(\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}\).

(d) exothermic means thermal energy is released to the surroundings

In an exothermic reaction, energy is transferred from the reacting chemicals to the surroundings.
This is usually observed as a rise in temperature of the surroundings.

(e)(i) carbon: 6 electrons; hydrogen: 1 electron

In a neutral atom, the number of electrons equals the number of protons.
Carbon has a proton number of 6, so it has 6 electrons.
Hydrogen has a proton number of 1, so it has 1 electron.

(e)(ii) 0 neutrons

Number of neutrons = nucleon number − proton number.
For hydrogen: \(1 – 1 = 0\) neutrons.

(f) carbon shares one electron pair with each of the four hydrogen atoms

Methane forms four single covalent bonds, one between carbon and each hydrogen atom.
Each bond is shown as a shared pair of electrons, with one dot (from carbon) and one cross (from hydrogen) in each overlapping region.
All four hydrogen atoms end up with a full outer shell of 2 electrons, and carbon ends up with a full outer shell of 8.

Question 9

(a) A school orchestra is practising.
Table 9.1 shows the highest and lowest sound frequencies of some of the musical instruments in the orchestra.
(i) State what is meant by the frequency of a wave.
(ii) State which instrument in Table 9.1 produces the sound with the lowest pitch.
(iii) State which instrument in Table 9.1 produces sound with the widest range of frequencies.
(iv) State the normal audible frequency range for a healthy human ear.
(b) A flute is made from a nickel alloy. The volume of the alloy used to make the flute is 90 cm3.
The mass of the flute is 801 g.
(i) Calculate the density of the alloy. State the unit of your answer.
(ii) Calculate the weight of the flute. The gravitational field strength \( g \) is 10 N/kg.

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

• Topic P3.1 — General properties of waves (Part (a)(i))
• Topic P3.4 — Sound (Part (a)(ii), (a)(iii), (a)(iv))
• Topic P1.4 — Density (Part (b))

▶️ Answer/Explanation

(a)(i) the number of waves produced (or passing a point) per second

Frequency describes how many complete wave cycles occur in one second.
It is measured in hertz, Hz, where 1 Hz equals one wave per second.

(a)(ii) piano

Pitch is directly related to frequency — a lower frequency gives a lower pitch.
The piano has the lowest frequency in the table, at 30 Hz.
So the piano produces the sound with the lowest pitch.

(a)(iii) piano

Range = highest frequency − lowest frequency for each instrument.
The piano’s range is \(4200 – 30 = 4170\,\text{Hz}\), the largest of the four instruments.

(a)(iv) 20 Hz to 20 000 Hz

This is the typical range of frequencies a healthy human ear can detect.
Sounds below 20 Hz are infrasound, and sounds above 20 000 Hz are ultrasound.

(b)(i) 8.90 g/cm³

Density = mass ÷ volume.
Density \(= \dfrac{801\,\text{g}}{90\,\text{cm}^3} = 8.90\,\text{g/cm}^3\).

(b)(ii) 8.01 N

Weight = mass × gravitational field strength, using mass in kilograms.
\(801\,\text{g} = 0.801\,\text{kg}\), so weight \(= 0.801 \times 10 = 8.01\,\text{N}\).

Question 10

(a) Plants use different tissues to transport substances around the plant.
Circle two parts of a plant that are adapted for transport from the list below.
capillaries        chloroplasts        fatty tissue        guard cells  
phloem        vena cava        xylem
(b) Fig. 10.1 is a diagram of a plant cell.
(i) Name the cell shown in Fig. 10.1 and state its function.
(ii) Identify the parts labelled X and Y in Fig. 10.1.
(c) A scientist investigates the conditions needed for the germination of seeds.
She sets up four experiments A–D with different conditions.
Table 10.1 shows the conditions for each experiment.
Place a tick (✓) in Table 10.1 to identify the experiment where the seeds will germinate.
(d) Germination is an enzyme-controlled reaction.
The investigation is repeated with boiled seeds.
Describe the effect of boiling on the germination of seeds.
Give one reason for your answer.

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

• Topic B8.1 — Xylem and phloem (Part (a))
• Topic B8.2 — Water uptake (Part (b))
• Topic B15.3 — Sexual reproduction in plants (germination conditions, Part (c), (d))

▶️ Answer/Explanation

(a) phloem and xylem

Xylem transports water and mineral ions and provides support.
Phloem transports sucrose and amino acids (translocation).
Vena cava and capillaries are transport structures in animals, not plants.

(b)(i) name: root hair cell; function: absorption of water and mineral ions

The cell shown has a long, thin extension that increases its surface area.
This shape is characteristic of a root hair cell.
Its large surface area increases the rate of absorption of water and mineral ions from the soil.

(b)(ii) X: cell wall; Y: nucleus

X is the outer boundary layer of the cell, which is the cell wall.
Y is the structure inside the cytoplasm that controls the cell, the nucleus.

(c) 

(d) effect: no germination; reason: boiling denatures the enzymes needed for germination

Boiling the seeds exposes them to a very high temperature.
This denatures the enzymes that control the metabolic reactions involved in germination.
Without functioning enzymes, the seeds cannot germinate.

Question 11

(a) Fig. 11.1 shows iron rusting.
(i) Iron rusts when two other substances are present. State the names of these two substances.
(ii) Describe and explain one method used to prevent the rusting of iron.
(b) Stainless steel is an alloy of iron.
State one use for stainless steel.
(c) Solid iron melts at 1538 °C to become liquid (molten) iron.
Describe one difference in the properties of a solid compared to a liquid.
(d) Melting is one of the processes involved when a substance changes state.
Fig. 11.2 shows other processes involved when substances change state.
Identify processes A, B, and C.

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

• Topic C9.5 — Corrosion of metals (Part (a))
• Topic C9.3 — Alloys and their properties (Part (b))
• Topic C1.1 — Solids, liquids and gases (Part (c), (d))

▶️ Answer/Explanation

(a)(i) oxygen and water

Rusting is a chemical reaction between iron, oxygen, and water.
If either oxygen or water is absent, rusting does not occur.

(a)(ii) painting/greasing/coating with plastic — creates a barrier that excludes oxygen and water

Painting the iron surface forms a physical barrier over the metal.
This barrier keeps oxygen and water away from the iron surface.
Without contact with both oxygen and water, rusting cannot take place.

(b) cutlery (knives, forks, spoons)

Stainless steel resists rusting and corrosion.
This makes it ideal for items in regular contact with moisture and food, such as cutlery.

(c) a solid has a fixed shape; a liquid takes the shape of its container

In a solid, particles are held in fixed positions by strong forces of attraction.
In a liquid, particles are close together but can move past one another.
This allows a liquid to flow and take up the shape of whatever container it is in, while a solid keeps its own shape.

(d) A: boiling; B: condensing; C: freezing

A is the change from liquid to gas, which is boiling.
B is the change from gas back to liquid, which is condensing.
C is the change from liquid to solid, which is freezing.

Question 12

(a) Describe how to show that a radioactive isotope is releasing γ-rays but not α-particles or β-particles.
(b) In a nuclear reactor, the fission of uranium-235 takes place.
(i) Describe what happens to the nucleus of a uranium-235 atom during nuclear fission.
(ii) The half-life of uranium-235 is 704 million years.
A sample of uranium-235 has a mass of 0.1 g.
Calculate how many grams of uranium-235 will remain in the sample after 704 million years.
(iii) Uranium-235 and uranium-238 are two isotopes of uranium.
Explain what is meant by isotope.
(c) A nuclear power station generates electricity. One use of electricity is to power an electric motor.
In a d.c. electric motor, a current-carrying coil in a magnetic field experiences a turning effect.
State two factors that can be changed to increase the turning effect in a d.c. motor.

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

• Topic P5.2.2 — The three types of nuclear emission (Part (a))
• Topic P5.1 — The nucleus (Part (b)(i), (b)(iii))
• Topic P5.2.4 — Half-life (Part (b)(ii))
• Topic P4.5.5 — The d.c. motor (Part (c))

▶️ Answer/Explanation

(a) show that the radiation penetrates lead / thick material, but a lighter absorber (paper/aluminium) would stop α and β

Alpha particles are stopped by paper, and beta particles are stopped by a few mm of aluminium.
Gamma rays are far more penetrating and pass through several cm of lead.
If a detector still registers radiation through a thick lead absorber, this confirms the source is emitting γ-rays and not α- or β-particles.

(b)(i) the nucleus splits into two smaller nuclei, releasing neutrons and energy

A uranium-235 nucleus absorbs a neutron, making it unstable.
The unstable nucleus splits into two smaller (daughter) nuclei.
This releases further neutrons along with a large amount of energy.

(b)(ii) 0.05 g

One half-life (704 million years) means exactly one half of the sample has decayed.
Remaining mass \(= \dfrac{0.1\,\text{g}}{2} = 0.05\,\text{g}\).

(b)(iii) atoms of the same element with the same proton number but different numbers of neutrons

Isotopes have identical proton (atomic) numbers, so they are the same element.
They differ in nucleon (mass) number because they have different numbers of neutrons.
Uranium-235 and uranium-238 both have 92 protons but 143 and 146 neutrons respectively.

(c) increase the current; increase the number of turns on the coil (or increase the strength of the magnetic field)

A larger current in the coil produces a greater force on the coil in the magnetic field.
Increasing the number of turns multiplies this force across more loops of wire.
A stronger magnetic field also increases the force on the current-carrying coil, giving a greater turning effect.

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