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Question 1

(a) It is recommended that people eat a balanced diet.
Place a tick (✓) next to the sentence that best describes a balanced diet.
(b) The boxes on the left show some nutrients. The boxes on the right show why the nutrients are needed by the body.
Draw lines to link each nutrient with why it is needed by the body.
(c) List the three chemical elements that make up carbohydrates.
(d) Benedict’s solution can be used to test for the presence of one type of carbohydrate. Name the carbohydrate that Benedict’s solution is used to test for.
(e) Name the component of the diet that prevents constipation.
(f) Eating less sugar can help prevent tooth decay. Describe one other way of taking care of teeth.
(g) Circle the two processes that occur in the mouth.
ingestion    digestion    egestion    fertilisation    photosynthesis    pollination    transpiration

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

• Topic B7.1 — Diet (Parts (a), (b), (e), (f))
• Topic B4.1 — Biological molecules (Part (c), (d))
• Topic B7.3 — Digestion (Part (g))

▶️ Answer/Explanation

(a) A balanced diet contains all the required nutrients in the correct amounts

A balanced diet is not simply about eating fruit and vegetables or avoiding fats and salt.
It must supply every required nutrient — carbohydrates, fats, proteins, vitamins, minerals, fibre and water — in the correct proportions for the body’s needs.

(b)

carbohydrate → main source of energy
fats → insulation
protein → used for growth and repair
vitamin D → for bones and teeth

(c) Carbon, hydrogen and oxygen

Carbohydrates are compounds made up of only these three elements.
Their general formula can be written as \( \text{C}_x(\text{H}_2\text{O})_y \), reflecting the ratio of hydrogen to oxygen as in water.

(d) Reducing sugar

Benedict’s solution is a blue solution that turns brick-red on heating with a reducing sugar (such as glucose).
It does not directly test for non-reducing sugars like sucrose without prior hydrolysis.

(e) Fibre

Fibre (roughage) is not digested but adds bulk to the food in the gut.
This bulk stimulates peristalsis, helping to prevent constipation.

(f) Regular brushing of teeth

Regular brushing removes plaque and food debris that bacteria use to produce acids.
This helps prevent the acids from eroding tooth enamel and causing decay.

(g) Ingestion and digestion

Ingestion is the taking of food into the body through the mouth.
Digestion begins in the mouth through chewing (mechanical) and salivary amylase action (chemical) on starch.
Egestion, fertilisation, photosynthesis, pollination and transpiration do not occur in the mouth.

Question 2

(a) Copper and sodium are metals. Copper is a transition element. Sodium is not a transition element. It is found in Group I of the Periodic Table.
Some properties of metallic elements are listed.
A act as a catalyst
B form coloured compounds
C good conductor of electricity
D good conductor of thermal energy
E malleable
F non-magnetic
State the letters (A to F) of the two properties that describe copper but do not describe sodium.
(b) Copper(II) oxide is heated with carbon. Copper and carbon dioxide are made.
(i) Construct the word equation for the reaction between copper(II) oxide and carbon.
(ii) State the chemical test for carbon dioxide gas and the observation for a positive result.
(iii) Explain why copper(II) oxide is described as a basic oxide.
(c) Metals can be coated with a layer of copper using electroplating. Electroplating uses the process of electrolysis.
Use words from the list to complete the sentence to define the term electrolysis. Each word may be used once or not at all.
covalent    electricity    gas    ionic    molten    solid    solution    time    water
Electrolysis always involves the breakdown of …………………………………… compounds when …………………………………… or in aqueous …………………………………… by the passage of …………………………………… .
(d) Bronze is a mixture of copper and tin.
(i) State the term used to describe a mixture of metals.
(ii) Apart from cost, suggest why bronze is used to make coins but pure copper is not used to make coins.

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

• Topic C8.4 — Transition elements (Part (a)); Topic C9.3 — Alloys and their properties (Part (d))
• Topic C9.6 — Extraction of metals, C7.2 — Oxides (Part (b))
• Topic C4.1 — Electrolysis (Part (c))

▶️ Answer/Explanation

(a) A and B

Copper is a transition element, so it can act as a catalyst and form coloured compounds.
Sodium is a Group I metal and does not show these transition-metal properties.
Both metals are good conductors of electricity and heat and are malleable, so C, D and E do not distinguish them.

(b)(i) copper(II) oxide + carbon → copper + carbon dioxide

Carbon reduces copper(II) oxide by removing the oxygen from it.
Copper metal and carbon dioxide gas are formed as products.

(b)(ii) Test: bubble the gas through limewater; Observation: limewater turns cloudy/milky

Carbon dioxide reacts with the calcium hydroxide in limewater.
This forms an insoluble precipitate of calcium carbonate, causing the cloudiness.

(b)(iii) It produces a solution with pH above 7 / reacts with acid to form a salt and water

Copper(II) oxide is a metal oxide.
Metal oxides are basic and neutralise acids, forming a salt and water, which is characteristic of basic oxides.

(c) ionic; molten; solution; electricity

Electrolysis is the breakdown of an ionic compound using electricity.
This can only happen when the ions are free to move, i.e. when the compound is molten or dissolved in water.
The passage of electricity through the free ions causes them to move to the electrodes and be discharged.

(d)(i) Alloy

An alloy is a mixture of two or more metals (or a metal and a non-metal).
Bronze is an alloy formed from copper and tin.

(d)(ii) Bronze is harder/tougher/stronger than pure copper

In pure copper, layers of identical atoms can slide over each other easily, making it soft.
Adding tin atoms of a different size disrupts this regular arrangement, making bronze harder and more durable for coins.

Question 3

(a) X-rays and γ-radiation are both forms of ionising radiation used in hospitals.
(i) State one adverse effect of ionising radiation on the human body.
(ii) State one use of X-rays in a hospital.
(iii) Fig. 3.1 shows an incomplete electromagnetic spectrum. Write γ-radiation and X-rays in their correct positions in Fig. 3.1.
(iv) State one property that is the same for all electromagnetic waves.
(b) A radioactive isotope is used in medical tests as a radioactive tracer.
Fig. 3.2 shows the results of an experiment to measure how the radioactivity of the isotope changes with time.
Use Fig. 3.2 to determine the half-life of the isotope in hours. Show your working.
(c) Ultrasound waves are also used in hospitals.
Ultrasound waves are sound waves with a frequency greater than the highest audible frequency of a human.
(i) State the meaning of the term frequency.
(ii) Suggest a frequency for ultrasound waves.
State the unit of your answer.
(iii) An ultrasound wave travels 21 cm in 0.00025 s.
Calculate the speed of the ultrasound wave in m/s.

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

• Topic P3.3 — Electromagnetic spectrum (Part (a))
• Topic P5.2.4 — Half-life (Part (b))
• Topic P3.4 — Sound (Part (c))

▶️ Answer/Explanation

(a)(i) Causes cancer / mutation of cells

Ionising radiation has enough energy to remove electrons from atoms and molecules in living cells.
This can damage DNA, leading to mutations that may cause cancer.

(a)(ii) Detecting broken bones / CT scanning

X-rays pass through soft tissue but are absorbed by denser material such as bone.
This difference in absorption is used to produce images that show fractures or other internal structures.

(a)(iii)

The electromagnetic spectrum is arranged in order of decreasing frequency (increasing wavelength): gamma, X-rays, ultraviolet, visible, infrared, microwave, radio waves.
γ-radiation has the highest frequency, so it is placed before X-rays.

(a)(iv) All travel at the same speed in a vacuum \((3\times10^8\, \text{m/s})\)

All electromagnetic waves are transverse waves that can travel through a vacuum.
Despite differing in frequency and wavelength, they all travel at the speed of light in a vacuum.

(b) Half-life = 6 hours

From the graph, the activity starts at 800 counts/s at \(t=0\).
It falls to 400 counts/s (half of the initial value) at approximately \(t=6\) hours.
This time taken for the activity to halve is the half-life, so half-life \(=6\) hours.

(c)(i) Number of waves (complete oscillations) passing a fixed point per second

Frequency describes how often a wave repeats in a given time.
It is measured in Hertz (Hz), where \(1\, \text{Hz} = 1\) wave per second.

(c)(ii) Above 20 000 Hz (e.g. 25 000 Hz), unit: Hz

Ultrasound is defined as sound with a frequency higher than the upper limit of human hearing.
The upper limit of human hearing is about 20 000 Hz, so any suggested value above this is acceptable, with the unit Hz.

(c)(iii) Speed = 840 m/s

Convert the distance to metres: \(21\, \text{cm} = 0.21\, \text{m}\).
Use \( \text{speed} = \dfrac{\text{distance}}{\text{time}} = \dfrac{0.21}{0.00025} \).
This gives speed \(=840\, \text{m/s}\).

Question 4

(a) Human immunodeficiency virus (HIV) is a sexually transmitted infection. The number of new HIV infections in one country was monitored.
The results are shown in Fig. 4.1.
The number of new infections has decreased since 2002.
(i) Calculate the difference in number of new HIV infections between 2002 and 2009.
(ii) Suggest two reasons why the number of new HIV infections has decreased since 2002.
(iii) Place a tick (✓) in the box to show one way HIV can be transmitted.
(b) HIV infects white blood cells.
Fig. 4.2 shows a photomicrograph of some blood.
A white blood cell can be seen in the centre.
(i) Name the part of the white blood cell labelled X in Fig. 4.2.
(ii) Name the other type of cells visible in Fig. 4.2.
(iii) State two functions of white blood cells.
(iv) Name the part of the blood that transports hormones.

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

• Topic B10.1 — Diseases and immunity (Part (a))
• Topic B9.4 — Blood (Part (b))

▶️ Answer/Explanation

(a)(i) 3900

From the bar chart, the number of new infections in 2002 is about 7000.
In 2009 it is about 3100, so the difference \(=7000-3100=3900\).

(a)(ii) Any two from: use of condoms; screening blood transfusions; education; use of clean needles/needle exchanges; regular HIV testing; preventative medication; practise of abstinence

Public health measures such as condom use and needle exchange programmes reduce transmission routes.
Education and regular testing help people avoid risky behaviours and seek early treatment, reducing further spread.

(a)(iii) Through breast milk

HIV is transmitted through bodily fluids such as blood, semen, vaginal fluids and breast milk.
It is not transmitted by holding hands, sharing utensils, or genetic inheritance.

(b)(i) Nucleus

The dark-staining structure in the centre of the white blood cell is its nucleus.
White blood cells, unlike red blood cells, retain a nucleus.

(b)(ii) Red blood cells

The surrounding smaller, biconcave cells without a nucleus are red blood cells.
They are much more numerous than white blood cells in a blood smear.

(b)(iii) Phagocytosis; antibody production

Phagocytes engulf and digest pathogens directly.
Lymphocytes produce antibodies that target and help destroy specific pathogens.

(b)(iv) Plasma

Plasma is the liquid component of blood.
It transports dissolved substances including hormones, nutrients, and waste products around the body.

Question 5

(a) Lithium, sodium and potassium are alkali metal elements in the Periodic Table.
Table 5.1 shows the melting points of lithium, sodium and potassium.
State the trend in the melting points of the elements from lithium to potassium.
(b) An atom of sodium has a nucleon number (mass number) of 23 and a proton number (atomic number) of 11. Fig. 5.1 shows the structure of an atom of sodium.
(i) On Fig. 5.1, complete the labels for the sodium atom.
(ii) State the electronic structure for this sodium atom.
(c) Sodium and chlorine react to form sodium chloride.
Fig. 5.2 shows the electronic structure of a sodium atom and a chlorine atom.
Draw diagrams to show the electronic structures of a sodium ion and of a chloride ion when sodium reacts with chlorine.
Include the charge for each ion.
(d) Sodium and chlorine are elements. Sodium chloride is a compound.
Describe the difference between an element and a compound.

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

• Topic C8.2 — Group I properties (Part (a))
• Topic C2.2 — Atomic structure (Part (b))
• Topic C2.4 — Ionic bonding (Part (c))
• Topic C2.1 — Elements, compounds and mixtures (Part (d))

▶️ Answer/Explanation

(a) Melting point decreases down the group (from lithium to potassium)

As you move down Group I, the atoms get larger and the metallic bonding becomes weaker.
Weaker metallic bonds require less energy to break, so the melting point decreases.

(b)(i) Nucleus contains 11 protons and 12 neutrons

The nucleon number (23) minus the proton number (11) gives the number of neutrons: \(23-11=12\).
The two unlabelled particles in the centre of Fig. 5.1 should therefore be labelled proton and neutron.

(b)(ii) 2.8.1

Sodium has 11 electrons arranged in shells.
These fill as 2 in the first shell, 8 in the second shell, leaving 1 in the third (outer) shell, giving 2.8.1.

(c) Sodium ion: 2.8, charge +1; Chloride ion: 2.8.8, charge −1

Sodium loses its single outer electron to form a stable ion with the electronic structure 2.8 and a charge of +1.
Chlorine gains that electron into its outer shell to form a stable ion with the electronic structure 2.8.8 and a charge of −1.

(d) An element contains only one type of atom; a compound contains two or more elements chemically combined

Sodium and chlorine are each made of a single type of atom, so they are elements.
When they react, their atoms bond chemically in a fixed ratio to form sodium chloride, a compound with different properties from either element.

Question 6

(a) An information booklet about an electric oven states that the weight of the oven is 50 kg. Explain why this statement is incorrect.
(b) The oven contains two lamps connected in parallel. One lamp has a resistance of 600 Ω and the other lamp has a resistance of 1200 Ω.
Circle the correct value for the combined resistance of the two lamps connected in parallel.
400 Ω      600 Ω      900 Ω      1200 Ω      1800 Ω
Explain your answer.
(c) The oven contains a fan driven by an electric motor.
Fig. 6.1 shows a simple d.c. electric motor.
State two ways of increasing the turning effect on the coil.
(d) Fig. 6.2 shows a metal saucepan filled with water being heated.
(i) The arrow shows the start of a convection current.
Draw more arrows on Fig. 6.2 to show the convection current in water.
(ii) When the base of the metal saucepan is heated, the metal expands.
State one example where the thermal expansion of a metal is a problem.
(e) When the water is heated in the saucepan, some of the water evaporates.
Eventually the temperature of the water reaches boiling point.
(i) State the boiling point of water.
(ii) State the meaning of the term boiling point.

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

• Topic P1.3 — Mass and weight (Part (a))
• Topic P4.3.2 — Series and parallel circuits (Part (b))
• Topic P4.5.5 — The d.c. motor (Part (c))
• Topic P2.3.2 — Convection (Part (d)(i))
• Topic P2.2.1 — Thermal expansion of solids, liquids and gases (Part (d)(ii))
• Topic P2.2.2 — Melting, boiling and evaporation (Part (e))

▶️ Answer/Explanation

(a) Mass is measured in kg, not weight

Weight is a force caused by gravity acting on a mass, so it should be measured in newtons (N), not kilograms.
Using \(W=mg\), 50 kg of mass has a weight of about \(50 \times 9.8 = 490\, \text{N}\), not 50 kg.

(b) 400 Ω

For resistors in parallel, \( \dfrac{1}{R} = \dfrac{1}{600} + \dfrac{1}{1200} = \dfrac{2}{1200}+\dfrac{1}{1200} = \dfrac{3}{1200} \).
So \(R = \dfrac{1200}{3} = 400\, \Omega\), which is less than either individual resistance, as expected for a parallel combination.

(c) Increase the current through the coil; increase the strength of the magnetic field (or add more turns to the coil)

The turning effect (torque) on a current-carrying coil in a magnetic field depends on the current, the field strength, and the number of turns.
Increasing any of these factors increases the force on the coil and therefore its turning effect.

(d)(i) Arrows showing water rising above the heated base, moving across, then sinking down the sides

Water heated at the base becomes less dense and rises.
Cooler, denser water sinks to replace it, setting up a continuous circular (convection) current.

(d)(ii) Railway tracks / bridges buckling

Metal expands when heated, and if no gaps are left for this expansion, the structure can buckle or crack.
Railway tracks and bridges are common examples where expansion gaps are needed to prevent this problem.

(e)(i) 100 °C

This is the standard boiling point of water at normal atmospheric pressure.

(e)(ii) The temperature at which a liquid changes into a gas (at a given pressure)

At the boiling point, particles throughout the liquid have enough energy to overcome the forces holding them together.
This allows the liquid to change to a gas throughout its whole volume, not just at the surface as in evaporation.

Question 7

Fig. 7.1 is a photomicrograph of a cross-section of a root.
(a) Identify the parts of the root labelled A and B in Fig. 7.1.
(b) The cell labelled C absorbs mineral ions from the soil.
(i) Name this cell.
(ii) Name one other substance absorbed by the cell labelled C in Fig. 7.1.
(c) Chlorophyll is needed for photosynthesis.
(i) Name the mineral ion needed to make chlorophyll.
(ii) State the word equation for photosynthesis.
(d) Fig. 7.2 is a diagram of a seed germinating underground.
(i) Draw two arrows on Fig. 7.2 to show the direction the root and shoot will grow.
(ii) There is no light reaching the seed underground.
Name the stimulus the root would be responding to in Fig. 7.2.
(iii) State two environmental conditions seeds need to germinate.

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 B6.1 — Photosynthesis (Part (c))
• Topic B13.1 — Coordination and response, tropisms (Part (d))

▶️ Answer/Explanation

(a) A: xylem; B: phloem

Xylem transports water and mineral ions from the roots to the rest of the plant.
Phloem transports dissolved sugars (sucrose) and amino acids made or stored in the plant, in both directions.

(b)(i) Root hair cell

Root hair cells have long, thin extensions that greatly increase their surface area.
This adaptation maximises the uptake of water and mineral ions from the soil.

(b)(ii) Water

Root hair cells absorb water by osmosis alongside the active uptake of mineral ions.
Both substances then move into the xylem for transport around the plant.

(c)(i) Magnesium

Magnesium ions are needed to synthesise chlorophyll molecules.
Without enough magnesium, plants cannot make sufficient chlorophyll and may show yellowing of leaves.

(c)(ii) Carbon dioxide + water → glucose + oxygen

This equation summarises photosynthesis, which uses light energy absorbed by chlorophyll.
Carbon dioxide and water are converted into glucose, with oxygen released as a by-product.

(d)(i) Shoot arrow pointing upwards; root arrow pointing downwards

Shoots grow upwards, away from the pull of gravity, so they can reach light at the surface.
Roots grow downwards, in the direction of gravity, to anchor the plant and reach water/minerals.

(d)(ii) Gravity

Since no light reaches the seed underground, the root cannot be responding to light.
Instead it shows a positive gravitropic response, growing in the direction gravity pulls.

(d)(iii) Any two from: suitable/warm temperature; oxygen; water/moisture

Germinating seeds need warmth for enzyme activity to proceed at a suitable rate.
They also need oxygen for respiration and water to activate enzymes and allow the embryo to grow.

Question 8

(a) Fig. 8.1 shows three hydrocarbon molecules X, Y and Z.
Hydrocarbon molecule X is unsaturated.
(i) Explain why molecule X is unsaturated.
(ii) State the name of molecule X.
(iii) An aqueous solution of element P is used to test if hydrocarbons X and Y are saturated or unsaturated. State the name of element P.
(iv) Describe what, if anything, is observed when an aqueous solution of element P is mixed with hydrocarbon molecule X and with hydrocarbon molecule Y.
(b) When hydrocarbon molecule Y is completely combusted in oxygen, carbon dioxide and water are made.
(i) Balance the symbol equation for this reaction.
\( \text{CH}_4 + \ldots\text{O}_2 \longrightarrow \text{CO}_2 + \ldots\text{H}_2\text{O} \)
(ii) This reaction is an exothermic reaction. State what is meant by an exothermic reaction.
(c) Ethanol has the formula \( \text{C}_2\text{H}_5\text{OH} \).
(i) Explain why ethanol is not a hydrocarbon.
(ii) State two methods of producing ethanol.

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

• Topic C11.5 — Alkenes and unsaturation (Part (a))
• Topic C11.4 — Combustion / exothermic reactions (Part (b))
• Topic C11.6 — Alcohols (Part (c))

▶️ Answer/Explanation

(a)(i) It has a carbon-carbon double bond

Unsaturated hydrocarbons contain at least one C=C double bond.
This is in contrast to saturated hydrocarbons, which only contain single C–C bonds.

(a)(ii) Ethene

Molecule X has two carbon atoms joined by a double bond, each bonded to two hydrogen atoms.
This structure corresponds to ethene, \( \text{C}_2\text{H}_4 \).

(a)(iii) Bromine

An aqueous solution of bromine (bromine water) is used to distinguish saturated from unsaturated hydrocarbons.

(a)(iv) With X: decolourises/becomes colourless; with Y: stays orange/does not decolourise

Bromine water reacts with the C=C double bond in ethene (X) in an addition reaction, losing its orange colour.
Methane (Y) is saturated and has no double bond, so it does not react and the bromine water remains orange.

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

Balancing the equation requires 2 oxygen molecules to supply enough oxygen atoms for both the \(\text{CO}_2\) and the 2 \(\text{H}_2\text{O}\) molecules formed.
This ensures the number of C, H and O atoms are equal on both sides.

(b)(ii) A reaction that releases (thermal) energy to the surroundings

In an exothermic reaction, the energy released when new bonds form is greater than the energy needed to break the existing bonds.
This net release of energy usually causes the surrounding temperature to increase.

(c)(i) It contains oxygen / does not contain only carbon and hydrogen

Hydrocarbons are compounds made up of only carbon and hydrogen atoms.
Ethanol, \(\text{C}_2\text{H}_5\text{OH}\), also contains oxygen, so it cannot be classified as a hydrocarbon.

(c)(ii) Fermentation of sugars; reaction of ethene with steam

Fermentation uses yeast to convert sugars into ethanol and carbon dioxide.
Alternatively, ethanol can be produced by reacting ethene with steam in the presence of a catalyst.

Question 9

(a) Fig. 9.1 shows an aircraft on a runway.
Use the letters A, B, C or D to complete the sentences. Each letter may be used once, more than once or not at all.
When the aircraft is at rest on the runway, force A is equal to force ………….. and also force B is equal to force ………….. .
When the aircraft starts to accelerate along the runway, forces ………….. and ………….. are unbalanced.
(b) Fig. 9.2 shows the speed-time graph for the aircraft during part of its flight when it is travelling at constant height.
(i) Label with a cross (X) a part of the flight when the aircraft is accelerating.
(ii) State which section of the graph shows the aircraft travelling with no acceleration. Explain your answer.
(c) The aircraft fuel is a non-renewable energy source obtained from petroleum.
(i) Identify the form of energy stored in aircraft fuel.
(ii) Name two renewable energy sources.

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

• Topic P1.5.1 — Effects of forces (Part (a))
• Topic P1.2 — Motion (Part (b))
• Topic P1.6.3 — Energy resources (Part (c))

▶️ Answer/Explanation

(a) Force A = Force C; Force B = Force D; forces B and D become unbalanced

At rest, the upward force (A, lift/reaction) balances the downward force (C, weight), and the forward force (B, thrust) balances the backward force (D, drag/friction).
As the aircraft accelerates, the thrust (B) exceeds the resistive force (D), making them unbalanced and producing acceleration.

(b)(i) Cross placed on the rising section of the graph (near P)

Acceleration corresponds to a section of the graph where the speed is increasing over time.
This is shown by the upward-sloping line near the start of the graph.

(b)(ii) Section Q; because the line is horizontal, showing constant speed

A horizontal line on a speed-time graph means the speed is not changing with time.
Since acceleration is the rate of change of speed, a constant speed means the acceleration is zero.

(c)(i) Chemical energy

Aircraft fuel stores energy in its chemical bonds.
This chemical energy is released as thermal/kinetic energy when the fuel is burned in the engines.

(c)(ii) Any two from: solar, wind, tidal, geothermal, hydroelectric (HEP)

Renewable energy sources are naturally replenished and do not run out on a human timescale.
Examples include solar, wind, tidal, geothermal and hydroelectric power.

Question 10

(a) A farmer keeps ponies. The ponies show variation in height. The farmer sells the smaller ponies for more money than the larger ponies.
(i) Name the type of variation shown by differences in height of the ponies.
(ii) Complete the sentences to describe the method the farmer uses to increase the number of smaller ponies on the farm.
The farmer selects the ponies with the desirable feature.
These ponies are then ………………………… .
The ………………………… offspring are then selected and used for ………………………… .
This process is then ………………………… over many generations.
(iii) State the name of the process the farmer uses.
(b) The inheritance of sex in ponies is the same as in humans.
(i) Complete Table 10.1 to show the inheritance of sex.
(ii) State the ratio of male to female offspring shown in Table 10.1.
(c) Chromosomes contain genes. Define the term gene.

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

• Topic B17.1 — Variation (Part (a)(i))
• Topic B17.2 — Selection (Parts (a)(ii)–(iii))
• Topic B16.3 — Monohybrid inheritance (Part (b))
• Topic B16.1 — Chromosomes and genes (Part (c))

▶️ Answer/Explanation

(a)(i) Continuous variation

Height can take any value across a range rather than falling into a few distinct categories.
This range of values, often influenced by multiple genes and the environment, is characteristic of continuous variation.

(a)(ii) bred; smallest; breeding; repeated

Selected ponies with the desired feature (small size) are bred together.
The smallest offspring from this cross are then chosen and bred again, and this selection process is repeated over many generations to enhance the trait.

(a)(iii) Selective breeding

This is the process of choosing organisms with desirable characteristics to breed, so those characteristics become more common in future generations.

(b)(i)

Males contribute either an X or a Y chromosome, while females always contribute an X chromosome.
Combining these gives the four possible offspring genotypes: XX, XY, XX, XY, as shown completing the table.

(b)(ii) 1:1

Since two of the four possible combinations are XX (female) and two are XY (male), the male to female ratio is equal.
This gives a ratio of 1:1.

(c) A gene is a length of DNA that codes for a (specific) protein

Chromosomes are made of DNA, and each gene is a section of this DNA.
Each gene carries the instructions needed to produce a particular protein, determining an inherited characteristic.

Question 11

(a)(i) Table 11.1 shows information about three colourless liquids J, K and L.
Complete Table 11.1 by inserting the pH for pure water.
(ii) Name one gas that causes acid rain.
(iii) Name the indicator used to find the pH of a liquid.
(b) A student reacts dilute sulfuric acid with four metals. The student’s observations are shown in Table 11.2.
Place the four metals in order of their reactivity from the most reactive to the least reactive.
(c) Table 11.2 shows that magnesium reacts rapidly with sulfuric acid.
(i) State the name of one of the products of this reaction.
(ii) Suggest two ways of increasing the rate of reaction between magnesium and dilute sulfuric acid.
(iii) The gas formed in this reaction is not a greenhouse gas. State the names of two greenhouse gases.

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

• Topic C7.1 — The characteristic properties of acids and bases (Part (a)(i), (iii))
• Topic C10.2 — Air quality and climate (Part (a)(ii), (c)(iii))
• Topic C9.4 — Reactivity series (Part (b))
• Topic C6.2 — Rate of reaction (Part (c))

▶️ Answer/Explanation

(a)(i) 7

Pure water is neutral, neither acidic nor alkaline.
On the pH scale, neutral substances have a pH of exactly 7.

(a)(ii) Sulfur dioxide (or nitrogen dioxide)

Sulfur dioxide is released from burning fossil fuels containing sulfur impurities.
It dissolves in atmospheric water to form dilute sulfurous/sulfuric acid, which falls as acid rain.

(a)(iii) Universal indicator

Universal indicator changes to a range of different colours depending on the pH of the solution.
These colours are compared to a chart to estimate the pH value.

(b) Lithium > magnesium > iron > copper

The more vigorous the observed reaction, the more reactive the metal.
Lithium reacts explosively (most reactive), followed by magnesium (rapid), iron (slow), and copper, which does not react at all (least reactive).

(c)(i) Hydrogen (or magnesium sulfate)

When a reactive metal reacts with a dilute acid, it produces a salt and hydrogen gas.
Here, magnesium reacting with sulfuric acid produces magnesium sulfate and hydrogen.

(c)(ii) Increase the temperature; increase the concentration of the acid (or increase surface area of magnesium)

Raising the temperature gives particles more kinetic energy, causing more frequent and successful collisions.
Increasing the acid’s concentration (or the metal’s surface area) also increases the frequency of collisions between reacting particles.

(c)(iii) Carbon dioxide; methane

Both carbon dioxide and methane absorb infrared radiation and contribute to the greenhouse effect.
Hydrogen, the gas formed here, does not have this property and is not classed as a greenhouse gas.

Question 12

(a) A bicycle has a front lamp, X, and a rear lamp, Y, connected in parallel across a battery. Both lamps are controlled by a single switch.
(i) Draw a circuit diagram using standard electrical symbols showing two lamps connected in parallel across a battery. Include the switch in the diagram.
(ii) When the switch is closed, lamp X has a resistance of 6.0 Ω.
The potential difference across the lamp is 3.0 V.
Calculate the current in lamp X.
(b) Bicycle frames can be made from either steel or aluminium.
(i) Suggest and explain a simple way of deciding whether the frame of the bicycle is made from steel or aluminium.
(ii) A bicycle frame is made from aluminium.
A block of aluminium has a mass of 8100 g and a volume of 3000 cm³.
Calculate the density of aluminium.
(c) The bicycle has a mirror to help the cyclist see behind him.
The cyclist sees a police car in his mirror. This is shown in Fig. 12.1.
(i) Use Fig. 12.1 to describe two characteristics of an image seen in a plane mirror apart from size.

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

• Topic P4.3.2 — Parallel circuits and current calculations (Part (a))
• Topic P1.4 — Density (Part (b))
• Topic P3.2.1 — Reflection and plane mirror images (Part (c))

▶️ Answer/Explanation

(a)(i) Battery, switch in series with both lamps, and lamps X and Y arranged in parallel branches

The switch must be placed in the main circuit so that opening it disconnects both lamps at once.
Each lamp is drawn on its own separate parallel branch so the same potential difference acts across both, and each has an independent current path.

(a)(ii) 0.5 A

Using Ohm’s law, \( I = \dfrac{V}{R} \).
Substituting the given values, \( I = \dfrac{3.0}{6.0} = 0.5\, \text{A} \).

(b)(i) Use a magnet: steel is magnetic, aluminium is not

Steel contains iron and is attracted to a magnet, so it will stick.
Aluminium is not magnetic, so a magnet will not stick to an aluminium frame, allowing the two metals to be distinguished.

(b)(ii) 2.7 g/cm³

Density is calculated using \( \text{density} = \dfrac{\text{mass}}{\text{volume}} \).
Substituting the values, \( \text{density} = \dfrac{8100}{3000} = 2.7\, \text{g/cm}^3 \).

(c)(i) Upright; laterally inverted

The image in a plane mirror is the same way up as the object, so it is described as upright.
It is also laterally inverted, meaning left and right are reversed compared with the object.

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