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Question 1

(a) An athlete monitors her pulse rate during different types of activity.
Fig. 1.1 shows the results.
Use Fig. 1.1 to complete these sentences.
The activity with the highest pulse rate is ……………………………….. .
Two activities have the same pulse rate. They are ……………………………….. and ……………………………….. .
The athlete’s pulse rate was 54 beats per minute when the activity is ……………………………….. .
(b) Fig. 1.2 is a diagram of the heart.
(i) Draw an X on Fig. 1.2 to identify the position of one ventricle.
(ii) State the function of the part labelled Y in Fig. 1.2.
(iii) Identify the part labelled Z in Fig. 1.2.
(iv) Name the type of tissue the wall of the heart is made from.
(v) State the function of the heart.
(c) Name one of the main blood vessels to or from the:
lungs ………………………………..
kidney. ………………………………..

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

• Topic B9.2 — Heart (Parts (a), (b))
• Topic B9.3 — Blood vessels (Part (c))

▶️ Answer/Explanation

(a) running; cycling and walking; sleeping

Reading the bar chart, running has the tallest bar at just under 140 bpm.
Cycling and walking both reach the same height, around 110 bpm.
Sleeping is the only bar that reaches 54 bpm.

(b)(i) X marked on either ventricle

The ventricles are the lower, thick-walled chambers of the heart.
They pump blood out into the arteries.

(b)(ii) Ensures one-way flow of blood

Y is a valve at the base of an artery leaving the heart.
It closes to stop blood flowing backwards into the heart.

(b)(iii) Septum

Z is the muscular wall dividing the left and right sides of the heart.
It prevents oxygenated and deoxygenated blood from mixing.

(b)(iv) Muscle (cardiac muscle)

The heart wall must contract and relax continuously throughout life.
Muscle tissue is the only tissue capable of this repeated contraction.

(b)(v) Pumps blood around the body

Contraction of the heart muscle generates pressure.
This pressure pushes blood through the blood vessels to all body tissues.

(c) Lungs: pulmonary artery / pulmonary vein; Kidney: renal artery / renal vein

The pulmonary artery carries deoxygenated blood to the lungs, and the pulmonary vein returns oxygenated blood.
The renal artery supplies blood to the kidney and the renal vein carries blood away from it.

Question 2

(a) Petroleum is a fossil fuel.
Name two other fossil fuels.
(b) Complete the sentences using words or phrases from the list.
Each word or phrase may be used once, more than once or not at all.
bitumen    chromatography    filtration    fractional distillation
gases    hydrocarbons    naphtha    refinery gas    solids
Petroleum is a mixture of ………………… .
The fractions in petroleum are separated using …………………. .
The fraction used as a feedstock for making chemicals is the …………………. fraction.
(c) Octane, \( C_8H_{18} \), is a hydrocarbon fuel.
(i) State the number of different elements in one molecule of octane.
(ii) State the total number of atoms in one molecule of octane.
(iii) When fuels burn, the reaction produces a temperature increase. State the name given to all reactions that produce a temperature increase.
(iv) State the chemical test for carbon dioxide and the observation for a positive result.

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

• Topic C11.3 — Fuels (Parts (a), (b), (c)(i)–(ii))
• Topic C5.1 — Exothermic and endothermic reactions (Part (c)(iii))
• Topic C12.5 — Identification of ions and gases (Part (c)(iv))

▶️ Answer/Explanation

(a) coal; natural gas

Fossil fuels form over millions of years from the remains of dead organisms.
Coal forms from ancient plant material and natural gas forms alongside petroleum deposits.

(b) hydrocarbons; fractional distillation; naphtha

Petroleum is a mixture of hydrocarbon compounds of varying chain length.
Fractional distillation separates these by their different boiling points.
The naphtha fraction is the feedstock used to make petrochemicals such as plastics.

(c)(i) Two

The formula \( C_8H_{18} \) contains only carbon and hydrogen atoms.

(c)(ii) 26

Adding the subscripts: \( 8 + 18 = 26 \) atoms per molecule.

(c)(iii) Exothermic

Exothermic reactions release energy to the surroundings as heat.
Combustion always releases heat, so it is always exothermic.

(c)(iv) Test: bubble the gas through limewater; Observation: limewater turns milky

Carbon dioxide reacts with the calcium hydroxide in limewater.
This forms insoluble calcium carbonate, which turns the solution cloudy/milky.

Question 3

A student uses her laptop computer.
(a) The laptop screen acts as a plane mirror.
Fig. 3.1 shows a ray of light reflected by the laptop screen.
(i) Name the line labelled XY.
(ii) Label the angle of incidence with the letter \( i \).
(iii) The angle of incidence is \( 40^\circ \). State the angle of reflection.
(b) The laptop contains two speakers each with a resistance of \( 8 \, \Omega \).
(i) The current in one speaker is 3A.
Calculate the potential difference (p.d.) across this speaker.
(ii) The two speakers are connected in parallel.
The combined resistance of the two speakers is one of the following values.
4Ω    8Ω    16Ω    64Ω
State the correct value of the combined resistance. Explain your answer.
(iii) Fig. 3.2 shows circuit symbols for four electrical components found in the laptop.
Identify the four electrical components.
(c) Fig. 3.3 shows the laptop being closed.
Calculate the moment of the force about the pivot in Nm.

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

• Topic P3.2.1 — Reflection of light (Part (a))
• Topic P4.2.4 — Resistance (Part (b)(i)–(ii))
• Topic P4.3.1 — Circuit diagrams and circuit components (Part (b)(iii))
• Topic P1.5.2 — Turning effect of forces (Part (c))

▶️ Answer/Explanation

(a)(i) Normal

The dashed line XY is drawn perpendicular to the mirror surface.
It is the reference line from which the angles of incidence and reflection are measured.

(a)(ii) Angle of incidence labelled \( i \)

The angle of incidence is the angle between the incident ray and the normal.
It is labelled on the same side as the incoming ray.

(a)(iii) \( 40^\circ \)

By the law of reflection, the angle of incidence equals the angle of reflection.
So the angle of reflection is also \( 40^\circ \).

(b)(i) 24 V

Using Ohm’s law: \( V = IR \).
\( V = 3 \, \text{A} \times 8 \, \Omega = 24 \, \text{V} \).

(b)(ii) 4 Ω

For resistors in parallel: \( \dfrac{1}{R_{total}} = \dfrac{1}{8} + \dfrac{1}{8} = \dfrac{1}{4} \).
The combined resistance of resistors in parallel is always less than the smallest individual resistance, so \( R_{total} = 4 \, \Omega \).

(b)(iii) Cell; variable resistor; lamp; switch

Each symbol matches a standard circuit component symbol.
The long/short parallel lines represent a cell, the rectangle with a diagonal arrow is a variable resistor, the circle with a cross is a lamp, and the break in the line is a switch.

(c) 2.9 Nm

Moment = force × perpendicular distance from the pivot.
Convert distance: \( 24 \, \text{cm} = 0.24 \, \text{m} \).
Moment \( = 12 \, \text{N} \times 0.24 \, \text{m} = 2.88 \, \text{Nm} \approx 2.9 \, \text{Nm} \).

Question 4

(a) The inheritance of smooth or wrinkled skin in pea plants is controlled by a single gene.
• The allele for smooth skin is R.
• The allele for wrinkled skin is r.
Fig. 4.1 is a photograph of two peas.
• Pea A has wrinkled skin.
• Pea B has smooth skin.
(i) Table 4.1 shows the genotypes and genotype descriptions of the peas shown in Fig. 4.1.
Complete Table 4.1.
(ii) A scientist crossed two pea plants and observed the results.
Complete the genetic diagram in Fig. 4.2 to identify the parental gametes.
(iii) State the ratio of smooth peas to wrinkled peas from Fig. 4.2.
(b) Fertilisation in plants occurs when the nuclei of the male and female gametes fuse.
Name these two gametes.
(c) State the name of the female gamete in humans.
(d) Table 4.2 contains one term and two definitions linked to inheritance.
Complete Table 4.2.

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

• Topic B16.3 — Monohybrid inheritance (Part (a))
• Topic B15.3 — Sexual reproduction in plants (Part (b))
• Topic B15.2 — Sexual reproduction (Part (c))
• Topic B16.1 — Chromosomes and genes (Part (d))

▶️ Answer/Explanation

(a)(i) 

Pea A shows the recessive wrinkled phenotype, so it must carry two recessive alleles: rr.
Pea B is Rr, meaning it carries two different alleles, which is described as heterozygous.

(a)(ii) 

The Punnett square shows offspring genotypes RR, Rr, Rr and rr.
Working backwards, one parent must contribute R and r, and the other parent must also contribute R and r.

(a)(iii) smooth 3 : wrinkled 1

Of the four genotypes produced (RR, Rr, Rr, rr), three contain at least one dominant R allele and show the smooth phenotype.
Only rr is wrinkled, giving a 3:1 ratio.

(b) Pollen; ovule

Pollen carries the male nucleus and is transferred to the stigma during pollination.
The ovule contains the female nucleus and develops into the seed after fertilisation.

(c) Egg cell / ovum

The egg cell (ovum) is the female gamete produced in the human ovary.

(d) chromosome; gene = a length of DNA that codes for a protein; allele

A chromosome is the thread-like DNA structure described in the first row.
A gene is defined as a length of DNA that codes for a protein.
An allele is a version/alternative form of a gene.

Question 5

(a) Aluminium is a metal.
Two physical properties of metals are that they are good thermal conductors and good electrical conductors.
State two other physical properties of metals.
(b) Duralumin is an alloy of 95% aluminium and 5% copper.
(i) Calculate the mass of aluminium used in 1000 kg of duralumin.
(ii) State why aluminium alloys are used in aircraft parts.
(c) Aluminium is extracted from its ore by electrolysis.
(i) State the name of the ore of aluminium used.
(ii) Define electrolysis.
(iii) Aluminium cannot be extracted from its ore by heating with carbon.
Name one metal which can be extracted from its ore by heating with carbon.
(d) Aluminium ores must be conserved.
(i) State why aluminium ores must be conserved.
(ii) Suggest how aluminium ores may be conserved.

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

• Topic C9.1 — Properties of metals (Part (a))
• Topic C9.3 — Alloys and their properties (Part (b))
• Topic C9.6 — Extraction of metals (Part (c), (d))
• Topic C4.1 — Electrolysis (Part (c)(ii))

▶️ Answer/Explanation

(a) High melting point; malleable (or ductile)

Metals have strong metallic bonding, which gives them high melting and boiling points.
The layered structure of metal atoms allows layers to slide, making metals malleable and ductile.

(b)(i) 950 kg

95% of 1000 kg is aluminium.
Mass = \( \dfrac{95}{100} \times 1000 = 950 \, \text{kg} \).

(b)(ii) Low density / high tensile strength

Aluminium alloys are light, reducing the overall weight of the aircraft.
This makes the aircraft more fuel-efficient while remaining strong enough for structural use.

(c)(i) Bauxite

Bauxite is the main aluminium-containing ore, mainly composed of aluminium oxide.

(c)(ii) Breakdown of an ionic compound (when molten or in aqueous solution) by the passage of an electric current

Electrolysis decomposes an ionic compound into its elements.
This only occurs when the ions are free to move, i.e. when molten or dissolved.

(c)(iii) Iron

Iron is less reactive than aluminium, so it can be displaced from its oxide by carbon during heating.
Aluminium is too reactive for this method and requires electrolysis instead.

(d)(i) Aluminium ore is a finite resource being used up faster than it can be replaced

Ores take millions of years to form naturally.
Continued mining without conservation will eventually exhaust the supply.

(d)(ii) Recycling

Recycling aluminium reduces the need to mine and process new bauxite ore.
It also uses far less energy than extracting aluminium by electrolysis from scratch.

Question 6

Many types of radiation are used in hospitals.
(a) Fig. 6.1 shows an infrared thermometer used to measure body temperature.
(i) Place infrared radiation in the correct place in the incomplete electromagnetic spectrum shown in Fig. 6.2.
(ii) Electromagnetic radiation is used in hospitals. On Fig. 6.3, draw one straight line from each radiation to its correct medical use. One line has been drawn for you.
(b) Ionising radiation from radioactive sources is used in hospitals.
(i) Place α-radiation, β-radiation and γ-radiation in order of their relative ionising effect.
greatest ionising effect   ………………………………………………
                                            ………………………………………………
least ionising effect         ………………………………………………
(ii) State one harmful effect of ionising radiation on the human body.
(c) The isotope iodine-131 is used in hospitals.
(i) State the meaning of the term isotope.
(ii) The half-life of iodine-131 is 8 days.
A sample of iodine-131 is left for 16 days.
The mass of iodine-131 remaining is 0.05 g.
Calculate the mass of iodine-131 in the sample at the start.
(d) In the hospital, the audible frequency range of a patient’s hearing is measured.
The result is a range from 100 Hz to 15 000 Hz.
State how this compares to the average range of audible frequencies for a healthy human ear.
(e) A power station supplies electricity to the hospital. The power station uses petroleum as a fuel.
Complete Fig. 6.4 to show the energy transformations that occur in the power station.

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

• Topic P3.3 — Electromagnetic spectrum (Part (a))
• Topic P5.2.2 — The three types of nuclear emission (Part (b)(i))
• Topic P5.2.5 — Applications and safety precautions (Part (b)(ii))
• Topic P5.1 — The nucleus (Part (c)(i))
• Topic P5.2.4 — Half-life (Part (c)(ii))
• Topic P3.4 — Sound (Part (d))
• Topic P1.6.1 — Energy (Part (e))

▶️ Answer/Explanation

(a)(i) Infrared placed between ultraviolet and radio waves (third box from the right)

The EM spectrum in order of increasing frequency is: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
Infrared sits between microwaves and visible light, i.e. two places to the left of ultraviolet in this table.

(a)(ii) γ-radiation → treating cancer; X-rays → diagnosing broken bones

Gamma rays are highly penetrating and can destroy cancerous cells, so they are used in cancer treatment.
X-rays pass through soft tissue but are absorbed by bone, making them useful for imaging fractures.

(b)(i) Greatest: α-radiation; then β-radiation; least: γ-radiation

Alpha particles are large and highly charged, so they ionise strongly over a short range.
Gamma rays have no charge and are the least ionising but the most penetrating.

(b)(ii) Cancer / cell mutation

Ionising radiation can damage DNA within living cells.
This damage can cause mutations, which may lead to cancer or cell death.

(c)(i) Atoms of the same element with the same number of protons but different numbers of neutrons

Isotopes have identical proton (atomic) numbers, giving them the same chemical properties.
They differ in neutron number, so their nucleon (mass) numbers are different.

(c)(ii) 0.2 g

16 days is equal to 2 half-lives, since \( 16 \div 8 = 2 \).
Working backwards: \( 0.05 \, \text{g} \times 2 \times 2 = 0.2 \, \text{g} \).

(d) Narrower than the average human range of 20 Hz to 20 000 Hz

The average healthy human ear can detect frequencies from about 20 Hz to 20 000 Hz.
The patient’s lowest audible frequency (100 Hz) is higher than average, and their highest audible frequency (15 000 Hz) is lower than average, showing reduced hearing range at both ends.

(e) Chemical (potential) → thermal → kinetic → electrical

Burning petroleum releases stored chemical potential energy as heat (thermal energy).
This thermal energy boils water to produce steam, which turns a turbine, transferring the energy to kinetic energy, and finally the generator converts this to electrical energy.

Question 7

Fig. 7.1 is a diagram of the male reproductive system.
(a) The boxes on the left show the letters of some of the parts in Fig. 7.1.
The boxes on the right show the functions of these parts.
Draw lines to link each letter to its correct function.
(b) Sperm need a high rate of respiration for movement.
State the word equation for aerobic respiration.
(c) Sperm is an example of a type of animal cell.
The list shows some components of cells.
Circle two components that you would expect to find in a sperm cell.
cell membrane       cell wall      chloroplast
cytoplasm      vacuole
(d) State the name of the cell that is formed when gametes fuse.
(e) Name the part of the cell that contains the genetic material.

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

• Topic B15.4 — Sexual reproduction in humans (Part (a))
• Topic B12.1 — Respiration (Part (b))
• Topic B2.1 — Cell structure (Parts (c), (e))
• Topic B15.2 — Sexual reproduction (Part (d))

▶️ Answer/Explanation

(a) 

A is the testis, where sperm cells are made.
B is a gland (e.g. seminal vesicle/prostate) that produces the fluid sperm swim in.
C is the sperm duct, which carries sperm from the testis to the urethra.

(b) Glucose + oxygen → carbon dioxide + water

Aerobic respiration releases energy from glucose using oxygen.
The waste products are carbon dioxide and water.

(c) Cell membrane and cytoplasm

Sperm cells are animal cells, so they lack a cell wall, chloroplast and vacuole (which are plant-cell features).
Like all animal cells, they have a cell membrane and cytoplasm.

(d) Zygote

Fertilisation is the fusion of a sperm nucleus and an egg nucleus.
The resulting single cell is called a zygote.

(e) Nucleus

The nucleus contains the chromosomes, which carry the cell’s genetic material (DNA).

Question 8

(a) Table 8.1 shows the names of eight gases.
(i) One of the gases in Table 8.1 has molecules with the formula \( Cl_2 \). State the name of this gas.
(ii) State the name of the gas from Table 8.1 that is a product of the incomplete combustion of carbon-containing substances.
(iii) State the name of the gas from Table 8.1 that is 78% of clean air.
(iv) State the name of the gas from Table 8.1 that is a greenhouse gas.
(v) State the name of the gas from Table 8.1 that is a noble gas.
(b) Fig. 8.1 shows apparatus a student uses to investigate the rate of reaction between calcium carbonate and dilute hydrochloric acid.
The student adds a single piece of calcium carbonate to the dilute hydrochloric acid.
(i) State the name of the gas collected in the measuring cylinder.
(ii) Predict how the pH of the water changes as the gas bubbles through it. Explain your answer.
(iii) The student repeats the experiment using the same mass of calcium carbonate and the same volume of dilute hydrochloric acid.
Suggest two changes the student can make to their experiment to increase the rate of reaction.

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

• Topic C2.5 — Simple molecules and covalent bonds (Part (a)(i))
• Topic C10.2 — Air quality and climate (Part (a)(ii)–(iv))
• Topic C8.4 — Transition elements / Group VIII noble gases (Part (a)(v))
• Topic C6.2 — Rate of reaction (Part (b)(i), (iii))
• Topic C7.1 — The characteristic properties of acids and bases (Part (b)(ii))

▶️ Answer/Explanation

(a)(i) Chlorine

Chlorine gas exists as diatomic molecules of formula \( Cl_2 \).

(a)(ii) Carbon monoxide

When there isn’t enough oxygen for complete combustion, carbon monoxide (rather than carbon dioxide) is formed.

(a)(iii) Nitrogen

Clean, dry air is approximately 78% nitrogen and 21% oxygen, with the remainder being noble gases and carbon dioxide.

(a)(iv) Methane

Methane traps thermal energy in the atmosphere, contributing to global warming, so it is classed as a greenhouse gas.

(a)(v) Helium

Helium is a Group VIII element with a full outer electron shell, making it an unreactive noble gas.

(b)(i) Carbon dioxide

The reaction between a carbonate and an acid always produces carbon dioxide gas, along with a salt and water.

(b)(ii) pH decreases

Carbon dioxide is an acidic, non-metal oxide.
When it dissolves in water it forms a weak acid, lowering the pH.

(b)(iii) Increase acid concentration; increase temperature (or increase surface area of the calcium carbonate)

A higher acid concentration increases the frequency of collisions between reacting particles.
A higher temperature gives particles more kinetic energy, again increasing the collision frequency and rate.

Question 9

(a) Fig. 9.1 shows a wind surfer on a surfboard, driven by the wind, sailing at a constant speed across the water.
Four forces J, K, L and M acting on the surfboard are shown.
(i) Explain why force K and force M must be equal and opposite.
(ii) Identify force L.
(iii) Work is done by the wind to move the surfboard across the water.
State the two quantities needed to calculate the work done by the wind.
(b) Fig. 9.2 represents a water wave.
(i) On Fig. 9.2, label the amplitude of the wave with a double headed arrow (↔ or ↕).
(ii) The waves have a frequency of 0.1 Hz. Explain what is meant by a frequency of 0.1 Hz.
(c) Water molecules in the sea are able to form water vapour above the sea.
During this process, the more energetic molecules escape from the surface of the sea.
(i) Suggest the effect this will have on the energy of the water molecules remaining in the sea water.
(ii) Suggest the effect this will have on the temperature of the sea water.
(d) Some sea water has a volume of \( 5.0 \, \text{m}^3 \) and a mass of 5120 kg.
Calculate the density of the sea water.

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

• Topic P1.5.1 — Effects of forces (Part (a)(i))
• Topic P1.3 — Mass and weight (Part (a)(ii))
• Topic P1.6.2 — Work (Part (a)(iii))
• Topic P3.1 — General properties of waves (Part (b))
• Topic P2.2.2 — Melting, boiling and evaporation (Part (c))
• Topic P1.4 — Density (Part (d))

▶️ Answer/Explanation

(a)(i) The surfboard is moving at constant speed, so there is no resultant force

An object moving at constant speed has zero acceleration.
For the resultant force to be zero, the forward force K must exactly balance the opposing force M.

(a)(ii) Weight (gravitational force)

Force L acts vertically downward on the surfboard.
This is the weight of the surfer and board due to gravity.

(a)(iii) Force and distance

Work done is calculated using \( W = F \times d \).
So both the force applied by the wind and the distance moved in that direction are needed.

(b)(i) Amplitude labelled from the equilibrium (midline) to the crest or trough

Amplitude is the maximum displacement of the wave from its rest position.
It should be drawn as a vertical double-headed arrow from the centre line to the peak (or trough) of the wave.

(b)(ii) One complete wave passes a point every 10 seconds

Frequency is the number of complete waves passing a point per second.
A frequency of \( 0.1 \, \text{Hz} \) means \( \dfrac{1}{0.1} = 10 \) seconds per wave.

(c)(i) The energy of the remaining molecules decreases

The most energetic molecules are the ones that escape as vapour.
This leaves molecules with lower average energy behind in the liquid.

(c)(ii) The temperature decreases (evaporative cooling)

Temperature depends on the average kinetic energy of the particles.
Since the average energy of the remaining water molecules falls, the temperature of the sea water decreases.

(d) \( 1024 \, \text{kg/m}^3 \)

Density is calculated using \( \rho = \dfrac{m}{V} \).
\( \rho = \dfrac{5120}{5.0} = 1024 \, \text{kg/m}^3 \).

Question 10

(a) Water is lost from leaves by transpiration. This causes a loss in mass.
A student records the mass of leaves from a plant.
He places the leaves under a heat lamp.
He records the mass of the leaves every 24 hours for 5 days.
The results are shown in Table 10.1.
(i) Calculate the total decrease in mass between day 1 and day 5.
(ii) The investigation is repeated at a lower temperature.
The statements show some predictions.
Tick (✓) one box to show the correct prediction.
(b) State the process by which water is lost from the surfaces of the mesophyll cells during transpiration.
(c) State the name of the part of the leaf where water exits the plant.
(d) A plant obtains water from the soil. Describe how water enters the plant and is transported to the mesophyll cells in the leaves.
(e) One use of water in a plant is for photosynthesis.
(i) State one other use of water in a plant.
(ii) State two other requirements of photosynthesis.

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

• Topic B8.3 — Transpiration (Parts (a), (b), (c))
• Topic B8.2 — Water uptake (Part (d))
• Topic B6.1 — Photosynthesis (Part (e))

▶️ Answer/Explanation

(a)(i) 57 g

Total decrease = mass on day 1 − mass on day 5.
\( 115 – 58 = 57 \, \text{g} \).

(a)(ii) The decrease in mass will be less than in the first investigation

A lower temperature reduces the rate of evaporation from the mesophyll cells.
This slows transpiration, so less water (and mass) is lost over the same time period.

(b) Evaporation

Water changes from liquid to vapour at the moist surfaces of the mesophyll cells.
This vapour then diffuses out of the leaf.

(c) Stomata

Stomata are small pores, mainly on the underside of the leaf, through which water vapour diffuses out.

(d) Water enters via root hair cells by osmosis, passes through root cortex cells, and is transported up the xylem to the leaves

Root hair cells have a large surface area, allowing efficient water uptake from the soil by osmosis.
Water then moves across the root cortex cells and into the xylem vessels.
The xylem carries the water up the stem to the mesophyll cells in the leaf.

(e)(i) Support (turgor pressure) / as a solvent

Water entering plant cells by osmosis creates turgor pressure, which keeps the cells rigid and supports the plant.

(e)(ii) Light; carbon dioxide (or a suitable temperature / chlorophyll)

Photosynthesis requires light energy to drive the reaction.
It also requires carbon dioxide as a raw material to build glucose.

Question 11

(a) Fig. 11.1 shows part of Group I of the Periodic Table.
(i) State the electronic structure of a potassium atom.
(ii) Describe how the electronic structure of potassium is related to its group number.
(iii) The proton number of a potassium atom is 19.
The nucleon number of this potassium atom is 39.
State the numbers of electrons and neutrons in this potassium atom.
(iv) Complete Table 11.1 to show the charges and approximate relative masses of an electron and a neutron.
(b) Potassium, K, is an element. Potassium hydroxide, KOH, is a compound.
Explain the difference between an element and a compound.
(c) Balance the symbol equation for the reaction between potassium and water.
…….K  +  …….\( H_2O \)  →  …….KOH  +  \( H_2 \)

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

• Topic C2.2 — Atomic structure and the Periodic Table (Part (a)(i)–(iv))
• Topic C2.1 — Elements, compounds and mixtures (Part (b))
• Topic C8.2 — Group I properties (Part (c))

▶️ Answer/Explanation

(a)(i) 2,8,8,1

Potassium has 19 electrons.
These fill the shells as 2, 8, 8, then the final electron sits alone in the fourth shell.

(a)(ii) The number of outer-shell electrons equals the group number

Potassium is in Group I, so it has 1 electron in its outermost shell.
This single outer electron is what gives Group I elements their similar reactive chemical properties.

(a)(iii) Electrons = 19; Neutrons = 20

In a neutral atom, the number of electrons equals the number of protons, so electrons = 19.
Neutrons = nucleon number − proton number = \( 39 – 19 = 20 \).

(a)(iv) 

Electrons carry a single negative charge and have negligible mass compared to protons and neutrons.
Neutrons are electrically neutral and have approximately the same mass as a proton.

(b) Element — contains only one type of atom; Compound — contains two or more elements chemically combined

Potassium metal (K) is made of only potassium atoms, so it is an element.
Potassium hydroxide (KOH) contains potassium, oxygen and hydrogen atoms bonded together, so it is a compound.

(c) 2K + 2\( H_2O \) → 2KOH + \( H_2 \)

Balancing potassium: 2 K atoms on each side.
Balancing oxygen and hydrogen: 2 water molecules give 2 KOH plus 1 \( H_2 \) molecule, balancing all atoms.

Question 12

(a) Fig. 12.1 shows a large snow tractor used in Antarctica.
The snow tractor has large continuous tracks.
These tracks allow the snow tractor to move across the snow without sinking.
Explain why a tractor with normal wheels would sink into the snow.
(b) When gasoline (petrol) burns in the engine of the snow tractor, carbon dioxide gas and water vapour are produced.
State which of the diagrams, X, Y or Z in Fig. 12.2, shows the arrangement of gaseous carbon dioxide molecules.
Give a reason for your answer.
(c)(i) The snow tractor accelerates.
State the form of energy gained as the tractor accelerates.
(c)(ii) The snow tractor moves up a hill at constant speed.
State the form of energy gained as the tractor moves up the hill.
(d) Fig. 12.3 shows a distance-time graph for the snow tractor moving at constant speed.
Calculate this constant speed.

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

• Topic P1.7 — Pressure (Part (a))
• Topic C1.1 — Solids, liquids and gases (Part (b))
• Topic P1.6.1 — Energy (Part (c))
• Topic P1.2 — Motion (Part (d))

▶️ Answer/Explanation

(a) Normal wheels have a smaller contact area, so pressure is greater

Pressure is force divided by contact area: \( P = \dfrac{F}{A} \).
The large continuous tracks spread the tractor’s weight over a much bigger area than narrow wheels, reducing the pressure and stopping it sinking.

(b) Diagram Z

In a gas, particles are far apart, move freely and are randomly arranged.
Diagram Z shows widely spaced, randomly arranged molecules, matching the gaseous state of carbon dioxide.

(c)(i) Kinetic energy

As the tractor speeds up, its kinetic energy store increases because kinetic energy depends on speed.

(c)(ii) Gravitational potential energy

Moving up a hill increases the tractor’s height.
This increases its gravitational potential energy store, even though its speed (and so kinetic energy) stays constant.

(d) 0.5 m/s

Speed = distance ÷ time, using a straight-line reading from the graph.
From the graph, the tractor covers 8 m in 16 s: \( \dfrac{8}{16} = 0.5 \, \text{m/s} \).

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