2023 Cambridge IGCSE Sciences - Co-ordinated (Double) (0654) Practice Paper with Answers

(a)(i) \(a = \frac{v - u}{t} = \frac{12\text{ m/s} - 0}{5.0\text{ s}} = 2.4\text{ m/s}^2\)
(ii) \(d = \frac{1}{2} \times t \times v = \frac{1}{2} \times 5.0\text{ s} \times 12\text{ m/s} = 30\text{ m}\)
(b)(i) Resultant force = 0 N because the speed is constant / acceleration is zero.
(ii) \(KE = \frac{1}{2}mv^2 = \frac{1}{2} \times 15\text{ kg} \times (12\text{ m/s})^2 = 1080\text{ J}\)
(c) \(W = m \times g = 2.0\text{ kg} \times 10\text{ N/kg} = 20\text{ N}\)

(a)(i)
- Formula/working: \(12 / 5.0\) [1]
- Value and unit: \(2.4\text{ m/s}^2\) [1]
(a)(ii)
- Working: \(0.5 \times 5.0 \times 12\) [1]
- Value: \(30\text{ m}\) [1]
(b)(i)
- Value: \(0\text{ N}\) [1]
- Reason: Constant speed / zero acceleration [1]
(b)(ii)
- Working: \(0.5 \times 15 \times 12^2\) [1]
- Value: \(1080\text{ J}\) [1]
(c)
- Working: \(2.0 \times 10\) [1]
- Value: \(20\text{ N}\) [1]

(a)(i) Protons: 17, Neutrons: 20 (37 - 17), Electrons: 17
(ii) Atoms of the same element with the same number of protons but different numbers of neutrons.
(b)(i) Covalent bonding; electrons are shared between non-metal atoms.
(ii) The carbon atom shares two pairs of electrons with each of the two sulfur atoms, forming two double covalent bonds. This allows all three atoms to achieve a stable outer shell of 8 electrons.
(c) Covalent compounds have lower melting/boiling points than ionic compounds (or do not conduct electricity in molten/liquid states).

(a)(i)
- 2 marks for all three correct (Protons = 17, Neutrons = 20, Electrons = 17)
- 1 mark if two of these are correct
(a)(ii)
- Atoms of same element / same proton number [1]
- Different number of neutrons [1]
(b)(i)
- Covalent [1]
- Electrons are shared [1]
(b)(ii)
- Two double bonds / four shared electrons between C and each S atom [1]
- Total of four shared pairs / eight bonding electrons in the molecule [1]
(c)
- Lower melting/boiling point [1] OR poor/no electrical conductivity when liquid [1]
- Accept any correct comparison [1]

(a) Water moves from the soil into the root hair cells by osmosis, down a water potential gradient (soil has higher water potential than root hair cell cytoplasm), across a partially permeable membrane.
(b)(i) Hollow tubes with no end walls, and walls thickened with lignin.
(ii) Water evaporates from the mesophyll cell surfaces into the air spaces, and water vapour diffuses out of the leaves through stomata. This loss of water creates a tension/pull (transpiration pull) that draws up a continuous column of water molecules, held together by cohesion.
(c) Phloem tissue; transports substances both upwards and downwards (from source to sink).

(a)
- Osmosis [1]
- Down a water potential gradient / soil has higher water potential than cytoplasm [1]
- Across a partially permeable membrane [1]
(b)(i)
- No end walls / hollow tubes / dead cells [1]
- Lignified/thickened walls [1]
(b)(ii)
- Water evaporates from mesophyll cells [1]
- Water vapour diffuses out of stomata [1]
- Creates tension/pull drawing up water column due to cohesion [1]
(c)
- Phloem [1]
- Bidirectional / up and down / from source to sink [1]

(a)(i) Pepsin / protease; pH 1.5 - 2.5 (acidic pH).
(ii) Amino acids.
(b)(i) Incisors have a chisel-shaped, sharp edge and are used for biting and cutting food, whereas molars have a broad, flat surface with ridges and are used for crushing and grinding food.
(ii) Bacteria feed on sugar/food left on teeth, producing acid as they respire. This acid dissolves the calcium-rich enamel and dentine, leading to tooth decay.
(c) Vitamin C (ascorbic acid).

(a)(i)
- Pepsin / protease [1]
- Acidic pH / pH 1.5–2.5 [1]
(a)(ii)
- Amino acids [1]
(b)(i)
- Incisor structure: chisel-shaped/sharp AND function: biting/cutting [1.5]
- Molar structure: broad/ridged flat AND function: grinding/crushing [1.5]
(b)(ii)
- Bacteria respire sugar / produce acid [1]
- Acid attacks/dissolves enamel [1]
- Reaches dentine / creates cavity [1]
(c)
- Vitamin C / ascorbic acid [1]

(a)(i) Circuit diagram must show: a battery symbol, a variable resistor symbol (rectangle with diagonal arrow), and a fixed resistor symbol (rectangle) all connected in a single loop (series).
(ii) \(V = I \times R = 1.5\text{ A} \times 6.0\ \Omega = 9.0\text{ V}\)
(iii) \(P = I^2 R = (1.5\text{ A})^2 \times 6.0\ \Omega = 2.25 \times 6.0 = 13.5\text{ W}\) (or \(P = V \times I = 9.0\text{ V} \times 1.5\text{ A} = 13.5\text{ W}\))
(b)(i) Iron; it is magnetically soft, meaning it is easily magnetised and demagnetised when the current is switched on and off.
(ii) Increase the current flowing through the coil, and increase the number of turns in the coil.

(a)(i)
- Correct symbols for battery, variable resistor, and fixed resistor [1]
- All components connected correctly in series [1]
(a)(ii)
- Formula/working: \(1.5 \times 6.0\) [1]
- Value and unit: \(9.0\text{ V}\) [1]
(a)(iii)
- Formula/working: \(1.5^2 \times 6.0\) or \(9.0 \times 1.5\) [1]
- Value and unit: \(13.5\text{ W}\) [1]
(b)(i)
- Iron [1]
- Magnetically soft / easily demagnetised when current is off [1] (Do NOT accept steel)
(b)(ii)
- Increase the current [1]
- Increase the number of turns/loops of the coil [1]

(a)(i) Reactivity increases down the group. Down the group, the atoms have more electron shells, so the outer electron is further from the positive nucleus. There is a weaker electrostatic attraction between the nucleus and the outer electron, making it easier to lose the single outer electron.
(ii) Any two from: melts into a ball, floats/moves on the surface of the water, fizzes/bubbles/effervesces, dissolves/disappears.
(b)(i) Bromine is a liquid; iodine is a solid.
(ii) Colour change: colourless to brown (or orange/red-brown).
Ionic equation: \(\text{Cl}_2(\text{g}) + 2\text{I}^-(\text{aq}) \rightarrow 2\text{Cl}^-(\text{aq}) + \text{I}_2(\text{aq})\)

(a)(i)
- Reactivity increases down the group [1]
- Outer shell electron is further from the nucleus / atom gets larger [1]
- Weaker attraction / electron lost more easily [1]
(a)(ii)
- Any two observations: melts into ball / floats / fizzes or bubbles / moves rapidly on surface / disappears [2]
(b)(i)
- Bromine is liquid [1]
- Iodine is solid [1]
(b)(ii)
- Turns brown/orange/red-brown [1]
- Correct ionic reactants and products: \(\text{Cl}_2 + 2\text{I}^- \rightarrow 2\text{Cl}^- + \text{I}_2\) [1]
- Balanced equation [1]

(a)(i) \(3.0 \times 10^8\text{ m/s}\)
(ii) \(\lambda = \frac{v}{f} = \frac{3.0 \times 10^8\text{ m/s}}{2.4 \times 10^9\text{ Hz}} = 0.125\text{ m}\) (or \(1.3 \times 10^{-1}\text{ m}\) or \(12.5\text{ cm}\))
(b)(i) In a longitudinal wave, the vibrations of the particles are parallel to the direction of energy transfer.
(ii) Speed increases and wavelength increases (frequency remains constant).
(c)(i) Refraction
(ii) As the ray enters the glass, it bends towards the normal. As it leaves the glass back into air, it bends away from the normal.

(a)(i)
- \(3.0 \times 10^8\text{ m/s}\) [1]
(a)(ii)
- Working: \(3.0 \times 10^8 / 2.4 \times 10^9\) [1]
- Value and unit: \(0.125\text{ m}\) (or \(12.5\text{ cm}\)) [1]
(b)(i)
- Vibrations/oscillations [1]
- Parallel to energy transfer direction [1]
(b)(ii)
- Speed increases [1]
- Wavelength increases [1]
(c)(i)
- Refraction [1]
(c)(ii)
- Enters: bends towards normal [1]
- Leaves: bends away from normal [1]

(a)(i) Connect the reaction flask to a gas syringe using a delivery tube. Measure the volume of carbon dioxide gas produced at regular time intervals using a stopwatch. (Alternatively, place the flask on a balance and record the decrease in mass over time.)
(ii) A higher concentration means there are more acid particles per unit volume. This results in more frequent collisions (more collisions per second) between the reactant particles, which increases the rate of successful collisions and thus the rate of reaction.
(b)(i) A substance that increases the rate of a chemical reaction, but remains chemically unchanged at the end of the reaction.
(ii) A catalyst provides an alternative pathway for the reaction that has a lower activation energy, meaning a higher proportion of reacting particles have enough energy to react upon collision.

(a)(i)
- Measure volume of gas / decrease in mass [1]
- Use gas syringe / balance [1]
- Record time / use stopwatch [1]
(a)(ii)
- More particles per unit volume / particles closer [1]
- More frequent collisions [1]
- Increased rate of successful/effective collisions [1]
(b)(i)
- Speeds up reaction [1]
- Chemically unchanged / mass remains constant at end [1]
(b)(ii)
- Alternative reaction pathway [1]
- Lower activation energy [1]

(a) (i) The potometer is filled with water and a leafy shoot is inserted. The joint is sealed. An air bubble is introduced into the capillary tube. The distance moved by the bubble along a scale per unit time (e.g. per minute) is measured to estimate the rate of transpiration.

(ii) Increasing wind speed increases the rate of transpiration. Wind blows away the water vapour that accumulates around the surface of the leaf / stomata. This maintains a steep water vapour concentration gradient between the inside of the leaf and the outside air, causing faster diffusion of water vapour out of the stomata.

(b) (i) Any two from:
- Hollow tubes / no cytoplasm / no living contents to allow unobstructed flow.
- Lignified / thick walls to prevent the vessels from collapsing under tension.
- End walls between cells are broken down / absent to form continuous tubes.
- Pits in walls to allow lateral movement of water.

(ii) Translocation in phloem is an active process that requires energy / active transport (whereas xylem transport is passive / driven by transpiration pull). Translocation transports sucrose and amino acids (whereas xylem transports water and mineral ions). Translocation occurs in both upwards and downwards directions (whereas xylem transport is in the upwards direction only).

(a)(i) Max 2 marks:
- measure distance moved by bubble [1]
- in a given/measured time / per unit time [1]

(a)(ii) Max 3 marks:
- rate increases [1]
- wind moves/removes water vapour from around the leaf / stomata [1]
- maintains/increases the concentration gradient [1]

(b)(i) Max 2 marks:
- hollow tubes / no cytoplasm / no living contents [1]
- lignified/thick walls [1]
- no end walls / continuous tubes [1]

(b)(ii) Max 3 marks:
- active process / requires energy / active transport vs passive in xylem [1]
- transport of sucrose/amino acids vs water/mineral ions in xylem [1]
- transport is in both directions (up and down) vs upwards only in xylem [1]

(a) (i) \(\text{C}_{10}\text{H}_{22} \rightarrow \text{C}_8\text{H}_{18} + \text{C}_2\text{H}_4\)

(ii) High temperature (approx. \(450^\circ\text{C}\) to \(800^\circ\text{C}\)) and a catalyst (silica / alumina / zeolite).

(b) (i) Test: Bromine water / aqueous bromine.
Octane (alkane): Stays orange / brown / yellow / no change.
Ethene (alkene): Decolourises / turns colourless.

(ii) Draw a chain of four carbon atoms linked by single bonds, with two hydrogen atoms attached to each carbon atom. Single bonds on the ends with extension lines to show the continuation of the polymer chain.

(a)(i) Max 2 marks:
- correct formula of ethene, \(\text{C}_2\text{H}_4\) [1]
- fully balanced equation [1]

(a)(ii) Max 2 marks:
- high temperature / temp in range \(450^\circ\text{C}\) to \(800^\circ\text{C}\) [1]
- catalyst / named catalyst e.g. silica/alumina/zeolite [1]

(b)(i) Max 3 marks:
- bromine water starting colour is orange/brown/yellow [1]
- result with octane: stays orange/brown/yellow / no reaction [1]
- result with ethene: decolourises / turns colourless [1]

(b)(ii) Max 3 marks:
- only single bonds between carbon atoms in the chain [1]
- four carbon atoms shown with extension bonds at the ends [1]
- eight hydrogen atoms correctly attached to the carbon atoms [1]

(a) (i) \(a = \frac{v - u}{t} = \frac{8.0 - 0}{12.0} = 0.67\text{ m/s}^2\) (or \(2/3\text{ m/s}^2\))

(ii) \(KE = \frac{1}{2} m v^2 = \frac{1}{2} \times 75 \times 8.0^2 = 2400\text{ J}\)

(b) (i) \(W = m g h = 75 \times 10 \times 15 = 11250\text{ J}\)

(ii) Total energy input = \(P \times t = 300 \times 50 = 15000\text{ J}\).
Efficiency = \(\frac{\text{useful energy output}}{\text{total energy input}} \times 100\% = \frac{11250}{15000} \times 100\% = 75\%\).

(a)(i) Max 3 marks:
- formula: \(a = \Delta v / t\) [1]
- calculation: \(0.67\) / \(0.667\) [1]
- unit: \(\text{m/s}^2\) [1]

(a)(ii) Max 2 marks:
- formula: \(KE = \frac{1}{2} m v^2\) or correct substitution [1]
- calculation: \(2400\text{ J}\) [1]

(b)(i) Max 2 marks:
- formula: \(W = mgh\) or correct substitution [1]
- calculation: \(11250\text{ J}\) [1]

(b)(ii) Max 3 marks:
- calculate total energy input: \(15000\text{ J}\) [1]
- formula: \(\text{efficiency} = (\text{useful energy} / \text{total energy}) \times 100\%\) [1]
- calculation: \(75\%\) [1]

(a) (i) \(\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} = \frac{1}{4.0} + \frac{1}{6.0} = \frac{3}{12} + \frac{2}{12} = \frac{5}{12}\)
\(R_p = \frac{12}{5} = 2.4\ \Omega\)

(ii) \(I = \frac{V}{R_p} = \frac{12}{2.4} = 5.0\text{ A}\)

(iii) The voltage across \(R_1\) is \(12\text{ V}\) (parallel circuit).
\(P = \frac{V^2}{R_1} = \frac{12^2}{4.0} = \frac{144}{4.0} = 36\text{ W}\)
(Alternatively: current through \(R_1\) is \(I_1 = \frac{12}{4.0} = 3.0\text{ A}\), Power \(P = I_1^2 \times R_1 = 3.0^2 \times 4.0 = 36\text{ W}\))

(b) (i) Electromagnetic induction.

(ii) Any three from:
- Move the wire faster / increase the speed of movement.
- Use a stronger magnet / increase the magnetic field strength.
- Increase the length of wire in the magnetic field / use a coil with more turns.
- Move the wire at a right angle (\(90^\circ\)) to the magnetic field lines.

(a)(i) Max 2 marks:
- formula: \(1/R_p = 1/R_1 + 1/R_2\) or \(R_p = (R_1 \times R_2)/(R_1 + R_2)\) or correct substitution [1]
- calculation: \(2.4\ \Omega\) [1]

(a)(ii) Max 2 marks:
- formula: \(I = V/R\) or correct substitution [1]
- calculation: \(5.0\text{ A}\) [1]

(a)(iii) Max 2 marks:
- calculate current in \(R_1\) as \(3.0\text{ A}\) OR state voltage as \(12\text{ V}\) [1]
- calculation: \(36\text{ W}\) [1]

(b)(i) Max 1 mark:
- electromagnetic induction [1]

(b)(ii) Max 3 marks (any three from):
- move the wire faster [1]
- stronger magnetic field / stronger magnet [1]
- more turns of wire / longer wire [1]
- move perpendicular to field lines [1]