Question 1
(a)(i)-(ii) Subtopic: B6.1 Photosynthesis
(b)(i)-(ii) Subtopic: B6.2 Leaf structure
(c) Subtopic: B6.1 Photosynthesis
(a) The graph in Fig. 1.1 shows the effect of light intensity on the rate of photosynthesis.
(i) Describe the results shown in Fig. 1.1.
▶️Answer/Explanation
The graph shows that as light intensity increases, the rate of photosynthesis increases proportionally at first. However, beyond a certain point (labeled X), the rate of photosynthesis plateaus and no longer increases with further increases in light intensity.
(ii) Explain the reasons for the shape of the part of the graph labelled X.
▶️Answer/Explanation
The plateau occurs because light intensity is no longer the limiting factor for photosynthesis. At this point, other factors such as carbon dioxide concentration or temperature become limiting. The plant cannot photosynthesize faster even with more light because it’s constrained by these other factors.
(b) Fig. 1.2 shows a cross-section through a leaf.
(i) Describe two features of the leaf shown in Fig. 1.2 that allow efficient gas exchange to occur.
▶️Answer/Explanation
1. Presence of stomata (pores) that allow gases to enter and exit the leaf. 2. Large air spaces in the spongy mesophyll layer that provide a large surface area for gas exchange.
(ii) On Fig. 1.2, use a label line to label an example of a cell that is best adapted for photosynthesis. Include the name of the cell.
▶️Answer/Explanation
The palisade mesophyll cell should be labeled. These cells are located near the upper surface of the leaf and contain many chloroplasts, making them ideally adapted for photosynthesis.
(c) State the chemical formulae of the two products of photosynthesis.
▶️Answer/Explanation
1. C6H12O6 (glucose) 2. O2 (oxygen)
Question 2
(a)(i)-(iii) Subtopic: C9.6 Extraction of metals
(b)(i)-(iv) Subtopic: C4.1 Electrolysis
(c)(i)-(ii) Subtopic: C9.6 Extraction of metals
(a) Carbon is used to extract zinc from zinc oxide, ZnO.
(i) Write a balanced symbol equation for this reaction.
▶️Answer/Explanation
C + 2ZnO → CO2 + 2Zn
Explanation: This is a redox reaction where carbon acts as the reducing agent. The carbon is oxidized to CO2 while the zinc oxide is reduced to zinc metal.
(ii) Zinc oxide consists of Zn2+ and O2- ions. State which ion is being reduced in this reaction. Explain your answer in terms of the movement of electrons.
▶️Answer/Explanation
The Zn2+ ion is being reduced.
Explanation: Reduction involves gain of electrons. In this reaction, each Zn2+ ion gains 2 electrons to become neutral Zn atoms (Zn2+ + 2e– → Zn).
(iii) Explain why carbon cannot be used to extract aluminium from aluminium oxide.
▶️Answer/Explanation
Aluminium is more reactive than carbon in the reactivity series. Carbon cannot reduce aluminium oxide because carbon isn’t a strong enough reducing agent to remove oxygen from aluminium oxide. Additional note: This is why aluminium is extracted by electrolysis rather than chemical reduction.
(b) Aluminium is extracted by the electrolysis of aluminium oxide. Aluminium oxide consists of Al3+ and O2- ions. Fig. 2.1 shows the industrial apparatus used to produce aluminium.
(i) State the name of an ore that contains aluminium.
▶️Answer/Explanation
Bauxite
Note: Bauxite is the primary ore of aluminium, consisting mainly of aluminium oxide (Al2O3) with impurities.
(ii) Explain why aluminium oxide must be in a liquid state for electrolysis to occur.
▶️Answer/Explanation
The ions (Al3+ and O2-) need to be mobile to move towards the electrodes. In solid state, the ions are fixed in position and cannot move to complete the electrical circuit.
Key point: Ionic compounds only conduct electricity when molten or dissolved because their ions are free to move.
(iii) Explain why cryolite is mixed with aluminium oxide for use in this electrolysis.
▶️Answer/Explanation
Cryolite (Na3AlF6) lowers the melting point of aluminium oxide from about 2072°C to about 950°C, making the process more energy-efficient and economical.
Practical benefit: This significant reduction in operating temperature saves substantial energy costs in industrial production.
(iv) Write the ionic half-equation for the reaction occurring at the cathode during this electrolysis.
▶️Answer/Explanation
Al3+ + 3e– → Al
Explanation: At the cathode (negative electrode), aluminium ions gain electrons (reduction) to form molten aluminium metal that collects at the bottom of the cell.
(c) Aluminium ore is a finite resource, so aluminium must be conserved.
(i) State what is meant by the term finite resource.
▶️Answer/Explanation
A finite resource is one that is non-renewable and will eventually run out because it is being used faster than it can be naturally replaced.
Examples: Fossil fuels, metal ores, and other minerals are all finite resources.
(ii) Suggest how aluminium can be conserved.
▶️Answer/Explanation
Recycling aluminium products (e.g., cans, foil, car parts).
Benefits: Recycling uses only 5% of the energy needed to extract new aluminium from ore, and aluminium can be recycled indefinitely without losing quality.
Question 3
(a)(i)-(iii) Subtopic: P4.2.2 Electric current / P4.2.5 Electrical energy and electrical power
(b)(i)-(iv) Subtopic: P4.5.2 The a.c. generator
(c) Subtopic: P3.4 Sound
Fig. 3.1 shows a motorcycle with a rear lamp.
(a) The lamp has a resistance of 30Ω and is powered by a 12V battery.
(i) Show that the current in the lamp is 0.40A.
▶️Answer/Explanation
Using Ohm’s Law: V = IR → I = V/R = 12V/30Ω = 0.40A
Calculation steps: 1. Identify known values: V = 12V, R = 30Ω 2. Rearrange Ohm’s Law to solve for current (I) 3. Substitute values: I = 12/30 = 0.40A
(ii) Calculate the power used by the lamp. Show your working.
▶️Answer/Explanation
Power = Voltage × Current = 12V × 0.40A = 4.8W
Alternative methods: – P = I²R = (0.40)² × 30 = 4.8W – P = V²/R = 12²/30 = 4.8W
(iii) Calculate the charge that passes through the lamp in 30 minutes. Show your working.
▶️Answer/Explanation
Charge = Current × Time = 0.40A × (30 × 60)s = 720C
Unit conversion: – 30 minutes = 30 × 60 = 1800 seconds – Q = I × t = 0.40 × 1800 = 720 Coulombs
(b) The battery is charged by an a.c. generator. Fig. 3.2 shows a simple a.c. generator.
(i) On Fig. 3.2, label the slip rings with the letter R.
▶️Answer/Explanation
Slip rings should be labeled on the rotating part of the generator where the coil connects to the external circuit.
Function: Slip rings maintain continuous electrical contact while allowing the coil to rotate, producing alternating current (AC).
(ii) On Fig. 3.2, label the coil with the letter C.
▶️Answer/Explanation
The coil is the rotating loop of wire between the magnet poles. Key feature: As this coil cuts through magnetic field lines, it induces the alternating current.
(iii) On Fig. 3.2, show the direction of the magnetic field with an arrow (→).
▶️Answer/Explanation
The arrow should point from the North pole (N) to the South pole (S) of the magnet. Convention: Magnetic field lines always run from north to south outside the magnet.
(iv) The output is an alternating current. Describe the difference between direct current (d.c.) and alternating current (a.c.).
▶️Answer/Explanation
Direct current (DC) flows in one constant direction, while alternating current (AC) periodically reverses direction. Key differences: – DC: Electrons flow one way (e.g., batteries) – AC: Electrons oscillate back/forth (e.g., mains electricity) – AC can be easily transformed to different voltages
(c) The motorcycle engine is noisy and emits sound waves that pass through the air. The sound waves pass through the air as a series of compressions (C) and rarefactions (R).
Fig. 3.3 shows the positions of the compressions and rarefactions as the sound wave passes through the air.
Suggest how and explain why the positions of the compressions and rarefactions change if the pitch of the sound increases.
▶️Answer/Explanation
When pitch increases: 1. Frequency increases (more waves per second) 2. Wavelength decreases (compressions/rarefactions get closer together) 3. Wave speed remains constant (in same medium) Scientific explanation: Higher pitch means higher frequency sound waves, which have shorter wavelengths while maintaining the same speed in a given medium (v = fλ).
Question 4
(a)-(d) Subtopic: B19.1 Habitat destruction / B18.3 Carbon cycle
The pie chart in Fig. 4.1 shows the different causes of deforestation in a country.
(a) Calculate the total percentage of deforestation caused by agriculture.
▶️Answer/Explanation
74%
Calculation: Livestock agriculture (13%) + Arable agriculture (22%) + Slash-and-burn agriculture (39%) = 74% total agricultural deforestation
Note: Firewood and logging are not considered agricultural activities in this context.
(b) Describe how slash-and-burn agriculture can increase the carbon dioxide concentration in the atmosphere.
▶️Answer/Explanation
1. Burning vegetation releases stored carbon as CO2 through combustion
2. Dead plants that would normally absorb CO2 via photosynthesis are removed
3. Soil carbon is oxidized and released when exposed by burning
Long-term impact: The destroyed forest can no longer act as a carbon sink, leading to net increase in atmospheric CO2.
(c) Describe the undesirable effects of deforestation on soil.
▶️Answer/Explanation
1. Soil erosion: Tree roots no longer hold soil together, allowing wind/water to wash it away
2. Nutrient depletion: Lack of leaf litter reduces organic matter returning to soil
3. Desertification: Soil becomes dry and infertile without tree cover
4. Increased flooding: Reduced water absorption by roots leads to surface runoff
Ecological impact: Loss of topsoil makes regeneration much more difficult.
(d) Forests are ecosystems. Define the term ecosystem.
▶️Answer/Explanation
An ecosystem is a community of living organisms (biotic factors) interacting with each other and their physical environment (abiotic factors) in a specific area.
Key components: 1. Producers, consumers, decomposers
2. Energy flow and nutrient cycling
3. Physical factors like soil, water, climate
4. Dynamic equilibrium between components
Question 5
(a) Subtopic: C11.3 Fuels / C11.6 Alcohols
(b) Subtopic: C11.1 Formulas and terminology
(c)(i)-(ii) Subtopic: C11.6 Alcohols / C10.2 Air quality and climate
Petroleum is the raw material for the production of many useful substances. Fig. 5.1 shows processes A, B and C that can be used in the production of ethanol.
(a) Name the processes by drawing one line from each process to its name.
▶️Answer/Explanation
A → Fractional distillation
B → Cracking
C → Fermentation
Process explanations: 1. Fractional distillation separates crude oil into fractions like diesel
2. Cracking breaks large hydrocarbons into smaller ones like ethane
3. Fermentation converts sugars (from crops) into ethanol
(b) The formula of ethanol is C2H5OH. Explain why ethanol is not a hydrocarbon.
▶️Answer/Explanation
Ethanol contains an oxygen atom (in the -OH hydroxyl group), while hydrocarbons contain only hydrogen and carbon atoms.
Key difference: The presence of the functional group (-OH) makes it an alcohol, not a pure hydrocarbon.
(c) Fig. 5.2 shows a camping stove which uses ethanol as the fuel.
Complete combustion of ethanol produces carbon dioxide and water. The balanced equation for this reaction is shown.
C2H5OH + 3O2 → 2CO2 + 3H2O
The stove uses 22 g of ethanol to boil 1 dm3 of water.
(i) Complete steps 1 to 3 to calculate the maximum mass of carbon dioxide produced when boiling 1 dm3 of water.
Show your working.
[Mr : carbon dioxide, 44; ethanol, 46]
Step 1
Calculate the number of moles in 22 g of ethanol.
Step 2
Calculate the number of moles of carbon dioxide produced when 22 g of ethanol burns.
Step 3
Calculate the mass of carbon dioxide produced when boiling 1 dm3 of water.
▶️Answer/Explanation
Step 1: Moles of ethanol = mass/Mr = 22/46 = 0.478 mol
Step 2: Moles of CO2 = 2 × moles ethanol = 2 × 0.478 = 0.956 mol
Step 3: Mass CO2 = moles × Mr = 0.956 × 44 = 42.1 g
Stoichiometric notes: – The equation shows 1 mole ethanol → 2 moles CO2 – Mr values must be used accurately – Final answer should be rounded to 2 significant figures (42 g)
(ii) A similar stove uses butane as the fuel. Butane produces less carbon dioxide when boiling 1 dm3 of water. Suggest whether using the butane stove or the ethanol stove causes less damage to the environment. Explain your answer.
▶️Answer/Explanation
Butane stove causes less environmental damage because: 1. Produces less CO2 per unit energy (lower carbon footprint) 2. CO2 is a greenhouse gas contributing to climate change 3. Complete combustion of butane is more efficient
Additional consideration: Ethanol may be renewable (from plants), but butane’s lower emissions make it preferable for climate impact.
Question 6
(a)(i)-(ii) Subtopic: P3.3 Electromagnetic spectrum
(b)(i)-(iv) Subtopic: P3.4 Sound / P3.1 General properties of waves
(a) The visible light produced by the headlamps of a train is part of the electromagnetic spectrum.
(i) Write visible light in the correct position in the incomplete electromagnetic spectrum in Fig. 6.1.
▶️Answer/Explanation
Correct order: gamma → ultraviolet → visible light → microwaves
Full EM spectrum: Gamma → X-rays → UV → Visible → Infrared → Microwaves → Radio waves
Key property: Visible light has wavelengths between 400-700 nm, between UV and infrared.
(ii) All electromagnetic waves travel at the same speed. State the speed of light in a vacuum.
▶️Answer/Explanation
3 × 108 m/s (300,000,000 m/s)
Fundamental constant: This is the maximum speed at which all information in the universe can travel, denoted by the symbol ‘c’ in physics equations.
(b) The approaching train can be heard through the air and as a ringing sound in the steel rails. The speed of sound in air is 330 m/s and the speed of sound in steel is 6000 m/s.
(i) Suggest a value for the speed of sound through water. Explain your answer.
▶️Answer/Explanation
Approximately 1500 m/s (accept 1200-1600 m/s)
Explanation: Sound travels faster in liquids than gases (air = 330 m/s) but slower than in solids (steel = 6000 m/s). Water molecules are more densely packed than air but less rigidly bonded than steel. Scientific basis: Speed depends on medium density and elasticity.
(ii) Calculate the time difference between a sound travelling 0.50 km through air and 0.50 km through steel rails. Show your working.
▶️Answer/Explanation
Calculations: 1. Time in air = distance/speed = 500/330 ≈ 1.515 s 2. Time in steel = 500/6000 ≈ 0.0833 s 3. Difference = 1.515 – 0.0833 ≈ 1.43 s
Key steps: – Convert km to m (0.5 km = 500 m) – Use time = distance/velocity for both media – Subtract the smaller time from the larger
(iii) The train emits sound waves with a frequency of 500 Hz which travel through the air at a speed of 330 m/s. Calculate the wavelength of these waves. Show your working.
▶️Answer/Explanation
Using v = fλ → λ = v/f = 330/500 = 0.66 m
Wave equation breakdown: – v = wave speed (330 m/s) – f = frequency (500 Hz) – λ = wavelength (m)
Practical significance: This wavelength is similar to human body size, affecting how we perceive train horns.
(iv) Sound waves are longitudinal waves. Visible light waves are transverse waves. Describe the differences between longitudinal and transverse waves in terms of the direction of travel of the waves, and the direction of oscillation or vibration.
▶️Answer/Explanation
Longitudinal waves (sound): – Vibrations parallel to wave direction – Create compressions and rarefactions – Require a medium (can’t travel in vacuum)
Transverse waves (light): – Vibrations perpendicular to wave direction – Have crests and troughs – Can travel through vacuum
Visual difference: Imagine pushing a slinky vs shaking a rope.
Question 7
(a)(i)-(iii) Subtopic: B3.1 Diffusion
(b) Subtopic: B3.1 Diffusion
(c) Subtopic: B12 Respiration
(a) A student investigates the effect of temperature on the rate of diffusion of red dye into agar jelly cubes.
The student prepares three cubes of agar jelly A, B and C.
- Each cube is equal in size.
- A is kept at 30 °C, B is kept at 25 °C, C is kept at 20 °C.
- Three separate containers of red dye are also kept at 30 °C, 25 °C and 20 °C.
- Each cube is immersed in red dye equal to its temperature for 10 minutes.
- The cubes are then removed from the dye and cut in half.
Fig. 7.1 shows the cubes cut in half.
Table 7.1 shows the results.
(i) Calculate the rate of diffusion for cube A.
▶️Answer/Explanation
0.10 cm per min
Calculation: Rate = Diffusion distance/Time = 1.0 cm/10 min = 0.10 cm/min
Experimental observation: The higher temperature (30°C) shows fastest diffusion, consistent with kinetic theory.
(ii) Use the results in Table 7.1 to describe the relationship between temperature and the rate of diffusion.
▶️Answer/Explanation
As temperature increases, the rate of diffusion increases (positive correlation).
Scientific explanation: 1. Higher temperature → greater kinetic energy of dye molecules
2. More frequent and energetic collisions
3. Faster net movement from high to low concentration
(iii) State one variable, other than the size of the cubes, that should be kept constant in this investigation.
▶️Answer/Explanation
Possible answers: • Concentration of red dye
• Immersion time (10 minutes)
• Type of agar jelly
• pH of the solution
Control importance: Keeping these constant ensures only temperature affects results (fair test).
(b) Explain why the red dye diffuses into the agar jelly.
▶️Answer/Explanation
1. Concentration gradient exists (high dye concentration outside → low inside jelly)
2. Dye molecules move randomly (Brownian motion)
3. Net movement down concentration gradient until equilibrium
Molecular level: Dye particles collide with agar pores and gradually spread through available spaces.
(c) Materials diffuse in and out of living cells. Name the gas produced by respiration that diffuses out of cells.
▶️Answer/Explanation
Carbon dioxide (CO2)
Biological context: This waste product of aerobic respiration moves from high concentration in cells to lower concentration in blood/capillaries.
Question 8
(a)(i)-(ii) Subtopic: C2.3 Isotopes / C1.2 Diffusion
(b) Subtopic: C2.3 Isotopes
(c)(i)-(ii) Subtopic: C8.3 Group VII properties
(d) Subtopic: C8.3 Group VII properties
(a) (i) Using information in the Periodic Table, calculate the relative molecular masses of the gases nitrogen and chlorine.
▶️Answer/Explanation
Mr(nitrogen) = 28 (N2 = 14×2)
Mr(chlorine) = 71 (Cl2 = 35.5×2)
Calculation note: Both nitrogen and chlorine exist as diatomic molecules (N2, Cl2) in their natural state.
(ii) Using your answer to (a)(i), state and explain which of these two gases diffuses at the greater rate.
▶️Answer/Explanation
Nitrogen diffuses faster because: 1. Lighter molecules (Mr 28 vs 71) 2. Graham’s Law: rate ∝ 1/√(molecular mass) 3. At same temperature, lighter molecules have higher average velocity
Practical example: This explains why nitrogen leaks faster from containers than chlorine.
(b) Chlorine occurs naturally as a mixture of mainly two isotopes, chlorine-35 and chlorine-37. Complete Table 8.1 to show some information about the atomic structures of these isotopes.
▶️Answer/Explanation
Completed table:
Key concepts: 1. Neutrons = nucleons – protons
2. Neutral atoms have electrons = protons
3. Isotopes differ only in neutron number
(c) A student mixes colourless aqueous solutions of chlorine and sodium bromide. Fig. 8.1 shows the apparatus she uses.
(i) A reaction occurs when chlorine solution is mixed with sodium bromide solution. Predict and explain the student’s observation when these solutions are mixed.
▶️Answer/Explanation
Observation: Solution turns orange/yellow
Explanation: 1. Chlorine (more reactive) displaces bromine from sodium bromide
2. Orange color indicates bromine formation
3. Redox reaction: Cl2 + 2NaBr → 2NaCl + Br2
Chemical test: This demonstrates halogen reactivity trends (Cl > Br)
(ii) Write a word equation for the reaction that occurs when these solutions are mixed.
▶️Answer/Explanation
chlorine + sodium bromide → bromine + sodium chloride
Balanced form: Cl2 + 2NaBr → Br2 + 2NaCl
Reaction type: Displacement reaction showing halogen reactivity series
(d) The student adds an orange solution of bromine to a colourless solution of sodium fluoride. Predict and explain the student’s observation when the solution of bromine is added to the solution of sodium fluoride.
▶️Answer/Explanation
Observation: No color change/orange color remains
Explanation: 1. Bromine is less reactive than fluorine 2. No displacement occurs (Br cannot displace F) 3. Solution remains orange as bromine doesn’t react Key principle: Reactivity decreases down Group 7 (F > Cl > Br > I)
Question 9
(a)(i)-(ii) Subtopic: P1.2 Motion
(b) Subtopic: P2.3.3 Radiation
(c) Subtopic: P5.2.5 Applications and safety precautions
(d) Subtopic: P5.2.3 Radioactive decay
(a) During a mission to the Moon in 1971, an astronaut dropped a feather and a hammer. The feather and hammer were released from the same height at the same time. Both fell for 1.3 s, and landed at the same time. The acceleration due to gravity on the Moon is 1.6 m/s². Assume that the Moon has no atmosphere.
(i) On Fig. 9.1 draw the speed-time graph for the falling feather.
▶️Answer/Explanation
Graph characteristics: 1. Straight line from origin (0,0) with constant gradient
2. Gradient = acceleration = 1.6 m/s²
3. Terminates at (1.3, 2.08) since v = u + at = 0 + (1.6 × 1.3)
Key points: • No air resistance → constant acceleration
• Final speed = 1.6 × 1.3 = 2.08 m/s
• Both objects follow identical graphs on Moon
(ii) The experiment is repeated on Earth. State two differences in the results obtained. Explain your answers.
▶️Answer/Explanation
Difference 1: Hammer reaches ground first
Explanation: Earth’s atmosphere causes air resistance, which affects feather more due to its larger surface area-to-mass ratio
Difference 2: Both objects fall faster (reach higher speeds)
Explanation: Earth’s gravity (9.81 m/s²) > Moon’s gravity (1.6 m/s²)
Additional note: On Earth, the feather would flutter irregularly due to air currents
(b) The astronaut wears a white suit rather than a black suit. Suggest and explain a reason for this.
▶️Answer/Explanation
Reason: White reflects thermal radiation while black absorbs it
Explanation: 1. Moon has extreme temperature variations (+127°C to -173°C) 2. White color minimizes heat absorption in sunlight 3. Helps maintain stable body temperature
Scientific basis: White surfaces have high albedo (reflectance) for visible and infrared light
(c) The astronaut is exposed to more ionising radiation than people who remain on the Earth. State one harmful effect of ionising radiation on the human body.
▶️Answer/Explanation
Possible effects: 1. DNA damage/mutations 2. Increased cancer risk 3. Radiation sickness (acute exposure) 4. Cellular damage
Most relevant: Cancer risk increases with radiation dose (stochastic effect)
(d) Alpha radiation is one form of ionising radiation. An isotope of plutonium, 23994Pu, decays by alpha emission to produce an isotope of uranium. Use the correct nuclide notation to write a symbol equation for this decay process.
23994Pu → …………………… + ……………………
▶️Answer/Explanation
23994Pu → 23592U + 42He
Nuclear principles: 1. Mass number decreases by 4 (239 → 235)
2. Atomic number decreases by 2 (94 → 92)
3. Alpha particle is helium nucleus (4He)
Conservation: Both mass and charge are conserved in the equation
Question 10
(a)(i)-(ii) Subtopic: B9.3 Blood vessels
(b) Subtopic: B9.3 Blood vessels
(c) Subtopic: B9.2 Heart
(d)(i)-(ii) Subtopic: B13.2 Hormones
(a) Fig. 10.1 shows a cross-section through a vein when seen under a light microscope.
(i) On Fig. 10.1 draw two label lines to identify the:
- lumen
- wall of the vein.
▶️Answer/Explanation
Labeling instructions:
1. Lumen: Central empty space where blood flows
2. Wall: Outer layered structure surrounding lumen
Key features: • Vein walls are thinner than arteries • Lumen typically appears collapsed in microscope slides • Contains valves (though not visible in cross-section)
(ii) Name one structure of veins not visible in Fig. 10.1.
▶️Answer/Explanation
Valves
Valve function: Prevent backflow of blood, especially in limbs against gravity
(b) Explain why the wall of an artery is much thicker than the wall of a vein.
▶️Answer/Explanation
1. Pressure: Arteries withstand higher blood pressure from heart contractions
2. Elastic tissue: More smooth muscle/elastin to accommodate pulse surges
3. Structural need: Maintain shape under pressure (veins can collapse)
Physiological difference: Arterial blood pressure ~120/80 mmHg vs venous ~10 mmHg
(c) Coronary heart disease is caused by a blockage in the coronary arteries. State two lifestyle factors that increase the risk of coronary heart disease.
▶️Answer/Explanation
Primary risk factors: 1. Smoking (damages artery linings)
2. High-fat diet (leads to atherosclerosis)
3. Lack of exercise
4. Chronic stress
5. Obesity
Mechanism: These promote plaque buildup (atheroma) in coronary arteries
(d) Hormones are released into blood.
(i) Name the hormone that
- is released in stressful situations
- decreases the glucose concentration of the blood.
▶️Answer/Explanation
Stress hormone: Adrenaline (epinephrine)
Glucose-lowering hormone: Insulin
Physiological roles: • Adrenaline – “fight or flight” response from adrenal medulla
• Insulin – promotes glucose uptake by cells from pancreas
(ii) Auxin is a plant hormone. State the effect of auxin on plant cells.
▶️Answer/Explanation
Primary effect: Promotes cell elongation (in shoots)
Additional roles: • Apical dominance • Phototropism/gravitropism • Root initiation • Prevents leaf abscission
Mechanism: Softens cell walls by activating proton pumps
Question 11
(a)(i)-(ii) Subtopic: C6.2 Rate of reaction
(b) Subtopic: C7.3 Preparation of salts
(c) Subtopic: C2.6 Giant covalent structures
(a) A student investigates the rate of reaction of calcium carbonate with dilute hydrochloric acid. The word equation for the reaction is shown.
calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
Fig. 11.1 shows some of the apparatus he uses.
(i) Suggest what other equipment he needs and how he would use it to calculate the rate of carbon dioxide produced. You may draw on Fig. 11.1 to help your answer.
▶️Answer/Explanation
Equipment needed: 1. Gas syringe OR inverted measuring cylinder over water
2. Stopwatch
Method: • Connect gas collection device to flask • Measure gas volume at regular time intervals • Calculate rate as volume/time (e.g., cm³/min)
Alternative method: Measure mass loss as CO₂ escapes (using balance)
(ii) He carries out the experiment using dilute hydrochloric acid at 20°C. He repeats the experiment at 30°C. Fig. 11.2 shows his results.
State and explain the differences between the graphs in terms of the movement of reacting particles.
▶️Answer/Explanation
Differences: 1. Higher initial rate at 30°C (steeper curve)
2. Reaches completion faster at 30°C
Particle-level explanation: • More particles have ≥ activation energy at higher temp • More frequent successful collisions per second • Particles move faster with greater kinetic energy
(b) Lead chloride is an insoluble salt. Describe a method of making solid lead chloride from reactants chosen from Table 11.1.
▶️Answer/Explanation
Reactants: Lead nitrate + sodium chloride (both soluble)
Method: 1. Mix solutions to form precipitate: Pb(NO₃)₂ + 2NaCl → PbCl₂↓ + 2NaNO₃
2. Filter to collect insoluble PbCl₂
3. Wash with distilled water
4. Dry between filter papers
Key point: Must choose two soluble compounds that form PbCl₂
(c) Lead chloride has a melting point of 501°C. Explain how the structure of lead chloride causes it to have a high melting point.
▶️Answer/Explanation
Explanation: 1. Giant ionic lattice structure
2. Strong electrostatic forces between Pb²⁺ and Cl⁻ ions
3. Requires substantial energy to overcome these bonds
Comparison: Much higher than molecular compounds (e.g., water 0°C)
Question 12
(a) Subtopic: P1.6.3 Energy resources
(b) Subtopic: P2.1.3 Pressure changes
(c) Subtopic: P1.5.3 Centre of gravity
(d)(i)-(iii) Subtopic: P3.2.2 Refraction of light / P3.2.3 Thin converging lens
(e) Subtopic: P2.1.1 States of matter
Fig. 12.1 shows a solar-powered golf cart, with solar cells on the roof.
The solar cells produce electrical energy using solar energy. The Sun is the source of this energy.
(a) Name two energy resources that do not have the Sun as their source of energy.
▶️Answer/Explanation
1. Geothermal
2. Nuclear
3. Tidal (primarily from Moon’s gravity)
4. Fossil fuels (ancient solar energy, but technically not current sun)
Key distinction: These derive energy from Earth’s internal heat, atomic nuclei, or gravitational forces
(b) During the golf cart’s journey, the temperature in the tyres increases. The volume of air in the tyres does not change. Explain in terms of molecules the effect on the pressure of a gas due to an increase in temperature at constant volume.
▶️Answer/Explanation
Explanation: 1. Molecules gain kinetic energy and move faster
2. More frequent collisions with tyre walls
3. Each collision exerts greater force
4. Result: Increased pressure (Gay-Lussac’s Law: P ∝ T at constant V)
Real-world example: Tyre pressure warnings in hot weather
(c) The golf cart often travels across sloping fields so stability is important in its design. Fig. 12.2 shows the cart on a slope.
The center of mass of the golf cart is shown by the letter X. State the effect of raising the center of mass of the golf cart on its stability.
▶️Answer/Explanation
Effect: Decreases stability (more likely to tip over)
Physics principle: • Higher CoM increases torque when tilted • Smaller angle needed to move CoM beyond base support • Wider wheelbase would counteract this effect
(d) A spectator takes a photograph of a golfer with a camera. The camera uses a thin converging lens to focus light rays onto the light sensor inside the camera.
(i) Complete the ray diagram in Fig. 12.3 to show this.
▶️Answer/Explanation
Ray diagram rules: 1. Parallel rays converge to focal point 2. Rays through lens center continue straight 3. Image forms where rays intersect sensor Key point: Real, inverted image forms on sensor plane
(ii) The lens is made from glass. Glass has a refractive index of 1.33. Define refractive index in terms of the speed of light in a vacuum and in glass.
▶️Answer/Explanation
Definition: Refractive index = speed of light in vacuum / speed of light in medium
Mathematically: n = c/v
Example: n=1.33 means light travels 1.33× slower in glass than vacuum
(iii) The image produced by the lens on the light sensor is a real image. Describe the difference between a real image and a virtual image.
▶️Answer/Explanation
Real image: • Formed by actual light rays converging • Can be projected on a screen • Inverted (usually) Virtual image: • Apparent intersection of light rays • Cannot be projected • Upright (e.g., mirrors)
(e) Describe in terms of the forces between the atoms why solids have a fixed shape.
▶️Answer/Explanation
Explanation: 1. Strong intermolecular forces (ionic/metallic/covalent) 2. Particles vibrate about fixed positions 3. Regular lattice structure resists deformation
Contrast: Unlike liquids/gases where particles can slide past each other
Question 13
(a) Subtopic: B5 Enzymes
(b) Subtopic: B5 Enzymes / B4 Biological molecules
Enzymes are biological catalysts with a specific shape.
(a) Explain the importance of the shape of an enzyme.
▶️Answer/Explanation
Key points about enzyme shape: 1. Active site has complementary shape to substrate (lock-and-key model)
2. Specific 3D structure enables selective catalysis
3. Shape determines which reactions enzyme catalyzes
4. Denaturation (shape change) destroys function
Biological significance: Ensures metabolic pathways remain organized and efficient
(b) A student tests different solutions for the nutrients they contain. Table 13.1 shows the results.
One of the solutions A, B, C, D or E contains an enzyme. Using the information in Table 13.1 identify which solution contains an enzyme. Explain your answer.
▶️Answer/Explanation
Solution C contains an enzyme.
Evidence: 1. Biuret test (purple): Indicates presence of proteins (enzymes are proteins)
2. Benedict’s test (red): Shows reducing sugars present (enzyme substrate/product)
3. Iodine test (blue-black): Starch present (possible enzyme substrate)
Key reasoning: Only solution showing protein presence (purple Biuret) while also having biological activity (sugar changes)