Question 1
(a) Subtopic: B12 Respiration
(b) Subtopic: B12 Respiration
(a) Carbon dioxide is produced during the anaerobic respiration of yeast.
A baker investigates the optimum temperature required for the anaerobic respiration of yeast for bread-making.
Fig. 1.1 is a graph of the results.
(i) State the average number of bubbles of carbon dioxide produced per minute at 45 °C.
▶️Answer/Explanation
Answer: 6
Explanation: At 45°C on the x-axis of Fig. 1.1, the corresponding y-axis value for the average number of bubbles is 6 per minute. This is read directly from the graph where the temperature line at 45°C intersects with the curve.
(ii) Anaerobic respiration of yeast is controlled by enzymes. Use evidence from Fig. 1.1 to support this statement.
▶️Answer/Explanation
Answers (any two):
– There is an optimum temperature (around 40-50°C) where bubble production peaks
– Above the optimum temperature, the rate decreases
– This shows enzyme denaturation at higher temperatures
Explanation: The graph shows typical enzyme behavior with a peak activity at optimal temperature (bell curve). The decrease after the peak temperature indicates enzyme denaturation, which is characteristic of enzyme-controlled reactions.
(iii) Apart from controlling the temperature, suggest one way the baker could increase the number of carbon dioxide bubbles produced per minute.
▶️Answer/Explanation
Answer: Increase the concentration of glucose/sugar/nutrients or use more yeast
Explanation: Since yeast needs sugar for anaerobic respiration, increasing the substrate (glucose) concentration would provide more material for the reaction. Alternatively, adding more yeast increases the number of enzyme-containing organisms available for the reaction.
(b) Table 1.1 shows some of the features of aerobic and anaerobic respiration.
Complete Table 1.1 by placing a tick (✓) in the boxes to show the correct features of each type of respiration.
▶️Answer/Explanation
Completed Table:
Explanation:
1. Aerobic respiration produces CO₂, requires O₂, and releases energy
2. Animal anaerobic respiration produces lactic acid and releases energy
3. Yeast anaerobic respiration produces CO₂ (not lactic acid) and releases energy
Question 2
(a)(i)-(ii) Subtopic: C11.5 Alkenes
(b) Subtopic: C2.5 Simple molecules and covalent bonds
(c)(i)-(ii) Subtopic: C11.5 Alkenes
Ethene, C2H4, and propene, C3H6, are in the same homologous series.
(a) (i) Define the term homologous series.
▶️Answer/Explanation
Answer: A family of organic compounds with:
– The same general formula
– Similar chemical properties
– Gradual variation in physical properties
– Each member differs by CH2 from the next
Explanation: A homologous series is characterized by a constant increment (CH2) between members, leading to predictable patterns in properties while maintaining similar reactivity due to the same functional group.
(ii) Name the homologous series to which ethene and propene belong.
▶️Answer/Explanation
Answer: Alkenes
Explanation: Both ethene (C2H4) and propene (C3H6) contain one carbon-carbon double bond (C=C), which is the defining feature of the alkene series (general formula CnH2n).
(b) Atoms in a molecule of ethene are held together by covalent bonds. Fig. 2.1 shows the outer shell electrons in a carbon atom and a hydrogen atom.
In the space below, draw the dot-and-cross diagram to show all the outer shell electrons in a molecule of ethene.
▶️Answer/Explanation
Answer:
H H
· ·
C::C
· ·
H H
Key features:
1. Two carbon atoms double-bonded (4 shared electrons shown as ::)
2. Each carbon forms 2 single bonds with hydrogen atoms (2 shared electrons per C-H bond)
3. All atoms achieve full outer shells (octet for C, duplet for H)
Explanation: Ethene’s dot-cross diagram must show:
– The C=C double bond (main functional group)
– Correct electron distribution (2 shared pairs between C atoms, 1 shared pair per C-H bond)
– Clear distinction between bonding pairs and lone pairs (though ethene has no lone pairs)
(c) Ethane is produced by the addition reaction between ethene and hydrogen.
(i) Write the symbol equation for the addition reaction between ethene and hydrogen.
▶️Answer/Explanation
Answer: C2H4 + H2 → C2H6
Explanation: This is a hydrogenation reaction where:
– The C=C double bond breaks
– Two hydrogen atoms add across the double bond
– The product (ethane) is saturated (no double bonds)
– Nickel catalyst is typically used in practice
(ii) Predict the product formed when propene reacts with hydrogen. Explain your answer.
▶️Answer/Explanation
Product: Propane (C3H8)
Explanation:
– Propene (C3H6) is an alkene with one C=C bond
– Hydrogen adds across the double bond (addition reaction)
– The product follows the same pattern as ethene → ethane
– All alkenes undergo similar hydrogenation to form alkanes
The reaction equation would be: C3H6 + H2 → C3H8
Question 3
(a)(i)-(ii) Subtopic: P3.3 Electromagnetic spectrum
(b)(i)-(ii) Subtopic: P1.6.1 Energy
(c) Subtopic: P5.2.3 Radioactive decay
(a) X-rays and γ-radiation are both used in hospitals.
(i) Place X-rays and γ-radiation in their correct places in the incomplete electromagnetic spectrum in Fig. 3.1.
▶️Answer/Explanation
Answer:
From left to right in the blank boxes:
1. X-rays immediately to the right of ultraviolet
2. γ-radiation in the far right box
Explanation:
The correct order of the electromagnetic spectrum is:
radio → microwave → infra-red → visible → ultraviolet → X-rays → gamma rays
X-rays have higher frequency/shorter wavelength than UV, and gamma rays are the highest frequency/shortest wavelength.
(ii) Suggest one use of γ-radiation in a hospital.
▶️Answer/Explanation
Answer (any one):
– Cancer treatment (radiotherapy)
– Sterilizing medical equipment
– Radioactive tracers in medical imaging
Explanation:
Gamma rays are used medically because:
1. Their high energy can kill cancer cells (radiotherapy)
2. They can penetrate packaging to sterilize equipment without physical contact
3. Radioisotopes like technetium-99m emit γ-rays for diagnostic imaging
(b) A hospital has a generator for use in an emergency if the mains electricity supply fails. The generator is powered by an engine that uses diesel fuel.
(i) Describe the three energy transfers involved in generating electrical energy from diesel fuel.
▶️Answer/Explanation
Answer:
1. Chemical energy → Thermal energy (combustion of diesel)
2. Thermal energy → Kinetic energy (expansion of gases drives pistons)
3. Kinetic energy → Electrical energy (generator rotation induces current)
Explanation:
The energy conversion sequence is:
– Burning diesel releases chemical energy as heat
– Heat causes gas expansion that moves engine components
– Mechanical motion rotates the generator coil in a magnetic field, producing electricity
(ii) The generator is described as having an efficiency of 25%. Describe what is meant by this statement.
▶️Answer/Explanation
Answer: Only 25% of the input energy from diesel is converted to useful electrical energy; the rest is lost (mainly as heat).
Explanation:
Efficiency = (useful output energy / total input energy) × 100%
25% efficiency means for every 100J of chemical energy in diesel:
– 25J becomes electrical energy
– 75J is wasted (engine heat, sound, friction etc.)
(c) The isotope strontium-89 is used in the treatment of bone cancer. Strontium-89 decays by beta-particle emission to produce yttrium-89.
Use the correct nuclide notation to complete the symbol equation for this β-decay process.
▶️Answer/Explanation
Answer: 8938Sr → 8939Y + 0-1e
Explanation:
Beta decay involves:
1. A neutron → proton + electron
2. Atomic number increases by 1 (38→39), mass number unchanged (89)
3. The emitted beta particle (0-1e) is an electron from the nucleus
4. Yttrium (Y) has atomic number 39
Question 4
(a) Subtopic: B17.2 Selection
(b) Subtopic: B17.2 Selection
(c) Subtopic: B17.2 Selection
Fig. 4.1 is a picture of a racehorse.
(a) Racehorses have been selectively bred to win races. Outline the process of selective breeding to produce racehorses.
▶️Answer/Explanation
Answer (3 key steps):
1. Identify and select parent horses with desired traits (speed, stamina, physique)
2. Breed these selected horses together
3. Choose offspring with the best racing performance to breed again
4. Repeat the process over many generations
Explanation:
Selective breeding involves:
– Artificial selection by humans (not natural selection)
– Choosing specific traits to enhance (unlike random mating)
– Gradual improvement through successive generations
– Often involves keeping detailed pedigree records
(b) Describe one similarity and one difference between selective breeding and natural selection.
▶️Answer/Explanation
Similarity:
– Both processes involve the inheritance of favorable traits
– Both lead to changes in characteristics over generations
Difference:
– Selective breeding is directed by humans (artificial), while natural selection is driven by environmental pressures
– Selective breeding targets specific human-desired traits, while natural selection favors traits for survival/reproduction
Explanation:
The key distinction is the selecting force – humans vs environment. Both rely on genetic variation and heritability.
(c) Explain why selective breeding is not an example of adaptation.
▶️Answer/Explanation
Answer: Adaptation results from natural selection for survival in an environment, while selective breeding involves artificial selection for human-preferred traits.
Explanation:
– Adaptations develop through environmental pressures over long timescales
– Selective breeding produces changes quickly according to human preferences
– Racehorses may have traits (like thin legs) that wouldn’t necessarily help in nature
– True adaptations improve survival in wild conditions
Question 5
(a)(i)-(ii) Subtopic: C6.2 Rate of reaction
(b) Subtopic: C6.2 Rate of reaction
(c)(i)-(ii) Subtopic: C5.1 Exothermic and endothermic reactions
(d) Subtopic: C3.3 The mole and the Avogadro constant
(a) Ammonia is manufactured in the Haber process. In this process nitrogen reacts with hydrogen. Nitrogen and hydrogen are obtained from the raw materials air, methane and steam.
(i) Hydrogen is obtained when methane reacts with steam. Balance the symbol equation.
CH4 + …… H2O → …… H2 + CO2
▶️Answer/Explanation
Answer: CH4 + 2H2O → 4H2 + CO2
Explanation:
Balancing steps: 1. Count atoms on both sides (left: 1C, 4H, 2O; right: 1C, 2H, 2O) 2. Balance H atoms by adding coefficient 4 to H2 3. Now balance O atoms by adding coefficient 2 to H2O 4. Verify all atoms balance (1C, 8H, 2O on both sides)
(ii) Nitrogen can be obtained when hydrogen is burned in air. Name the substance removed from air when hydrogen burns.
▶️Answer/Explanation
Answer: Oxygen
Explanation:
– Air is ~78% N2, 21% O2 – Burning hydrogen removes oxygen via: 2H2 + O2 → 2H2O – Nitrogen remains as it’s unreactive at these conditions – This leaves nearly pure nitrogen for the Haber process
(b) Fig. 5.1 shows the conditions inside the reaction vessel in the Haber process.
State and explain the purpose of the iron in the reaction vessel.
▶️Answer/Explanation
Answer: Iron acts as a catalyst – it speeds up the reaction without being consumed.
Explanation: 1. Provides alternative reaction pathway with lower activation energy 2. Increases rate of both forward (N2+3H2→2NH3) and reverse reactions 3. Allows economic operation at lower temperatures than would otherwise be needed 4. Surface of iron helps break strong N≡N triple bond
(c) Fig. 5.2 is an energy level diagram for the reaction between nitrogen and hydrogen.
(i) Explain how the energy level diagram shows that the reaction is exothermic.
▶️Answer/Explanation
Answer: Products (ammonia) are at lower energy level than reactants (N2+H2), showing net energy release.
Explanation: – Exothermic = energy given out to surroundings – Energy difference (ΔH) is negative – Bond forming in NH3 releases more energy than needed to break N2 and H2 bonds – Typical ΔH for Haber process = -92 kJ/mol
(ii) Explain why a high temperature is needed to obtain a high rate of reaction. Use ideas about the movement and energy of molecules and about activation energy in your answer.
▶️Answer/Explanation
Answer (3 key points): 1. More molecules have energy ≥ activation energy 2. Increased collision frequency between molecules 3. More successful collisions per unit time
Explanation: Despite being exothermic, high temperature is needed because: – N2 triple bond requires much energy to break (high Ea) – Compromise between rate (favored by high T) and yield (favored by low T) – 450°C provides optimal balance for industrial production
(d) A chemical company produces 3.4×109 g of ammonia. The equation for the reaction is:
N2 + 3H2 → 2NH3
Complete steps 1 to 4 to calculate the volume of hydrogen, measured at room temperature and pressure, used to make this ammonia.
[Ar : H,1; N,14]
molar gas volume = 24 dm3 at room temperature and pressure.
step 1
Show that the relative molecular mass of ammonia is 17.
step 2
Calculate the number of moles of ammonia produced.
step 3
Calculate the number of moles of hydrogen used.
step 4
Calculate the volume of hydrogen used.
▶️Answer/Explanation
Answer: 1. Mr(NH3) = 14 + (1×3) = 17 2. Moles NH3 = mass/Mr = 3.4×109/17 = 2.0×108 mol 3. Moles H2 = (3/2)×2.0×108 = 3.0×108 mol (from 3:2 ratio) 4. Volume = moles × 24 = 3.0×108 × 24 = 7.2×108 dm3
Explanation: – Step 1: N=14, H=1 → NH3 = 14+3 = 17 – Step 2: Convert mass to moles using n=m/M – Step 3: Use stoichiometric ratio from equation – Step 4: At RTP, 1 mole gas = 24 dm3
Question 6
(a) Subtopic: P3.4 Sound
(b)(i)-(iii) Subtopic: P3.4 Sound
(c) Subtopic: P3.4 Sound
(d) Subtopic: P3.1 General properties of waves
(e) Subtopic: P2.1.1 States of matter
(a) Dolphins are a species of aquatic mammal. Dolphins produce sound waves in the frequency range 200 Hz–130 000 Hz.
State the audible frequency range for a human.
▶️Answer/Explanation
Answer: 20 Hz to 20 000 Hz (20 kHz)
Explanation: – Human hearing range is significantly narrower than dolphins’ – Lower limit (~20Hz) is felt as vibrations rather than heard as tones – Upper limit decreases with age (presbycusis) – Dolphins use ultrasound (>20kHz) for echolocation
(b) (i) Dolphins locate fish using very high frequency sound called ultrasound. They detect ultrasound reflected from the fish. A dolphin emits a pulse of ultrasound with a frequency of 50 000 Hz. The ultrasound pulse reflects off a fish 20 m away, and returns to the dolphin.
The speed of ultrasound in water is 1500 m/s. Calculate the time taken for the ultrasound pulse to reflect off the fish and return to the dolphin.
▶️Answer/Explanation
Answer: 0.027 s (or 2.7×10-2 s)
Calculation: 1. Total distance = 20 m to fish + 20 m back = 40 m 2. time = distance/speed = 40/1500 = 0.0266… s 3. Round to 2 significant figures → 0.027 s
Explanation: – Frequency is irrelevant for time calculation – Must account for round-trip distance – Ultrasound travels faster in water than air (~4× faster)
(ii) Calculate the wavelength of ultrasound waves with a frequency of 50 000 Hz.
▶️Answer/Explanation
Answer: 0.03 m (or 3×10-2 m)
Calculation: 1. v = fλ → λ = v/f 2. λ = 1500/50000 = 0.03 m
Explanation: – Wavelength in water is shorter than in air for same frequency – 3 cm wavelength allows detection of small objects – Higher frequency → shorter wavelength → better resolution
(iii) The dolphin changes the frequency of the sound it emits to 100 000 Hz. Suggest what effect, if any, this will have on the time taken for the pulse to travel to the fish and return to the dolphin.
Explain your answer.
▶️Answer/Explanation
Answer: No change in time
Explanation: – Wave speed in water depends on medium properties, not frequency – Distance remains unchanged (still 20 m to fish) – Only wavelength changes (halves to 1.5 cm) – Time calculation still uses t = d/v with same v and d
(c) Ultrasound waves travel at 1500 m/s through water. Suggest the speed of these waves through air. Explain your answer.
▶️Answer/Explanation
Answer: ~340 m/s (accept 300-350 m/s)
Explanation: – Sound travels slower in gases than liquids – Air is less dense and less elastic than water – Molecular spacing greater in gases → slower energy transfer – Exact speed depends on temperature (≈343 m/s at 20°C)
(d) Ultrasound waves are longitudinal waves. Electromagnetic waves are transverse waves. Describe the differences between longitudinal and transverse waves.
Your description should refer to the direction of propagation of the waves and the direction of oscillation or vibration. You may draw a diagram if it helps your answer.
▶️Answer/Explanation
Answer:
Longitudinal waves: – Particle oscillations parallel to wave direction – Compressions and rarefactions – Cannot be polarized
Transverse waves: – Particle oscillations perpendicular to wave direction – Crests and troughs – Can be polarized
Examples: – Longitudinal: sound, ultrasound, seismic P-waves – Transverse: light, radio, seismic S-waves
(e) At room temperature, water is a liquid. When water is cooled sufficiently, it turns to ice, a solid. Describe the differences between water and ice, in terms of the forces between molecules and the motion of molecules.
▶️Answer/Explanation
Answer:
Water (liquid): – Molecules can move/slide past each other – Hydrogen bonds constantly break/reform – Variable shape, fixed volume
Ice (solid): – Molecules vibrate in fixed positions – Rigid hydrogen bond network (hexagonal lattice) – Fixed shape and volume – Lower density than liquid (unusual property)
Key difference: Degree of molecular freedom and bond stability
Question 7
(a)(i)-(iii) Subtopic: B7.2 Digestive system
(b)(i)-(iii) Subtopic: B5 Enzymes
(a) Fig. 7.1 shows the alimentary canal and associated organs.
(i) On Fig. 7.1, label the organ where bile is produced with a label line and the correct name.
▶️Answer/Explanation
Answer: Liver (correctly labeled on diagram)
Explanation: – Bile is produced by hepatocytes in the liver – Stored in the gallbladder (but not produced there) – Emulsifies fats in the small intestine – Contains bile salts and cholesterol
(ii) Lipase is produced in the pancreas. On Fig. 7.1, draw an X to identify the pancreas.
▶️Answer/Explanation
Answer: X placed on pancreas (behind stomach, near duodenum)
Explanation: – Pancreas is both endocrine (insulin) and exocrine (digestive enzymes) – Produces pancreatic lipase, amylase, and proteases – Releases enzymes into pancreatic duct leading to duodenum
(iii) Name one part of the alimentary canal where mechanical digestion occurs.
▶️Answer/Explanation
Answer: Mouth (or stomach)
Explanation: Mouth: – Teeth chew food (mastication) – Tongue manipulates food – Increases surface area for enzymes
Stomach: – Muscular churning (peristalsis) – Mixes food with gastric juices – Forms chyme
(b) A student investigates the action of lipase on the fats present in milk. Lipase is a digestive enzyme.
- A mixture of milk and sodium carbonate solution is added to two test-tubes, A and B.
- A few drops of indicator are added to each test-tube and the solutions turn pink.
- The indicator turns pink in alkaline solutions and colourless in acidic solutions.
- Lipase is added to test-tube A and lipase and bile salts are added to test-tube B.
- The student times how long it takes for the indicator to turn colourless.
Table 7.1 shows the results.
(i) The solutions in test-tubes A and B become acidic. State the type of substance produced which causes the solutions to become acidic.
▶️Answer/Explanation
Answer: Fatty acids
Explanation: – Lipase breaks down triglycerides (fats) into fatty acids and glycerol – Fatty acids are carboxylic acids (R-COOH) – Release H+ ions → lower pH → acidic conditions – Sodium carbonate neutralizes acids initially (hence pink indicator)
(ii) Calculate the difference in time it takes between test-tube A and test-tube B to become acidic.
▶️Answer/Explanation
Answer: 41 seconds (254 – 213)
Explanation: – Simple subtraction of recorded times – Shows bile salts accelerate fat digestion – Quantitative comparison of enzyme activity
(iii) Explain why the contents of test-tube B become acidic more quickly than test-tube A.
▶️Answer/Explanation
Answer (3 key points): 1. Bile salts emulsify fats → increase surface area
2. More substrate available for lipase to act on
3. Faster breakdown of triglycerides → quicker fatty acid production
Explanation: – Bile breaks large fat globules into smaller droplets – Lipase can access more triglyceride molecules simultaneously – Demonstrates importance of bile in fat digestion – Without bile, fat digestion is less efficient
Question 8
(a) Subtopic: C2.4 Ions and ionic bonds
(b)(i)-(ii) Subtopic: C7.3 Preparation of salts
(c)(i)-(ii) Subtopic: C4.1 Electrolysis
(a) A student tries to draw the lattice structure of a crystal of sodium chloride. The student knows that sodium chloride is a salt consisting of sodium ions, Na+, and chloride ions, Cl–.
Fig. 8.1 shows their diagram.
State two reasons why their diagram is incorrect.
▶️Answer/Explanation
Answer (any two):
1. Ions should be in a regular, repeating 3D pattern (cubic lattice)
2. Each Na+ should be surrounded by 6 Cl– and vice versa
3. Equal numbers of Na+ and Cl– should be shown
4. Alternating arrangement of positive and negative ions is missing
Explanation: – NaCl forms an ionic lattice with 1:1 ratio – Each ion has 6 opposite-charge neighbors in octahedral arrangement – Diagram likely shows random distribution rather than ordered structure – No areas of charge imbalance should exist in the lattice
(b) A technician has run out of the insoluble salt, lead chloride. He has a good supply of the salts shown in Table 8.1, and has recorded their solubilities.
(i) He prepares a precipitate of lead chloride by reacting lead nitrate and sodium chloride. Explain why he chooses these salts.
▶️Answer/Explanation
Answer:
1. Both reactants are soluble (provide Pb2+ and Cl– ions)
2. Product (PbCl2) is insoluble → forms precipitate
3. Other products (NaNO3) remain soluble
Explanation: – Double displacement reaction: Pb(NO3)2 + 2NaCl → PbCl2↓ + 2NaNO3 – Need soluble sources of both Pb2+ (lead nitrate) and Cl– (sodium chloride) – Alternative combinations would either not provide needed ions or produce soluble products
(ii) Write the word equation for this reaction.
▶️Answer/Explanation
Answer: lead nitrate + sodium chloride → sodium nitrate + lead chloride
Explanation: – Word equations show reactants → products – Must include all reactants and products – Indicate physical states if required (lead chloride would have (s) for solid) – Balanced equation: 1:2:2:1 ratio
(c) Fig. 8.2 shows apparatus used to demonstrate the electrolysis of concentrated aqueous sodium chloride.
Before electrolysis occurs the electrolyte is purple because it contains litmus solution. Bubbles of gas are observed at both electrodes.
(i) Bubbles of chlorine are formed at the anode. Predict the change in colour of the electrolyte around the anode.
▶️Answer/Explanation
Answer: Bleached/colorless
Explanation: – Chlorine is a bleaching agent – Reacts with litmus dye molecules – Oxidation breaks chromophores in dye – Distinct from simple acid-base color changes
(ii) Explain how chlorine atoms form at the anode.
▶️Answer/Explanation
Answer:
1. Chloride ions (Cl–) are attracted to anode
2. Each Cl– loses one electron (oxidation)
3. Forms chlorine atoms: Cl– → Cl + e–
4. Two chlorine atoms combine to form Cl2 gas
Explanation: – Anode = oxidation (loss of electrons) – More favorable than water oxidation in concentrated NaCl – 2Cl– → Cl2 + 2e– (overall equation) – Test for chlorine: bleached damp litmus paper
Question 9
(a)(i)-(iii) Subtopic: P2.3.3 Radiation
(b) Subtopic: P1.5 Force
(c)(i)-(ii) Subtopic: P4.2.5 Electrical energy and electrical power
(a) Fig. 9.1 shows two trains.
The trains are identical, except one is painted black and one is painted white. Both have shiny surfaces.
The trains are both stored at a station on a sunny day.
(i) State the method of energy transfer by which energy passes from the Sun to the Earth.
▶️Answer/Explanation
Answer: Radiation (or electromagnetic radiation)
Explanation: – Energy travels as electromagnetic waves – Requires no medium (can travel through vacuum) – Includes visible light, infrared, and ultraviolet – Distinct from conduction/convection which need matter
(ii) After four hours the temperature inside each train is measured.
The temperature inside the train painted black is 40 °C.
The temperature inside the train painted white is 30 °C.
Suggest a reason for this difference in temperature.
▶️Answer/Explanation
Answer: Black surfaces absorb more radiation than white surfaces
Explanation: – Black is a good absorber of all wavelengths – White reflects more visible light (appears bright) – Absorbed radiation converts to thermal energy – Real-world application: why white cars stay cooler
(iii) Explain what would happen to the temperature inside the train painted white if the painted surface was not shiny.
▶️Answer/Explanation
Answer: Temperature would increase (compared to shiny white)
Explanation: – Shiny surfaces reflect more radiation – Matt/dull surfaces absorb more radiation – Still less than black, but more than shiny white – Practical example: shiny vs. matte white paint
(b) A train of mass 450,000 kg slows down with a constant deceleration of 0.6 m/s2 until the train stops. Calculate the force needed to cause the train to decelerate by 0.6 m/s2.
▶️Answer/Explanation
Answer: 270,000 N
Calculation: 1. F = ma 2. F = 450,000 kg × 0.6 m/s2 3. F = 270,000 N
Explanation: – Deceleration is negative acceleration – Force opposes motion (friction/braking) – Direction matters in vector terms – Real-world context: train braking systems
(c) The train has two headlamps connected in parallel. The lamps each have a power rating of 350 W and are operated with a potential difference of 75 V.
(i) Show that the current through each headlamp is 4.7 A.
▶️Answer/Explanation
Calculation: 1. P = IV → I = P/V 2. I = 350 W / 75 V 3. I = 4.666… A ≈ 4.7 A
Explanation: – Power equation for electrical devices – Parallel connection means full voltage across each lamp – Current splits from power source – Significant figures consideration
(ii) Calculate the combined resistance of these two lamps connected in parallel.
▶️Answer/Explanation
Answer: 8.0 Ω
Method 1: 1. Rsingle = V/I = 75/4.666… = 16.07 Ω 2. 1/Rtotal = 1/16.07 + 1/16.07 3. Rtotal = 8.0 Ω
Method 2: 1. Total current = 4.666… × 2 = 9.333… A 2. Rtotal = V/Itotal = 75/9.333… 3. Rtotal = 8.0 Ω
Explanation: – Parallel resistance formula – Alternative approach using total current – Halving of resistance for identical parallel components – Practical electrical circuit design
Question 10
(a)(i)-(ii) Subtopic: B3.2 Osmosis
(b) Subtopic: B8.1 Xylem and phloem
(c)(i)-(ii) Subtopic: B8.3 Transpiration
Water is taken into roots through the root hair cells by osmosis.
(a) (i) Complete the sentence to define the term osmosis.
Osmosis is the net movement of water …… from a region of higher water potential (…… solution) to a region of lower water potential (concentrated solution), through a partially permeable ……
▶️Answer/Explanation
Answer: Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.
Explanation: – Passive process (no energy required) – Water moves down concentration gradient – Membrane allows water but blocks solutes – Key for maintaining cell turgor in plants
(ii) Describe how the root hair cells are adapted for water uptake.
▶️Answer/Explanation
Answer: – Long, thin extensions (root hairs) increase surface area – Thin cell walls reduce diffusion distance – Large permanent vacuole maintains water potential gradient – Many mitochondria provide energy for active transport of minerals
Explanation: – Surface area adaptation crucial (can increase by 10-20×) – Typical length: 0.1-10mm – Work with mycorrhizal fungi in many plants – Create osmotic gradient by absorbing mineral ions
(b) Name the term used to describe how water molecules are held together in the xylem.
▶️Answer/Explanation
Answer: Cohesion
Explanation: – Hydrogen bonding between water molecules – Creates continuous water column in xylem – Works with adhesion (to xylem walls) – Enables transpiration pull under tension
(c) A student investigates the effect of humidity on the rate of transpiration.
The apparatus in Fig. 10.1 is used to measure the rate of water uptake by a plant shoot. This is approximately equal to the rate of transpiration.
The student determines the rate of water uptake by measuring the distance travelled by the air bubble in two minutes. The investigation is repeated with a clear plastic bag over the plant shoot to increase the humidity.
The results are shown in Table 10.1.
(i) Deduce the units used for the rate of water uptake in Table 10.1.
▶️Answer/Explanation
Answer: mm/min
Explanation: – Calculated as distance/time (18mm/2min = 9mm/min) – Potometer measures relative rates, not absolute volumes – Alternative units could be mm3/min if capillary diameter known – Shows comparative water movement speed
(ii) Explain the reduced rate of water uptake by the shoot covered with the clear plastic bag.
▶️Answer/Explanation
Answer (3 key points): 1. Bag increases humidity around leaves
2. Reduces water potential gradient between leaf and air
3. Less evaporation from stomata → weaker transpiration pull
Explanation: – Humid air contains more water vapor – Saturation deficit is reduced – Stomata may partially close – Demonstrates how environmental conditions affect transpiration
Question 11
(a)(i)-(ii) Subtopic: C8.2 Group I properties
(b)(i)-(ii) Subtopic: C2.3 Isotopes
Fig. 11.1 shows part of Group I of the Periodic Table.
(a) Fig. 11.2 shows the apparatus a teacher uses to place a piece of potassium into a bowl of water.
(i) The teacher places the piece of potassium into the water. Describe her observations.
▶️Answer/Explanation
Answer (any two observations):
1. Metal moves rapidly across water surface
2. Melts into a shiny sphere (mp = 63°C)
3. Fizzing/gas bubbles produced (hydrogen)
4. Violet flame may appear
5. Solution turns pink (alkaline phenolphthalein indicator)
Explanation: – Reaction: 2K + 2H2O → 2KOH + H2 – Exothermic reaction melts potassium – Hydrogen gas ignites from reaction heat – Safety precautions essential (small piece used)
(ii) Predict how the observations would differ if she uses rubidium instead of potassium.
Explain your answer.
▶️Answer/Explanation
Answer: More violent reaction
Explanation: 1. Reactivity increases down Group 1
2. Rubidium has larger atomic radius → weaker metallic bonds
3. Outer electron more easily lost
4. Faster reaction rate, more heat produced
5. May explode on contact with water
Trend: Li (steady) < Na (moderate) < K (vigorous) < Rb (violent) < Cs (explosive)
(b) Two isotopes of potassium are potassium-39 and potassium-41.
(i) Complete Table 11.1.
▶️Answer/Explanation
Answer:
Explanation: – Atomic number (protons) defines the element (K always has 19) – Neutrons = mass number – protons (39-19=20, 41-19=22) – Neutral atoms have equal protons and electrons – Isotopes differ only in neutron number
(ii) Predict if there are any differences in the reactions of these isotopes with water.
Explain your answer.
▶️Answer/Explanation
Answer: No difference in chemical reactions
Explanation: 1. Chemical properties depend on electron configuration
2. Isotopes have identical electron arrangements
3. Only nuclear/radioactive properties differ
4. Reaction rates may vary slightly (kinetic isotope effect) but products identical
5. Both produce KOH and H2 identically
Note: K-40 is radioactive (natural abundance 0.012%), but K-39 and K-41 are stable
Question 12
(a) Subtopic: P1.5 Force
(b)(i)-(iii) Subtopic: P4.5.2 The a.c. generator
(c) Subtopic: P4.2.2 Electric current
(d) Subtopic: P3.2.2 Refraction of light
A fishing boat floats on the sea.
(a) A heavy anchor is dropped from the boat and accelerates as it falls through the water to the sea bed. Name the downward force that makes the anchor accelerate.
▶️Answer/Explanation
Answer: Weight
Explanation: – Weight = mass × gravitational field strength (W=mg) – Acts vertically downward toward Earth’s center – Greater than upthrust/buoyancy force in this case – Causes net downward acceleration (Fnet = ma)
(b) The boat has a small generator to generate electricity.
Fig. 12.1 shows a simple generator.
(i) On Fig. 12.1 label a slip ring with the letter R.
▶️Answer/Explanation
Answer: R placed on circular metal rings contacting brushes
Explanation: – Slip rings maintain electrical contact during rotation – Made of conductive material (usually copper) – Different from split-ring commutator in DC motors – Allow continuous rotation without twisting wires
(ii) Describe how the use of slip rings produces an alternating voltage output from the rotating coil.
▶️Answer/Explanation
Answer (2 key points):
1. Coil cuts magnetic field lines, inducing voltage
2. As coil rotates 180°, direction of cutting reverses → voltage polarity switches
Explanation: – Faraday’s Law: changing flux induces EMF – Output follows sine wave pattern – Frequency depends on rotation speed – Each full rotation produces one AC cycle – Essential for AC generators (alternators)
(iii) On the grid in Fig. 12.2, sketch a graph of voltage output against time for the generator, when the coil is rotating at a constant speed.
▶️Answer/Explanation
Answer: Smooth sine curve with:
– Regular peaks and troughs
– Equal amplitude above/below zero
– Constant frequency
Explanation: – Mathematically: V = V0sin(2πft) – Peak voltage depends on:
• Magnetic field strength
• Number of coil turns
• Rotation speed
– Zero voltage when coil parallel to field
(c) An electric heater on the boat uses the electricity generated at 240 V. The current passing through the heater is 20 A. Calculate the charge passing through the heater in one hour.
State the unit of your answer.
▶️Answer/Explanation
Answer: 72,000 C (coulombs)
Calculation: 1. Q = It 2. Time = 1 hour = 3600 seconds 3. Q = 20 A × 3600 s = 72,000 C
Explanation: – Charge = current × time – SI unit is coulomb (C) – 1 A = 1 C/s – Real-world context: electric heating elements
(d) A fisherman on the boat is using a pair of binoculars to look at the sea. Binoculars use glass prisms to reflect light.
Fig. 12.3 shows part of a pair of binoculars. A ray of light is shown entering and leaving.
On Fig. 12.3, complete the ray diagram to show the path of the light ray through the two prisms.
▶️Answer/Explanation
Answer: Ray path showing:
1. Total internal reflection at 45° prism faces
2. Correct 90° deviation at each reflection
3. Parallel input/output rays
Explanation: – Porro prism design (double reflection) – Critical angle for glass ≈ 42° (45° > θc → TIR) – Image inversion correction – Compact optical path folding
Question 13
(a) Subtopic: B13.2 Hormones
(b)(i)-(ii) Subtopic: B13.2 Hormones
(c)(i)-(ii) Subtopic: B13.3 Homeostasis
(a) Adrenaline is a hormone. Describe how adrenaline is transported around the body.
▶️Answer/Explanation
Answer: Through the bloodstream (in blood plasma)
Explanation: – Secreted by adrenal medulla directly into blood – Water-soluble hormone (derived from amino acids) – Circulates throughout entire body – Faster than nervous system but slower than neurotransmitters – Half-life of ~2-3 minutes
(b) When a person is scared, adrenaline is released causing the concentration of glucose in the blood to increase.
(i) Suggest why an increase in blood glucose concentration might be needed when someone is scared.
▶️Answer/Explanation
Answer (2 key reasons):
1. Provides energy for “fight or flight” response
2. Fuels increased muscle contraction for rapid movement
Explanation: – Glucose → ATP through respiration – Immediate energy requirement – Prepares body for physical action – Complements other effects like increased heart rate
(ii) Describe two other effects of adrenaline on the body.
▶️Answer/Explanation
Answer (any two):
1. Increases heart rate and blood pressure
2. Dilates pupils (mydriasis)
3. Redirects blood flow to muscles (vasodilation)
4. Increases breathing rate (bronchodilation)
5. Stimulates glycogen breakdown in liver
Explanation: – All effects prepare body for emergency action – Acts on multiple target organs simultaneously – Effects mediated through α and β adrenergic receptors – Short-term stress response
(c) The body tries to maintain blood glucose concentration within certain limits. If the blood glucose concentration exceeds these limits, the body responds to return the blood glucose concentration to normal.
(i) Name the term used to describe this mechanism.
▶️Answer/Explanation
Answer: Negative feedback
Explanation: – Reversal of deviations from set point – Maintains homeostasis – Opposite to positive feedback (e.g., childbirth) – Involves sensors (pancreas), control center, and effectors
(ii) Describe how the liver and pancreas work to reduce the blood glucose concentration if it gets too high.
▶️Answer/Explanation
Answer (3 key steps):
1. Pancreatic β-cells detect high glucose → secrete insulin
2. Liver converts glucose to glycogen (glycogenesis)
3. Body cells increase glucose uptake
Explanation: – Insulin = key hypoglycemic hormone – Liver stores ~100g glycogen – Muscle cells also store glycogen – Adipose tissue converts glucose to fats – Occurs after meals (postprandial state)