Question 1
(a)(i)-(ii) Subtopic: B12 Respiration
(b) Subtopic: B5 Enzymes
(c) Subtopic: B12 Respiration
(d) Subtopic: B12 Respiration
(a) A scientist investigates the production of carbon dioxide by anaerobic respiration in yeast. Two different sugars are used, glucose and sucrose. The scientist measures the volume of carbon dioxide produced.
The results are shown in Fig. 1.1.
(i) Calculate the difference in volume of carbon dioxide produced in the first 20 minutes by yeast using glucose and by yeast using sucrose.
▶️Answer/Explanation
Answer: 0.9 cm³
Explanation: From the graph, at 20 minutes:
– Glucose produces ~1.1 cm³
– Sucrose produces ~0.2 cm³
Difference = 1.1 – 0.2 = 0.9 cm³
(ii) Describe one use of the production of carbon dioxide by anaerobic respiration in yeast.
▶️Answer/Explanation
Answer: Bread making OR Carbonated alcoholic drinks
Explanation: In bread making, CO2 causes dough to rise. In brewing, CO2 carbonates beverages. Both utilize yeast’s anaerobic respiration.
(b) The investigation is repeated using yeast and glucose at 80°C. Explain why no carbon dioxide is produced at this temperature. Use ideas about enzymes in your answer.
▶️Answer/Explanation
Answer: 1. High temperature denatures enzymes
2. Shape of active site changes
3. Substrate no longer fits enzyme
4. Enzymes can’t catalyze anaerobic respiration
Explanation: At 80°C, enzymes in yeast become denatured – their 3D structure changes permanently. This alters the active site so substrates (glucose) can’t bind, stopping the metabolic reactions that produce CO2.
(c) Explain why a mixture of only yeast and water would not produce carbon dioxide.
▶️Answer/Explanation
Answer: No glucose/sucrose/sugar to break down into CO2
Explanation: Anaerobic respiration requires a sugar substrate (like glucose) to break down. Water alone doesn’t provide the necessary carbon molecules for CO2 production.
(d) Complete the sentences to define the term anaerobic respiration.
Anaerobic respiration is the …… reactions in cells that break down nutrient molecules to release …… without using …… .
▶️Answer/Explanation
Answer: 1. chemical
2. energy
3. oxygen
Explanation: Anaerobic respiration is the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen. This contrasts with aerobic respiration which requires oxygen.
Question 2
(a) Subtopic: C6.1 Physical and chemical changes
(b) Subtopic: C2.1 Elements, compounds and mixtures
(c) Subtopic: C2.4 Ions and ionic bonds
(d) Subtopic: C1.2 Diffusion
(a) Table 2.1 shows examples of chemical and physical changes.
Complete Table 2.1 by putting ticks (✓) in the correct columns.
| chemical change | physical change | |
|---|---|---|
| burning magnesium | ✓ | |
| melting ice | ✓ | |
| rusting iron | ||
| dissolving salt in water | ||
| boiling water | ||
| neutralising an acid with a base |
▶️Answer/Explanation
Answer:
| rusting iron | ✓ | |
| dissolving salt in water | ✓ | |
| boiling water | ✓ | |
| neutralising an acid with a base | ✓ |
Explanation:
– Chemical changes form new substances (rusting = iron oxide, neutralisation = salt+water)
– Physical changes don’t create new substances (state changes = melting/boiling, dissolving = reversible)
(b) Magnesium, Mg, is an element. Water, H2O, is a compound. Describe what is meant by an element and a compound.
▶️Answer/Explanation
Answer:
Element: Made of only one type of atom
Compound: Contains atoms of two or more elements chemically joined together
Explanation:
– Magnesium (Mg) consists solely of Mg atoms → element
– Water (H2O) has hydrogen and oxygen atoms bonded → compound
Compounds have fixed ratios (e.g., always 2H:1O in water) and different properties from their constituent elements.
(c) A list of particles is shown.
Cu CO2 H2 Na OH– S Zn2+
Write each symbol or formula in Table 2.2 to show whether the particles are atoms, ions or molecules. One has been done for you.
▶️Answer/Explanation
Answer:
Explanation:
– Atoms: Single elemental symbols (Cu, Na, S) with no charge
– Ions: Charged particles (OH– = hydroxide ion, Zn2+ = zinc ion)
– Molecules: Groups of atoms covalently bonded (CO2 = carbon dioxide, H2 = hydrogen gas)
(d) Fig. 2.1 shows an experiment to investigate diffusion of gases.
Ammonia gas, NH3, and hydrogen chloride gas, HCl, diffuse along the tube. When the gases meet they react to form a white cloud of ammonium chloride. The ammonium chloride forms at the end of the tube nearest to the hydrochloric acid.
Explain why.
▶️Answer/Explanation
Answer:
1. Ammonia molecules are lighter (lower molecular mass)
2. Ammonia diffuses faster than hydrogen chloride
Explanation:
– NH3 molecular mass = 17 g/mol vs HCl = 36.5 g/mol
– Graham’s Law: lighter gases diffuse faster → NH3 travels further in same time
– White ring forms closer to HCl end because NH3 covers more distance
Question 3
(a) Subtopic: P3.4 Sound
(b)(i)-(ii) Subtopic: P1.5 Force
(b)(iii) Subtopic: P1.2 Motion
(c)(i)-(ii) Subtopic: P2.2.2 Melting, boiling and evaporation
(d) Subtopic: P2.3.3 Radiation
(a) An athletics race is started using a starting pistol. The sound from the starting pistol passes through the air and reaches the ears of the athletes. Sound waves pass through the air as a series of compressions and rarefactions. Describe one difference between a compression and a rarefaction.
▶️Answer/Explanation
Answer:
Compression is a region of high pressure (molecules closer together), while rarefaction is a region of low pressure (molecules farther apart).
Explanation:
Sound waves are longitudinal waves that transfer energy through alternating:
– Compressions: Dense regions where air particles are pushed together (higher pressure)
– Rarefactions: Sparse regions where particles are spread apart (lower pressure)
This creates the characteristic wave pattern of sound transmission through air.
(b) An athlete in the race has a mass of 70 kg. Her acceleration is 1.6 m/s2.
(i) Calculate the force needed to give this acceleration.
▶️Answer/Explanation
Answer: 112 N
Working:
Using Newton’s Second Law: F = ma
= 70 kg × 1.6 m/s2
= 112 N
Explanation:
The force required is directly proportional to both mass and acceleration. This calculation shows the substantial force needed for athletic performance.
(ii) The athlete reaches a maximum speed of 8 m/s. Calculate the kinetic energy of the athlete when moving at this speed.
▶️Answer/Explanation
Answer: 2240 J
Working:
KE = ½mv2
= ½ × 70 kg × (8 m/s)2
= 35 × 64
= 2240 J
Explanation:
Kinetic energy increases with the square of velocity – doubling speed quadruples KE. This shows why sprint finishes require significant energy.
(iii) Explain the difference between the terms speed and velocity.
▶️Answer/Explanation
Answer:
Speed is a scalar quantity (magnitude only), while velocity is a vector quantity (magnitude and direction).
Explanation:
– Speed: How fast an object moves (e.g., 8 m/s)
– Velocity: Speed in a specific direction (e.g., 8 m/s due North)
In races, velocity matters more as runners must maintain direction along the track.
(c) At the end of the race, the athlete is sweating. The sweat of the athlete evaporates faster on a hot day.
(i) Suggest in terms of molecules why this happens.
▶️Answer/Explanation
Answer:
More molecules have sufficient kinetic energy to escape the liquid surface.
Explanation:
Higher temperatures:
– Increase average kinetic energy of water molecules
– More molecules overcome surface tension and intermolecular forces
– Evaporation rate increases as more molecules transition to vapor phase
(ii) State one other way by which the rate of evaporation from the surface of a liquid can be increased.
▶️Answer/Explanation
Answer:
Increasing surface area OR Increasing air flow/wind
Explanation:
– Surface area: More liquid exposed to air → more evaporation sites
– Air flow: Removes water vapor near surface → maintains concentration gradient
Athletes often use towels to increase surface area and fans to increase air flow.
(d) At the end of a long race athletes are sometimes wrapped in a shiny foil blanket to reduce thermal energy losses. Explain why the shiny foil blanket helps reduce energy losses.
▶️Answer/Explanation
Answer:
1. Shiny surface is a poor radiator of heat
2. Reflects thermal radiation back to the body
3. Traps insulating air layer
Explanation:
The blanket works through multiple mechanisms:
– Radiation: Reflective surface minimizes heat loss via infrared radiation
– Conduction: Air trapped between foil layers is a poor conductor
– Convection: Prevents wind from carrying away body heat
This helps maintain core temperature after intense exercise.
Question 4
(a) Subtopic: B7.2 Digestive system
(b) Subtopic: B7.3 Digestion
(c) Subtopic: B7.2 Digestive system
(a) Fig. 4.1 is a diagram of the alimentary canal and associated organs.
Table 4.1 shows the functions of some parts shown in Fig. 4.1. Complete Table 4.1.
| name of part | letter in Fig. 4.1 | function |
|---|---|---|
| salivary gland | produces salivary amylase | |
| gall bladder | ||
| D | produces lipase, protease and amylase | |
| produces bile |
▶️Answer/Explanation
Answer:
| salivary gland | A | produces salivary amylase |
| gall bladder | H | stores bile |
| pancreas | D | produces lipase, protease and amylase |
| liver | J | produces bile |
Explanation:
The digestive system has specialized organs with distinct functions:
– Salivary glands (A): Begin starch digestion with amylase
– Gall bladder (H): Stores and concentrates bile from liver
– Pancreas (D): Major digestive enzyme producer (works in duodenum)
– Liver (J): Produces bile for fat emulsification
(b) Explain why gastric juice in the stomach contains hydrochloric acid.
▶️Answer/Explanation
Answer:
1. Provides optimal pH for pepsin (protease enzyme)
2. Denatures harmful bacteria/pathogens
3. Helps break down food tissues
Explanation:
The stomach’s acidic environment (pH ~1.5-3.5):
– Enzyme activation: Converts pepsinogen to active pepsin for protein digestion
– Protection: Destroys most ingested microorganisms
– Digestion: Denatures proteins and dissolves mineral complexes
– Absorption: Facilitates iron and calcium absorption later
(c) Name the part of the alimentary canal where these processes occur:
- absorption of water
- egestion
- ingestion.
▶️Answer/Explanation
Answer:
– Absorption of water: large intestine
– Egestion: anus
– Ingestion: mouth
Explanation:
The digestive process follows this sequence:
1. Ingestion: Food enters via mouth (mechanical breakdown begins)
2. Absorption: Most nutrients in small intestine, water mainly in large intestine
3. Egestion: Elimination of undigested matter through anal canal
Note: Egestion differs from excretion (removal of metabolic waste)
Question 5
(a)-(b) Subtopic: C11.5 Alkenes
(c) Subtopic: C5.1 Exothermic and endothermic reactions
(d) Subtopic: C11.6 Alcohols
The alkenes are a homologous series. The general formula for the alkenes is CnH2n. The alkanes are another homologous series.
(a) State the general formula for the alkanes.
▶️Answer/Explanation
Answer: CnH2n+2
Explanation:
Alkanes are saturated hydrocarbons with:
– Single bonds only (C-C)
– Maximum hydrogen atoms
– General formula shows 2 more H atoms than alkenes (CnH2n)
Example: Methane (CH4), Ethane (C2H6)
(b) Propene, C3H6, is an alkene. Complete Fig. 5.1 to show the structure of a propene molecule. Show all of the atoms and all of the covalent bonds.
▶️Answer/Explanation
Answer:
Explanation:
Key features of alkene structure:
1. Double bond between two carbons (C=C)
2. Trigonal planar geometry at double bond
3. No rotation around double bond
Propene specifically has:
– 3 carbon chain
– Double bond between C1 and C2
– Methyl group (-CH3) on C2
(c) Ethene is also an alkene. Ethene reacts with steam to form ethanol.
This reaction is exothermic. Explain why. Use ideas about bond breaking and bond making.
▶️Answer/Explanation
Answer:
1. Bond breaking absorbs energy (endothermic)
2. Bond forming releases energy (exothermic)
3. More energy is released than absorbed
Explanation:
Energy changes in the reaction:
– Breaking: C=C (612 kJ/mol) + H-O (463 kJ/mol) → requires energy
– Forming: C-C (348 kJ/mol) + C-O (358 kJ/mol) + O-H (463 kJ/mol) → releases energy
Net energy change = -91 kJ/mol (exothermic)
Industrial application: This process hydrates ethene to make ethanol at 300°C with phosphoric acid catalyst
(d) Ethanol is an alcohol. Describe how ethanol is made by fermentation.
▶️Answer/Explanation
Answer:
1. Sugar solution (e.g., glucose) with yeast
2. Anaerobic conditions (no oxygen)
3. Temperature 25-40°C (optimum for enzymes)
4. Chemical equation: C6H12O6 → 2C2H5OH + 2CO2
Explanation:
Fermentation key points:
– Microorganism: Yeast (Saccharomyces cerevisiae) provides enzymes
– Conditions: Air lock prevents oxidation to acetic acid
– Byproducts: CO2 bubbles indicate activity
– Limitations: Ethanol concentration >15% kills yeast
Comparison: Slower but more sustainable than ethene hydration
Question 6
(a) Subtopic: P1.4 Density
(b) Subtopic: P2.3.3 Radiation
(c)(i) Subtopic: P3.3 Electromagnetic spectrum
(c)(ii) Subtopic: P3.1 General properties of waves
(d) Subtopic: P3.2 Light
(a) The volume of the Sun is \(1.4 \times 10^{27} \, \text{m}^3\). The average density of the Sun is \(1410 \, \text{kg/m}^3\). Calculate the mass of the Sun.
▶️Answer/Explanation
Answer: \(2.0 \times 10^{30} \, \text{kg}\)
Solution:
To calculate mass, we use the formula:
\[ \text{mass} = \text{density} \times \text{volume} \]
Given:
\[ \text{density} = 1410 \, \text{kg/m}^3 \\ \text{volume} = 1.4 \times 10^{27} \, \text{m}^3 \]
Now, multiply the values:
\[ \text{mass} = 1410 \times 1.4 \times 10^{27} = 1974 \times 10^{27} \, \text{kg} \]
Rounding to 2 significant figures:
\[ \text{mass} = 2.0 \times 10^{30} \, \text{kg} \]
(b) Explain why the Sun transfers energy to the Earth mainly by radiation and not by conduction or convection.
▶️Answer/Explanation
Answer: Only radiation can travel through a vacuum, while conduction and convection require a medium.
Explanation:
– Radiation (e.g., infrared, visible light) can travel through the vacuum of space because it consists of electromagnetic waves that do not require a medium.
– Conduction requires direct contact between particles, and convection requires the movement of fluids (liquids or gases). Since space is a vacuum (no particles), these methods cannot transfer energy from the Sun to Earth.
(c) The Sun emits γ-radiation and visible light. Both of these radiations are part of the electromagnetic spectrum.
(i) Place γ-radiation and visible light in their correct places in the incomplete electromagnetic spectrum shown in Fig. 6.1.
▶️Answer/Explanation
Answer:
| radio waves | infrared | visible light | ultraviolet | γ-radiation |
Explanation:
The electromagnetic spectrum is ordered by increasing frequency (or decreasing wavelength):
1. Radio waves (lowest frequency)
2. Infrared
3. Visible light
4. Ultraviolet
5. X-rays
6. Gamma rays (highest frequency)
(ii) State why both these radiations take the same time to travel from the Sun to the Earth.
▶️Answer/Explanation
Answer: Both travel at the same speed (speed of light, \(3 \times 10^8 \, \text{m/s}\)).
Explanation:
All electromagnetic waves, regardless of frequency or wavelength, travel at the same speed in a vacuum (\(3 \times 10^8 \, \text{m/s}\)). Since γ-radiation and visible light are both part of the electromagnetic spectrum, they take the same time to travel from the Sun to Earth.
(d) Visible light from the Sun can be reflected, refracted and diffracted.
Describe what happens to a wave when it is:
- reflected
- refracted
- diffracted
▶️Answer/Explanation
Answer:
Reflected: The wave changes direction as it bounces off a surface, obeying the law of reflection (angle of incidence = angle of reflection).
Refracted: The wave changes direction and speed as it passes from one medium to another due to a change in density, e.g., light bending when entering water.
Diffracted: The wave spreads out or bends around obstacles or through openings, especially when the gap size is comparable to the wavelength.
Explanation:
– Reflection occurs when waves encounter a barrier and rebound, like light reflecting off a mirror.
– Refraction happens when waves cross a boundary between media (e.g., air to glass), changing speed and direction.
– Diffraction is most noticeable when waves pass through narrow gaps or around small objects, causing them to spread out.
Question 7
(a)(i)-(iii) Subtopic: B13.1 Coordination and response
(b) Subtopic: B13.1 Coordination and response
(c) Subtopic: B13.1 Coordination and response
(a) Fig. 7.1 is a photomicrograph of a human eye.
(i) Identify parts labelled A, B and C in Fig. 7.1.
▶️Answer/Explanation
Answer:
A: Iris
B: Cornea
C: Lens
Explanation:
– The iris (A) is the colored part that controls pupil size.
– The cornea (B) is the transparent outer layer that refracts light.
– The lens (C) further refracts light to focus it on the retina.
(ii) Draw an X on Fig. 7.1 to show the position of the blind spot.
▶️Answer/Explanation
Answer: X should be placed where the optic nerve exits the eye (no photoreceptors present).
Explanation:
The blind spot is located at the optic disc, where the optic nerve connects to the retina. This area lacks rod and cone cells, making it insensitive to light.
(iii) Describe the changes that occur in the eye when changing focus to view a distant object.
▶️Answer/Explanation
Answer:
1. Ciliary muscles relax
2. Suspensory ligaments tighten
3. Lens becomes thinner/flatter
Explanation:
For distant vision:
– The ciliary muscles relax, reducing tension on the suspensory ligaments.
– The suspensory ligaments pull taut, flattening the lens.
– This reduces refractive power, allowing parallel light rays from distant objects to focus on the retina.
(b) The list shows examples of involuntary and voluntary responses. Place ticks (✓) to show all the examples of involuntary responses.
▶️Answer/Explanation
Answer:
✓ breathing
✓ heart beating
✓ sweating
Explanation:
Involuntary responses are controlled by the autonomic nervous system and occur without conscious thought:
– Breathing (automatic, though can be temporarily controlled)
– Heartbeat (regulated by pacemaker cells)
– Sweating (thermoregulation response)
Voluntary responses (reading, running, writing) require conscious effort.
(c) Sense organs form part of the peripheral nervous system. State the two parts that form the central nervous system.
▶️Answer/Explanation
Answer:
1: Brain
2: Spinal cord
Explanation:
The central nervous system (CNS) consists of:
1. Brain – Processes information and coordinates responses
2. Spinal cord – Conducts nerve impulses and mediates reflexes
The peripheral nervous system includes all nerves outside the CNS (e.g., sensory and motor neurons).
Question 8
(a) Subtopic: C8.4 Transition elements
(b) Subtopic: C2.7 Metallic bonding
(c)(i) Subtopic: C9.6 Extraction of metals
(c)(ii) Subtopic: C3.2 Relative masses of atoms and molecules
(d) Subtopic: C6.2 Rate of reaction
Iron is a transition metal.
(a) State two properties of transition metals that are not properties of all metals.
▶️Answer/Explanation
Answer:
1: Form colored compounds
2: Act as catalysts
Alternative accepted answers: High melting points / High density / Variable oxidation states
Explanation:
Transition metals have unique properties due to their incomplete d-subshell:
– Colored compounds arise from d-d electron transitions
– Catalytic activity (e.g., Fe in Haber process) due to variable oxidation states
– Unlike Group I metals (e.g., Na), they typically have higher densities and melting points
(b) Describe the metallic bonding in a metal. You may draw a labelled diagram to help your answer.
▶️Answer/Explanation
Answer:
1: Lattice of positive ions
2: ‘Sea’ of delocalized electrons
Explanation:
Metallic bonding consists of:
– A regular lattice of positive metal ions (cations)
– Delocalized electrons that move freely throughout the structure
These free electrons explain properties like:
– Electrical conductivity (electrons carry current)
– Malleability (layers can slide without breaking bonds)
(c) Hematite contains iron oxide, Fe2O3. Iron is extracted from iron oxide in a blast furnace.
(i) Describe how iron is extracted from iron oxide. Do not describe how impurities are removed. You can use balanced symbol equations in your answer.
▶️Answer/Explanation
Answer:
1: C + O2 → CO2
2: C + CO2 → 2CO
3: Fe2O3 + 3CO → 2Fe + 3CO2
Explanation:
The extraction occurs in three stages:
1. Coke burns to form CO2 (exothermic)
2. CO2 reacts with more coke to form reducing agent CO
3. Iron oxide is reduced by CO to produce molten iron
Temperature: ~1500°C in blast furnace
(ii) Silicon dioxide, SiO2, is an impurity that needs to be removed from the blast furnace. The silicon dioxide reacts with calcium oxide, CaO.
CaO + SiO2 → CaSiO3
Calculate the mass of calcium oxide needed to remove 21 kg of silicon dioxide, SiO2.
[Ar; Ca, 40; O, 16; Si, 28]
▶️Answer/Explanation
Answer: 19.6 kg
Solution:
1. Calculate molar masses:
– SiO2 = 28 + (16×2) = 60 g/mol
– CaO = 40 + 16 = 56 g/mol
2. Mole ratio is 1:1 (from equation)
3. Moles of SiO2 = 21,000g / 60g/mol = 350 mol
4. Mass of CaO needed = 350 mol × 56 g/mol = 19,600 g = 19.6 kg
(d) A blast furnace works at a very high temperature. Reactions are faster at higher temperatures. Explain why reactions are faster at higher temperatures. Use ideas about collisions between particles.
▶️Answer/Explanation
Answer:
1: Particles have higher kinetic energy/move faster
2: More particles have energy ≥ activation energy
3: Increased collision frequency
Explanation:
According to collision theory:
– Higher temperature increases particle velocity
– More particles overcome the activation energy barrier
– More successful collisions per unit time
– Frequency of collisions increases as particles move faster
Question 9
(a)(i)-(ii) Subtopic: P5.2.3 Radioactive decay
(b)(i) Subtopic: P3.1 General properties of waves
(b)(ii) Subtopic: P3.3 Electromagnetic spectrum
(b)(iii) Subtopic: P3.4 Sound
(b)(iv) Subtopic: P5.2.5 Applications and safety precautions
(a) Astatine-211 (At-211) decays by the emission of α-particles. The α-particles emitted by At-211 are used to destroy cancer cells. Small quantities of At-211 are injected directly into the site of the cancer.
(i) Explain why At-211 is only effective when injected directly into the cancer.
▶️Answer/Explanation
Answer: α-radiation has low penetration power (stopped by few cm of air/paper/skin)
Explanation:
– Alpha particles are large and highly ionizing but have very short range (≈50μm in tissue)
– Direct injection ensures radiation affects only cancer cells without damaging healthy tissues
– If administered systemically, α-particles would be absorbed before reaching the tumor
(ii) At-211 decays by α-particle emission to produce an isotope of bismuth. Use nuclide notation to complete a symbol equation for this decay process.
▶️Answer/Explanation
Answer:
Explanation:
α-decay follows these rules:
1. Mass number decreases by 4: 211 → 207
2. Atomic number decreases by 2: 85 → 83
3. The α-particle is a helium nucleus (42He)
Bismuth-207 is a stable isotope
(b) X-rays and ultrasound waves are used by doctors in hospitals.
(i) X-rays are transverse waves and ultrasound waves are longitudinal waves. Describe the difference between a transverse wave and a longitudinal wave.
▶️Answer/Explanation
Answer:
– Transverse waves: Oscillations perpendicular to energy transfer direction (e.g., light/X-rays)
– Longitudinal waves: Oscillations parallel to energy transfer direction (e.g., sound/ultrasound)
Visualization:
• Transverse: ↗️↘️ (like shaking a rope up-down)
• Longitudinal: ⇨⇦⇨ (like compressing a spring)
(ii) X-rays have a wavelength of 1.1×10-9 m and travel at 3.0×108 m/s. Calculate the frequency of X-rays.
▶️Answer/Explanation
Answer: 2.73 × 1017 Hz
Solution:
Using the wave equation:
f = (3.0 × 108) ÷ (1.1 × 10-9)
f = 2.727… × 1017 Hz ≈ 2.73 × 1017 Hz
(iii) Ultrasound waves are used to scan unborn babies. Ultrasound waves have a frequency too high to be heard by a healthy human ear. Using your knowledge of the range of audible frequencies for a healthy human ear, suggest a frequency for ultrasound waves.
▶️Answer/Explanation
Answer: >20,000 Hz (typical medical ultrasound: 2-18 MHz)
Explanation:
Human hearing range is 20 Hz – 20,000 Hz. Ultrasound is defined as:
– Above 20,000 Hz (inaudible to humans)
– Medical imaging uses MHz frequencies for better resolution (1 MHz = 106 Hz)
(iv) Suggest a reason why it is not safe to scan unborn babies with X-rays.
▶️Answer/Explanation
Answer: X-rays cause ionization/cell damage/DNA mutations/risk of cancer
Explanation:
– X-rays are ionizing radiation that can:
• Damage fetal cells during rapid development
• Increase cancer risk later in life
• Cause mutations in DNA
– Ultrasound uses non-ionizing sound waves, making it safer for prenatal scans
Question 10
(a)(i)-(ii) Subtopic: B8.3 Transpiration
(b) Subtopic: B8.1 Xylem and phloem
(c)(i) Subtopic: B6.2 Leaf structure
(c)(ii)-(iii) Subtopic: B6.1 Photosynthesis
(a) Fig. 10.1 is a sketch graph showing the effect of humidity on the rate of transpiration.
(i) Explain the change in rate of transpiration shown in Fig. 10.1.
▶️Answer/Explanation
Answer:
1. Higher humidity means more water vapor in air
2. Reduces concentration gradient between leaf and air
3. Decreases diffusion of water vapor from stomata
Explanation:
The graph shows an inverse relationship because:
– At low humidity (dry air): Steep water potential gradient → rapid transpiration
– At high humidity (moist air): Small gradient → slower water loss
– Key mechanism: Transpiration depends on vapor pressure deficit (difference between saturated and actual vapor pressure)
(ii) State one other factor that affects the rate of transpiration.
▶️Answer/Explanation
Answer:
Temperature / Wind speed / Light intensity / Soil water availability
Explanation:
Other controlling factors:
– Temperature: ↑Temp → ↑Evaporation rate (kinetic energy of water molecules)
– Wind: Removes humid air near leaf → maintains gradient
– Light: Triggers stomatal opening (via guard cell photosynthesis)
– Soil water: Limited supply → stomatal closure to prevent wilting
(b) Transpiration pull moves water through xylem vessels. State how water molecules are held together.
▶️Answer/Explanation
Answer:
Hydrogen bonds / Cohesion forces
Explanation:
The cohesion-tension theory depends on:
1. Cohesion: H-bonding between H2O molecules creates continuous column
2. Adhesion: H2O binds to xylem walls (cellulose) via polar attraction
3. Surface tension: Maintains unbroken column under tension (up to -30 MPa)
This allows water ascent >100m in tall trees without breaking
(c) Xylem is a specialised tissue in plants. The palisade mesophyll layer is another specialised tissue in plants.
(i) Describe two ways the palisade mesophyll cells are adapted for photosynthesis.
▶️Answer/Explanation
Answer:
1. Many chloroplasts (high chlorophyll concentration)
2. Columnar arrangement (perpendicular to surface for optimal light capture)
3. Thin cell walls (short diffusion path for CO2)
Explanation:
Palisade cells are the “photosynthetic factories”:
– Chloroplasts can move within cells to optimize light absorption
– Tight packing minimizes light scattering between cells
– Located just below epidermis to intercept light before spongy mesophyll
Typical density: 200-400 chloroplasts per cell
(ii) State the raw materials required for photosynthesis.
▶️Answer/Explanation
Answer:
Carbon dioxide and water
Explanation:
The photosynthetic equation:
6CO2 + 6H2O → C6H12O6 + 6O2
– CO2 enters through stomata (diffusion)
– H2O comes from xylem (root absorption)
– Both are oxidized/reduced in the Calvin cycle and light reactions
(iii) State the source of energy needed for the process of photosynthesis.
▶️Answer/Explanation
Answer:
Light energy (typically sunlight)
Explanation:
Energy conversion process:
1. Photons absorbed by chlorophyll (peak absorption at 430nm & 662nm)
2. Excites electrons to higher energy levels
3. Energy converted to chemical energy (ATP + NADPH)
4. Drives carbon fixation in Calvin cycle
Only 1-3% of incident light is actually used in photosynthesis
Question 11
(a)-(b) Subtopic: C2.2 Atomic structure and the Periodic Table
(c)(i)-(ii) Subtopic: C2.4 Ions and ionic bonds
(d)(i)-(ii) Subtopic: C8.3 Group VII properties
(e) Subtopic: C3.2 Relative masses of atoms and molecules
Fig. 11.1 shows part of the Periodic Table.
(a) Describe the relationship between the Group number and the number of electrons in the outer shell.
▶️Answer/Explanation
Answer:
The Group number equals the number of electrons in the outer shell (for main group elements).
Explanation:
– Group I: 1 valence electron (e.g., Na: 2,8,1)
– Group II: 2 valence electrons (e.g., Mg: 2,8,2)
– Group VII: 7 valence electrons (e.g., Cl: 2,8,7)
Exceptions:
– Transition metals (Groups 3-12) don’t follow this pattern
– Helium (Group VIII) has 2 valence electrons despite group number
(b) Magnesium, Mg, is in Group II. Magnesium has a proton number of 12. State the electronic structure of a magnesium atom.
▶️Answer/Explanation
Answer: 2.8.2
Explanation:
Electron configuration breakdown:
1. Protons = 12 → neutral atom has 12 electrons
2. First shell: 2 electrons (maximum capacity)
3. Second shell: 8 electrons
4. Third shell: Remaining 2 electrons (valence electrons)
This explains Mg’s:
– +2 oxidation state (loses 2 valence e⁻)
– Metallic bonding (delocalized valence electrons)
(c) Sodium forms bonds with chlorine. Sodium is in Group I. Chlorine is in Group VII.
(i) Sodium chloride is an ionic compound. Fig. 11.2 shows a sodium ion. Complete Fig. 11.2 to show a chloride ion.
▶️Answer/Explanation
Answer:
Explanation:
Ion formation process:
– Sodium: Loses 1 e⁻ → Na⁺ (2,8)
– Chlorine: Gains 1 e⁻ → Cl⁻ (2,8,8)
Key properties:
– Na⁺: Smaller radius than atom (lost electron shell)
– Cl⁻: Larger radius than atom (electron-electron repulsion)
– Charge imbalance creates electrostatic attraction
(ii) Ionic compounds, such as sodium chloride, have a lattice structure. Describe the lattice structure of sodium chloride.
▶️Answer/Explanation
Answer:
1. Regular 3D arrangement of alternating Na⁺ and Cl⁻ ions
2. Each Na⁺ surrounded by 6 Cl⁻ (octahedral coordination)
3. Held by strong electrostatic forces (ionic bonds)
Explanation:
Crystal structure details:
– Face-centered cubic unit cell
– Lattice energy: -787 kJ/mol (very stable)
– Properties: High melting point (801°C), brittle, soluble in water
– Scale: Repeats over ~10²³ atoms in macroscopic crystal
(d) Table 11.1 shows some information about the Group VII elements (halogens).
(i) Identify the state of iodine at room temperature.
▶️Answer/Explanation
Answer: solid
Explanation:
Halogen state trends:
– F/Cl: Gases (weak London forces between small molecules)
– Br: Liquid (intermediate strength forces)
– I: Solid (stronger forces between larger electron clouds)
– At: Predicted solid (not shown in table)
Room temperature = 25°C (between iodine’s mp/bp)
(ii) Suggest the melting point of chlorine and the boiling point of bromine. Use trends down the Group.
▶️Answer/Explanation
Answer:
– Chlorine mp: Between -220°C and -7°C (e.g., -101°C)
– Bromine bp: Between -35°C and 184°C (e.g., 59°C)
Explanation:
Trend explanation:
1. Down the group: Increasing molecular size
2. Stronger London forces: More electron clouds → more temporary dipoles
3. Result: Higher mp/bp with increasing atomic number
Actual values:
– Cl mp = -101.5°C
– Br bp = 58.8°C
(e) Chlorine has a relative atomic mass of 35.5. Define relative atomic mass.
▶️Answer/Explanation
Answer:
1. Average mass of naturally occurring atoms of an element
2. On a scale where carbon-12 has a mass of exactly 12 units
Explanation:
Key points about Ar:
– Calculation: Weighted average of isotopes (³⁵Cl = 75%, ³⁷Cl = 25%)
– Units: Dimensionless (relative to ¹²C standard)
– Example: (35×75 + 37×25)/100 = 35.5
– Purpose: Allows calculation of reacting masses in chemical equations
Question 12
(a) Subtopic: P1.2 Motion
(b)(i)-(ii) Subtopic: P4.2.4 Resistance
(c)(i)-(iv) Subtopic: P4.5.2 The a.c. generator
(a) Fig. 12.1 shows the speed-time graph for part of a train journey.
Calculate the acceleration of the train at 5 s.
▶️Answer/Explanation
Answer: 1.8 m/s²
Working:
Acceleration = gradient of speed-time graph
= (18 m/s – 0 m/s) ÷ (10 s – 0 s)
= 18 ÷ 10 = 1.8 m/s²
Explanation:
– The graph shows uniform acceleration (straight line)
– At 5s, the train is halfway through acceleration phase
– Typical metro train acceleration ranges 0.8-1.3 m/s² (this is slightly higher)
– Force required = mass × acceleration (not calculated here)
(b) The train has two large headlamps connected in parallel. The lamps have a power rating of 360 W and are operated with a potential difference of 80 V.
(i) Show that the resistance of each lamp is 18 Ω.
▶️Answer/Explanation
Working:
1. Power (P) = V²/R → R = V²/P
2. R = (80 V)² ÷ 360 W
3. R = 6400 ÷ 360 = 17.78 Ω ≈ 18 Ω
Explanation:
– Uses power formula for resistive loads
– Rounding to 2 significant figures matches question requirement
– Actual resistance might vary with temperature (not considered here)
– Higher wattage lamps would have lower resistance
(ii) Calculate the combined resistance of the two lamps connected together in parallel.
▶️Answer/Explanation
Answer: 9 Ω
Working:
1/Rtotal = 1/R₁ + 1/R₂
= 1/18 + 1/18 = 2/18 = 1/9
→ Rtotal = 9 Ω
Explanation:
– Parallel resistors divide current paths
– Total resistance is always less than individual resistors
– Practical benefit: If one lamp fails, the other stays lit
– Current draw: I = V/R = 80V/9Ω ≈ 8.89 A total
(c) The electricity for the lamps is produced by a generator. Fig. 12.2 shows a simple generator.
(i) Describe how rotating the coil at constant speed induces an alternating voltage.
▶️Answer/Explanation
Answer:
1. Coil cuts magnetic field lines → induces EMF (Faraday’s Law)
2. Direction of cutting reverses every half-rotation
3. Produces sinusoidal voltage that alternates polarity
Explanation:
– Key physics: ε = -NΔΦ/Δt (flux linkage change)
– Maximum EMF when coil perpendicular to field (90°)
– Zero EMF when coil parallel to field (0°/180°)
– Commercial generators use slip rings and brushes
(ii) On the grid in Fig. 12.3, sketch a graph of voltage output against time for the generator when the coil rotates at constant speed.
▶️Answer/Explanation
Answer:
Explanation:
– Pure sine wave shape (no distortion)
– Equal positive and negative peaks (symmetrical)
– Constant frequency (regular wave spacing)
– Amplitude depends on rotation speed and field strength
(iii) The coil is rotated faster. Suggest two effects this will have on the alternating voltage output.
▶️Answer/Explanation
Answer:
1. Increased output voltage (greater amplitude)
2. Increased frequency (more cycles per second)
Explanation:
– Voltage: More flux cut per second → higher EMF
– Frequency: Directly proportional to rotation speed (f = rpm/60)
– Practical limit: Mechanical stress at high speeds
– Power stations maintain constant 50/60 Hz frequency
(iv) The permanent magnets in the generator shown in Fig. 12.2 are made from steel rather than iron. Suggest why.
▶️Answer/Explanation
Answer:
Steel retains magnetism longer (hard magnetic material)
Explanation:
– Steel: High retentivity → maintains strong field
– Iron: Soft magnetic material → would demagnetize faster
– Modern alternatives: Alnico or rare-earth magnets
– Generator efficiency depends on consistent magnetic field strength