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(a)(i) Sensory neurone transmits electrical impulses from the receptor (e.g., pain receptor in skin) to the central nervous system. (ii) Synapses act as junctions between neurones, ensuring that nerve impulses travel in only one direction. This is because neurotransmitter chemicals are only released from one side of the gap. (iii) Reflex actions do not require conscious thought, are rapid, and automatic, whereas voluntary actions are initiated by conscious decisions from the brain and are typically slower. (b)(i) Auxin is produced in the shoot tip and diffuses down. Under unilateral light, auxin moves to the shaded side. This higher concentration of auxin causes cells on the shaded side to elongate more, resulting in the shoot bending towards the light. (ii) Auxin is synthesized at the tip of the shoot. (iii) Roots grow downwards in response to gravity, which is positive geotropism / gravitropism.

(a)(i) Sensory neurone [1] (a)(ii) Ensures impulses travel in one direction only [1]; transmits chemical neurotransmitter across synaptic gap to trigger impulse in next neurone [1]. (a)(iii) Reflex is rapid/faster [1]; reflex is involuntary/automatic while voluntary involves conscious choice [1]. (b)(i) Auxin is produced at tip and diffuses downwards [1]; auxin accumulates on the shaded side [1]; causes cell elongation on the shaded side, making it bend [1]. (b)(ii) Tip of shoot [1]. (b)(iii) Gravitropism / geotropism [1].

(a)(i) A catalyst is defined as a substance that increases the rate of a chemical reaction and is not permanently changed or consumed by the reaction. (ii) In the lock and key hypothesis, the active site of the enzyme acts as the 'lock' and the substrate molecule acts as the 'key'. The active site has a highly specific shape complementary to the substrate. The substrate binds to the active site to form an enzyme-substrate complex, where the chemical reaction takes place, releasing the products. (b)(i) To ensure a valid investigation, other factors affecting enzyme action must be controlled. These include pH, concentration of enzyme, and concentration or volume of substrate. (ii) Above the optimum temperature, the increased thermal energy causes intense molecular vibrations, which break the weak chemical bonds maintaining the enzyme's structure. The enzyme denatures, changing the specific shape of its active site. The substrate can no longer fit, and the reaction stops.

(a)(i) Speeds up a chemical reaction [1]; is not changed/used up in the reaction [1]. (a)(ii) Active site has a complementary shape to the substrate [1]; substrate binds to active site [1] to form an enzyme-substrate complex [1]. (b)(i) pH [1]; enzyme concentration [1]; substrate concentration/volume [1]. (b)(ii) Heat causes excessive atomic vibrations within the protein [1]; the active site is denatured / permanently changed [1]; substrate can no longer fit [1].

(a)(i) Xylem vessels are specialized cells that are dead and empty of cytoplasm, forming hollow tubes with no end walls, allowing water to flow with minimal resistance. Additionally, their walls are reinforced with a tough substance called lignin, which provides mechanical strength and prevents the vessels from collapsing inward under the tension of transpiration pull. (ii) Water vapor evaporates from the surface of mesophyll cells into the air spaces inside the leaf, and then diffuses out of the leaf through stomata. This evaporation of water creates a water potential gradient. Because of the strong cohesive forces between water molecules (they stick together due to hydrogen bonding), a continuous column of water is pulled upwards through the xylem. (b)(i) In translocation, a source is a site in the plant where sucrose or amino acids are manufactured or mobilised (e.g., mature leaves), and a sink is any site where these substances are stored or used for growth/respiration (e.g., roots, flowers, fruits). (ii) Active transport is used to load sucrose into phloem sieve tubes against its concentration gradient. (iii) The main substances transported in xylem are water and dissolved inorganic mineral ions, while phloem transports organic molecules, specifically sucrose and amino acids.

(a)(i) Dead cells/no cytoplasm/hollow tubes with no end walls [1]; lignified cell walls [1]. (a)(ii) Water evaporates from mesophyll cells and diffuses out through stomata [1]; water molecules show cohesion / stick together [1]; this creates tension/suction that pulls the water column upwards [1]. (b)(i) Source: part where substances are produced/released, e.g., leaf [1]; Sink: part where substances are used/stored, e.g., root/growing shoot [1]; transport is from source to sink [1]. (b)(ii) Active transport [1]. (b)(iii) Xylem carries water/minerals AND phloem carries sucrose/amino acids [1].

(a)(i) Plant cells contain structural features absent in animal cells, notably a cell wall composed of cellulose and chloroplasts containing chlorophyll. A large central permanent vacuole is also a key difference. (ii) The palisade mesophyll cell is adapted by being elongated and positioned vertically directly below the upper epidermis of the leaf, which helps pack as many of these cells as possible where light intensity is highest. They are also packed with numerous chloroplasts to absorb the light energy needed for photosynthesis. (b) To calculate the actual size, use the formula: \( A = \frac{I}{M} \). First, convert the image size from mm to \(\mu\text{m}\): \( 40\text{ mm} \times 1000 = 40000\ \mu\text{m} \). Then, divide by the magnification: \( A = \frac{40000}{800} = 50\ \mu\text{m} \). (c) The hierarchical levels of biological organization from simplest to most complex are: cell, tissue, organ, organ system, and organism. (d) Ribosomes are small organelles found in the cytoplasm and on the rough endoplasmic reticulum that carry out translation, which is the process of synthesizing proteins by linking amino acids together.

(a)(i) Any two of: cellulose cell wall / chloroplasts / permanent vacuole [2]. (a)(ii) Packed with many chloroplasts [1]; arranged vertically / close to the upper surface to capture maximum light [1]. (b) Conversion of 40 mm to 40,000 micrometres (or showing calculation in mm) [1]; Formula: actual = image / magnification [1]; 50 micrometres (with unit) [1]. (c) cell -> tissue -> organ -> organ system -> organism [1]. (d) Protein synthesis [2] (accept: making proteins / translation [1] out of [2]).

(a)(i) A saturated hydrocarbon has only single bonds between carbon atoms (C-C bonds). An unsaturated hydrocarbon contains at least one carbon-carbon double bond (C=C bond). (ii) The standard test is adding bromine water (which is orange-brown). Alkanes do not react with bromine water in the absence of UV light, so the solution remains orange-brown. Alkenes rapidly react via an addition reaction across the double bond, decolourising the bromine water to colourless. (b)(i) Industrial cracking involves breaking long-chain alkanes into shorter, more useful alkanes and alkenes. By balancing the atoms: \(C_{10}H_{22} \rightarrow C_2H_4 + C_8H_{18}\). The remaining hydrocarbon is octane, \(C_8H_{18}\). (ii) The industrial process requires a high temperature in the range of \(500-700^\circ\text{C}\) and a catalyst such as silicon dioxide (silica) or aluminium oxide (alumina). (c)(i) In poly(ethene), the carbon-carbon double bonds of the ethene monomers break, allowing them to link together with single bonds. Two repeating units are represented as: \(-(CH_2-CH_2-CH_2-CH_2)-\) with open bonds at each end. (ii) Ethene molecules join together via addition polymerisation, in which the double bonds break open to form a single long-chain polymer with no other products formed.

(a)(i) Saturated has only single C-C bonds, unsaturated has at least one double C=C bond [1]. (a)(ii) Add bromine water / aqueous bromine [1]; alkane: remains orange [1]; alkene: decolourises / goes from orange to colourless [1]. (b)(i) \(C_8H_{18}\) [1]. (b)(ii) High temperature (approx. 500-700 degrees C) [1]; alumina/silica/zeolite catalyst [1]. (c)(i) Correct single C-C bonds across four carbons [1]; hydrogens and open bonds at each end indicating polymer chain extension [1]. (c)(ii) Addition [1].

(a)(i) The combined resistance \(R_p\) of two parallel resistors is given by \( \frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} \). Here, \( \frac{1}{R_p} = \frac{1}{4.0} + \frac{1}{6.0} = 0.25 + 0.1667 = 0.4167\ \Omega^{-1} \). Reciprocating: \( R_p = \frac{1}{0.4167} = 2.4\ \Omega \). (ii) The total current \(I\) is calculated using Ohm's law: \( I = \frac{V}{R_p} = \frac{12.0\text{ V}}{2.4\ \Omega} = 5.0\text{ A} \). (iii) In a parallel circuit, the voltage across each branch is equal to the supply voltage. Therefore, the voltage across the \(4.0\ \Omega\) resistor is 12.0 V. Using the power equation: \( P = \frac{V^2}{R} = \frac{12.0^2}{4.0} = \frac{144}{4.0} = 36.0\text{ W} \). (b)(i) To increase the induced e.m.f., we can increase the rate at which magnetic field lines are cut. This can be achieved by moving the wire faster, using a stronger magnetic field, or using a coil with more turns of wire instead of a single wire. (ii) Lenz's law states that the direction of the induced current is always such that it opposes the change in magnetic flux that produced it (e.g., creating a magnetic pole that repels an approaching magnet).

(a)(i) Correct parallel formula: \( 1/R = 1/R_1 + 1/R_2 \) [1]; 2.4 \(\Omega\) [1]. (a)(ii) Formula: \( I = V/R \) [1]; 5.0 A [1]. (a)(iii) Formula: \( P = V^2/R \) (or equivalent) [1]; 36 W (or J/s) [1]. (b)(i) Any two of: move the wire faster [1]; use a stronger magnet [1]; use a coil with more turns [1]. (b)(ii) Direction of current [1] opposes the change that caused it [1].

(a)(i) Isotopes are atoms of the same element that contain the identical number of protons (and thus the same atomic number) but have a different number of neutrons (leading to a different nucleon/mass number). (ii) During beta (\(\beta^-\)) decay, a neutron within the unstable nucleus decays into a proton and an electron. The proton remains in the nucleus, increasing the atomic number by 1, and the high-energy electron (the beta particle) is emitted. (iii) In a nuclear equation, mass and charge must balance. Carbon-14 (charge 6) decays to Nitrogen-14 (charge 7). The missing particle must have a mass of 0 and a charge of -1. Hence, the particle is an electron, \(^{0}_{-1}\text{e}\) or \(\beta^-\). (b)(i) Half-life is the average time taken for half the radioactive nuclei in a sample to decay, or the time for the activity/count rate to fall to half of its initial value. (ii) To go from an initial activity of 24.0 Bq to 3.0 Bq: after 1 half-life: \( 24.0 / 2 = 12.0\text{ Bq} \); after 2 half-lives: \( 12.0 / 2 = 6.0\text{ Bq} \); after 3 half-lives: \( 6.0 / 2 = 3.0\text{ Bq} \). Therefore, 3 half-lives have elapsed. (iii) The age of the wood is calculated by multiplying the number of half-lives by the duration of one half-life: \( 3 \times 5730\text{ years} = 17190\text{ years} \). (iv) Ionising radiation has enough energy to ionise atoms in living cells, which can damage DNA molecules, leading to genetic mutations, cell death, or cancer.

(a)(i) Same number of protons [1]; different number of neutrons [1]. (a)(ii) A neutron turns into a proton (and an electron is emitted) [1]. (a)(iii) \(^{0}_{-1}\text{e}\) or \(^{0}_{-1}\beta\) [1]. (b)(i) Time taken for the activity / number of radioactive nuclei to halve [1]. (b)(ii) Showing decay steps: \( 24 \rightarrow 12 \rightarrow 6 \rightarrow 3 \) [1]; 3 half-lives [1]. (b)(iii) \( 3 \times 5730 = 17190\text{ years} \) [1]. (b)(iv) Can damage DNA / cause cancer / cause cell mutations / cause radiation burns [1].

(a)(i) According to Snell's law, the refractive index \(n\) is given by: \( n = \frac{\sin i}{\sin r} \). Substituting the values: \( 1.5 = \frac{\sin 40^\circ}{\sin r} \). Rearranging gives: \( \sin r = \frac{\sin 40^\circ}{1.5} = \frac{0.64279}{1.5} = 0.42853 \). Solving for \(r\): \( r = \arcsin(0.42853) \approx 25.4^\circ \). (ii) Light travels slower in glass than in air because glass is an optically denser medium. This decrease in speed causes the wave front to slow down on one side first, causing the path of light to change direction (bend towards the normal). (iii) The critical angle is defined as the angle of incidence in an optically denser medium (like glass) which produces an angle of refraction of \(90^\circ\) in the less dense medium (like air). (b)(i) In a longitudinal wave, the oscillations/vibrations of particles are parallel to the direction of wave travel (energy transfer). In a transverse wave, the oscillations are perpendicular (at a right angle) to the direction of wave travel. (ii) Using the wave equation: \( v = f \lambda \). Rearranging to solve for wavelength: \( \lambda = \frac{v}{f} = \frac{340\text{ m/s}}{250\text{ Hz}} = 1.36\text{ m} \).

(a)(i) Correct formula: \( n = \sin i / \sin r \) [1]; rearrangement: \( \sin r = \sin 40^\circ / 1.5 \) [1]; angle \( r = 25.4^\circ \) (accept range 25.3 to 25.4) [1]. (a)(ii) Speed of light decreases in glass [1]; the change in speed causes the bending/refraction [1]. (a)(iii) Angle of incidence in the denser medium [1] which results in an angle of refraction of 90 degrees [1]. (b)(i) Longitudinal: vibrations are parallel to wave travel [1]; Transverse: vibrations are perpendicular [1]. (b)(ii) Formula rearrangement: \( \lambda = v/f \) and correct calculation: 1.36 m [1].

(a) (i) A reflex action is an automatic (or involuntary) response that occurs extremely rapidly. It serves a protective function to prevent serious injury.

(ii) The stimulus (heat) is detected by temperature/pain receptors in the skin. This generates an electrical impulse which travels along the sensory neurone to the central nervous system (spinal cord). The impulse is passed across a synapse to a relay neurone, and then across another synapse to a motor neurone. The motor neurone carries the impulse to the effector (biceps muscle of the arm), which contracts to pull the hand away.

(b) (i) Adrenaline is secreted by the adrenal glands.

(ii) Physiological changes:
1. Increased heart rate: increases blood flow to muscles, supplying them with more oxygen and glucose for rapid aerobic respiration.
2. Conversion of glycogen to glucose in the liver: increases blood glucose levels to provide substrate for cellular respiration in active tissues.

Part (a)(i) [Total: 2 marks]
- Any two from: fast/rapid [1], automatic/involuntary [1], protective/does not involve decision-making by the brain [1].

Part (a)(ii) [Total: 3 marks]
- Sensory neurone mentioned and carries impulse from receptor to spinal cord [1].
- Relay neurone mentioned and passes impulse across spinal cord/synapses [1].
- Motor neurone mentioned and carries impulse from CNS to effector/muscle causing contraction [1].

Part (b)(i) [Total: 1 mark]
- Adrenal gland [1].

Part (b)(ii) [Total: 4 marks]
- State change 1: e.g. Increased heart rate / increased breathing rate / pupils dilate [1].
- Explanation 1: corresponding explanation (e.g. to deliver more oxygen/glucose to muscles for respiration, or better vision to spot danger) [1].
- State change 2: different physiological change [1].
- Explanation 2: corresponding explanation [1].

(a) Cracking involves breaking down a large alkane into a smaller alkane and an alkene. Subtracting the atoms of octane from the reactant: \(\text{C}_{12} - \text{C}_8 = \text{C}_4\) and \(\text{H}_{26} - \text{H}_{18} = \text{H}_8\). The balanced equation is: \(\text{C}_{12}\text{H}_{26} \rightarrow \text{C}_8\text{H}_{18} + \text{C}_4\text{H}_8\).

(b) (i) The molecular formula is \(\text{C}_4\text{H}_8\) (butene).
(ii) The displayed formula showing all atoms and bonds of but-1-ene is:
H H H H
| | | |
H - C - C - C = C - H
| | |
H H H

(c) (i) Since the monomer is butene, the polymer is poly(butene).
(ii) During polymerisation, the double bond opens up. The repeating unit is written with single bonds extending outside parentheses:
H H
| |
-[C - C]-
| |
H CH2CH3

(d) Add aqueous bromine (bromine water) to separate samples. Octane (alkane) does not react with bromine water, so the solution remains orange/brown. Alkene Z (butene), being an unsaturated hydrocarbon, undergoes an addition reaction with bromine, causing the solution to quickly decolourise (turn from orange/brown to colourless).

Part (a) [Total: 2 marks]
- \(\text{C}_4\text{H}_8\) as the second product [1].
- Fully balanced equation: \(\text{C}_{12}\text{H}_{26} \rightarrow \text{C}_8\text{H}_{18} + \text{C}_4\text{H}_8\) [1].

Part (b)(i) [Total: 1 mark]
- \(\text{C}_4\text{H}_8\) [1].

Part (b)(ii) [Total: 1 mark]
- Correct displayed structure of butene showing all atoms and bonds including the double bond [1].

Part (c)(i) [Total: 1 mark]
- Poly(butene) or polybutene [1].

Part (c)(ii) [Total: 2 marks]
- Single \(\text{C}-\text{C}\) bond in the center with continuation bonds shown on both sides [1].
- Correct groups attached to the carbons matching the monomer butene [1].

Part (d) [Total: 3 marks]
- Reagent: Bromine water / aqueous bromine [1].
- Observation with octane: Remains orange / yellow / brown / no change [1].
- Observation with alkene Z: Decolourises / turns colourless [1].

(a) (i) Ohm's law states that current is directly proportional to potential difference, provided physical conditions such as temperature remain constant. In a filament lamp, the passage of current heating up the filament increases its temperature. The metal lattice ions in the filament vibrate with greater amplitude, increasing the rate of collisions between conduction electrons and the lattice. This causes the resistance of the lamp to increase as voltage increases, resulting in a non-linear current-voltage relationship.

(ii) Power \(P = I^2 R\)
\(P = (0.40\text{ A})^2 \times 15\ \Omega = 0.16 \times 15 = 2.4\text{ W}\).

(b) (i) In a series circuit, the total voltage of the source is divided among the components:
\(V_{\text{total}} = V_{\text{lamp}} + V_R\)
\(12\text{ V} = 4.5\text{ V} + V_R\)
\(V_R = 12 - 4.5 = 7.5\text{ V}\).

(ii) The current is the same throughout a series circuit, so the current through the resistor \(R\) is \(0.30\text{ A}\).
Using Ohm's law:
\(R = \frac{V_R}{I} = \frac{7.5\text{ V}}{0.30\text{ A}} = 25\ \Omega\).

(iii) Time \(t = 5.0\text{ minutes} = 5.0 \times 60 = 300\text{ s}\).
Energy transferred \(E = V_{\text{total}} \times I \times t\)
\(E = 12\text{ V} \times 0.30\text{ A} \times 300\text{ s} = 1080\text{ J}\) (or \(1.08\text{ kJ}\)).

Part (a)(i) [Total: 3 marks]
- Current heats up the filament / temperature increases [1].
- Lattice ions vibrate more [1].
- More collisions between electrons and ions increases the resistance [1].

Part (a)(ii) [Total: 2 marks]
- Recall of \(P = I^2 R\) [1].
- Correct calculation: \(2.4\text{ W}\) (must include units) [1].

Part (b)(i) [Total: 2 marks]
- Use of series voltage relationship: \(12 - 4.5\) [1].
- Correct calculation: \(7.5\text{ V}\) [1].

Part (b)(ii) [Total: 2 marks]
- Use of \(R = \frac{V}{I}\) [1].
- Correct calculation: \(25\ \Omega\) [1].

Part (b)(iii) [Total: 1 mark]
- Correct calculation: \(1080\text{ J}\) (or \(1.1\text{ kJ}\)) [1].

(a) (i) Using Snell's law:
\(n = \frac{\sin(i)}{\sin(r)} = \frac{\sin(50.0^\circ)}{\sin(31.0^\circ)} = \frac{0.7660}{0.5150} \approx 1.49\).

(ii) Refractive index is related to speed by \(n = \frac{c}{v}\):
\(1.49 = \frac{3.0 \times 10^8}{v}\)
\(v = \frac{3.0 \times 10^8}{1.49} \approx 2.0 \times 10^8\text{ m/s}\).

(b) (i) Light waves are transverse waves, meaning their vibrations are perpendicular to the direction of energy transfer. Sound waves are longitudinal waves, meaning their vibrations are parallel to the direction of energy transfer.

(ii) Sound waves require a medium to travel and propagate via particle collisions. Since the solid plastic block has particles packed closely together, sound travels faster in it than in air. Conversely, light travels slower in the plastic block than in air because of the higher refractive index of the medium.

(c) (i) Exposure to ultraviolet radiation can cause skin cancer, premature skin aging, or eye damage like cataracts.
(ii) Gamma rays are highly ionising radiations that can cause mutations in DNA, leading to cancer, or kill cells directly.

Part (a)(i) [Total: 2 marks]
- Recall and use of \(n = \frac{\sin(i)}{\sin(r)}\) [1].
- Correct calculation: \(1.49\) (accept answers in range \(1.48\) to \(1.50\)) [1].

Part (a)(ii) [Total: 2 marks]
- Use of \(v = \frac{c}{n}\) [1].
- Correct calculation: \(2.0 \times 10^8\text{ m/s}\) (must include correct unit) [1].

Part (b)(i) [Total: 2 marks]
- Light is transverse [1].
- Sound is longitudinal [1].

Part (b)(ii) [Total: 2 marks]
- Sound travels faster in the plastic block than in air [1].
- Light travels slower in the plastic block than in air [1].

Part (c)(i) [Total: 1 mark]
- Skin cancer / sunburn / premature aging of skin / cataracts [1].

Part (c)(ii) [Total: 1 mark]
- Cell mutation / cancer / killing cells / damage to DNA [1].