This guide covers Unit 5 Principles and Applications of Science II from the Pearson BTEC Level 3 National in Applied Science (2016 specification). Unit 5 is assessed by an external exam set and marked by Pearson, so this page gives you model answers to exam-style questions, fully worked calculations in chemistry, biology and physics, and clear advice on how to turn Pass-level recall into Distinction-level explanation.
What Unit 5 Principles and Applications of Science II asks you to do
Unit 5 is the second-year science core. It builds on Unit 1 and moves from basic structure and bonding into applied chemistry, human physiology and thermal and mechanical physics. You sit separate biology, chemistry and physics sections, and each one mixes short recall, calculations and longer open-response questions set in a real context such as a chemical plant, a hospital ward or an engineering workshop.
Many students search for “Unit 5 assignment answers” because their teacher sets practice papers, topic tests or revision tasks as homework. The approach on this page works for all of them: learn the core content, practise the calculations until the method is automatic, and write structured explanations that always link the science to its application.
Topics covered in Unit 5
| Topic | What it covers |
|---|---|
| A: Properties and uses of substances (chemistry) | A1 relating properties to the uses and production of substances (for example amphoteric oxides, transition metal catalysts, extraction by electrolysis); A2 structures, reactions and properties of commercially important organic compounds (alkanes, alkenes, naming, bonding, addition polymerisation); A3 energy changes in industry (enthalpy changes, exothermic and endothermic reactions, calorimetry). |
| B: Organs and systems (biology) | B1 the cardiovascular system (heart structure, cardiac cycle, ECGs, cardiovascular disease); B2 ventilation and gas exchange in the lungs (mechanism of breathing, alveoli, spirometry); B3 urinary system structure and function (nephron, ultrafiltration, selective reabsorption, ADH, dialysis and transplant); B4 cell transport mechanisms (diffusion, osmosis, active transport). |
| C: Thermal physics, materials and fluids (physics) | C1 thermal physics in domestic and industrial applications (specific heat capacity, latent heat, gas laws, heat engines and heat pumps, efficiency); C2 materials (stress, strain, Young modulus, Hooke’s law, elastic and plastic behaviour, creep); C3 fluids in motion (viscosity, laminar and turbulent flow, drag, streamlining, lift on an aerofoil). |
How Unit 5 is graded
Because Unit 5 is an exam, there are no P/M/D assignment criteria. Pearson marks your paper and converts the raw mark into a unit grade of Near Pass, Pass, Merit or Distinction using grade boundaries set for each series. The table below shows what the examiners reward at each level.
| Level of answer | What it shows | How to evidence it in the exam |
|---|---|---|
| Pass-level answers | Accurate recall of facts, labels and definitions; simple one-step calculations. | Use correct terms (ultrafiltration, systole, enthalpy change, Young modulus). Show the formula and units in every calculation. |
| Merit-level answers | Explanations that link cause and effect; multi-step calculations; interpreting graphs and data. | Use “because” and “therefore” chains. Quote values from the graph or table given. Rearrange formulae correctly and give answers to sensible significant figures. |
| Distinction-level answers | Evaluation and justified judgements in unfamiliar contexts; comparing options; discussing limitations. | In the longer questions, weigh at least two options, give advantages and disadvantages, and end with a clear, justified conclusion that refers back to the context. |
How to answer Topic A: properties and uses of substances
Chemistry questions usually start with a structure or a reaction and ask you to explain why it matters in industry. Examiners want the link between structure, property and use.
- For organic compounds, name the homologous series, draw or describe the functional group and explain the reaction type (substitution for alkanes, addition for alkenes).
- For catalysts, explain that they provide an alternative pathway with a lower activation energy, and say why transition metals work well (variable oxidation states, ability to adsorb reactants).
- For enthalpy, define the term, state the sign convention (negative for exothermic) and show every step of a calorimetry calculation.
Example paragraph: Ethene is used to make poly(ethene) because its carbon–carbon double bond can open up. The double bond contains a pi bond, which is weaker than the sigma bond and is an area of high electron density, so it reacts readily in addition reactions. In addition polymerisation, the pi bond in each monomer breaks and the carbon atoms form new single bonds with neighbouring monomers, producing a long saturated chain. Because the polymer chains are held together only by weak intermolecular forces, low-density poly(ethene) is flexible and has a low melting point, which makes it suitable for carrier bags and film packaging.
How to answer Topic B: organs and systems
Biology questions often give you data such as an ECG trace, a spirometer graph or the composition of filtrate and urine, and ask you to interpret it.
- State what the data shows (for example, glucose present in filtrate but absent in urine).
- Explain the process responsible (selective reabsorption in the proximal convoluted tubule by active transport and co-transport).
- Apply it to the context (why glucose appears in urine in uncontrolled diabetes: the carrier proteins become saturated).
Example paragraph: During exercise the patient’s tidal volume rose from 0.5 dm³ to 1.8 dm³ and breathing rate from 12 to 30 breaths per minute. This happens because respiring muscles produce more carbon dioxide, which lowers blood pH. Chemoreceptors detect the change and the medulla sends more frequent impulses to the intercostal muscles and diaphragm, so breathing becomes deeper and faster. Pulmonary ventilation increases, which maintains a steep concentration gradient across the alveolar wall so that oxygen diffuses into the blood and carbon dioxide diffuses out more quickly.
How to answer Topic C: thermal physics, materials and fluids
Physics questions are calculation-heavy and usually set in a domestic or industrial context: a refrigerator, a car engine, a loaded cable or an aircraft wing.
- Write the equation first, substitute with units, then give the answer with units and a sensible number of significant figures.
- Convert temperatures to kelvin for gas laws and heat engine efficiency.
- For stress–strain graphs, identify the limit of proportionality, elastic limit, yield point and ultimate tensile strength, and explain what each tells an engineer.
- For fluids, explain drag and lift in terms of pressure difference and flow pattern, not just “it is streamlined”.
Example paragraph: The aerofoil produces lift because its shape and angle of attack make air flow faster over the upper surface than the lower surface. Faster-moving air has a lower pressure, so there is a pressure difference across the wing, and this difference acting over the wing area produces an upward force. If the angle of attack is increased too far, the flow separates from the upper surface and becomes turbulent, the pressure difference falls and the wing stalls, which is why pilots must stay within a safe range of angles.
Worked example
These calculations match the style of Unit 5 questions. Check each step against your own working.
1. Enthalpy change of neutralisation (Topic A3)
50.0 cm³ of 1.00 mol dm⁻³ hydrochloric acid is mixed with 50.0 cm³ of 1.00 mol dm⁻³ sodium hydroxide. The temperature rises by 6.8 °C. Assume the solution has a density of 1.00 g cm⁻³ and a specific heat capacity of 4.18 J g⁻¹ K⁻¹.
- Mass of solution = 100 g
- q = mcΔT = 100 × 4.18 × 6.8 = 2842 J = 2.84 kJ
- Moles of acid = 0.0500 dm³ × 1.00 mol dm⁻³ = 0.0500 mol
- ΔH = −2.84 kJ ÷ 0.0500 mol = −56.8 kJ mol⁻¹ (negative because the reaction is exothermic)
2. Cardiac output (Topic B1)
A patient has a stroke volume of 70 cm³ and a heart rate of 72 beats per minute.
- Cardiac output = stroke volume × heart rate = 70 × 72 = 5040 cm³ min⁻¹ = 5.04 dm³ min⁻¹
3. Spring constant and stored energy (Topic C2)
A 12 N load extends a spring by 3.0 cm within its limit of proportionality.
- k = F ÷ x = 12 N ÷ 0.030 m = 400 N m⁻¹
- Elastic potential energy = ½kx² = 0.5 × 400 × (0.030)² = 0.18 J
4. Heating water and heat engine efficiency (Topic C1)
A 2.4 kW element heats 2.0 kg of water from 15 °C to 65 °C (c = 4200 J kg⁻¹ K⁻¹).
- Q = mcΔT = 2.0 × 4200 × 50 = 420 000 J
- Minimum time = energy ÷ power = 420 000 ÷ 2400 = 175 s (real time is longer because some energy heats the kettle and surroundings)
A heat engine works between 600 K and 300 K. Maximum (ideal) efficiency = 1 − Tcold ÷ Thot = 1 − 300 ÷ 600 = 0.50 or 50%. A real engine is less efficient because of friction, heat losses and incomplete combustion; saying this earns the evaluation marks.
Common mistakes that cost marks
- Leaving out the sign of ΔH, or giving it as positive for an exothermic reaction.
- Using degrees Celsius instead of kelvin in gas law or efficiency calculations.
- Mixing units: centimetres with metres in Hooke’s law, or cm³ with dm³ in moles calculations.
- Describing the nephron without naming the process at each region (ultrafiltration in the glomerulus, selective reabsorption in the proximal tubule, water reabsorption controlled by ADH in the collecting duct).
- Reading an ECG without linking each wave to an event (P wave to atrial depolarisation, QRS complex to ventricular depolarisation, T wave to ventricular repolarisation).
- Writing “it is stronger” or “it is better” in evaluation questions without saying stronger than what, by how much or why.
- Ignoring the context given in the question. If the question is about a refrigerator, your answer must be about the refrigerator.
How to move from Merit to Distinction
The highest marks in Unit 5 come from the extended open-response questions at the end of each section. These ask you to evaluate, compare or justify. To reach Distinction:
- Plan for 30 seconds before writing. List two or three points for and against.
- Use data from the question, such as efficiency values, flow rates or blood test results, to support each point.
- Compare options directly. For kidney failure, compare dialysis and transplant on survival, quality of life, cost, availability of donors and the risk of rejection.
- Reach a justified conclusion that answers the exact question asked, and acknowledge a limitation of your judgement.
- Practise past papers and mark them against the published mark schemes so you can see how marks are awarded for each level of response.
FAQs
Is Unit 5 an exam or an assignment?
Unit 5 is an external exam set and marked by Pearson. Your centre may set practice tasks or mock papers during the course, but the final unit grade comes from the exam.
Which topics in Unit 5 have the most calculations?
Physics (specific heat capacity, gas laws, efficiency, stress, strain and Young modulus) and chemistry (enthalpy changes and moles) carry most of the calculation marks. Biology may include cardiac output, pulmonary ventilation or magnification.
How should I revise the organs and systems topic?
Draw and label the heart, lungs and nephron from memory, then explain each structure’s function in one sentence. Practise interpreting ECG traces and spirometer graphs because data questions appear often.
Can I resit Unit 5?
Pearson’s rules normally allow one resit of an external assessment. Your exams officer will confirm the dates and the current arrangements.
How is Unit 5 different from Unit 1?
Unit 1 Principles and Applications of Science I covers cells, bonding, the periodic table and waves. Unit 5 builds on it with organic chemistry, enthalpy, human body systems and thermal and mechanical physics.
Need one-to-one support from a subject specialist? Our BTEC Level 3 assignment help service covers planning, feedback on drafts and referencing.
For coursework in the same qualification, see our Unit 4 Laboratory Techniques and their Application guide. If you would like support with practice answers or your science coursework, you can get expert help with your BTEC assignment.
