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13 June 2026

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A complete revision and exam practice pack for SB8b Factors Affecting Diffusion, covering the Pearson Edexcel GCSE Biology (9–1) Separate Science specification for this topic (B8.4B, B8.5B).

This pack contains three components:

Topic Mastery Sheet (PDF) - a comprehensive reference covering the three factors in Fick’s law, concentration definitions and units, and how to interpret diffusion graphs. Fick’s law is presented as a proportionality statement: rate of diffusion ∝ (surface area × concentration difference) ÷ thickness of membrane. Each factor is described in terms of whether increasing it increases or decreases the rate of diffusion, using the terms directly proportional (surface area, concentration gradient) and inversely proportional (membrane thickness). Concentration is defined as the amount of a substance in a certain volume - the exact wording required by the Edexcel mark scheme, distinguishing it from “amount” (which has no volume component). A worked concentration calculation uses the figures from the Edexcel higher tier paper: 300 g of urea in 400 cm³ gives 300 ÷ 400 = 0.75 g cm⁻³. The graph interpretation section explains why diffusion rate decreases over time in a U-tube experiment - as urea diffuses through the membrane, the concentration gradient decreases, reducing the rate. The effect of doubling the concentration is explained: the graph starts at twice the height on the y-axis and follows the same curved shape. Biological applications of Fick’s law are given for both alveoli and intestinal villi.

Student Exam Practice Sheet (PDF + DOCX) - six exam-style questions. Q1 is the multiple choice question on the definition of concentration directly from the Edexcel mark scheme (answer: A, 1 mark). Q2 is the concentration calculation from the Edexcel higher tier paper (2 marks). Q3 asks students to state Fick’s law and describe how each factor affects diffusion rate (3 marks). Q4 asks students to use Fick’s law to explain why rate decreases over time (2 marks). Q5 asks students to explain how alveoli maximise each of the three factors in Fick’s law (3 marks). Q6 asks students to predict and describe how a graph would differ if the urea concentration were doubled, requiring both a starting point twice as high and the same curved shape (2 marks).
Teacher Answer Key (PDF + DOCX) - a full tick-point mark scheme. The Q1 answer is A. The Q2 answer is 0.75 g cm⁻³ with a note that two marks are awarded for a correct answer with no working shown. The Q6 mark scheme specifies that both features - starts at twice the height on the y-axis AND follows the same curved shape - are required for the two marks.

©BoxsiderResources. Licensed for classroom use by the purchasing teacher. Not for redistribution or resale.

Get this resource as part of a bundle and save up to 40%

A bundle is a package of resources grouped together to teach a particular topic, or a series of lessons, in one place.

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SB8 Exchange and Transport in Animals | Complete Topic Mastery Bundle | Edexcel GCSE Biology (9–1) Separate Science

A complete revision and exam practice bundle covering the full **SB8 Exchange and Transport in Animals** unit of the Pearson Edexcel GCSE Biology (9-1) Separate Science specification. This bundle brings together all 5 individual topic packs into one discounted resource, giving teachers and students everything they need to master this unit from first teaching through to final exam preparation. Each pack in this bundle has been built directly from the official Edexcel specification, teaching and learning materials, and mark schemes. Every answer has been verified against the Edexcel mark scheme. Every question is written in authentic Edexcel exam style with correct command words, mark allocations and answer space. This bundle contains 5 complete topic packs: **SB8a Efficient Transport and Exchange**: Covers the substances transported into and out of the body, their functions, the adaptations of the lungs for gas exchange, surface area to volume ratio calculations, and why SA:V ratio determines the need for specialised transport systems. **SB8b Factors Affecting Diffusion**: Covers the definition of concentration and correct units, how surface area, concentration gradient and distance each affect the rate of diffusion, and Fick's law calculations. **SB8c The Circulatory System**: Covers the components and function of the circulatory system, the functions and adaptations of arteries, veins and capillaries, and the roles of erythrocytes, phagocytes, lymphocytes, platelets and plasma. **SB8d The Heart**: Covers the structure of the heart, the route of blood flow through all four chambers, how valves and differing ventricular muscle thicknesses adapt the heart to its function, and cardiac output calculations using the heart rate and stroke volume equation. **SB8e Cellular Respiration**: Covers why organisms need to respire, the word equations for aerobic and anaerobic respiration in humans, why respiration is exothermic, and a comparative analysis of aerobic and anaerobic respiration. Every pack in this bundle contains five files. A **Topic Mastery Sheet** (PDF) - a comprehensive reference covering the full specification for that subtopic. Each sheet includes full specification coverage with spec reference codes, all key definitions and mechanisms explained in depth, worked examples using actual Edexcel exam figures, comparison tables and process diagrams, common errors explicitly flagged with the correct exam language, and a stretch and challenge section for students targeting Grade 8-9. A **Student Exam Practice Sheet** (PDF and DOCX) - five to seven exam-style questions escalating from recall through to extended writing. Questions use correct Edexcel command words, include mark allocations, and are sized with appropriate answer space. The DOCX version allows teachers to adapt questions for their class. A **Teacher Answer Key** (PDF and DOCX) - a full tick-point mark scheme verified against the official Edexcel mark scheme. Each answer includes the exact wording required, examiner notes on what is and is not accepted, full working for all calculation questions, and level descriptors for any extended writing questions. All resources are designed for whole-class use in mixed ability settings. Higher tier content is clearly tagged throughout. Separate Science B-tier content is identified where applicable. Questions escalate from foundation recall to higher extended writing within every sheet, so every student is working towards excellence without anyone being left behind or held back. Suitable for end-of-topic revision lessons, independent study, homework, intervention sessions, exam preparation in Year 10 and Year 11, cover lessons, and as a take-home revision pack for students. Teachers can project the Topic Mastery Sheet, set the Student Sheet as classwork or homework, and mark against the Answer Key without any additional preparation. Buying **this bundle saves approximately 40%** compared to purchasing each pack individually. All 25 files are included in a single download. ©BoxsiderResources. All resources are licensed for single classroom use by the purchasing teacher. Not for redistribution or resale.

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