Source: https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-3-diffusion [Revision notes](https://senecalearning.com/en-gb/revision-notes.md) › [A Level](https://senecalearning.com/en-gb/revision-notes/a-level.md) › [Biology](https://senecalearning.com/en-gb/revision-notes/a-level/biology.md) › [AQA](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa.md) › Diffusion # Diffusion Biology: AQA A Level, topic 2.3.3 ## Simple Diffusion Diffusion is the net movement of particles from an area of high concentration to an area of lower concentration. ### Diffusion ![Diffusion](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/1.3.1%20Diffusion%20of%20gases-min.png) - Diffusion describes the passive movement of particles in fluids (liquids and gases). - Molecules move randomly but tend to move into any space available until it is evenly distributed. - So, the net movement of particles will be towards the area of lower concentration or down a concentration gradient. - Substances such as CO2, O2 and urea can move in and out of cells across cell membranes via diffusion. ### E.g. Perfume ![E.g. Perfume](https://image-v2.cdn.app.senecalearning.com/courseImages/chemistry/10.4.2%20NPK%20fertilisers/perfume-min.jpg) - When you spray perfume, the smell diffuses across the room from the area of high concentration (where you just sprayed it) to the area of low concentration (the other side of the room). ## Facilitated Diffusion In facilitated diffusion, molecules diffuse through carrier proteins or channel proteins spanning across the membrane. ### Large or polar molecules ![Large or polar molecules](https://image-v2.cdn.app.senecalearning.com/2018-09/e0e02c7c-784b-492e-8e10-a09138e54120/ribosome-protein-.jpg) - Some materials are too large to move through the membrane. - Other materials are polar molecules that are repelled by the hydrophobic part of the membrane. - These materials move across the membrane by facilitated diffusion. ### Facilitated diffusion ![Facilitated diffusion](https://image-v2.cdn.app.senecalearning.com/2018-09/226557e7-8ec2-4b55-8de4-220540f590a7/active-passive-transport-concentration-gradient-.png) - Facilitated diffusion describes the net movement of particles down a concentration gradient (i.e. from a region of high concentration to a region of lower concentration). - Facilitated diffusion is a passive process so it does NOT use energy. ### Channel proteins ![Channel proteins](https://image-v2.cdn.app.senecalearning.com/2018-09/bff5ee02-da00-4d84-82fd-1ccf8a18a3d0/channel-carrier-protein-transport-.jpg) - Facilitated diffusion takes place through channel proteins. - Channel proteins allow polar compounds to avoid the non-polar central layer of the plasma membrane. - The non-polar layer would slow or prevent entry into the cell. - Aquaporins are channel proteins that allow water to pass through the membrane. ### Carrier proteins ![Carrier proteins](https://image-v2.cdn.app.senecalearning.com/2018-09/bff5ee02-da00-4d84-82fd-1ccf8a18a3d0/channel-carrier-protein-transport-.jpg) - Facilitated diffusion takes place through carrier proteins. - When a substance binds to carrier proteins, there is a change in the shape of the carrier protein. - This change in shape moves the substance from the outside of the cell to the inside. ## Factors Affecting Diffusion The rate of diffusion can speed up or slow down based on the following factors: ### Concentration gradient ![Concentration gradient](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/1.3.1%20Diffusion%20and%20active%20transport/color-2174051_640-min.jpg) - The concentration gradient is linked to the difference in concentration between two areas. - The bigger the difference in concentration between two areas, the greater the concentration gradient and the faster the rate of diffusion. ### Temperature ![Temperature](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/1.3.1%20Diffusion%20and%20active%20transport/thermometer-1614708_640-min%20-%20Edited-min.png) - The higher the temperature, the faster the rate of diffusion. ### Membrane surface area ![Membrane surface area](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/1.3.1%20Diffusion%20and%20active%20transport/pexels-photo-459486-min.jpg) - The larger the surface area of the membrane that a substance is diffusing through (e.g. the membrane around a cell), the faster the rate of diffusion. ### Thickness of membrane ![Thickness of membrane](https://image-v2.cdn.app.senecalearning.com/2018-09/548e1361-01c5-43c5-be45-8d6deaffbef0/wall-membrane-thick.jpg) - The thicker the exchange surface, the slower the rate of diffusion. ### Channel or carrier proteins ![Channel or carrier proteins](https://image-v2.cdn.app.senecalearning.com/2018-09/63fc5ca5-28ac-40c9-85e7-df3765bad4ca/Channel-Protein-transport-exhange-cell-.png) - The higher the concentration gradient, the faster the rate of facilitated diffusion until an equilibrium is reached and the rate will level off. - The number of channel or carrier proteins affects the rate of facilitated diffusion. The more proteins, the faster the rate. ## Test yourself on Diffusion - What do we call the net movement of particles from an area of high concentration to an area of lower concentration? - In which state of substance does diffusion NOT happen? - Which of the following substances can diffuse across cell membranes? - What two proteins allow facilitated diffusion? - Which of the following statements about facilitated diffusion are true? [Practise this topic for free](https://app.senecalearning.com/classroom/course/d0ce0c30-6417-11e8-8edc-d9cd1c890408/section/96780429-b243-45c3-80ca-9379b025888f/session) - Previous topic: [2.3.2 A-A* (AO3/4) - Membrane Structure](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-2-a-a-ao34-membrane-structure.md) - Next topic: [2.3.4 Osmosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-4-osmosis.md) ## Biology: AQA A Level contents ### 1 Biological Molecules - 1.1 Monomers & Polymers - [1.1.1 Monomers & Polymers](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-1-1-monomers-and-polymers.md) - [1.1.2 Condensation & Hydrolysis Reactions](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-1-2-condensation-and-hydrolysis-reactions.md) - 1.2 Carbohydrates - [1.2.1 Structure of Carbohydrates](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-2-1-structure-of-carbohydrates.md) - [1.2.2 Types of Polysaccharides](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-2-2-types-of-polysaccharides.md) - [1.2.3 End of Topic Test - Monomers, Polymers and Carbs](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-2-3-end-of-topic-test-monomers-polymers-and-carbs.md) - [1.2.4 Exam-Style Question - Carbohydrates](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-2-4-exam-style-question-carbohydrates.md) - [1.2.5 A-A* (AO3/4) - Carbohydrates](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-2-5-a-a-ao34-carbohydrates.md) - 1.3 Lipids - [1.3.1 Triglycerides & Phospholipids](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-3-1-triglycerides-and-phospholipids.md) - [1.3.2 Types of Fatty Acids](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-3-2-types-of-fatty-acids.md) - [1.3.3 Testing for Lipids](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-3-3-testing-for-lipids.md) - [1.3.4 Exam-Style Question - Fats](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-3-4-exam-style-question-fats.md) - [1.3.5 A-A* (AO3/4) - Lipids](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-3-5-a-a-ao34-lipids.md) - 1.4 Proteins - [1.4.1 The Peptide Chain](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-1-the-peptide-chain.md) - [1.4.2 Investigating Proteins](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-2-investigating-proteins.md) - [1.4.3 Primary & Secondary Protein Structure](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-3-primary-and-secondary-protein-structure.md) - [1.4.4 Tertiary & Quaternary Protein Structure](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-4-tertiary-and-quaternary-protein-structure.md) - [1.4.5 Enzymes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-5-enzymes.md) - [1.4.6 Factors Affecting Enzyme Activity](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-6-factors-affecting-enzyme-activity.md) - [1.4.7 Enzyme-Controlled Reactions](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-7-enzyme-controlled-reactions.md) - [1.4.8 End of Topic Test - Lipids & Proteins](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-8-end-of-topic-test-lipids-and-proteins.md) - [1.4.9 A-A* (AO3/4) - Enzymes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-9-a-a-ao34-enzymes.md) - [1.4.10 A-A* (AO3/4) - Proteins](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-10-a-a-ao34-proteins.md) - [1.4.11 Diagnostic Misconceptions - Enzyme Inhibitors](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-4-11-diagnostic-misconceptions-enzyme-inhibitors.md) - 1.5 Nucleic Acids - [1.5.1 DNA & RNA](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-5-1-dna-and-rna.md) - [1.5.2 Nucleotides](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-5-2-nucleotides.md) - [1.5.3 Polynucleotides](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-5-3-polynucleotides.md) - [1.5.4 DNA Replication](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-5-4-dna-replication.md) - [1.5.5 Exam-Style Question - Nucleic Acids](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-5-5-exam-style-question-nucleic-acids.md) - [1.5.6 A-A* (AO3/4) - Nucleic Acids](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-5-6-a-a-ao34-nucleic-acids.md) - 1.6 ATP - [1.6.1 Structure of ATP](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-6-1-structure-of-atp.md) - [1.6.2 Hydrolysis of ATP](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-6-2-hydrolysis-of-atp.md) - [1.6.3 Resynthesis of ATP](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-6-3-resynthesis-of-atp.md) - [1.6.4 End of Topic Test - Nucleic Acids & ATP](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-6-4-end-of-topic-test-nucleic-acids-and-atp.md) - 1.7 Water - [1.7.1 Importance of Water](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-7-1-importance-of-water.md) - [1.7.2 Structure of Water](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-7-2-structure-of-water.md) - [1.7.3 Properties of Water](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-7-3-properties-of-water.md) - [1.7.4 A-A* (AO3/4) - Water](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-7-4-a-a-ao34-water.md) - 1.8 Inorganic Ions - [1.8.1 Inorganic Ions](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-8-1-inorganic-ions.md) - [1.8.2 End of Topic Test - Water & Inorganic Ions](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/1-8-2-end-of-topic-test-water-and-inorganic-ions.md) ### 2 Cells - 2.1 Cell Structure - [2.1.1 Introduction to Cells](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-1-1-introduction-to-cells.md) - [2.1.2 Eukaryotic Cells & Organelles](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-1-2-eukaryotic-cells-and-organelles.md) - [2.1.3 Eukaryotic Cells & Organelles 2](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-1-3-eukaryotic-cells-and-organelles-2.md) - [2.1.4 Prokaryotes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-1-4-prokaryotes.md) - [2.1.5 A-A* (AO3/4) - Organelles](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-1-5-a-a-ao34-organelles.md) - [2.1.6 Methods of Studying Cells](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-1-6-methods-of-studying-cells.md) - [2.1.7 Microscopes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-1-7-microscopes.md) - [2.1.8 End of Topic Test - Cell Structure](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-1-8-end-of-topic-test-cell-structure.md) - [2.1.9 Exam-Style Question - Cells](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-1-9-exam-style-question-cells.md) - [2.1.10 A-A* (AO3/4) - Cells](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-1-10-a-a-ao34-cells.md) - 2.2 Mitosis & Cancer - [2.2.1 Mitosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-2-1-mitosis.md) - [2.2.2 Stages of Mitosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-2-2-stages-of-mitosis.md) - [2.2.3 Investigating Mitosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-2-3-investigating-mitosis.md) - [2.2.4 Cancer](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-2-4-cancer.md) - [2.2.5 A-A* (AO3/4) - The Cell Cycle](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-2-5-a-a-ao34-the-cell-cycle.md) - 2.3 Transport Across Cell Membrane - [2.3.1 Cell Membrane Structure](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-1-cell-membrane-structure.md) - [2.3.2 A-A* (AO3/4) - Membrane Structure](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-2-a-a-ao34-membrane-structure.md) - [2.3.3 Diffusion](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-3-diffusion.md) - [2.3.4 Osmosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-4-osmosis.md) - [2.3.5 Active Transport](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-5-active-transport.md) - [2.3.6 End of Topic Test - Mitosis, Cancer & Transport](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-6-end-of-topic-test-mitosis-cancer-and-transport.md) - [2.3.7 Exam-Style Question - Membranes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-7-exam-style-question-membranes.md) - [2.3.8 A-A* (AO3/4) - Membranes & Transport](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-8-a-a-ao34-membranes-and-transport.md) - [2.3.9 A-A*- Mitosis, Cancer & Transport](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-3-9-a-a-mitosis-cancer-and-transport.md) - 2.4 Cell Recognition & the Immune System - [2.4.1 Immune System](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-1-immune-system.md) - [2.4.2 Phagocytosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-2-phagocytosis.md) - [2.4.3 T Lymphocytes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-3-t-lymphocytes.md) - [2.4.4 B Lymphocytes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-4-b-lymphocytes.md) - [2.4.5 Antibodies](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-5-antibodies.md) - [2.4.6 Primary & Secondary Response](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-6-primary-and-secondary-response.md) - [2.4.7 Vaccines](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-7-vaccines.md) - [2.4.8 HIV](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-8-hiv.md) - [2.4.9 Ethical Issues](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-9-ethical-issues.md) - [2.4.10 End of Topic Test - Immune System](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-10-end-of-topic-test-immune-system.md) - [2.4.11 Exam-Style Question - Immune System](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-11-exam-style-question-immune-system.md) - [2.4.12 A-A* (AO3/4) - Immune System](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-12-a-a-ao34-immune-system.md) - [2.4.13 Diagnostic Misconceptions - Humoral vs Cellular](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/2-4-13-diagnostic-misconceptions-humoral-vs-cellular.md) ### 3 Substance Exchange - 3.1 Surface Area to Volume Ratio - [3.1.1 Size & Surface Area](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-1-1-size-and-surface-area.md) - [3.1.2 A-A* (AO3/4) - Cell Size](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-1-2-a-a-ao34-cell-size.md) - 3.2 Gas Exchange - [3.2.1 Single-Celled Organisms](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-1-single-celled-organisms.md) - [3.2.2 Multicellular Organisms](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-2-multicellular-organisms.md) - [3.2.3 Control of Water Loss](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-3-control-of-water-loss.md) - [3.2.4 Human Gas Exchange](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-4-human-gas-exchange.md) - [3.2.5 Ventilation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-5-ventilation.md) - [3.2.6 Dissection](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-6-dissection.md) - [3.2.7 Measuring Gas Exchange](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-7-measuring-gas-exchange.md) - [3.2.8 Lung Disease](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-8-lung-disease.md) - [3.2.9 Lung Disease Data](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-9-lung-disease-data.md) - [3.2.10 End of Topic Test - Gas Exchange](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-10-end-of-topic-test-gas-exchange.md) - [3.2.11 A-A* (AO3/4) - Gas Exchange](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-2-11-a-a-ao34-gas-exchange.md) - 3.3 Digestion & Absorption - [3.3.1 Overview of Digestion](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-3-1-overview-of-digestion.md) - [3.3.2 Digestion in Mammals](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-3-2-digestion-in-mammals.md) - [3.3.3 Absorption](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-3-3-absorption.md) - [3.3.4 End of Topic Test - Substance Exchange & Digestion](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-3-4-end-of-topic-test-substance-exchange-and-digestion.md) - [3.3.5 A-A* (AO3/4) - Substance Ex & Digestion](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-3-5-a-a-ao34-substance-ex-and-digestion.md) - 3.4 Mass Transport - [3.4.1 Haemoglobin](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-1-haemoglobin.md) - [3.4.2 Oxygen Transport](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-2-oxygen-transport.md) - [3.4.3 The Circulatory System](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-3-the-circulatory-system.md) - [3.4.4 The Heart](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-4-the-heart.md) - [3.4.5 Blood Vessels](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-5-blood-vessels.md) - [3.4.6 Cardiovascular Disease](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-6-cardiovascular-disease.md) - [3.4.7 Heart Dissection](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-7-heart-dissection.md) - [3.4.8 Xylem](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-8-xylem.md) - [3.4.9 Phloem](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-9-phloem.md) - [3.4.10 Investigating Plant Transport](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-10-investigating-plant-transport.md) - [3.4.11 End of Topic Test - Mass Transport](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-11-end-of-topic-test-mass-transport.md) - [3.4.12 A-A* (AO3/4) - Mass Transport](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-12-a-a-ao34-mass-transport.md) - [3.4.13 Diagnostic Misconceptions - Concentration Gradient](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-13-diagnostic-misconceptions-concentration-gradient.md) - [3.4.14 Diagnostic Misconceptions - Cardiac Cycle](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-14-diagnostic-misconceptions-cardiac-cycle.md) - [3.4.15 Diagnostic Misconceptions - Carrying Capacity](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-15-diagnostic-misconceptions-carrying-capacity.md) - [3.4.16 Diagnostic Misconceptions - Translocation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/3-4-16-diagnostic-misconceptions-translocation.md) ### 4 Genetic Information & Variation - 4.1 DNA, Genes & Chromosomes - [4.1.1 DNA](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-1-1-dna.md) - [4.1.2 Genes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-1-2-genes.md) - [4.1.3 Non-Coding Genes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-1-3-non-coding-genes.md) - [4.1.4 The Genetic Code](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-1-4-the-genetic-code.md) - [4.1.5 A-A* (AO3/4) - DNA](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-1-5-a-a-ao34-dna.md) - 4.2 DNA & Protein Synthesis - [4.2.1 Protein Synthesis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-2-1-protein-synthesis.md) - [4.2.2 Transcription & Translation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-2-2-transcription-and-translation.md) - [4.2.3 End of Topic Test - DNA, Genes & Protein Synthesis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-2-3-end-of-topic-test-dna-genes-and-protein-synthesis.md) - [4.2.4 Exam-Style Question - Protein Synthesis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-2-4-exam-style-question-protein-synthesis.md) - [4.2.5 A-A* (AO3/4) - Coronavirus Translation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-2-5-a-a-ao34-coronavirus-translation.md) - [4.2.6 A-A* (AO3/4) - Transcription](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-2-6-a-a-ao34-transcription.md) - [4.2.7 A-A* (AO3/4) - Translation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-2-7-a-a-ao34-translation.md) - 4.3 Mutations & Meiosis - [4.3.1 Mutations](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-3-1-mutations.md) - [4.3.2 Meiosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-3-2-meiosis.md) - [4.3.3 A-A* (AO3/4) - Meiosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-3-3-a-a-ao34-meiosis.md) - [4.3.4 Meiosis vs Mitosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-3-4-meiosis-vs-mitosis.md) - [4.3.5 End of Topic Test - Mutations, Meiosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-3-5-end-of-topic-test-mutations-meiosis.md) - [4.3.6 A-A* (AO3/4) - DNA,Genes, CellDiv & ProtSynth](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-3-6-a-a-ao34-dnagenes-celldiv-and-protsynth.md) - [4.3.7 Diagnostic Misconceptions - Meiosis vs Mitosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-3-7-diagnostic-misconceptions-meiosis-vs-mitosis.md) - 4.4 Genetic Diversity & Adaptation - [4.4.1 Genetic Diversity](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-4-1-genetic-diversity.md) - [4.4.2 Natural Selection](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-4-2-natural-selection.md) - [4.4.3 A-A* (AO3/4) - Natural Selection](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-4-3-a-a-ao34-natural-selection.md) - [4.4.4 Adaptations](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-4-4-adaptations.md) - [4.4.5 Investigating Natural Selection](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-4-5-investigating-natural-selection.md) - [4.4.6 End of Topic Test - Genetic Diversity & Adaptation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-4-6-end-of-topic-test-genetic-diversity-and-adaptation.md) - [4.4.7 A-A* (AO3/4) - Genetic Diversity & Adaptation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-4-7-a-a-ao34-genetic-diversity-and-adaptation.md) - 4.5 Species & Taxonomy - [4.5.1 Courtship Behaviour](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-5-1-courtship-behaviour.md) - [4.5.2 Phylogeny](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-5-2-phylogeny.md) - [4.5.3 Classification](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-5-3-classification.md) - [4.5.4 DNA Technology](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-5-4-dna-technology.md) - [4.5.5 A-A* (AO3/4) - Species & Taxonomy](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-5-5-a-a-ao34-species-and-taxonomy.md) - 4.6 Biodiversity Within a Community - [4.6.1 Biodiversity](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-6-1-biodiversity.md) - [4.6.2 Index of diversity](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-6-2-index-of-diversity.md) - [4.6.3 Agriculture](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-6-3-agriculture.md) - [4.6.4 End of Topic Test - Species,Taxonomy& Biodiversity](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-6-4-end-of-topic-test-speciestaxonomyand-biodiversity.md) - [4.6.5 A-A* (AO3/4) - Species,Taxon&Biodiversity](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-6-5-a-a-ao34-speciestaxonandbiodiversity.md) - 4.7 Investigating Diversity - [4.7.1 Genetic Diversity](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-7-1-genetic-diversity.md) - [4.7.2 Quantitative Investigation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/4-7-2-quantitative-investigation.md) ### 5 Energy Transfers (A2 only) - 5.1 Photosynthesis - [5.1.1 Overview of Photosynthesis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-1-1-overview-of-photosynthesis.md) - [5.1.2 Photoionisation of Chlorophyll](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-1-2-photoionisation-of-chlorophyll.md) - [5.1.3 Production of ATP & Reduced NADP](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-1-3-production-of-atp-and-reduced-nadp.md) - [5.1.4 Cyclic Photophosphorylation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-1-4-cyclic-photophosphorylation.md) - [5.1.5 Light-Independent Reaction](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-1-5-light-independent-reaction.md) - [5.1.6 A-A* (AO3/4) - Photosynthesis Reactions](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-1-6-a-a-ao34-photosynthesis-reactions.md) - [5.1.7 Limiting Factors](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-1-7-limiting-factors.md) - [5.1.8 Photosynthesis Experiments](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-1-8-photosynthesis-experiments.md) - [5.1.9 End of Topic Test - Photosynthesis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-1-9-end-of-topic-test-photosynthesis.md) - [5.1.10 A-A* (AO3/4) - Photosynthesis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-1-10-a-a-ao34-photosynthesis.md) - 5.2 Respiration - [5.2.1 Overview of Respiration](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-2-1-overview-of-respiration.md) - [5.2.2 Anaerobic Respiration](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-2-2-anaerobic-respiration.md) - [5.2.3 A-A* (AO3/4) - Anaerobic Respiration](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-2-3-a-a-ao34-anaerobic-respiration.md) - [5.2.4 The Link Reaction](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-2-4-the-link-reaction.md) - [5.2.5 The Krebs Cycle](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-2-5-the-krebs-cycle.md) - [5.2.6 Oxidative Phosphorylation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-2-6-oxidative-phosphorylation.md) - [5.2.7 Respiration Experiments](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-2-7-respiration-experiments.md) - [5.2.8 End of Topic Test - Respiration](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-2-8-end-of-topic-test-respiration.md) - [5.2.9 A-A* (AO3/4) - Respiration](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-2-9-a-a-ao34-respiration.md) - [5.2.10 Diagnostic Misconceptions - Aerobic vs Anaerobic](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-2-10-diagnostic-misconceptions-aerobic-vs-anaerobic.md) - 5.3 Energy & Ecosystems - [5.3.1 Biomass](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-3-1-biomass.md) - [5.3.2 Production & Productivity](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-3-2-production-and-productivity.md) - [5.3.3 Agricultural Practices](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-3-3-agricultural-practices.md) - 5.4 Nutrient Cycles - [5.4.1 Nitrogen Cycle](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-4-1-nitrogen-cycle.md) - [5.4.2 Phosphorous Cycle](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-4-2-phosphorous-cycle.md) - [5.4.3 Fertilisers & Eutrophication](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-4-3-fertilisers-and-eutrophication.md) - [5.4.4 End of Topic Test - Nutrient Cycles](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-4-4-end-of-topic-test-nutrient-cycles.md) - [5.4.5 A-A* (AO3/4) - Energy,Ecosystems&NutrientCycles](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/5-4-5-a-a-ao34-energyecosystemsandnutrientcycles.md) ### 6 Responding to Change (A2 only) - 6.1 Nervous Communication - [6.1.1 Survival](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-1-1-survival.md) - [6.1.2 Plant Responses](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-1-2-plant-responses.md) - [6.1.3 Animal Responses](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-1-3-animal-responses.md) - [6.1.4 Reflexes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-1-4-reflexes.md) - [6.1.5 End of Topic Test - Reflexes, Responses & Survival](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-1-5-end-of-topic-test-reflexes-responses-and-survival.md) - [6.1.6 Receptors](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-1-6-receptors.md) - [6.1.7 The Human Retina](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-1-7-the-human-retina.md) - [6.1.8 Control of Heart Rate](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-1-8-control-of-heart-rate.md) - [6.1.9 End of Topic Test - Receptors, Retina & Heart Rate](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-1-9-end-of-topic-test-receptors-retina-and-heart-rate.md) - 6.2 Nervous Coordination - [6.2.1 Neurones](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-2-1-neurones.md) - [6.2.2 Action Potentials](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-2-2-action-potentials.md) - [6.2.3 Speed of Transmission](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-2-3-speed-of-transmission.md) - [6.2.4 End of Topic Test - Neurones & Action Potentials](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-2-4-end-of-topic-test-neurones-and-action-potentials.md) - [6.2.5 Synapses](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-2-5-synapses.md) - [6.2.6 Types of Synapse](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-2-6-types-of-synapse.md) - [6.2.7 Medical Application](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-2-7-medical-application.md) - [6.2.8 End of Topic Test - Synapses](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-2-8-end-of-topic-test-synapses.md) - [6.2.9 A-A* (AO3/4) - Nervous Comm&Coord](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-2-9-a-a-ao34-nervous-commandcoord.md) - 6.3 Muscle Contraction - [6.3.1 Skeletal Muscle](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-3-1-skeletal-muscle.md) - [6.3.2 Sliding Filament Theory](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-3-2-sliding-filament-theory.md) - [6.3.3 Contraction](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-3-3-contraction.md) - [6.3.4 Slow & Fast Twitch Fibres](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-3-4-slow-and-fast-twitch-fibres.md) - [6.3.5 End of Topic Test - Muscles](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-3-5-end-of-topic-test-muscles.md) - [6.3.6 A-A* (AO3/4) - Muscle Contraction](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-3-6-a-a-ao34-muscle-contraction.md) - 6.4 Homeostasis - [6.4.1 Overview of Homeostasis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-1-overview-of-homeostasis.md) - [6.4.2 Blood Glucose Concentration](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-2-blood-glucose-concentration.md) - [6.4.3 Controlling Blood Glucose Concentration](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-3-controlling-blood-glucose-concentration.md) - [6.4.4 End of Topic Test - Blood Glucose](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-4-end-of-topic-test-blood-glucose.md) - [6.4.5 Primary & Secondary Messengers](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-5-primary-and-secondary-messengers.md) - [6.4.6 Diabetes Mellitus](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-6-diabetes-mellitus.md) - [6.4.7 Measuring Glucose Concentration](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-7-measuring-glucose-concentration.md) - [6.4.8 Osmoregulation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-8-osmoregulation.md) - [6.4.9 Controlling Blood Water Potential](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-9-controlling-blood-water-potential.md) - [6.4.10 ADH](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-10-adh.md) - [6.4.11 End of Topic Test - Diabetes & Osmoregulation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-11-end-of-topic-test-diabetes-and-osmoregulation.md) - [6.4.12 A-A* (AO3/4) - Homeostasis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-12-a-a-ao34-homeostasis.md) - [6.4.13 Diagnostic Misconceptions - Effect of ADH](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/6-4-13-diagnostic-misconceptions-effect-of-adh.md) ### 7 Genetics & Ecosystems (A2 only) - 7.1 Genetics - [7.1.1 Key Terms in Genetics](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-1-1-key-terms-in-genetics.md) - [7.1.2 Inheritance](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-1-2-inheritance.md) - [7.1.3 Linkage](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-1-3-linkage.md) - [7.1.4 Multiple Alleles & Epistasis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-1-4-multiple-alleles-and-epistasis.md) - [7.1.5 Chi-Squared Test](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-1-5-chi-squared-test.md) - [7.1.6 End of Topic Test - Genetics](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-1-6-end-of-topic-test-genetics.md) - [7.1.7 A-A* (AO3/4) - Genetics](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-1-7-a-a-ao34-genetics.md) - [7.1.8 Diagnostic Misconceptions - Dihybrid Inheritance](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-1-8-diagnostic-misconceptions-dihybrid-inheritance.md) - [7.1.9 Diagnostic Misconceptions - Sex Linkage](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-1-9-diagnostic-misconceptions-sex-linkage.md) - 7.2 Populations - [7.2.1 Populations](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-2-1-populations.md) - [7.2.2 Hardy-Weinberg Principle](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-2-2-hardy-weinberg-principle.md) - 7.3 Evolution - [7.3.1 Variation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-1-variation.md) - [7.3.2 Natural Selection & Evolution](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-2-natural-selection-and-evolution.md) - [7.3.3 End of Topic Test - Populations & Evolution](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-3-end-of-topic-test-populations-and-evolution.md) - [7.3.4 Types of Selection](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-4-types-of-selection.md) - [7.3.5 Types of Selection Summary](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-5-types-of-selection-summary.md) - [7.3.6 Overview of Speciation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-6-overview-of-speciation.md) - [7.3.7 Causes of Speciation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-7-causes-of-speciation.md) - [7.3.8 Diversity](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-8-diversity.md) - [7.3.9 End of Topic Test - Selection & Speciation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-9-end-of-topic-test-selection-and-speciation.md) - [7.3.10 A-A* (AO3/4) - Populations & Evolution](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-10-a-a-ao34-populations-and-evolution.md) - [7.3.11 Diagnostic Misconceptions - Types of Speciation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-3-11-diagnostic-misconceptions-types-of-speciation.md) - 7.4 Populations in Ecosystems - [7.4.1 Overview of Ecosystems](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-4-1-overview-of-ecosystems.md) - [7.4.2 Niche](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-4-2-niche.md) - [7.4.3 Population Size](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-4-3-population-size.md) - [7.4.4 Investigating Population Size](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-4-4-investigating-population-size.md) - [7.4.5 End of Topic Test - Ecosystems & Population Size](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-4-5-end-of-topic-test-ecosystems-and-population-size.md) - [7.4.6 Succession](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-4-6-succession.md) - [7.4.7 Conservation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-4-7-conservation.md) - [7.4.8 End of Topic Test - Succession & Conservation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-4-8-end-of-topic-test-succession-and-conservation.md) - [7.4.9 A-A* (AO3/4) - Ecosystems](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/7-4-9-a-a-ao34-ecosystems.md) ### 8 The Control of Gene Expression (A2 only) - 8.1 Mutation - [8.1.1 Mutations](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-1-1-mutations.md) - [8.1.2 Effects of Mutations](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-1-2-effects-of-mutations.md) - [8.1.3 Causes of Mutations](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-1-3-causes-of-mutations.md) - [8.1.4 Diagnostic Misconceptions - Gene Expression](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-1-4-diagnostic-misconceptions-gene-expression.md) - 8.2 Gene Expression - [8.2.1 Stem Cells](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-1-stem-cells.md) - [8.2.2 Stem Cells in Disease](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-2-stem-cells-in-disease.md) - [8.2.3 End of Topic Test - Mutation & Gene Epression](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-3-end-of-topic-test-mutation-and-gene-epression.md) - [8.2.4 A-A* (AO3/4) - Mutation & Stem Cells](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-4-a-a-ao34-mutation-and-stem-cells.md) - [8.2.5 Regulating Transcription](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-5-regulating-transcription.md) - [8.2.6 Epigenetics](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-6-epigenetics.md) - [8.2.7 Epigenetics & Disease](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-7-epigenetics-and-disease.md) - [8.2.8 Regulating Translation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-8-regulating-translation.md) - [8.2.9 Experimental Data](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-9-experimental-data.md) - [8.2.10 End of Topic Test - Transcription & Translation](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-10-end-of-topic-test-transcription-and-translation.md) - [8.2.11 Tumours](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-11-tumours.md) - [8.2.12 Correlations & Causes](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-12-correlations-and-causes.md) - [8.2.13 Prevention & Treatment](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-13-prevention-and-treatment.md) - [8.2.14 End of Topic Test - Cancer](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-14-end-of-topic-test-cancer.md) - [8.2.15 A-A* (AO3/4) - Gene Expression & Cancer](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-2-15-a-a-ao34-gene-expression-and-cancer.md) - 8.3 Genome Projects - [8.3.1 Using Genome Projects](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-3-1-using-genome-projects.md) - 8.4 Gene Technology - [8.4.1 Recombinant DNA](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-4-1-recombinant-dna.md) - [8.4.2 Producing Fragments](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-4-2-producing-fragments.md) - [8.4.3 Amplification](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-4-3-amplification.md) - [8.4.4 End of Topic Test - Genome Project & Amplification](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-4-4-end-of-topic-test-genome-project-and-amplification.md) - [8.4.5 Using Recombinant DNA](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-4-5-using-recombinant-dna.md) - [8.4.6 Medical Diagnosis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-4-6-medical-diagnosis.md) - [8.4.7 Genetic Fingerprinting](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-4-7-genetic-fingerprinting.md) - [8.4.8 End of Topic Test - Gene Technologies](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-4-8-end-of-topic-test-gene-technologies.md) - [8.4.9 A-A* (AO3/4) - Gene Technology](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/8-4-9-a-a-ao34-gene-technology.md) ### 9 Mathematical Skills - 9.1 Mathematical Skills - [9.1.1 Diagnostic Misconceptions - Converting Units](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/9-1-1-diagnostic-misconceptions-converting-units.md) - [9.1.2 Diagnostic Misconceptions - Correct Hypothesis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/9-1-2-diagnostic-misconceptions-correct-hypothesis.md) - [9.1.3 Diagnostic Misconceptions - Interpret Hypothesis](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/9-1-3-diagnostic-misconceptions-interpret-hypothesis.md) - [9.1.4 Diagnostic Misconceptions - Calculate Uncertainty](https://senecalearning.com/en-gb/revision-notes/a-level/biology/aqa/9-1-4-diagnostic-misconceptions-calculate-uncertainty.md)