Cells and organisation
Levels of organisation, animal and plant cells, specialised cells and stem cells.
Edexcel IGCSE Biology · Section 2
Structure & Functions in Living Organisms
Cells, biological molecules, enzymes, transport, nutrition, respiration, gas exchange, circulation, excretion and coordination. All videos are available on YouTube.
What this section covers
Section 2 is the largest part of the Biology course. It covers how organisms are built, how substances move, how plants and animals obtain materials and energy, and how body systems coordinate responses.
For revision, this section is best split into smaller blocks rather than treated as one long list.
Molecules and enzymes
Biological molecules, food tests, enzymes and enzyme practical work.
Movement and transport
Diffusion, osmosis, plant transport, transpiration, blood, heart and circulation.
Nutrition and energy
Photosynthesis, diet, digestion, absorption, respiration and energy in food.
Gas exchange and excretion
Plant gas exchange, breathing, smoking, excretion and kidney function.
Coordination and response
Homeostasis, hormones, nerves, reflexes, the eye and temperature control.
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1
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Levels of Organisation
Spec 2.1
How organelles, cells, tissues, organs and organ systems build up to a whole organism, with animal and plant examples.
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2
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Animal and Plant Cells
Spec 2.2-2.4
The parts of animal and plant cells, what each part does, and the features found only in plant cells.
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3
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Specialised Cells and Stem Cells (Triple)
Spec 2.5B-2.6B
How cells become specialised (differentiation), examples of specialised cells, and the uses and ethics of stem cells.
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4
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Biological Molecules
Spec 2.7-2.8
Carbohydrates, proteins and lipids — the elements they contain and the building blocks they are made from.
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5
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Food Tests
Spec 2.9
The Benedict's, iodine, Biuret and emulsion tests for sugars, starch, protein and fats, and their positive colour changes.
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6
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Enzymes
Spec 2.10-2.13
How enzymes work using the lock-and-key model, enzyme specificity, and the effect of temperature and pH on activity.
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7
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Investigating Enzymes Practical
Spec 2.12
Required practical: investigating how temperature affects the enzyme amylase, using starch and iodine.
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8
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Investigating Enzymes and pH
Spec 2.14B
Required practical: investigating how pH affects the enzyme amylase, using buffers and iodine.
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9
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Movement of Substances
Spec 2.15-2.16
Diffusion, osmosis and active transport compared — what moves, in which direction, and whether energy is needed.
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10
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Factors Affecting Diffusion and Movement Rate
Spec 2.16
Covers recall the four factors affecting movement rate, Explain each factor using particles and Apply the factors to biological exchange surfaces.
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11
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Diffusion and Non-Living Membrane Practicals
Spec 2.17
Covers investigate diffusion using agar cubes, Investigate osmosis through a non-living membrane and Identify variables, measurements and improvements.
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12
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Osmosis Practical
Spec 2.17
Required practical: investigating osmosis in potato tissue and calculating the percentage change in mass.
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13
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Photosynthesis
Spec 2.18-2.19
The word and balanced equations for photosynthesis, its raw materials and products, and the role of chlorophyll.
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14
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Limiting Factors
Spec 2.20
How light intensity, carbon dioxide and temperature limit the rate of photosynthesis, and the shape of each graph.
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15
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Leaf Tissues, Xylem and Phloem
Spec 2.21
Covers locate the lower epidermis, xylem and phloem in a leaf, Relate each tissue to its function and Distinguish the substances carried by xylem and phloem.
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16
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The Leaf and Minerals
Spec 2.21-2.22
The structure of a leaf and its adaptations for photosynthesis, plus why plants need magnesium and nitrate ions.
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17
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Photosynthesis Practical
Spec 2.23
Required practical: measuring the rate of photosynthesis in pondweed and how light intensity affects it.
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18
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Photosynthesis Starch Required Practicals
Spec 2.23
Covers test a leaf for starch safely, Investigate the need for light and carbon dioxide and Investigate the need for chlorophyll.
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19
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A Balanced Diet
Spec 2.24-2.26
The seven components of a balanced diet, their sources and functions, and how energy needs vary from person to person.
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20
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Vitamin A and Water in a Balanced Diet
Spec 2.25
Covers recall sources and functions of vitamin A, Explain why water is an essential dietary component and Link deficiency to biological effects.
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21
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Duodenum, Ileum, Colon and Rectum
Spec 2.27
Covers locate four named regions of the alimentary canal, State the main function of each region and Distinguish digestion, absorption and egestion.
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22
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The Digestive System
Spec 2.27-2.28
The parts of the alimentary canal, what each part does, and how food is moved along by peristalsis.
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23
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Digestive Enzymes and Bile
Spec 2.29-2.31
How amylase and maltase convert starch into glucose, what protease and lipase produce, where the enzymes are made, and the two roles of bile.
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24
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Absorption
Spec 2.32
How the villi in the small intestine are adapted for the fast, efficient absorption of digested food.
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25
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Energy in Food Practical
Spec 2.33B
Required practical: measuring the energy in a food sample by burning it to heat water, and the energy calculation.
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26
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Food Energy Practical: Reliable Measurements
Spec 2.33B
Covers calculate energy transferred per gram of food burned, Identify variables and reliability improvements and Evaluate major sources of heat loss.
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27
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Respiration
Spec 2.34-2.38
Aerobic and anaerobic respiration compared — the equations, the energy released, and lactic acid and fermentation.
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28
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ATP Uses in Living Cells
Spec 2.35
Covers link respiration to ATP production, Recall three cellular uses of ATP and Explain why ATP must be regenerated continuously.
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29
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Respiration Practical
Spec 2.39
Required practical: showing that respiring organisms release carbon dioxide and heat, using a control.
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30
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Gas Exchange in Plants
Spec 2.40B-2.44B
Net gas exchange in plants in the light and in the dark, and the compensation point where the two rates are equal.
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31
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Light and Gas Exchange
Spec 2.45B
Required practical: using hydrogencarbonate indicator to investigate the effect of light on gas exchange in plants.
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32
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Bronchioles and Pleural Membranes
Spec 2.46
Covers trace the route of air to the alveoli, State the roles of bronchioles and pleural membranes and Relate thorax structures to ventilation.
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33
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Breathing and the Lungs
Spec 2.46-2.48
The breathing system, how we breathe in and out, and how the alveoli are adapted for gas exchange.
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34
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Smoking and the Lungs
Spec 2.49
The harmful substances in tobacco smoke and their effects on the lungs, including emphysema and disease.
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35
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Exercise and Breathing
Spec 2.50
Required practical: how exercise affects breathing rate, why muscles need more oxygen, and the oxygen debt.
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36
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Investigating Carbon Dioxide in Exhaled Air
Spec 2.50
Covers compare carbon dioxide in inhaled and exhaled air, Use a suitable indicator and control and Design a safe and repeatable method.
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37
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Why Multicellular Organisms Need Transport Systems
Spec 2.51-2.53
Covers explain why diffusion is sufficient for unicellular organisms, Explain why multicellular organisms need transport systems and Recall the substances transported in plant phloem.
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38
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Transport in Plants
Spec 2.51-2.54
Xylem and phloem compared, and how root hair cells are adapted to absorb water and mineral ions.
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39
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Transpiration
Spec 2.55B-2.58B
What transpiration is, the four factors that affect its rate, and how a potometer measures water uptake.
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40
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The Blood
Spec 2.59-2.61
The four components of blood and their jobs, and how red blood cells are adapted to carry oxygen.
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41
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The Immune System
Spec 2.62-2.64B
How phagocytes and lymphocytes fight pathogens, why antibodies are specific, and how vaccines give immunity.
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42
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Heart Structure, Valves and Exercise
Spec 2.65-2.66
Covers identify the chambers, valves, septum and major vessels, Explain one-way blood flow through the heart and Explain why exercise increases heart rate.
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43
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The Heart
Spec 2.65-2.66
The four chambers of the heart, the path blood takes through it, and why the left ventricle wall is thickest.
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44
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Blood Vessels
Spec 2.67-2.68
Arteries, veins and capillaries compared, how each is adapted, and how coronary heart disease develops.
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45
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Double Circulation
Spec 2.69
The pulmonary and systemic circuits, and why a double circulation is more efficient than a single one.
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46
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Named Blood Vessels in the Circulatory System
Spec 2.69
Covers name the vessels serving the heart and lungs, Name the vessels serving the liver and kidneys and Trace blood through the double circulation.
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47
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Plant Excretion Through Stomata
Spec 2.70
Covers identify oxygen and carbon dioxide as plant waste products, Link each waste product to a metabolic process and Explain how gases leave through stomata.
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48
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Excretion
Spec 2.70-2.71
What excretion is, the three main excretory organs, and where the waste product urea comes from.
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49
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The Kidney and Nephron
Spec 2.72B-2.76B
How the kidney filters the blood by ultrafiltration and selective reabsorption to produce urine.
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50
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Nephron Regions and Selective Reabsorption
Spec 2.73B-2.77B
Covers label the urinary system and nephron regions, Explain ultrafiltration and selective reabsorption and Locate glucose and water reabsorption.
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51
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Water Balance and Kidney Failure
Spec 2.77B-2.79B
How ADH controls the water content of the blood by negative feedback, and treatments for kidney failure.
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52
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Homeostasis
Spec 2.80-2.82
What homeostasis is, the stimulus-receptor-effector-response pathway, and negative feedback.
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53
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Plant Responses Tropisms
Spec 2.83-2.85
Tropisms in plants — phototropism and gravitropism — and how the hormone auxin controls growth.
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54
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Nervous vs Hormonal
Spec 2.86
The nervous and hormonal systems compared — their speed, how long effects last, and how messages travel.
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55
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Nervous System and Reflexes
Spec 2.87-2.90
The central nervous system, the reflex arc, and how synapses pass impulses between neurones.
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56
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The Eye
Spec 2.91-2.92
The parts of the eye, how the eye focuses on near and far objects (accommodation), and the pupil reflex.
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57
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Eye Muscles, Ligaments and Responses
Spec 2.92
Covers explain accommodation for near and distant objects, Describe antagonistic control of pupil size and Link each muscle response to its effect.
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58
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Temperature Control
Spec 2.93
How the body keeps a constant core temperature — cooling down when too hot and warming up when too cold.
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59
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Hormones
Spec 2.94-2.95B
The endocrine system, the effects of adrenaline, and how insulin and glucagon control blood glucose.
Frequently asked questions
What is the difference between a plant cell and an animal cell?
Both have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a cell wall, chloroplasts and a large permanent vacuole.
What is the difference between diffusion, osmosis and active transport?
Diffusion moves particles from a high to a low concentration; osmosis is the movement of water across a partially permeable membrane; active transport moves particles from low to high concentration and needs energy.
What is the word equation for photosynthesis?
Carbon dioxide + water → glucose + oxygen, using light energy absorbed by chlorophyll.
What is the word equation for aerobic respiration?
Glucose + oxygen → carbon dioxide + water, releasing energy that is stored as ATP.
How are the alveoli adapted for gas exchange?
They give a large surface area, have walls only one cell thick, a moist lining and a rich blood supply, which together keep diffusion fast.
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