Pearson Edexcel International GCSE in Biology · 4BI1 · Free · no account needed

Topic 2 · Structures and functions in living organisms

The biggest topic by far: cells, enzymes, transport, photosynthesis, digestion, respiration, gas exchange, circulation, excretion and the nervous and hormonal systems. Roughly half the qualification lives here.

Every lesson here ends the same way: learn it, teach it to an AI pupil who asks the awkward question, then defend it against the thinker with the strongest claim on it — free · no account needed.

34 lessons, covering 95 specification statements.

What you need to know — the 95 statements, and where each one is taught

Every statement this topic carries, in the specification's own numbering, with Incandio's restatement of what it asks and the lesson that discharges it. Tick them off against your own copy of the specification: this is the topic's revision checklist, not a summary of it. Incandio is aligned to this specification. It is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording — the statement numbers are given so you can check every lesson against your own copy.

Statement	What it asks	Taught in
2.1	Levels of organisation: organelles, cells, tissues, organs and systems	Levels of Organisation
2.2	Cell structures: nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes, vacuole	Levels of Organisation
2.3	The function of each of those cell structures	Levels of Organisation
2.4	Similarities and differences between plant and animal cells	Comparing Cells, and Stem Cells
2.5	The importance of cell differentiation in producing specialised cells	Comparing Cells, and Stem Cells
2.6	Advantages and disadvantages of using stem cells in medicine	Comparing Cells, and Stem Cells
2.7	The chemical elements present in carbohydrates, proteins and lipids	Carbohydrates, Proteins and Lipids
2.8	Carbohydrates, proteins and lipids as large molecules built from smaller basic units	Carbohydrates, Proteins and Lipids
2.9 (practical)	Practical: test food samples for glucose, starch, protein and fat	Carbohydrates, Proteins and Lipids
2.10	Enzymes as biological catalysts in metabolic reactions	Enzymes: Catalysts With a Shape
2.11	How temperature affects enzyme function, including the shape of the active site	Enzymes: Catalysts With a Shape
2.12 (practical)	Practical: investigate the effect of temperature on enzyme activity	Enzymes: Catalysts With a Shape
2.13	How pH affects enzyme function by altering the active site	Enzymes and pH
2.14 (practical)	Practical: investigate the effect of pH on enzyme activity	Enzymes and pH
2.15	Diffusion, osmosis and active transport as the ways substances move into and out of cells	Diffusion, Osmosis and Active Transport
2.16	Factors affecting the rate of movement: surface area to volume ratio, distance, temperature, concentration gradient	Diffusion, Osmosis and Active Transport
2.17 (practical)	Practical: investigate diffusion and osmosis using living and non-living systems	Diffusion, Osmosis and Active Transport
2.18	Photosynthesis and its importance in converting light energy to chemical energy	Photosynthesis
2.19	The word equation and balanced symbol equation for photosynthesis	Photosynthesis
2.22	Mineral ions for plant growth: magnesium for chlorophyll, nitrate for amino acids	Photosynthesis
2.20	How carbon dioxide concentration, light intensity and temperature affect the rate of photosynthesis	What Limits Photosynthesis
2.23 (practical)	Practical: investigate photosynthesis — oxygen evolution, starch production, and the requirements for light, carbon dioxide and chlorophyll	What Limits Photosynthesis
2.21	The structure of the leaf and how it is adapted for photosynthesis	The Leaf: Structure and Gas Exchange
2.42	How the structure of the leaf is adapted for gas exchange	The Leaf: Structure and Gas Exchange
2.43	The role of stomata in gas exchange	The Leaf: Structure and Gas Exchange
2.24	The components of a balanced diet and their appropriate proportions	A Balanced Diet
2.25	Sources and functions of carbohydrate, protein, lipid, vitamins A, C and D, calcium, iron, water and dietary fibre	A Balanced Diet
2.26	How energy requirements vary with activity level, age and pregnancy	A Balanced Diet
2.27	Structure and function of the human alimentary canal	The Alimentary Canal
2.28	How peristalsis moves food through the gut	The Alimentary Canal
2.29	Digestive enzymes: amylase and maltase, proteases, lipases, and the products of each	Digestive Enzymes and Bile
2.30	Bile is produced by the liver and stored in the gall bladder	Digestive Enzymes and Bile
2.31	The role of bile in neutralising stomach acid and emulsifying lipids	Digestive Enzymes and Bile
2.32	How the small intestine is adapted for absorption, including the structure of a villus	Absorption and the Energy in Food
2.33 (practical)	Practical: investigate the energy content of a food sample	Absorption and the Energy in Food
2.34	How respiration produces ATP in living organisms	Respiration and ATP
2.35	ATP provides energy for cells	Respiration and ATP
2.37	Word and balanced symbol equation for aerobic respiration	Respiration and ATP
2.36	Differences between aerobic and anaerobic respiration	Anaerobic Respiration
2.38	Word equations for anaerobic respiration in plants and in animals	Anaerobic Respiration
2.39 (practical)	Practical: investigate the evolution of carbon dioxide and heat from respiring seeds or other organisms	Anaerobic Respiration
2.46	The structure of the thorax: ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli, pleural membranes	The Thorax and Ventilation
2.47	The role of the intercostal muscles and the diaphragm in ventilation	The Thorax and Ventilation
2.48	How alveoli are adapted for gas exchange by diffusion	Alveoli, Exercise and Smoking
2.49	Biological consequences of smoking for the lungs and circulatory system, including coronary heart disease	Alveoli, Exercise and Smoking
2.50 (practical)	Practical: investigate breathing in humans, including carbon dioxide release and the effect of exercise	Alveoli, Exercise and Smoking
2.51	Why simple unicellular organisms can rely on diffusion alone	Why Transport Systems Exist, and the Two Plant Vessels
2.52	The need for a transport system in multicellular organisms	Why Transport Systems Exist, and the Two Plant Vessels
2.53	The role of phloem in transporting sucrose and amino acids	Why Transport Systems Exist, and the Two Plant Vessels
2.54	The role of xylem in transporting water and mineral ions	Why Transport Systems Exist, and the Two Plant Vessels
2.55	How water is absorbed by root hair cells	Water Uptake and Transpiration
2.56	Transpiration as the evaporation of water from the surface of a plant	Water Uptake and Transpiration
2.57	How humidity, wind speed, temperature and light intensity affect transpiration rate	Water Uptake and Transpiration
2.58 (practical)	Practical: investigate environmental factors affecting transpiration from a leafy shoot	Water Uptake and Transpiration
2.59	The composition of blood: red cells, white cells, platelets and plasma	Blood
2.60	The role of plasma in transporting carbon dioxide, digested food, urea, hormones and heat	Blood
2.61	Adaptations of red blood cells for oxygen transport	Blood
2.62	How the immune system responds using phagocytes and lymphocytes	Immunity and Clotting
2.63	How vaccination produces memory cells and a faster secondary response	Immunity and Clotting
2.64	How platelets are involved in blood clotting	Immunity and Clotting
2.65	The structure of the heart and how it functions	The Heart, and What Goes Wrong With It
2.66	How heart rate changes during exercise and under adrenaline	The Heart, and What Goes Wrong With It
2.67	Factors that increase the risk of coronary heart disease	The Heart, and What Goes Wrong With It
2.68	How the structure of arteries, veins and capillaries relates to their function	Blood Vessels and the Circulation
2.69	The general structure of the circulation, including vessels to and from heart, lungs, liver and kidneys	Blood Vessels and the Circulation
2.70	Carbon dioxide and oxygen as waste products of plant metabolism, lost through stomata	Excretion: Getting Rid of What You Made
2.71	The excretory products of the lungs, kidneys and skin	Excretion: Getting Rid of What You Made
2.72	How the kidney carries out excretion and osmoregulation	The Kidney and the Nephron
2.73	The structure of the urinary system: kidneys, ureters, bladder, urethra	The Kidney and the Nephron
2.74	The structure of a nephron	The Kidney and the Nephron
2.75	Ultrafiltration in the Bowman's capsule and the composition of the filtrate	Ultrafiltration and Selective Reabsorption
2.76	How water is reabsorbed from the collecting duct	Ultrafiltration and Selective Reabsorption
2.77	Why selective reabsorption of glucose occurs at the proximal convoluted tubule	Ultrafiltration and Selective Reabsorption
2.78	The role of ADH in regulating the water content of the blood	ADH and the Water Balance of the Blood
2.79	Urine contains water, urea and ions	ADH and the Water Balance of the Blood
2.80	How organisms respond to changes in their environment	Homeostasis and the Control of Body Temperature
2.81	Homeostasis as the maintenance of a constant internal environment	Homeostasis and the Control of Body Temperature
2.82	A co-ordinated response requires a stimulus, a receptor and an effector	Homeostasis and the Control of Body Temperature
2.93	The role of the skin in temperature regulation: sweating, vasoconstriction, vasodilation	Homeostasis and the Control of Body Temperature
2.83	Plants respond to stimuli	Plant Responses, Tropisms and Auxin
2.84	The geotropic and phototropic responses of roots and stems	Plant Responses, Tropisms and Auxin
2.85	The role of auxin in the phototropic response of stems	Plant Responses, Tropisms and Auxin
2.86	Nervous and hormonal communication compared	The Nervous System, and the Two Ways a Body Sends a Message
2.87	The central nervous system and its links to sense organs by nerves	The Nervous System, and the Two Ways a Body Sends a Message
2.88	Receptors, electrical impulses along nerves, and rapid responses	The Nervous System, and the Two Ways a Body Sends a Message
2.89	The role of neurotransmitters at synapses	Synapses and the Reflex Arc
2.90	The structure and functioning of a simple reflex arc	Synapses and the Reflex Arc
2.91	The structure and function of the eye as a receptor	The Eye — Focusing, and the Pupil Reflex
2.92	How the eye focuses on near and distant objects and responds to light intensity	The Eye — Focusing, and the Pupil Reflex
2.94	Sources, roles and effects of adrenaline, insulin, testosterone, progesterone and oestrogen	The Hormones — Sources, Roles and Effects
2.95	Sources, roles and effects of ADH, FSH and LH	The Hormones — Sources, Roles and Effects
2.40	The role of diffusion in gas exchange	Gas Exchange in Plants, Day and Night
2.41	Gas exchange of carbon dioxide and oxygen in relation to respiration and photosynthesis	Gas Exchange in Plants, Day and Night
2.44	Respiration continues day and night; net gas exchange depends on light intensity	Gas Exchange in Plants, Day and Night
2.45 (practical)	Practical: investigate the effect of light on net gas exchange from a leaf using hydrogencarbonate indicator	Gas Exchange in Plants, Day and Night

The lessons

Levels of Organisation — From organelle to organism — the five-step ladder that every later topic in biology is built on. (2.1, 2.2, 2.3)
Comparing Cells, and Stem Cells — What plant and animal cells share and where they differ — then why a cell specialising is one of the most powerful ideas in biology. (2.4, 2.5, 2.6)
Carbohydrates, Proteins and Lipids — The three big food molecules — what they are made of, what they are built from, and how to test for them. (2.7, 2.8, 2.9)
Enzymes: Catalysts With a Shape — Why a protein with a hole in it speeds up a reaction, and why heat destroys that ability permanently. (2.10, 2.11, 2.12)
Enzymes and pH — Why acid ruins one enzyme and is the only condition another will work in — and how to find an enzyme's best pH by experiment. (2.13, 2.14)
Diffusion, Osmosis and Active Transport — The three ways anything gets into or out of a cell — which need energy, which do not, and what makes each one fast or slow. (2.15, 2.16, 2.17)
Photosynthesis — How a plant builds itself out of air, where the energy for that comes from, and the one job the soil is actually doing. (2.18, 2.19, 2.22)
What Limits Photosynthesis — Why brightening the light eventually stops working, how to read that off a graph, and the experiments that prove what a plant needs. (2.20, 2.23)
The Leaf: Structure and Gas Exchange — Every feature of a leaf is a solution to one conflict — letting carbon dioxide in through holes that also let water out. (2.21, 2.42, 2.43)
A Balanced Diet — Why you can eat plenty and still be starving — food does several separate jobs, and having enough of one does not cover the others. (2.24, 2.25, 2.26)
The Alimentary Canal — One long tube whose contents are still outside you, and the muscular squeeze that moves them along it. (2.27, 2.28)
Digestive Enzymes and Bile — The demolition tools that cut food molecules small enough to absorb — and the one secretion that does the job without being an enzyme at all. (2.29, 2.30, 2.31)
Absorption and the Energy in Food — How a tube half a square metre in area absorbs an entire diet — and how to measure the energy a food actually contains. (2.32, 2.33)
Respiration and ATP — What respiration is actually for, why every living cell does it every second, and why breathing is not the same thing at all. (2.34, 2.35, 2.37)
Anaerobic Respiration — The backup that runs without oxygen — why it is worth having, why it cannot last, and why bread and beer both depend on it. (2.36, 2.38, 2.39)
The Thorax and Ventilation — You cannot suck air in. Breathing works by changing the size of a sealed box — and every part of the chest is built for that one job. (2.46, 2.47)
Alveoli, Exercise and Smoking — Why a lung holds a tennis court's worth of surface, what exercise does to breathing, and exactly how smoking dismantles both. (2.48, 2.49, 2.50)
Why Transport Systems Exist, and the Two Plant Vessels — Diffusion is fast across a cell and hopeless across a body. That single fact explains why big organisms need plumbing — and what a plant's two pipes carry. (2.51, 2.52, 2.53, 2.54)
Water Uptake and Transpiration — A tall tree lifts water a hundred metres with no pump and no moving parts. The force comes from water evaporating out of its leaves. (2.55, 2.56, 2.57, 2.58)
Blood — Four components in one fluid — and each one is shaped, or shaped away, for exactly what it has to carry. (2.59, 2.60, 2.61)
Immunity and Clotting — You are a warm, wet, nutrient-rich environment. Two kinds of white cell — and one clever trick with a scab — are why nothing has eaten you yet. (2.62, 2.63, 2.64)
The Heart, and What Goes Wrong With It — Two pumps in one organ, and why the muscle that pushes blood everywhere can still starve for want of it. (2.65, 2.66, 2.67)
Blood Vessels and the Circulation — Three kinds of vessel, three different structures — and every difference between them comes down to pressure. (2.68, 2.69)
Excretion: Getting Rid of What You Made — Excretion is not the same as going to the toilet — and knowing exactly why is worth more marks than any list of organs. (2.70, 2.71)
The Kidney and the Nephron — The kidney does not pick out the waste. It throws almost everything away and then takes back what it wants — and that is a far cleverer design than it sounds. (2.72, 2.73, 2.74)
Ultrafiltration and Selective Reabsorption — Squeeze almost everything out of the blood by pressure, then spend energy buying back exactly what you need — including every last molecule of glucose. (2.75, 2.76, 2.77)
ADH and the Water Balance of the Blood — One hormone, one adjustable tap at the end of the nephron — and a loop that corrects the very thing that set it off. (2.78, 2.79)
Homeostasis and the Control of Body Temperature — Why the inside of you barely changes while the outside changes constantly — and exactly what the skin does about heat. (2.80, 2.81, 2.82, 2.93)
Plant Responses, Tropisms and Auxin — A plant has no eyes, no nerves and no muscles — and still gets its roots down and its shoots up every time. This is how. (2.83, 2.84, 2.85)
The Nervous System, and the Two Ways a Body Sends a Message — Electrical impulses down a wire, or a chemical posted into the blood — why a body needs both, and which job each one is for. (2.86, 2.87, 2.88)
Synapses and the Reflex Arc — Neurones do not touch. What crosses the gap between them, why the gap is there at all, and how a hand leaves a hot pan before you know it was hot. (2.89, 2.90)
The Eye — Focusing, and the Pupil Reflex — One sense organ, two adjustments: how the eye sharpens an image and how it controls the amount of light it lets in. (2.91, 2.92)
The Hormones — Sources, Roles and Effects — Eight chemical messengers, three kinds of job: prepare the body for action, hold a condition steady, or run a change that takes years. (2.94, 2.95)
Gas Exchange in Plants, Day and Night — Two opposite processes in one leaf, one of which never stops — and why what you can measure at the surface is only the difference between them. (2.40, 2.41, 2.44, 2.45)

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