Pearson Edexcel International GCSE in Biology · 4BI1
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.
34 lessons, covering 95 specification statements: 2.1 · 2.2 · 2.3 · 2.4 · 2.5 · 2.6 · 2.7 · 2.8 · 2.9 · 2.10 · 2.11 · 2.12 · 2.13 · 2.14 · 2.15 · 2.16 · 2.17 · 2.18 · 2.19 · 2.22 · 2.20 · 2.23 · 2.21 · 2.42 · 2.43 · 2.24 · 2.25 · 2.26 · 2.27 · 2.28 · 2.29 · 2.30 · 2.31 · 2.32 · 2.33 · 2.34 · 2.35 · 2.37 · 2.36 · 2.38 · 2.39 · 2.46 · 2.47 · 2.48 · 2.49 · 2.50 · 2.51 · 2.52 · 2.53 · 2.54 · 2.55 · 2.56 · 2.57 · 2.58 · 2.59 · 2.60 · 2.61 · 2.62 · 2.63 · 2.64 · 2.65 · 2.66 · 2.67 · 2.68 · 2.69 · 2.70 · 2.71 · 2.72 · 2.73 · 2.74 · 2.75 · 2.76 · 2.77 · 2.78 · 2.79 · 2.80 · 2.81 · 2.82 · 2.93 · 2.83 · 2.84 · 2.85 · 2.86 · 2.87 · 2.88 · 2.89 · 2.90 · 2.91 · 2.92 · 2.94 · 2.95 · 2.40 · 2.41 · 2.44 · 2.45
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)