ISLAC International Exam Prep

Every living cell has to move substances in and out — oxygen and glucose in, waste out, mineral ions absorbed from the soil. It does this in three ways: diffusion , osmosis and active transport . These three processes appear on every IGCSE Biology paper, from gas exchange to plant transport, so they are some of the most reliable marks you can revise. This lesson covers all three, with the exact worked example examiners use for the osmosis practical. 1. Why cells need transport — the cell membrane Every cell is surrounded by a cell membrane that is partially permeable (also called semi-permeable or selectively permeable ). It lets small molecules such as water and oxygen pass through, but blocks larger ones. This selective barrier is what makes controlled movement — especially osmosis — possible. 2. Diffusion Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. It i...

You already know that when the price of something goes up, people buy less of it. But by how much less? That single question is worth a surprising number of marks in IGCSE and O-Level Economics, and the tool that answers it is price elasticity of demand . This guide covers everything you need for the exam — the formula, how to read the answer, what makes demand elastic or inelastic, and the all-important link to a firm's revenue. Why the Law of Demand isn't enough The Law of Demand tells us that, ceteris paribus, a rise in price causes a fall in quantity demanded. That's the direction of the change. What it doesn't tell us is the size — and the size is what matters to a business deciding whether to raise its prices, or to a government deciding what to tax. What is price elasticity of demand? Price elasticity of demand (PED) measures how responsive the quantity demanded of a good is to a change in that good's own price. Picture an elastic band: some goods stretc...

Forces and motion is one of the highest-scoring topics in IGCSE Physics — and it all rests on three short rules written by Isaac Newton. Master them and you can explain almost any motion question in your exam. Sir Isaac Newton (portrait by Godfrey Kneller, 1689 — public domain, Wikimedia Commons) What is a force? A force is a push or a pull, measured in newtons (N) . Force is a vector — it has size and direction — so we draw forces as arrows. Always start with a free-body diagram : the object as a box with every force shown as a labelled arrow. Balanced vs unbalanced forces When forces are balanced , the resultant force is zero . When they are unbalanced , a resultant force remains. Add forces in the same direction and subtract those in opposite directions to find it. Newton's First Law (Inertia) An object stays at rest, or keeps moving at constant velocity in a straight line, unless a resultant force acts on it. Balanced forces mean the motio...

Every computer, phone and games console makes billions of decisions every second — using nothing but 1s and 0s . The components that make those decisions are called logic gates . This lesson covers all six gates you need for IGCSE / O-Level Computer Science, their truth tables, Boolean notation, and how to combine them into real circuits. AND OR NOT Binary: 1 and 0 In digital logic, 1 = TRUE / ON / HIGH voltage, and 0 = FALSE / OFF / LOW voltage. Every input and output of a logic gate is always one of these two values. What is a logic gate? A logic gate is an electronic component with one or more binary inputs and exactly one binary output . It follows a fixed rule, described by a truth table — a list of every input combination and the output it gives. The six logic gates Gate Rule Notation NOT Flips the input (0 to 1, 1 to 0) NOT A AND Output 1 only if all inputs are 1 A · B OR Output 1 if any input is 1 A + B NAND AND, then inverted (0 only if all 1s) N...

Quadratic equations appear on almost every IGCSE Maths paper, so solving them quickly and accurately is worth a lot of marks. This lesson covers the two methods you must know — factorising and the quadratic formula — plus the discriminant and what the solutions mean on a graph. What is a quadratic equation? A quadratic is any equation where the highest power of x is 2. In standard form it looks like ax² + bx + c = 0 , where a, b and c are numbers and a ≠ 0. Your first step in any question is to rearrange it into this form. What "solving" means The solutions (or roots ) of a quadratic are the values of x that make it equal to zero. On a graph, they are exactly where the U-shaped parabola crosses the x-axis. Most quadratics have two roots. Method 1 — Factorising Factorising uses one key idea: if two things multiply to give zero, at least one of them must be zero. When the coefficient of x² is 1, find two numbers that multiply to c and...

Why do some products sell out while others — just as good — sit on the shelf? The answer is almost always the marketing mix . For IGCSE and O-Level Business, the 4 Ps are one of the highest-value topics you can master: they appear again and again, and examiners love to test whether you can apply them to a real business. What is the marketing mix? The marketing mix is the combination of decisions a business controls to persuade customers to buy, summarised as the 4 Ps: Product, Price, Place and Promotion . Get all four right — and working together — and the product sells. Why the four Ps must be balanced The Ps are interdependent : change one and the others must adjust. A premium price needs premium quality and exclusive places to sell it. Cut the price and you may need to cut costs in the product too. If the Ps don't match, customers get a confusing message. P1 — Product The good or service itself. Businesses compete on function, quality, design...

Demand and supply is the core model of microeconomics — and one of the most heavily tested topics in IGCSE Economics. Get it right and you can explain how almost any price in the real world is set. This lesson covers the demand and supply curves , the difference between a movement and a shift , and how markets reach equilibrium . What is a market? A market is any arrangement that brings buyers and sellers together. Goods flow one way; money flows the other. Demand and effective demand Demand is not just wanting something. It must be backed by the ability to pay — that is effective demand . The law of demand says that, all else equal, price and quantity demanded move in opposite directions. Plot price against quantity and the demand curve slopes downward from left to right. Movement vs shift (demand) A change in the good's own price causes a movement along the curve — an expansion or contraction of demand. Anything other than the good's own pri...

Every photo, song, and message on a computer is stored as just two symbols: 0 and 1 . This is the binary number system , and it's one of the most exam-tested topics in IGCSE Computer Science. In this lesson you'll learn why computers use binary, how to convert between denary and binary both ways, how to add binary numbers, and how to spot an overflow error — the exact skills examiners reward. Why computers use binary Computers are electronic. Every component is either on or off — there is no in-between state. Two states are easy to build reliably and hard to confuse, so we map "on" to 1 and "off" to 0 . That single physical fact is why everything inside a computer is binary. Bits, nibbles and bytes A single binary digit is a bit . Four bits make a nibble . Eight bits make a byte — the standard unit you'll use throughout this topic. Place values in an 8-bit byte In an 8-bit byte each column has a fixed value, doubling from right to left. Mem...

How do plants turn sunlight into food? Photosynthesis is one of the most important reactions on Earth – it feeds almost every living thing and puts the oxygen into the air we breathe. This is a full, exam-focused guide for IGCSE & O Level Biology . Watch the video above, then use the notes below to revise. The big picture: light, water and carbon dioxide go in; glucose and oxygen come out. Image: Wikimedia Commons. 1. What is photosynthesis? Photosynthesis is the process by which green plants, algae and some bacteria use light energy (absorbed by chlorophyll ) to make glucose from carbon dioxide and water . Oxygen is released as a by-product. In short, light energy is transformed into chemical energy stored in glucose. Word equation carbon dioxide + water  —(light energy / chlorophyll)→  glucose + oxygen Balanced symbol equation 6CO 2 + 6H 2 O  →  C 6 H 12 O 6 + 6O 2 (in the presence of light energy and chlorophyll) 2. The raw materia...

 Welcome to ISLAC! We help students prepare for international exams with free video lessons on our YouTube channel and auto-graded practice quizzes in Google Classroom, where you can check your answers instantly. How it works: 1) Watch the lesson video on our YouTube channel (ISLAC). 2) Join the Google Classroom class for your subject using the code below. 3) Do the quiz for that lesson and see your score and explanations right away. Join your class at classroom.google.com with these codes: IGCSE Edexcel Physics - qrbewpjc IGCSE Edexcel Mathematics A - wkw432si IGCSE Edexcel Chemistry & Biology - cuhoy2r6 IGCSE Edexcel Business - 7g6miv47 IGCSE Edexcel Economics - ta2qvwfr IGCSE Computer Science - 6guhoy5h IELTS Preparation - oqypie7l IELTS students: visit our dedicated IELTS blog at islacielts.blogspot.com. New lessons, notes and past-paper walkthroughs are posted every week. Pick your subject from the Subjects menu to see everything for your course. Good luck with your studie...