Science for Year 7

🥽 Working scientifically Safety, equipment, fair tests, results and graphs

Scientists find things out by asking questions and testing their ideas carefully. In this chapter you learn to work safely in a lab, choose and use the equipment, plan a fair test, record your results and turn them into graphs and conclusions. You will use these skills in every other chapter.

Practice: Chapter test: working scientifically · Working scientifically: key words

• 🦺 Lab safety and hazard symbols Rules, goggles and the warning signs on bottles

  A school laboratory has flames, hot liquids, glass and chemicals, so it has rules that keep everyone safe. In this topic you learn the main lab rules, the warning symbols printed on bottles, and how scientists think about hazards and risks before a practical.

  Practice: Lab safety and hazard symbols

• ⚗️ Equipment and the Bunsen burner Beakers, flasks, measuring cylinders and a safe flame

  A cook uses a jug to measure and a pan to heat; scientists also pick the right tool for each job. Some equipment holds and mixes, some measures, some heats. Using the right piece in the right way keeps you safe and makes your results accurate.

  Practice: Equipment and the Bunsen burner

• 🎛️ Questions, variables and fair tests Change one thing, measure one thing, keep the rest the same

  Does sugar dissolve faster in warm water than in cold? Does a ball bounce higher if you drop it from higher up? To answer questions like these, scientists change one thing, measure another and keep everything else the same. This is called a fair test.

  Practice: Questions, variables and fair tests

• 📋 Measuring and recording results Units, tables, repeats, means and odd results

  "The water was 25" means nothing until you know whether it was 25 °C or 25 cm³. Careful measurements, with their units, written neatly in a table, are the raw material of every conclusion. In this topic you learn to read instruments, record results, repeat them and work out a mean.

  Practice: Measuring and recording results

• 📈 Graphs and conclusions Bar charts, line graphs, patterns and how good the data is

  A table full of numbers is hard to understand at a glance. Put the same numbers on a graph and the pattern jumps out. From the pattern you write a conclusion, and then you ask how much you can trust it.

  Practice: Graphs and conclusions

🔬 Cells Biology · the building blocks of every living thing

Every living thing is made of cells: you, an oak tree, a mushroom and the bacteria in yoghurt. Most cells are far too small to see, so in this chapter you will learn to use a microscope, find out what is inside animal and plant cells, and see how cells work together to build a whole body.

Practice: Chapter test: cells · Cells: key words

• 🌱 Living things The seven life processes: MRS GREN

  A cat is alive. A stone is not. A dead leaf was alive. Scientists decide what counts as living by checking for seven life processes. Every living thing does all seven at some time in its life.

  Practice: Living things

• 🔬 Using a microscope Its parts, making a slide and working out magnification

  Most cells are about a hundredth of a millimetre across, far too small to see with your eyes. A light microscope uses lenses to make them look hundreds of times bigger. Robert Hooke used one in 1665 to look at cork and was the first to call the tiny boxes he saw "cells".

  Practice: Using a microscope

• 🧫 Animal and plant cells Nucleus, cytoplasm, membrane, wall, chloroplasts and vacuole

  Animal and plant cells have the same basic parts, because both have to stay alive: release energy, make new materials and control what goes in and out. Plant cells have three extra parts, because plants make their own food and have no skeleton to hold them up.

  Practice: Animal and plant cells

• 🧬 Specialised cells Cells shaped for one job: sperm, nerve, root hair and more

  Your body has about 200 different kinds of cell. Most of them are specialised: their shape and parts suit one particular job, the way a key is shaped for one lock. Scientists say each one is adapted to its function.

  Practice: Specialised cells

• 🦠 Single-celled organisms Amoeba, euglena, yeast and bacteria

  You are made of millions of millions of cells. Some living things are made of just one. They are unicellular (single-celled) organisms. That one cell has to do all seven life processes by itself, so it has its own clever adaptations.

  Practice: Single-celled organisms

• 💨 Diffusion How substances get into and out of cells

  Spray perfume in one corner of a room and soon someone in the far corner can smell it, even if nothing in the room moves. The perfume particles spread out by themselves. This is diffusion, and it is how cells take in what they need and get rid of what they don't.

  Practice: Diffusion

• 🧩 From cells to organisms Cells, tissues, organs, organ systems and organisms

  A single muscle cell can't pump blood. But millions of them working together can: they make the heart. Living things that are made of many cells are organised in levels, each built from the one before.

  Practice: From cells to organisms

🦴 Body systems: skeleton, muscles and breathing Biology · how you stand, move and breathe

Right now your skeleton is holding you up, your muscles are keeping you upright and your lungs are taking in air many times a minute. In this chapter you find out how bones, joints and muscles work together to move you, and how your lungs get oxygen into your blood and carbon dioxide out of it.

Practice: Chapter test: body systems · Body systems: key words

• 🦴 The skeleton Support, protection, movement and making blood cells

  An adult skeleton has 206 bones. A baby is born with about 300, and some of them join together as it grows. Bones are not dead sticks: they are living organs that grow, mend themselves when they break and even make your blood.

  Practice: The skeleton

• 🦵 Joints Hinge, ball and socket and fixed joints; cartilage, ligaments and tendons

  Bend your elbow, then try to bend it the other way: you can't. A place where two bones meet is a joint, and each kind of joint lets the bones move in some directions but not in others.

  Practice: Joints

• 💪 Muscles and movement Muscles can only pull: antagonistic pairs

  You have more than 600 muscles. Every movement you make, from blinking to sprinting, happens because muscles contract. But a muscle can only pull, never push, and that is why muscles work in pairs.

  Practice: Muscles and movement

• 🫁 The lungs and gas exchange Trachea, bronchi, alveoli: oxygen in, carbon dioxide out

  Every cell in your body needs oxygen for respiration and makes carbon dioxide as waste. Your lungs swap one for the other: oxygen goes from the air into your blood, and carbon dioxide comes out of your blood into the air you breathe out. This swap is called gas exchange.

  Practice: The lungs and gas exchange

• 🌬️ Breathing Ribs, intercostal muscles, the diaphragm and lung volume

  Take a deep breath with your hands on your ribs: you can feel them move up and out. Your lungs have no muscles of their own. Muscles around them change the size of your chest, and air moves in or out.

  Practice: Breathing

• 🚭 Exercise, asthma and smoking What helps your lungs and what harms them

  Run up a flight of stairs and you soon breathe faster and deeper. Your lungs can do a lot more work when they need to. Regular exercise helps them; asthma and smoking make it harder for air to reach the alveoli.

  Practice: Exercise, asthma and smoking

👶 Human reproduction Biology · from puberty to a baby being born

Every person started life as a single cell, smaller than a full stop. In this chapter you find out how bodies change during puberty, what the male and female reproductive systems do, how a new life begins when a sperm meets an egg, and how a baby grows for nine months until it is born.

Practice: Chapter test: human reproduction · Human reproduction: key words

• 🧒 Adolescence and puberty How bodies and feelings change as you grow up

  At some point between the ages of about 8 and 14, a child's body starts to change into an adult's. These changes are called puberty. They happen during adolescence, the years between being a child and being an adult, when your feelings and the way you see the world change too.

  Practice: Adolescence and puberty

• 🚻 The reproductive systems The male and female reproductive organs and what they do

  To make a baby, a sperm cell from a man has to meet an egg cell from a woman. The reproductive system is all the organs that make these cells and bring them together, and in a woman also the organs where a baby grows. The male and female systems look very different because they do different jobs.

  Practice: The reproductive systems

• 📅 The menstrual cycle A 28-day cycle: periods and ovulation

  From puberty until about the age of 50, a woman's body gets ready for a possible pregnancy about once a month. An egg is released, and the lining of the uterus thickens to receive it. If the egg is not fertilised, the lining breaks down and leaves the body: this is a period. The repeating pattern is called the…

  Practice: The menstrual cycle

• 🥚 Fertilisation and implantation Sperm meets egg: how a pregnancy starts

  Every person began as one cell: an egg cell that a sperm cell had joined. That moment is called fertilisation. In this topic you follow the sperm and the egg until they meet, and then the tiny new embryo until it settles into the uterus.

  Practice: Fertilisation and implantation

• 🤰 Pregnancy and birth The placenta, the fetus, a healthy pregnancy and birth

  A pregnancy lasts about 40 weeks, a little over nine months. In that time a tiny ball of cells becomes a baby of about 3.5 kg. It cannot eat or breathe by itself, so everything it needs comes from its mother, through an organ called the placenta.

  Practice: Pregnancy and birth

🌸 Plant reproduction Biology · flowers, pollination, seeds and dispersal

A flower is not just there to look pretty: it is how a flowering plant makes the next generation. In this chapter you will find the male and female parts inside a flower, see how bees and the wind carry pollen between flowers, follow a flower as it turns into a fruit full of seeds, and find out how those seeds travel…

Practice: Chapter test: plant reproduction · Plant reproduction: key words

• 🌺 Flowers Stamens, carpels, petals and sepals

  We pick flowers for their colour and smell, but for the plant a flower is its reproductive organ: the part that makes seeds. Inside are male parts that make pollen and female parts that hold the ovules. Each part has a shape that suits its job.

  Practice: Flowers

• 🐝 Pollination Insects and wind carry pollen from flower to flower

  On a summer day a bumblebee visits hundreds of flowers. It is after nectar, but it also does the plants a huge favour: it carries their pollen from flower to flower. A flower cannot make seeds until pollen reaches its stigma.

  Practice: Pollination

• 🌰 Fertilisation, seeds and fruits How a flower becomes a fruit full of seeds

  A pollen grain sitting on a stigma is only halfway there. The male sex cell is in the pollen grain, at the top of the carpel; the female sex cell is in an ovule, deep inside the ovary. To make a seed, the two have to meet. Then the whole flower changes: the petals fall and the ovary becomes a fruit.

  Practice: Fertilisation, seeds and fruits

• 🍃 Seed dispersal and germination Wind, animals, water and explosions; how a seed starts to grow

  A big sycamore tree makes thousands of seeds every autumn. If they all fell straight down, the seedlings would grow up in the shade of their parent, fighting each other for everything. So plants have clever ways to send their seeds away: this is seed dispersal.

  Practice: Seed dispersal and germination

🦊 Ecosystems Biology · habitats, food chains, food webs and adaptations

No living thing lives alone. A fox needs rabbits to eat, the rabbits need grass, and the grass needs the soil that dead leaves and droppings rot into. In this chapter you find out where living things live and how scientists count them, who eats whom, how a change to one population spreads through the others, how…

Practice: Chapter test: ecosystems · Ecosystems: key words

• 🏞️ Habitats and communities Habitat, population, community, ecosystem and how to sample them

  A garden pond is home to frogs, water snails, pondweed and dragonfly larvae, and each of them depends on the others. Scientists who study how living things fit together are called ecologists. They use a few exact words for who lives where, and they find out how many there are by counting small samples.

  Practice: Habitats and communities

• 🔗 Food chains Producers and consumers: who eats whom

  Every mouthful you eat contains energy that started as sunlight. A plant trapped it, and perhaps an animal ate the plant before you ate the animal. A food chain shows this: what eats what, and which way the energy goes.

  Practice: Food chains

• 🕸️ Food webs and interdependence What happens when one population changes

  Most animals eat more than one kind of food, and many are eaten by more than one predator. So the food chains in a habitat join up into a food web. Because everything is linked, a change to one population spreads to the others: the living things in an ecosystem are interdependent.

  Practice: Food webs and interdependence

• 🐪 Adaptations and competition How living things are suited to where they live

  A polar bear would overheat in the desert, and a camel would freeze on the Arctic ice. Each is adapted to its own habitat: it has features that help it survive and reproduce there. Living things also compete with each other for what they need, and the best adapted are the most likely to win.

  Practice: Adaptations and competition

• ☠️ Toxins in food chains Poisons that build up from one link to the next

  In the 1950s and 1960s farmers sprayed their crops with pesticides such as DDT to kill insect pests. Nobody sprayed the birds, yet birds of prey such as the peregrine falcon became rare in Britain: some were poisoned, and many laid eggs with shells so thin that they broke. The poison had travelled up the food chain…

  Practice: Toxins in food chains

🧬 Variation and classification Biology · why living things differ and how we sort them

Look around your class: nobody is exactly like anyone else. Living things differ from each other, and scientists call these differences variation. In this chapter you find out where variation comes from and how to show it on a graph, what makes a species, and how scientists sort millions of living things into groups…

Practice: Chapter test: variation and classification · Variation and classification: key words

• 👪 Variation Differences between and within species; inherited or from the environment

  A robin, an oak tree and you are very different. But even two robins, or two pupils in your class, are never exactly the same. These differences are called variation. Some of them you were born with; others come from the way you live.

  Practice: Variation

• 📊 Continuous and discontinuous variation Height or blood group: which graph to draw

  Ask everyone in your class two questions: "How tall are you?" and "What is your blood group?" The heights could be any number: 148 cm, 151.5 cm, 153 cm. The blood groups can only be one of four answers. These are the two kinds of variation, and each needs its own kind of graph.

  Practice: Continuous and discontinuous variation

• 🐴 Species What makes a species, and why a mule is not one

  A Great Dane and a chihuahua look less alike than a horse and a donkey. Yet the two dogs belong to one species, and the horse and the donkey to two. What decides it is not how they look, but whether they can breed and have young that can breed too.

  Practice: Species

• 🗂️ Classification Kingdoms, vertebrates and invertebrates

  A library sorts its books into groups, so you can find the one you want among thousands. Scientists do the same with millions of living things: they sort them into groups by the features they share. This is called classification.

  Practice: Classification

• 🔑 Identification keys Yes-or-no questions that name a living thing

  You lift a log and find a tiny grey creature with lots of legs. What is it? An identification key tells you. You answer a question about what you can see, the answer leads you to the next question, and step by step you reach the name.

  Practice: Identification keys

🧊 Particles and their behaviour Chemistry · solids, liquids, gases and the particle model

Ice, liquid water and steam look nothing alike, yet they are the same substance. Everything around you is made of particles far too small to see, and they never stop moving. In this chapter you will use the particle model to explain why a solid keeps its shape, why water boils, how a smell spreads across a room, what…

Practice: Chapter test: particles and their behaviour · Particles: key words

• 🧊 Solids, liquids and gases The three states of matter and their properties

  A brick, a glass of orange juice and the air in a balloon behave very differently. You can stand a brick on its end, but juice runs everywhere if you spill it, and the air escapes the moment you untie the balloon. Scientists sort materials into three states of matter: solid, liquid and gas.

  Practice: Solids, liquids and gases

• ⚪ The particle model Arrangement, movement and spacing of particles

  Nobody can see a particle, not even with the best light microscope. But scientists can explain almost everything about solids, liquids and gases by imagining that every substance is made of tiny particles that are always moving. This idea is called the particle model.

  Practice: The particle model

• 🌡️ Changes of state Melting, freezing, boiling, evaporating, condensing and subliming

  An ice lolly melts in the sun, a puddle dries up, the bathroom mirror mists over after a shower. Each time a substance changes from one state to another, but it is still the same substance. Heating or cooling changes how much energy its particles have, and that changes how they are arranged and how they move.

  Practice: Changes of state

• 🌫️ Diffusion and Brownian motion Particles moving and mixing by themselves

  When someone opens a bag of crisps across the room, you soon smell them, even if nobody moves and no window is open. The smell spreads by itself, because its particles and the particles of the air are always moving and mixing. That spreading is called diffusion.

  Practice: Diffusion and Brownian motion

• 🎈 Gas pressure Particles hitting the walls of their container

  Blow up a balloon and it stays blown up, round and firm, although nothing solid holds it out. The air inside is pushing on the rubber from the inside, everywhere at once. That push is gas pressure, and the particle model explains where it comes from.

  Practice: Gas pressure

• ⚖️ Density How much mass is packed into a volume, and why ice floats

  Which is heavier, a kilogram of feathers or a kilogram of iron? Neither: they both have a mass of 1 kg. But the feathers fill a sack and the iron fits in your hand. Iron packs much more mass into each cubic centimetre: it has a much higher density.

  Practice: Density

⚛️ Elements, atoms and compounds Chemistry · what everything is made of

Everything around you, from the air you breathe to the phone in your pocket, is built from about 90 kinds of atom found in nature. In this chapter you will meet atoms and elements, learn the symbols chemists use, find your way around the periodic table, and see how atoms join together to make compounds with formulae…

Practice: Chapter test: elements, atoms and compounds · Elements, atoms and compounds: key words

• ⚛️ Atoms and elements The smallest particles of an element; Dalton's idea

  Cut a piece of copper wire in half, then in half again, and again. Could you go on for ever? No: in the end you would reach a single atom of copper, the smallest piece of copper there can be. Everything around you is made of atoms.

  Practice: Atoms and elements

• 🔤 Symbols and the periodic table One or two letters for each element, set out in groups and periods

  Chemists everywhere use the same short symbols for the elements, whatever language they speak. The symbols are set out in the periodic table, a chart that puts elements that behave alike next to each other. Learn to read it and you can predict how an element behaves before you have even seen it.

  Practice: Symbols and the periodic table

• 🔩 Metals and non-metals Shiny, strong conductors and the elements that are not

  About four out of every five elements are metals: think of iron in a bridge, copper in a wire or gold in a ring. Metals and non-metals have very different properties, and their properties decide what we use them for.

  Practice: Metals and non-metals

• 🧂 Compounds and molecules Atoms of different elements joined together

  Sodium is a soft metal that fizzes violently in water, and chlorine is a poisonous green gas. Join their atoms together and you get sodium chloride: the salt you sprinkle on your chips. When elements join, they make a brand-new substance called a compound.

  Practice: Compounds and molecules

• 🧮 Chemical formulae H₂O, CO₂, NaCl: what the letters and numbers mean

  Chemists don't write "a molecule made of two hydrogen atoms and one oxygen atom" every time they mean water. They write H2O. A chemical formula shows which elements are in a substance and how many atoms of each there are.

  Practice: Chemical formulae

🧪 Mixtures and separation Chemistry · pure substances, solutions and how to separate them

Hardly anything around you is a single pure substance: sea water, air, milk, fruit juice and ink are all mixtures. In this chapter you will find out what a chemist means by "pure", how substances dissolve, and how to separate mixtures by filtration, evaporation, distillation and chromatography: the methods used to…

Practice: Chapter test: mixtures and separation · Mixtures and separation: key words

• 💧 Pure substances and mixtures What pure means to a chemist, and how to test it

  A carton says "pure orange juice". A chemist would disagree: orange juice is a mixture of water, sugars, acids, vitamins and much more. To a chemist, pure means just one substance, with nothing else mixed in.

  Practice: Pure substances and mixtures

• 🥄 Dissolving and solutions Solute, solvent, solution and solubility

  Stir a spoonful of sugar into a cup of tea and it seems to vanish. It hasn't: you can still taste it. The sugar has dissolved: its particles have spread out between the water particles.

  Practice: Dissolving and solutions

• ☕ Filtration Separating an insoluble solid from a liquid

  When you make coffee with a paper filter, or drain pasta in a sieve, you are separating a solid from a liquid. In the lab, filtration does the same job: it separates an insoluble solid from a liquid.

  Practice: Filtration

• 🧂 Evaporation and crystallisation Getting a dissolved solid back out of a solution

  In hot countries, sea water is let into shallow ponds by the shore. The sun evaporates the water and leaves sea salt behind. In the lab, a Bunsen burner does the same job much faster.

  Practice: Evaporation and crystallisation

• 🫗 Distillation Getting pure water from salty water

  Evaporation gets the salt back from salty water, but the water escapes into the air. What if you want the water? Distillation catches the steam and cools it back into a liquid: pure water.

  Practice: Distillation

• 🖍️ Chromatography Separating the colours in an ink

  Black felt-tip ink looks like one colour, but it is often a mixture of several dyes. Chromatography separates them, so you can see what an ink, a food colouring or a dye is made of, and even match the ink on a forged note to the pen that wrote it.

  Practice: Chromatography

🍋 Acids and alkalis Chemistry · indicators, the pH scale and neutralisation

Lemon juice tastes sour, soap feels slippery and oven cleaner can burn your skin: lemon juice is an acid, soap and oven cleaner are alkalis. In this chapter you learn how to handle them safely, how to tell them apart with indicators, how to measure them on the pH scale, and what happens when acids react with alkalis…

Practice: Chapter test: acids and alkalis · Acids and alkalis: key words

• 🍋 Acids and alkalis around us Where we find them, and how to handle them safely

  The sour taste of a lemon, the sharp tang of vinegar on chips and the fizz in a can of lemonade all come from acids. Their chemical opposites, alkalis, are in soap, bleach and oven cleaner. Many acids and alkalis are harmless in food, but others can burn skin and blind eyes, so chemists handle them with care.

  Practice: Acids and alkalis around us

• 🌈 Indicators Litmus, red cabbage and universal indicator

  Most acids and alkalis are colourless liquids that look just like water, so you can't tell them apart by looking (and you must never taste them). Chemists use an indicator instead: a dye that changes colour depending on whether it is in an acid or an alkali.

  Practice: Indicators

• 🔢 The pH scale From 0 to 14: how strongly acidic or alkaline

  Lemon juice and stomach acid are both acids, but stomach acid is far more acidic. To say exactly how acidic or alkaline a solution is, chemists give it a number on the pH scale, which runs from 0 to 14.

  Practice: The pH scale

• 🤝 Neutralisation Acid + alkali → salt + water

  Heartburn is the burning feeling you get when stomach acid creeps up into your food pipe. An indigestion tablet makes it better by cancelling the acid out. That reaction, between an acid and a base, is called neutralisation, and it is one of the most useful reactions in chemistry.

  Practice: Neutralisation

• 🫧 Acids and metals Metal + acid → salt + hydrogen, and the squeaky pop test

  Drop a strip of magnesium into dilute acid and it fizzes, gets warm and slowly disappears. The bubbles are hydrogen, the lightest gas there is. Many metals react with acids like this, but not all of them: gold can sit in acid for years and stay shiny.

  Practice: Acids and metals

🔥 Chemical reactions Chemistry · new substances, word equations and energy

Toast browning, a bonfire burning, a bike chain rusting and a cake rising in the oven are all chemical reactions: new substances are being made. In this chapter you learn how to spot a reaction, how to write one down as a word equation, why no mass is ever lost, and the main kinds of reaction: burning, oxidation and…

Practice: Chapter test: chemical reactions · Chemical reactions: key words

• 🔄 Chemical and physical changes Signs that a new substance has been made

  Melt some chocolate and it is still chocolate: put it in the fridge and it sets again. Bake a cake and the eggs, flour and sugar turn into something completely new, which you can never turn back. The first is a physical change; the second is a chemical change, also called a chemical reaction.

  Practice: Chemical and physical changes

• 📝 Word equations and conservation of mass Reactants → products, and no atoms lost

  A recipe lists what you start with and what you end up with. Chemists write reactions down the same way, in a word equation: the substances that react, an arrow, then the new substances made. Writing reactions like this also shows something important: atoms are never lost, so mass never disappears.

  Practice: Word equations and conservation of mass

• 🔥 Combustion Burning fuels and the fire triangle

  A gas cooker, a campfire, a car engine and a birthday candle all rely on the same reaction: combustion, the scientific word for burning. A fuel reacts with oxygen and gives out energy as heat and light.

  Practice: Combustion

• 🧲 Oxidation and the reactivity of metals Metals reacting with oxygen, and which metals react most

  Leave a shiny new bike out in the rain and orange-brown rust soon creeps over it. The iron is reacting with oxygen from the air. Metals react with oxygen at very different speeds: a freshly cut piece of potassium goes dull in seconds, while gold stays bright for thousands of years.

  Practice: Oxidation and the reactivity of metals

• 🧱 Thermal decomposition Breaking a compound down by heating it

  Why do some cakes rise in the oven? Bicarbonate of soda in the mixture breaks down when it is heated, giving off bubbles of carbon dioxide that puff the cake up. Breaking a compound down by heating it is called thermal decomposition.

  Practice: Thermal decomposition

• 🌡️ Exothermic and endothermic reactions Reactions that give out heat and ones that take it in

  Open a hand warmer and it slowly gets hot: the iron powder inside is reacting with oxygen. Mix citric acid and bicarbonate of soda in water and the mixture goes cold. Every chemical reaction has an energy change: some give energy out to their surroundings, others take energy in.

  Practice: Exothermic and endothermic reactions

🌍 The Earth Earth science · Earth's structure, rocks and the rock cycle

The ground under your feet feels solid and still, but the Earth is always changing. Rocks are made, worn away and made again, the hot rock deep inside slowly churns, and we dig metals out of the crust to build almost everything we use. In this chapter you will look inside the Earth, meet the three kinds of rock…

Practice: Chapter test: The Earth · The Earth: key words

• 🌍 The structure of the Earth Crust, mantle and core, and the air around it

  The deepest hole ever drilled goes down about 12 km, yet the centre of the Earth is about 6370 km below us. Scientists worked out what is down there from earthquake waves, which change speed and direction as they pass from one layer into the next. If the Earth were an apple, the rocky crust we live on would be about…

  Practice: The structure of the Earth

• 🪨 Igneous, sedimentary and metamorphic rocks How each kind of rock is made

  A granite worktop, the white cliffs of Dover and a marble statue are all made of rock, but each was made in a completely different way. Geologists sort every rock into one of three groups by how it formed: igneous, sedimentary or metamorphic. How a rock formed decides what it looks like and how it behaves.

  Practice: Igneous, sedimentary and metamorphic rocks

• 🌧️ Weathering and erosion How rocks are broken down and carried away

  Old gravestones become hard to read, potholes open up in roads after a frosty winter, and mountains slowly crumble. Rock is broken down by the weather and by living things: this is weathering. The broken pieces are then carried away: this is erosion.

  Practice: Weathering and erosion

• ♻️ The rock cycle How rocks change from one kind into another

  The grains of sand on a beach may once have been part of a volcano, then a mountain, then a river bed. Rocks keep changing from one kind into another, and the same material is used again and again, like nature's own recycling. This never-ending loop is the rock cycle.

  Practice: The rock cycle

• ⛏️ Earth's resources and recycling Metals from ores, and why recycling matters

  A bike, a phone and a can of drink are all made from materials dug out of the Earth's crust. The Earth gives us metals, stone, sand for glass and clay for bricks. But there is only a certain amount of each, and once it has been used up it does not grow back.

  Practice: Earth's resources and recycling

🏋️ Forces and motion Physics · pushes, pulls, gravity and speed

Every time something starts to move, stops, speeds up, turns or changes shape, a force is at work. In this chapter you will learn to draw forces as arrows and add them up, find out what friction, springs and gravity do, and work out how fast things go from numbers and from graphs.

Practice: Chapter test: Forces and motion · Forces and motion: key words

• ➡️ What forces do Pushes and pulls in newtons; contact and non-contact forces

  Kick a ball, open a door, stretch a rubber band: each time you push or pull. A force is a push or a pull that acts when two objects interact. You cannot see a force, but you can always see what it does.

  Practice: What forces do

• ⚖️ Balanced and unbalanced forces Resultant force, and what it does to motion

  In a tug of war, both teams pull as hard as they can, yet the rope may not move at all: the forces are balanced. As soon as one team pulls harder, the rope moves their way. What happens to an object depends on all the forces on it added together.

  Practice: Balanced and unbalanced forces

• 🛷 Friction and drag Friction, air resistance and water resistance

  Without friction you could not walk, write or ride a bike: your shoes would slip, the pencil would slide off the paper and the brakes would do nothing. But friction also wears things out and wastes energy. Friction and drag are forces that act against motion.

  Practice: Friction and drag

• 🪀 Stretching and squashing Springs, extension and Hooke's law

  A trampoline, a bungee rope and the springs in a mattress all change shape when forces act on them, then spring back. Changing shape is called deformation. For a spring, the change can be measured, and it follows a simple rule.

  Practice: Stretching and squashing

• 🍎 Mass, weight and gravity W = m × g: why you weigh less on the Moon

  On the Moon, astronauts bound along in huge, slow steps, even in heavy spacesuits. Their bodies have not changed, but the Moon pulls on them about six times less strongly than the Earth does. So their mass is the same, but their weight is much smaller.

  Practice: Mass, weight and gravity

• 🏎️ Speed Speed = distance ÷ time

  In a race the winner covers the same distance as everyone else, but in the shortest time. Speed tells you how far something goes in a certain time: so many metres every second, or kilometres or miles every hour.

  Practice: Speed

• 📉 Distance–time graphs and relative motion Reading a journey from a graph

  A distance–time graph tells the story of a journey in a single line: when it set off, when it stopped, and when it went fastest. Learn to read its shape and you can work out the speed of each part.

  Practice: Distance–time graphs and relative motion

⚡ Energy Physics · energy stores, transfers, resources and bills

Everything that happens needs energy: a bus pulling away, a kettle boiling, your heart beating. Energy is never made and never destroyed: it moves from one store to another. In this chapter you will learn the energy stores, how energy is transferred and wasted, how much energy is in your food, where electricity comes…

Practice: Chapter test: energy · Energy: key words

• 🔋 Energy stores Chemical, kinetic, gravitational, elastic, thermal and more

  A sandwich, a stretched rubber band, a book on a high shelf and a mug of hot chocolate have something in common: each holds energy, ready to make something happen. Scientists describe energy by saying which store it is in.

  Practice: Energy stores

• 🔁 Energy transfers Energy is never made or destroyed, only moved and spread out

  Whenever anything happens, energy moves from one store to another. An apple falling, a kettle boiling and a phone charging are all energy transfers. However the energy moves, the total amount never changes, but some of it always ends up somewhere we didn't want it.

  Practice: Energy transfers

• 🥪 Energy in food Kilojoules on the label and what your body needs

  Food is your body's fuel. It has a chemical store of energy, which your cells release by respiration to keep you warm, move your muscles and help you grow. Every food packet tells you how much energy is inside.

  Practice: Energy in food

• 🌬️ Fuels and energy resources Fossil fuels and renewable resources

  Flick a switch and a lamp lights, but the energy came from far away: a gas-fired power station, a wind farm, a solar panel on a roof. An energy resource is anything with a store of energy that we can release in a useful way. Some will run out; others never will.

  Practice: Fuels and energy resources

• 💡 Power and paying for energy Watts, kilowatt-hours and the cost on the bill

  A 3000 W kettle boils a mug of water in about a minute; an 8 W lamp would need hours to transfer the same energy. The difference is power: how fast a device transfers energy. Power and time together decide how much energy you use, and how much you pay for it.

  Practice: Power and paying for energy

• 🌡️ Temperature and heating Conduction, convection, radiation and insulation

  Leave a mug of hot chocolate on the table and it cools down; a can from the fridge warms up. Energy always moves from hotter things to cooler things, in three ways: conduction, convection and radiation. Insulation slows all three down, which keeps homes warm and drinks hot.

  Practice: Temperature and heating

🔌 Electricity Physics · circuits, current, potential difference and resistance

Electricity lights your home, charges your phone and runs trains. In this chapter you will build circuits and draw them with symbols, measure the current that flows and the potential difference that pushes it, find out why homes are wired in parallel, see what resistance does, and make things stick and spark with…

Practice: Chapter test: electricity · Electricity: key words

• 🔌 Circuits and circuit symbols A complete loop, drawn with symbols

  Press a switch and the light comes on at once. That only works because there is an unbroken loop of wire from the cell, through the lamp and back again. That loop is a circuit, and scientists draw it with a set of simple symbols that everyone in the world can read.

  Practice: Circuits and circuit symbols

• 〰️ Current Measured in amps with an ammeter

  When a circuit is complete, charge flows all the way round it: through the wires, through the lamp and even through the cell. This flow of charge is the electric current. It starts everywhere in the loop at the same moment, which is why a light comes on as soon as you flick the switch.

  Practice: Current

• 🔋 Potential difference Measured in volts with a voltmeter

  A torch cell says 1.5 V, a smoke alarm battery 9 V, and the socket in your wall gives 230 V. The number in volts is the potential difference. It tells you how big a push the supply gives the charge, and how much energy the charge carries round the circuit.

  Practice: Potential difference

• 🔀 Series and parallel circuits One loop or several branches

  On some old strings of Christmas lights, when one bulb broke they all went out. When a bulb blows in your kitchen, the other lights in the house stay on. The difference is how they are connected: in series or in parallel.

  Practice: Series and parallel circuits

• 🧱 Resistance Conductors, insulators and resistance = p.d. ÷ current

  Why does current flow so easily through the copper inside a cable, but not at all through the plastic around it? And why does the thin wire in a toaster glow red-hot? The answer to both is resistance.

  Practice: Resistance

• 🎈 Static electricity Rubbing, charges, sparks and electric fields

  Pull a jumper over your head in the dark and you may see tiny sparks and hear them crackle. Rub a balloon on your hair and it sticks to the wall. This is static electricity: charge that has built up on an object and stays there, instead of flowing round a circuit.

  Practice: Static electricity

🔊 Sound Physics · vibrations, waves, hearing and echoes

Music, voices, birdsong and the rumble of traffic all reach you as sound. In this chapter you will find out how sounds are made, how they travel through air, water and solids, why some are loud or high and others quiet or low, how your ear turns them into signals for your brain, and how bats, ships and doctors use…

Practice: Chapter test: sound · Sound: key words

• 🥁 Making sounds Every sound starts with a vibration

  Tap a table, pluck a rubber band or hum a tune: each time, something moves backwards and forwards very fast. Every sound starts with a vibration. This topic is about what vibrates in instruments, in machines and in you.

  Practice: Making sounds

• 📣 How sound travels Through solids, liquids and gases, but never a vacuum

  Shout across a playground and your friend hears you a moment later. Nothing flies from your mouth to their ear: the air itself passes the vibration along, particle by particle. Sound needs particles to travel, which is why space is silent.

  Practice: How sound travels

• 🎵 Loudness and pitch Amplitude, frequency and what a wave trace shows

  A whisper and a shout, a tuba and a whistle: sounds differ in how loud they are and how high or low they are. Both depend on how the source vibrates, and with a microphone and an oscilloscope you can see the difference on a screen.

  Practice: Loudness and pitch

• 👂 Hearing How the ear works, and the range we can hear

  Your ears pick up tiny changes in the air pressure, far too small to feel, and turn them into electrical signals for your brain. Most of the ear is hidden inside the bone of your skull: the part you can see is only its entrance.

  Practice: Hearing

• 🦇 Echoes and ultrasound Reflected sound, sonar, scans and microphones

  Shout towards a cliff or in a big empty hall and your voice comes back a moment later. That is an echo: sound reflected from a surface. Bats, dolphins, ships and hospitals all use echoes to find things they can't see.

  Practice: Echoes and ultrasound

🌈 Light Physics · how light travels, reflects, bends and makes colours

Light lets you see the world. It carries energy from the Sun across empty space, bounces off mirrors, bends as it goes into water or glass, and splits into the colours of a rainbow. In this chapter you find out how light travels, how mirrors and lenses work, how your eye makes a picture, and why things have colours.

Practice: Chapter test: light · Light: key words

• ☀️ How light travels Light sources, straight lines, shadows and the speed of light

  At night, switch off every lamp and close the curtains: you can see nothing at all, not even your hand in front of your face. Your eyes need light. In this topic you find out where light comes from, how it travels, what happens when it meets different materials, and just how fast it goes.

  Practice: How light travels

• 🪞 Reflection Mirrors and the law of reflection

  Look into a mirror, a shiny spoon or a still pond and you see a picture of yourself. Every surface reflects some of the light that hits it, but only a very smooth one reflects it neatly enough to make an image. In this topic you learn the simple rule that every reflected ray follows.

  Practice: Reflection

• 🥤 Refraction and lenses Light bending as it passes from one material to another

  Put a straw in a glass of water and it looks broken at the surface. Look down into a swimming pool and it seems shallower than it really is. Both happen because light changes direction when it passes from one material into another. This is called refraction.

  Practice: Refraction and lenses

• 👁️ The eye and the camera How we see, and the pinhole camera

  Your eyes work like tiny cameras. Each one gathers light, focuses it into a sharp picture on a screen at the back, and turns that picture into signals for your brain. In this topic you meet the parts of the eye, then the simplest camera of all: a box with a pinhole.

  Practice: The eye and the camera

• 🎨 Colour White light, prisms, filters and coloured objects

  A rainbow after a shower, the shimmer on a soap bubble, every colour on a screen: they all come from white light. White light is not one colour but a mixture of many. In this topic you split it up, add coloured lights together, and find out why a red ball looks red.

  Practice: Colour

🪐 Space Physics · the Solar System, stars, seasons and the Moon

Look up on a clear night and you can see the Moon, a few planets and thousands of stars. In this chapter you will find out what is in our Solar System, how far away the stars are, why we have days, years and seasons, why the Moon seems to change shape, and how gravity holds it all together.

Practice: Chapter test: space · Space: key words

• ☀️ The Solar System The Sun, eight planets, moons and more

  The Sun, eight planets with their moons, dwarf planets, asteroids and comets: together they make up the Solar System. Everything in it travels round the Sun, held by the Sun's gravity.

  Practice: The Solar System

• 🌌 Stars, galaxies and light years The Sun is a star in a galaxy of billions

  On a dark night you can see a few thousand stars with your eyes alone. Each one is a sun, many of them bigger and brighter than ours: they look like tiny points only because they are so far away. To measure distances that big, astronomers use the light year.

  Practice: Stars, galaxies and light years

• 🌍 Days, years and seasons Spinning, orbiting and a tilted Earth

  Why is it dark at night? Why is a year 365 days long? Why are summer days so much longer than winter ones? All three answers come from the way the Earth moves: it spins, it orbits the Sun, and it is tilted.

  Practice: Days, years and seasons

• 🌙 The Moon Phases and eclipses

  The Moon is about a quarter as wide as the Earth and about 384 000 km away. Over a month it seems to change shape, from a thin crescent to a full disc and back again. It doesn't really change at all: we just see different amounts of its sunlit side.

  Practice: The Moon

• 🧑‍🚀 Gravity in space Weight on other planets, and what keeps things in orbit

  Gravity holds you on the ground, the Moon round the Earth and the Earth round the Sun, and it works across empty space without touching anything. In this topic you see how it keeps things in orbit, and why astronauts weigh less on the Moon.

  Practice: Gravity in space

🏁 Year 7 review Revision tips and the end-of-year test

You have reached the end of Year 7 science. Before the end-of-year test, look back over the year: the big idea of each chapter is below, with a link to go back to it. Then take the test at the bottom of this page.

Sections:

• How to revise 🧠
• The year in one table

Practice: End-of-year test: Science