National Year 9 Science

Chapters: 12

1. Working scientifically

Scientific attitudes · Experimental skills and investigations · Analysis and evaluation · Measurement

The Scientific Method – The scientific method is the careful way scientists find out how the world works. Observe something, ask a testable question, make a hypothesis (a clear, testable guess), test it with a fair experiment (change one variable, measure one, keep the rest the same), repeat and record data, analyse it, draw a conclusion and share it so others can check. Results that fail the test are useful too: they send you back to a new hypothesis.
Data Analysis – Data analysis means turning raw data into answers. It follows a cycle: ask a question, collect data, clean it (remove errors, repeats and blanks), organise and transform it, analyse it with summaries such as mean, median, range and patterns, show it with a good chart, and draw a careful conclusion. Watch for outliers, small samples and bias, and remember that a correlation between two things does not prove that one causes the other. Data must also be stored safely and used with permission.
Measurement and Units: How We Measure Anything – To measure something is to compare it with a fixed amount called a unit. Every measurement has a number and a unit. Scientists everywhere use the SI system, with seven base units such as the metre, kilogram and second. Prefixes like kilo (×1000), centi (÷100) and milli (÷1000) make units bigger or smaller. A good measurement starts at zero, is read with the eye straight above the mark, and is only as accurate as the smallest division (least count). Rounded values hide a small range, given by upper and lower bounds.

2. Biology: Structure and function of living organisms

Cells and organisation · The skeletal and muscular systems · Nutrition and digestion · Gas exchange systems · Reproduction · Health

The Cell: Basic Unit of Life – Every living thing is made of cells. Robert Hooke first saw cells in cork in 1665. Cells are prokaryotic (no true nucleus, like bacteria) or eukaryotic (true nucleus). Plant cells have a cell wall, chloroplasts and a big vacuole; animal cells do not. Each organelle has a job. Water enters and leaves cells by osmosis. Cells make new cells by mitosis (growth) and meiosis (sex cells).
The Skeletal System – The skeleton is the body's frame of 206 bones (adult). It has five main jobs: support and shape, protection, movement (with muscles), making blood cells in red marrow, and storing minerals like calcium. Bones meet at joints; hinge joints (elbow, knee) bend one way, ball-and-socket joints (shoulder, hip) move in all directions. Ligaments join bone to bone, tendons join muscle to bone, cartilage cushions the ends. Muscles only pull, so they work in antagonistic pairs such as biceps and triceps.
Human Digestive System and Heterotrophic Nutrition – Heterotrophs take ready-made food from other living things. Humans are holozoic: we eat whole food and break it down in a long tube, the alimentary canal. Teeth, saliva, stomach acid, enzymes, bile and pancreatic juice cut big food molecules into small ones that villi in the small intestine absorb into blood.
Respiration: Aerobic, Anaerobic and the Human Lungs – Respiration is the breakdown of food, usually glucose, inside cells to release energy, stored as ATP. With oxygen (aerobic) glucose is fully broken into carbon dioxide and water and gives much energy; without oxygen (anaerobic) it gives little energy and makes ethanol (yeast) or lactic acid (muscles). Our lungs bring oxygen to the blood through millions of alveoli.
Reproduction in Human Beings and Reproductive Health – At puberty, hormones from the brain make the testes and ovaries start working. The male system makes and carries sperm; the female system makes eggs and provides a place (uterus) where a baby develops. Fertilisation happens in the oviduct, and the embryo is fed through the placenta. Reproductive health includes safe choices, contraception, avoiding female foeticide, and preventing sexually transmitted diseases such as HIV/AIDS.
Health and Disease – Health is complete physical, mental and social well-being, not just the absence of disease. Communicable diseases are caused by pathogens (bacteria, viruses, fungi, protists) and spread from person to person, through air, water, food, touch or animals. Non-communicable diseases such as heart disease, diabetes, many cancers and high blood pressure do not spread; they are linked to genes, age and lifestyle. We prevent disease with hygiene, clean water, vaccines, a balanced diet, exercise, sleep, not smoking, and regular check-ups and self-checks. Antibiotics kill bacteria but not viruses; misusing them breeds resistant bacteria. Medicines must be taken as the leaflet or doctor says.

3. Biology: Material cycles and energy

Photosynthesis · Cellular respiration

Life Processes and Photosynthesis – Life processes are the jobs every living body must keep doing to stay alive: nutrition, respiration, transport and excretion. Green plants do nutrition by photosynthesis: using sunlight and chlorophyll, they turn carbon dioxide and water into glucose and give out oxygen.
Respiration: Aerobic, Anaerobic and the Human Lungs – Respiration is the breakdown of food, usually glucose, inside cells to release energy, stored as ATP. With oxygen (aerobic) glucose is fully broken into carbon dioxide and water and gives much energy; without oxygen (anaerobic) it gives little energy and makes ethanol (yeast) or lactic acid (muscles). Our lungs bring oxygen to the blood through millions of alveoli.

4. Biology: Interactions and interdependencies

Relationships in an ecosystem

Ecosystem, Food Chains and Energy Flow – An ecosystem is all the living things in a place plus the non-living things around them, working together. Energy enters as sunlight, passes one way up a food chain, and only about 10% moves to each next level.

5. Biology: Genetics and evolution

Inheritance, chromosomes, DNA and genes

Heredity and Mendel's Laws – Heredity is the passing of traits from parents to children through genes. Each parent gives one copy of every gene. A dominant copy hides a recessive one, which is why Mendel saw 3:1 in a monohybrid cross and 9:3:3:1 in a dihybrid cross. Genes are pieces of DNA that make proteins, and proteins build the trait.

6. Chemistry

The particulate nature of matter · Atoms, elements and compounds · Pure and impure substances · Chemical reactions · Energetics · The Periodic Table · Materials · Earth and atmosphere

The Particle Model of Matter – All matter is made of tiny particles that are always moving. In a solid they are close and only vibrate; in a liquid they are close but slide past each other; in a gas they are far apart and move fast in all directions. Heating gives particles more energy: either they move faster (temperature rises) or the forces between them are broken (the state changes while the temperature stays the same). Gas pressure comes from particles hitting the walls.
Atoms and Molecules – In a chemical reaction mass is neither created nor destroyed (conservation of mass), and a compound always has its elements in the same ratio by mass (constant proportions). Dalton explained both: matter is made of tiny atoms that join in small whole numbers. Atoms join to form molecules; charged atoms or groups are ions. Formulae are written by crossing valencies. Molecular mass (or formula unit mass for ionic compounds) is the sum of the atomic masses in the formula, in u.
Mixtures and Their Separation – A mixture has two or more substances mixed without any fixed ratio, and each keeps its own properties. Homogeneous mixtures (solutions) look the same everywhere; heterogeneous ones do not. By particle size we get solutions (< 1 nm), colloids (1–1000 nm) and suspensions (> 1000 nm). Colloids scatter light (Tyndall effect). Concentration tells how much solute is in a solution. We separate mixtures by using a difference in their parts: evaporation, crystallisation, distillation, chromatography, sublimation, centrifugation and coagulation.
Chemical Reactions and Balancing Equations – In a chemical reaction atoms are not made or destroyed; they only change partners. So a chemical equation must have the same number of each kind of atom on both sides. We balance it by changing the numbers in front of formulas, never the formulas themselves.
Exothermic and Endothermic Reactions – Energy is conserved in every reaction; it only moves between the chemicals and the surroundings. An exothermic reaction transfers energy to the surroundings, so the temperature rises (burning, neutralisation, respiration, hand warmers). An endothermic reaction takes energy in, so the temperature falls (thermal decomposition, citric acid + sodium hydrogencarbonate, photosynthesis, cold packs). A reaction profile shows reactants, products and the activation energy (the minimum energy needed to react). Breaking bonds takes energy in; making bonds gives energy out. ΔH = energy to break bonds − energy released making bonds; negative means exothermic.
The Periodic Table: Groups, Periods and Trends – The periodic table lists elements in order of atomic number (number of protons). Rows are periods; columns are groups. Elements in the same group have the same number of outer-shell electrons, so they react in similar ways. Mendeleev built an early table, left gaps for unknown elements and predicted their properties. Metals are on the left and bottom, non-metals on the right and top. Group 0 noble gases have full outer shells and are unreactive. Group 1 alkali metals get more reactive going down. Group 7 halogens get less reactive going down.
Metals and Non-metals: Properties and the Reactivity Series – Metals are usually shiny, hard, malleable, ductile and good conductors; non-metals are usually dull, brittle and poor conductors. Metals form basic oxides, react with water and dilute acids (giving hydrogen) and a more reactive metal pushes a less reactive one out of its salt solution. Listing metals from most to least reactive gives the reactivity series.
Earth as a System: Spheres and Energy – Earth is like one big machine with five parts: rock (geosphere), water (hydrosphere), ice (cryosphere), air (atmosphere) and life (biosphere). The Sun powers it. Sunlight comes as many kinds of rays (the electromagnetic spectrum). The Sun heats Earth unevenly, and that makes winds, breezes and ocean currents. Water, carbon, nitrogen and oxygen move round and round between the spheres in cycles. Humans now change these cycles, so we must use Earth carefully.

7. Physics: Energy

Calculation of fuel uses and costs · Energy changes and transfers · Changes in systems

Electric Power and Electrical Energy – Electric power is the rate of using electrical energy: P = VI = I²R = V²/R, in watts. Energy used = power × time. At home energy is measured in kilowatt-hours: 1 kWh = 1 unit = 3.6 × 10⁶ J. Bill = units × rate.
Energy Stores and Transfers – Energy is what makes things change. It is kept in stores (chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear) and moves between them by four pathways: a force doing work, an electric current, heating and radiation (light, sound). Energy is measured in joules (J). It is never made or destroyed; it only moves. Some always spreads out as heat, so no machine is 100% efficient.
Work, Energy and Power – Work is done when a force moves an object: W = F × s, measured in joules (J). Energy is the ability to do work. A moving body has kinetic energy ½mv²; a raised body has potential energy mgh. Energy is never made or destroyed, only changed from one form to another. Power is how fast work is done: P = W ÷ t, in watts. Simple machines like levers and pulleys let a small effort move a big load.

8. Physics: Motion and forces

Describing motion · Forces · Pressure in fluids · Balanced forces · Forces and motion

Motion: Distance, Speed, Velocity, Acceleration and Graphs – An object is in motion when its position changes with time. Distance is the full path length (a scalar); displacement is the straight gap from start to finish with a direction (a vector). Speed = distance ÷ time; velocity = displacement ÷ time. Acceleration = change in velocity ÷ time. The slope of an s–t graph gives velocity, the slope of a v–t graph gives acceleration, and the area under a v–t graph gives the distance. For uniform acceleration: v = u + at, s = ut + ½at², v² = u² + 2as.
Forces: Pushes and Pulls – A force is a push or a pull between two objects. It is measured in newtons (N). Contact forces need touching (push, friction, normal force, tension, buoyancy); non-contact forces act at a distance (gravity, magnetism, electric). A force is drawn as an arrow: start = point of application, direction, length = size. Forces can change an object's speed, direction or shape. If forces balance, a still object stays still (equilibrium). Forces always come in pairs: if A pushes B, B pushes A back equally (Newton's third law).
Pressure in Fluids and Pascal's Law – A fluid (liquid or gas) pushes on every surface it touches. Pressure is this normal force per area, P = F/A. Because of gravity, the fluid above a point has weight, so pressure grows with depth: P = P₀ + ρgh. Points at the same depth in a still liquid have the same pressure, whatever the vessel's shape. Pascal's law says an extra pressure applied to an enclosed fluid reaches every point equally. The hydraulic lift and brakes use this: a small force on a small piston becomes a big force on a big piston, F = f × A/a.
Force and Laws of Motion – A force is a push or a pull. Balanced forces (net force zero) do not change motion; an unbalanced force changes speed or direction. Friction opposes sliding. First law: a body keeps its state of rest or uniform motion unless an unbalanced force acts (inertia; heavier bodies have more inertia). Momentum p = mv. Second law: F = ma (rate of change of momentum), 1 N = 1 kg m/s². Third law: forces come in equal and opposite pairs acting on two different bodies. For a system with no outside force, internal forces cancel and total momentum is conserved.

9. Physics: Waves

Observed waves · Sound waves · Energy and waves · Light waves

Sound – Sound is made by vibrating objects. It travels through a medium (air, water, solids) as a longitudinal wave: particles move back and forth, making crowded parts (compressions) and spread-out parts (rarefactions). Frequency (Hz) sets the pitch, amplitude sets the loudness, and speed v = f × λ. Sound cannot travel in vacuum. Humans hear 20 Hz to 20,000 Hz; below is infrasound, above is ultrasound. Reflected sound gives echoes, used and controlled in buildings.
Light: Reflected, Absorbed or Transmitted – Light travels in straight lines at about 3 × 10⁸ m/s and needs no material to travel through. When it meets an object it can be reflected (bounce back), absorbed (taken in, warming the object) or transmitted (pass through). On a smooth surface the angle of incidence equals the angle of reflection. When light enters glass or water it slows and bends (refraction). A prism splits white light into a spectrum, and an object's colour is the colour it reflects.

10. Physics: Electricity and electromagnetism

Current electricity · Static electricity · Magnetism

Electric Current, Potential Difference and Electric Circuits – Electric current is the rate of flow of charge, I = Q/t, measured in amperes with an ammeter joined in series. Potential difference is the work done to move a unit charge between two points, V = W/Q, measured in volts with a voltmeter joined in parallel. Charge flows only in a closed circuit.
Static Electricity – Rubbing two different materials moves electrons from one to the other. The one that gains electrons becomes negative; the one that loses them becomes positive. Charge is never made or destroyed, only moved. Like charges repel and unlike charges attract. A charged object can pull a neutral one by induction. Earthing lets extra charge flow safely away.
Magnetic Effect of Electric Current – A wire carrying electric current makes a magnetic field around itself. The field forms circles around a straight wire, becomes nearly straight at the centre of a loop, and is uniform inside a solenoid, which then acts like a bar magnet.

11. Physics: Matter

Physical changes · Particle model · Energy in matter

Properties of Matter – Matter is anything that has mass and takes up space. Some properties, like mass and volume, depend on how much you have. Others, called characteristic properties, are the same for any amount of a pure substance and help identify it: density (mass ÷ volume), melting point, boiling point and solubility. In a physical change (melting, boiling, dissolving) no new substance forms and the total mass stays the same. In a chemical change a new substance forms. Particles are close in solids and liquids and far apart in gases, which is why gases have very low density; moving particles also explain diffusion and Brownian motion.
The Particle Model of Matter – All matter is made of tiny particles that are always moving. In a solid they are close and only vibrate; in a liquid they are close but slide past each other; in a gas they are far apart and move fast in all directions. Heating gives particles more energy: either they move faster (temperature rises) or the forces between them are broken (the state changes while the temperature stays the same). Gas pressure comes from particles hitting the walls.
Internal Energy – Everything is made of tiny particles. They move (kinetic energy) and are held by forces between them (potential energy). The total of all these energies is the internal energy U. Heating a substance raises its internal energy: either the particles move faster (temperature rises, Q = mcΔT) or bonds are broken (state changes at constant temperature, Q = mL). Doing work on it, like rubbing or squashing, also raises U.

12. Physics: Space physics

Space physics

The Solar System – The Solar System is the Sun and everything its gravity holds: 8 planets, their moons, dwarf planets, asteroids, comets and dust. The inner four planets (Mercury, Venus, Earth, Mars) are small and rocky. After the asteroid belt come the giants: gas giants Jupiter and Saturn, ice giants Uranus and Neptune. Gravity pulls planets towards the Sun while they move sideways, so they travel in orbits; closer planets move faster and have shorter years. It all formed about 4.6 billion years ago from a spinning cloud of gas and dust.