LOWKEY SMART

Write one line of working for every step: it is how you catch your own slips.

All living things are made of cells, the smallest units of life. Most cells are too small to see, so we use a light microscope to magnify them. Animal and plant cells both have: a nucleus, which contains the genetic material (DNA) and controls the cell; a cell membrane, which controls what enters and leaves the cell; cytoplasm, a jelly where most chemical reactions happen; and mitochondria, where respiration releases energy. Plant cells also have a cell wall made of cellulose, which strengthens the cell; chloroplasts, which contain green chlorophyll and are where photosynthesis happens; and a permanent vacuole filled with cell sap, which helps keep the cell firm. Animal cells do not have a cell wall, chloroplasts or a permanent vacuole.

Adding a prefix to the front of a word can change its meaning without changing the spelling of the root word. Before most words, add in- to make the opposite meaning (invisible). Before words starting with m or p, use im- (impossible, immature). Before l, use il- (illegal), and before r, use ir- (irregular). Always keep every letter of the root word when you add the prefix.

Many cells are specialised: their shape and parts are suited to one job. A red blood cell has no nucleus, which leaves more room to carry oxygen. A sperm cell has a tail so it can swim to the egg. A nerve cell is long and thin so it can carry electrical signals around the body. A root hair cell has a long, thin extension that gives it a large surface area for absorbing water from the soil. Living things made of many cells are organised in levels: similar cells working together form a tissue, different tissues working together form an organ, and organs working together form an organ system. For example, the heart is an organ in the circulatory system. The full order is cell, tissue, organ, organ system, organism.

A sentence can contain a main clause, which makes sense alone, and a subordinate clause, which cannot stand alone. A subordinating conjunction such as because, although or when joins the two. In 'She stayed inside because it was raining', 'because it was raining' is the subordinate clause.

All matter is made of tiny particles. In a solid, the particles are touching, in a regular pattern, and only vibrate in fixed positions, so a solid has a fixed shape and cannot be compressed (squashed). In a liquid, the particles are touching but arranged randomly and can move past each other, so a liquid flows, takes the shape of its container and cannot be compressed. In a gas, the particles are far apart and move quickly in random directions, so a gas can be compressed and spreads out to fill its container. Diffusion is when particles spread out from where there are lots of them (a high concentration) to where there are fewer (a low concentration). Diffusion happens in liquids and gases, and it is faster when they are hotter. Gas pressure is caused by gas particles hitting the walls of their container.

The workshop at the end of Mill Lane had stood locked for eleven years. Dust coated every shelf, and the narrow window let in only a grey, reluctant light. Cobwebs stretched between the shelves like fine grey thread, and the whole room smelled faintly of oil and sawdust. When the new owner finally turned the stiff key, the door groaned open to reveal rows of tools untouched since the last apprentice left. Old blueprints, curling at the edges, were pinned to the far wall, their ink faded almost to nothing. A leather apron still hung on its hook, stiff with age. Beneath a workbench, wrapped in oilcloth, lay a set of brass instruments that nobody could name. The owner lifted one carefully, turning it towards the window. Its dial trembled, then settled, as though it remembered how to work. Somewhere under the dust, this small, forgotten room still held a purpose, waiting patiently for someone curious enough to find it. By the time evening came, the owner had swept the floor and opened the window wide, letting fresh air chase away the years of silence.

Changing state is a physical change: no new substance is made, and it can be reversed. Melting is solid to liquid, and freezing is liquid to solid. Evaporation and boiling are liquid to gas, and condensation is gas to liquid. Sublimation is when a solid turns straight into a gas without melting first. A pure substance melts and boils at fixed temperatures: pure water melts at 0°C and boils at 100°C. When a substance is heated, its particles gain energy and move faster. Mass is conserved when a substance changes state, so 50 g of ice melts into 50 g of water.

An apostrophe shows that something belongs to someone. For one owner, add apostrophe s: the dog's lead. For a plural that already ends in s, add only an apostrophe: the dogs' leads. For a plural that does not end in s, add apostrophe s: the children's coats.

A force is a push or a pull. Forces are measured in newtons (N) using a newtonmeter. Contact forces act when objects touch, for example friction, air resistance and upthrust. Non-contact forces act at a distance, for example gravity, magnetic force and electrostatic force. We draw forces as arrows: the length of the arrow shows the size of the force, and the arrow points in its direction. If the forces on an object are balanced (equal and opposite), a still object stays still and a moving object keeps the same speed and direction. If the forces are unbalanced, the object speeds up, slows down or changes direction. The resultant force is the overall force: for two forces in opposite directions, subtract the smaller from the larger, and it acts in the direction of the larger one. Weight = mass × gravitational field strength, and on Earth the gravitational field strength is 10 N/kg.

Many English words are built from Greek and Latin roots. 'Tele' means far (telephone), 'graph' means write (autograph), 'scope' means see (telescope), 'phon' means sound (microphone), and 'bio' means life (biology). Knowing a root can help you guess the meaning of an unfamiliar word.

Speed tells you how far something travels in a certain time: speed = distance ÷ time. If distance is in metres (m) and time is in seconds (s), speed is in metres per second (m/s). If distance is in kilometres (km) and time is in hours (h), speed is in km/h. You can rearrange the formula: distance = speed × time, and time = distance ÷ speed. The formula gives the average speed for a journey, because the real speed usually changes along the way. On a distance-time graph, a horizontal (flat) line means the object is stationary (not moving), and a steeper line means a faster speed.

Tired of sitting in traffic? Meet the new community bike scheme transforming how this town moves. For just two pounds an hour, you can unlock a bright yellow bicycle from any of the thirty docking stations and pedal straight past the queues. Every bike is checked each morning, so brakes, lights and tyres are always reliable. Cycling to work doesn't only save money, it clears your head before a busy day and gets your heart pumping without a single gym fee. Local families love it too: children under twelve ride free with an adult, making weekend trips to the park cheaper and far more fun. Since the scheme launched, the number of cars parked outside the station has dropped by a third, and the air along the high street feels noticeably cleaner. Don't just take our word for it, try the scheme this week and feel the difference for yourself. Stations open at six every morning, so there is no excuse to sit in traffic tomorrow.