Physics: motion and force
Speed is the distance travelled divided by the time taken. Velocity is speed in a particular direction. Acceleration is the change in velocity divided by time.
Newton's second law states that force equals mass times acceleration. So a heavier object needs more force to reach the same acceleration as a lighter one.
Chemistry: matter and reactions
All matter is made of atoms. Atoms join to form molecules. A chemical reaction rearranges atoms, but the total number of atoms stays the same, which is why equations must balance.
An acid releases hydrogen ions in water and a base releases hydroxide ions. When an acid and a base react, they neutralise each other to form salt and water.
Biology: the living cell
The cell is the basic unit of life. Plant cells have a rigid cell wall and green chloroplasts, while animal cells do not.
Photosynthesis is how plants make food: they take in carbon dioxide and water and, using energy from sunlight, produce glucose and release oxygen.