All living organisms are made of cells. Animal cells have a nucleus, cell membrane, cytoplasm, and mitochondria. Plant cells also have a cell wall (cellulose), chloroplasts, and a large permanent vacuole.

Photosynthesis converts light energy into chemical energy (glucose). It occurs in the chloroplasts of plant cells.

Sexual reproduction involves the fusion of male and female gametes (sex cells), producing offspring with variation. Asexual reproduction produces genetically identical offspring (clones).

A food chain shows the transfer of energy between organisms. Energy flows from producers (plants) → primary consumers → secondary consumers → tertiary consumers. Only about 10% of energy is transferred to the next level.

An element contains only one type of atom. A compound contains two or more different elements chemically bonded together. A mixture contains two or more substances not chemically combined.

Matter exists in three states: solid, liquid, and gas. Particle theory explains properties based on how particles are arranged and how much energy they have.

The pH scale runs from 0 to 14. pH below 7 = acid; pH 7 = neutral; pH above 7 = alkali. Neutralisation: acid + base → salt + water.

A force is a push or pull measured in Newtons (N). Forces can change the speed, direction, or shape of an object. When forces are balanced, there is no change in motion (Newton's 1st Law).

Energy cannot be created or destroyed, only transferred or transformed (Law of Conservation of Energy). Useful energy is the output we want; wasted energy usually becomes heat.

Electric current is the flow of charge (electrons) around a circuit, measured in Amperes (A). Voltage (potential difference) is the "push" driving the current, measured in Volts (V). Resistance opposes current flow, measured in Ohms (Ω).