Key Stage 3 (KS3) Science – Cells Practice Test 2026 - Free KS3 Science Practice Questions and Study Guide

The primary function of the cell membrane is to control what enters and leaves the cell. This semi-permeable barrier is crucial for maintaining the internal environment of the cell, allowing it to carry out essential functions. The cell membrane is composed of a lipid bilayer with embedded proteins that facilitate the transport of substances. Through processes such as diffusion, osmosis, and active transport, the membrane regulates the movement of ions, nutrients, and waste products, ensuring that the cell can maintain homeostasis and respond to changes in its environment. This selective permeability is vital for the survival and proper functioning of cells, enabling them to communicate with each other and interact with their surroundings effectively.