How Do Substances Like CO2 and Water Move In and Out of the Cell?

Substances like carbon dioxide (CO₂) and water move in and out of the cell through simple processes such as diffusion, osmosis, and active transport depending on the type of substance. Cells are surrounded by a thin covering called the cell membrane. This membrane controls what goes in and out of the cell. It is called selectively permeable, meaning it allows only some substances to pass through easily while blocking others.

Ways Substances Move

• Diffusion: CO₂, oxygen, and other small molecules move from a region of high concentration to low concentration without using energy. For example, CO₂ moves out of the cell by diffusion since its concentration is higher inside the cell after respiration.
• Osmosis: This is the movement of water molecules from a region of high water concentration to low water concentration through a semi-permeable membrane.
• Active Transport: Some molecules move against the concentration gradient (from low to high concentration) using energy in the form of ATP.

Examples

• CO₂ produced in respiration diffuses out of the cell into the bloodstream.
• Water enters plant root cells by osmosis from the soil.
• Glucose and minerals may require active transport.