Transport Across Cell Membranes

This page focuses on the mechanisms of transport across cell membranes, explaining key concepts such as diffusion, active transport, and osmosis.

Diffusion is described as the passive movement of molecules from areas of high concentration to low concentration, requiring no energy. Active transport, in contrast, is explained as the movement of molecules against the concentration gradient, requiring energy and involving proteins in the cell membrane.

Definition: Osmosis is the diffusion of water molecules across a selectively permeable membrane from an area of high water concentration to an area of low water concentration.

The page details the molecules that can enter and exit cells through the membrane, such as oxygen and glucose entering, and carbon dioxide and urea exiting. It also explains that larger molecules like starch and proteins are too big to pass through membrane pores.

Example: Oxygen and glucose can enter cells through the membrane, while carbon dioxide and urea can exit. However, larger molecules like starch and proteins cannot pass through due to their size.

The effects of osmosis on plant and animal cells are described, introducing the concepts of turgid and plasmolysed cells. The page explains how plant cells can withstand water gain due to their cell walls, while animal cells may burst when they gain too much water.

Vocabulary: Turgid refers to a plant cell that has gained water and is swollen, while plasmolysed describes a plant cell that has lost water and has a shrunken cytoplasm.