Transport Across Cell Membranes

This page provides a comprehensive overview of the various mechanisms of transport across cell membranes, focusing on passive and active transport across cell membranes. It illustrates the key differences between diffusion, osmosis, and active transport, along with their effects on plant and animal cells.

Definition: Diffusion is the movement of molecules down a concentration gradient from high to low concentration, requiring no energy input.

Example: Carbon dioxide diffuses out of cells from a higher concentration inside the cell to a lower concentration outside the cell.

The page explains that glucose and oxygen diffuse into cells from a higher concentration outside to a lower concentration inside, demonstrating the principle of passive transport.

Definition: Active transport involves the movement of molecules and ions from a lower concentration to a higher concentration, requiring energy input.

The document provides detailed illustrations of how osmosis affects both plant and animal cells:

Example: Animal cells placed in a solution with higher water concentration compared to their cytoplasm will gain water, swell up, and potentially burst.

Vocabulary: Turgid refers to the swollen state of a plant cell when it's full of water.

Vocabulary: Plasmolysed describes the state of a plant cell when it has lost water and the cell membrane has pulled away from the cell wall.

The page also describes the structure of the cell membrane:

Highlight: The cell membrane is composed of a phospholipid bilayer and is selectively permeable, allowing only small and soluble molecules to cross.

Definition: Osmosis is defined as the movement of water molecules from a higher water concentration to a lower water concentration through a selectively permeable membrane.

This comprehensive overview provides essential information for understanding the difference between passive and active transport across cell membranes, making it an invaluable resource for students studying osmosis and diffusion in cell membrane transport biology.