Biology: Diffusion and Surface Area

Diffusion and Surface Area

• Diffusion occurs down a concentration gradient, with gas molecules moving from high to low concentration.
• It is a passive process, requiring no energy, and follows Fick's Law.
• Fick's Law states that the flux (J) is equal to the diffusion coefficient (D) multiplied by the concentration gradient (dφ/dx) across the membrane.

Factors Affecting Diffusion

• The diffusion coefficient (D) varies depending on the gas molecule size and membrane properties (viscosity, temperature, and hydrophobicity).
• The concentration gradient (dφ/dx) affects the rate of diffusion, with higher gradients resulting in faster diffusion.
• The thickness of the gas-exchanging surface also affects the rate of diffusion, with thinner surfaces allowing for faster diffusion.

Importance of Surface Area

• An increase in the available surface area increases the amount of gas that can diffuse in a given time.
• The amount of gas diffusing per unit time (dq/dt) is the product of the flux (J) and the surface area (A).
• Single-celled organisms have a high surface area to volume ratio, making their cell membrane adequate for gas exchange needs.
• As an organism increases in size, its surface area becomes inadequate for its gas-exchange needs, requiring specialized gas exchange surfaces.

Learn about the process of diffusion, the exchange of gases, and how it occurs down a concentration gradient. Understand the concept of passive transport and Fick's Law.