Lecture on Specialized Exchange Surfaces

Introduction

Specialized exchange surfaces: Parts of an organism for exchanging substances with the environment.
Examples include alveoli and villi in humans, and root hair cells and leaves in plants.

Alveoli:
- Located in lungs, at ends of bronchioles.
- Function: Exchange oxygen and carbon dioxide between air and blood.
Villi:
- Finger-like structures in the lining of the small intestine.
- Function: Absorb nutrients like glucose and amino acids.

Large Surface Area:
- Allows high rate of diffusion due to more molecules diffusing simultaneously.
- Examples: Numerous alveoli, thin villi, large flat leaves, and long thin projections of root hair cells.
Thin Surfaces:
- Short diffusion distance for substances, allowing quicker diffusion.
- Example: Water in root hair cells diffuses across a thin cell wall and membrane.
Permeability:
- Surfaces allow needed substances to diffuse across easily.
Good Blood Supply (in animals):
- Maintains concentration gradient; essential for continual diffusion.
- Example: Blood supply to villi ensures glucose is taken away quickly, maintaining concentration gradient.
Good Supply of External Medium:
- Ensures a constant concentration gradient with the external environment.
- Examples: Air supply in alveoli (oxygen concentration) and food in villi.

Key features: large surface area, thin surfaces, permeability, good blood supply, good external medium supply.

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