A. Diffusion:
* Definition: The movement of particles from an area of high concentration to an area of low concentration. This movement is driven by the concentration gradient, essentially the difference in concentration between the two areas.
* Key Points:
* Does not require energy (passive transport).
* Happens naturally due to the random motion of particles.
* Examples:
* Perfume spreading in a room: The scent molecules diffuse from where they are concentrated (the bottle) to where they are less concentrated (the air).
* Oxygen moving from the lungs into the blood: Oxygen is more concentrated in the lungs and moves into the blood where it is less concentrated.
B. Osmosis:
* Definition: The diffusion of water molecules across a selectively permeable membrane from a region of high water concentration to a region of low water concentration.
* Key Points:
* A specialized form of diffusion focused on water movement.
* The membrane must be selectively permeable, meaning it allows some substances to pass through but not others.
* Examples:
* Water moving from a freshwater lake into a fish's cells: The concentration of water is higher in the lake, and the fish's cells have a lower water concentration, so water moves in.
* Water moving from the blood into the intestines to help digest food: The concentration of water in the blood is higher, and the intestinal contents have a lower water concentration, so water moves in to aid digestion.
C. Facilitated Diffusion:
* Definition: The movement of particles across a membrane with the help of membrane proteins. These proteins act as channels or carriers to facilitate the movement.
* Key Points:
* Still considered passive transport because it doesn't require the cell to expend energy.
* The proteins help speed up the process of diffusion.
* Examples:
* Glucose entering a red blood cell: Glucose uses a transport protein to cross the cell membrane.
* Certain ions moving across a membrane: Specific ion channels allow the passage of specific ions like sodium or potassium.
D. Active Transport:
* Definition: The movement of particles across a membrane against their concentration gradient, from an area of low concentration to an area of high concentration. This process requires energy, usually in the form of ATP.
* Key Points:
* The cell must expend energy to move particles against their natural tendency to move down the concentration gradient.
* Often involves specific transport proteins.
* Examples:
* Sodium-potassium pump: This pump moves sodium ions out of the cell and potassium ions into the cell, both against their concentration gradients. This is essential for nerve impulse transmission.
* Uptake of nutrients by cells: Cells actively transport nutrients, like amino acids, into themselves even when the concentration inside the cell is already high.
In summary:
| Transport Type | Description | Energy Required | Example |
|---|---|---|---|
| Diffusion | Movement from high to low concentration | No | Perfume spreading |
| Osmosis | Diffusion of water across a semi-permeable membrane | No | Water moving from lake to fish cell |
| Facilitated Diffusion | Diffusion aided by membrane proteins | No | Glucose entering a red blood cell |
| Active Transport | Movement from low to high concentration | Yes | Sodium-potassium pump |
