Transport Mechanisms in Biology: Active vs. Passive

Current of the River: Represents different types of transport in biology.
- Downstream (with the current): Represents passive transport.
- Upstream (against the current): Represents active transport.

Definition: Movement of substances along a gradient without the use of energy.
- Concentration Gradient:
- Movement from high concentration to low concentration.
- Example: Molecules in a tube of water move from areas of high to low concentration, achieving equilibrium over time.
- Electrical Gradient:
- Movement along an electrical difference.
- Example: Positive particles are drawn towards negative particles while avoiding other positive ones, and vice versa.
- Energy Requirement: No energy is needed for passive transport; it happens naturally.

Definition: Movement of substances against a gradient, requiring energy.
- Direction: Moves from low concentration to high concentration or against an electrical gradient.
- Example: Sodium-Potassium Pump
- Cell Membrane Structure:
  - More potassium (K^+) ions inside the cell than outside.
  - More sodium (Na^+) ions outside the cell than inside.
- Passive Transport Example: Potassium ions can passively move inside the cell through a channel because the concentration is higher inside.
- Active Transport Example: Sodium ions are actively transported out of the cell using the sodium-potassium pump.
  - Process uses ATP (energy) to change the shape of the protein in the pump, allowing sodium to be pumped out against both concentration and electrical gradients.

Passive Transport: No energy required; occurs naturally based on gradients.
Active Transport: Requires energy (ATP) to move substances against gradients. It is essential for maintaining the necessary concentrations of ions in cells, such as sodium and potassium, for proper function.