Diffusion Model
Transport is essential for life because cells must import and export materials in order to maintain life-sustaining activities.Two types of transport move materials across the plasma membrane: passive transport and active transport.
Passive transport does not require the use of metabolic energy and materials flow down the concentration gradient.
Active transport uses energy (in the form of ATP) and materials flow against the concentration gradient.

The movement of substances with the concentration gradient.For example, when someone wears cologne or perfume, the aromatic molecules are initially concentrated on that person's skin. As the constant, random motion of the perfume molecules spreads them throughout the room, the aroma disperses. Even when the molecules rach equilibrium, spread evenly in the room, they will continue to move randomly.

Type od diffusion.The movement of water through a semipermeable membrane.Water moves from an area of higher concentration to an area of lower concentration, that is, toward the area where there is more solute, and thus less water. The area of less solute is caleed the hypotonic solution, and the area of more solute is called the hypertonic solution. If a semipermeable membrane separates the hypotonic solution from the hypertonic solution, water wil move across the membrane from the hypotonic to the hypertonic solution. No metabolic energy is involved.

Facilitated Diffusion:(passive)
The diffusion of a substnce across a membrane. It is "facilitated" because a transport protein in the membrane enhances the transport of the substance across the membrane.

Active Transport:
Uses energy (in the form of ATP) to make materials flow against the concentration gradient.