OSMOSIS AND DIFFUSION

In order for cells to survive and function properly, they must take in nutrients and get rid of wastes.

DIFFUSION Things that a cell needs, including food and oxygen, must be able to move into the cell.

This movement happens in two ways: ACTIVE TRANSPORT PASSIVE TRANSPORT

In active transport, the cell must use energy that it has obtained from food to move materials through the cell membrane. Ex. A fish swimming upstream.

In passive transport, materials are transported across the cell membrane without the expense of energy. Ex. A fish swimming downstream.

The main method by which materials move across the cell membrane is called DIFFUSION.

Diffusion is a form of passive transport, since materials diffuse without requiring the cell to expend energy.

How crowded together the particles of these materials are in a liquid is described as concentration. Perfume, coffee, poots

During diffusion, such particles move from an area where they are more concentrated to an area where they are less concentrated.

When the concentration is the same inside and outside of the cell, the system is said to have reached equilibrium.

Diffusion occurs when a cell and its surroundings are not at equilibrium. However, even after equilibrium is reached, particles continue to enter and leave the cell.

BEFORE DIFFUSION There is a higher concentration of particles outside the cell than inside the cell.

DURING DIFFUSION Particles move into the cell.

AFTER DIFFUSION The concentration of particles is the same outside and inside the cell.

Not all materials can pass through cell membranes. A membrane that allows substances to pass through it is said to be permeable.

Most cell membranes allow only certain substances to pass through them and are called selectively permeable.

The diffusion of water particles through a selectively permeable membrane is known as osmosis.

Water particles move in or out of a cell by osmosis to an area of lower concentration in order to reach equilibrium.