DIFFUSION Food water and other substances are made

DIFFUSION • Food, water, and other substances are made of different kinds of particles, such as molecules and ions. Particles are always moving, like dancers on a crowded dance floor.

• You can tell how particles will tend to move if you know how crowded they are. • Concentration refers to how crowded particles are. A juice concentrate is a very strong form of juice. It has many more juice particles than regular juice does.

When you mix the • In a concentrate, the concentrate with juice particles are very water, the juice crowded. particles spread out in the water. • They tend to move away from places where they are concentrated Thus, the particles become less concentrated.

Particles will continue to move from areas of high concentration to areas of low concentration until they reach equilibrium. • This process is called diffusion.

• Watch the demonstration with food coloring in water, then answer the following: Explain why the ink spreads out in the water. Use the words concentration and diffusion in your answer. The dye is very concentrated when it enters the water. The dye diffuses through the water to lower concentrated areas until equilibrium is

Diffusion Through a Cell Membrane • Cells also need food and water to live • Substances move into and out of the cell through its cell membrane • A cell membrane is like the cell’s skin.

• Just as ink diffuses in water, some substances can diffuse into and out of a cell through its cell membrane. • Particles of some substances can diffuse through proteins in the cell membrane. (facilitated diffusion)

• Diffusion is an important process that allows a cell to get substances it needs. • Complete the Vocabulary Review on your note sheet.

Reviewing Vocabulary 1. Some substances move into and out of cells by diffusion. 2. The word concentration refers to how crowded particles are. 3. Some particles diffuse into and out of cells through the cell membrane 4. Particles tend to move toward places where they have a low concentration. 5. Particles tend to move away from places where they have a high concentration 6. Give one example of diffusion in your home. cooking, sugar in tea, ‘cut the cheese’

OSMOSIS • Most of your body is made of water. • This water can move into and out of your cells • Water can enter and leave your cells by diffusion. When water DIFFUSES through a CELL MEMBRANE, the process is called OSMOSIS.

In the picture, water is diffusing through a cell membrane. Water particles Outside of Cell Membrane Inside of Cell Why is the water moving INTO the cell in the picture?

• Because water has a lower concentration inside the cell than outside the cell. • Water moves into the cell by OSMOSIS.

• What happens to the raisin after sitting in the water for a while? It becomes larger Why does this happen?

• Water molecules have a lower concentration inside the raisin. Outside the raisin, water molecules are crowded. Water molecules diffuse into the raisin by osmosis.

PASSIVE TRANSPORT • Cells do not use energy to move particles by osmosis or diffusion • Particles move freely into and out of cells. This kind of movement is called PASSIVE TRANSPORT Complete the Vocabulary Review. Diffusion, Osmosis and facillitated diffusion are all types of passive transport

Vocabulary Review 1. One example of osmosis is water diffusing into a raisin. 2. Cells do not work to move molecules by passive transport. 3. Two forms of passive transport are osmosis and diffusion. 4. In diffusion and osmosis, particles move by themselves. 5. Water molecules tend to move to places where they have a low concentration. 6. Give one way that osmosis is similar to diffusion. Both move from high to low concentration.

Active vs. Passive Transport • Passive Transport – does not require energy. Particles move from high to low concentration. • Active Transport – does require energy because molecules are moving from low to high concentration

Endocytosis • Some things the cells needs are too large to pass through the cell membrane. • The cell membrane can surround a large particle located outside the cell. The membrane forms a sac around the particle. Then the sac opens inside the cell.

Large particle leave the cell in sacs too. Inside a cell, a sac forms around large waste particles. • The sac moves to the membrane and then opens outside the cell. • Waste particle move OUTSIDE the cell. • This process of moving large particles OUT of the membrane is called EXOCYTOSIS.

Cells Maintain Balance • The cell controls its food and water content by moving ions, molecules, and larger particles into or out of itself. This is how the cell maintains homeostasis. • Homeostasis Simulation http: //trc. ucdavis. edu/biosci 10 v/bis 10 v/media/c h 17/hot_guy. html • Complete the Vocabulary Review

Vocabulary Review 1. Cells use energy to move molecules by active transport. 2. Diffusion and osmosis are two kinds of passive transport. 3. Some molecules are too large to pass through the cell membrane. 4. Cells take in large molecules by endocytosis. 5. Cells must maintain a balance, called homeostasis.