Correct page 13  Go to the class website (westada.org/domain/2368)  Go to the assignments tab and open the assignment “ KEY ”  Correct any wrong answers on your paper—Answers will vary for #4, 7, 9-14  When finished, read page 80-81

TRANSPORT IN CELLS

Cells must let in needed materials like oxygen and food molecules. They also must remove waste products such as carbon dioxide and water. The molecules must move through the cell membrane in order to get in or out. The cell membrane is selectively permeable.

This means that some substances can pass through the membrane while others cannot. An example of something that is selectively permeable is a window screen. The screen allows fresh air in, while keeping bugs out. When molecules move in and out of cells it is called transport.

One type of transport is diffusion. Diffusion is the main method by which molecules move across the cell membrane. Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. What is concentration?

Diffusion happens because molecules are always moving. Molecules bounce off one another and spread each other out. Draw a picture of diffusion below.

Osmosis is a specific type of diffusion. Because water is so important to living things, the movement of water gets a special name…OSMOSIS! Osmosis is the movement of water molecules from an area of higher concentration to an area of lower concentration. Sound familiar? Osmosis and diffusion are the same, except osmosis is the movement of water specifically.

Both osmosis and diffusion do not require energy from the cell. They are called passive transport (passive=no energy required). Sometimes a cell needs to move substances the opposite way of diffusion and osmosis. To do this, the cell must use energy. This is called active transport (active=energy required).

Active transport is the movement of molecules from an area of lower concentration to an area of higher concentration. Some substances that are carried into and out of cells this way are calcium, potassium, and sodium. Active transport can happen two different ways: engulfing and transport proteins.

Engulfing means the cell surrounds the substance completely and then forms a vacuole to take up the substance. Transport proteins are found in the cell membrane. Substances can move through the proteins if the cell needs them. Complete the Venn diagram below to show the relationship between passive and active transport. Use the word bank provided.