1. The Cell in Its Environment
Lesson 4

2. Something Good in the Air
You’re in your bedroom studying, and you smell something good. Someone is cooking Dinner! How did the smell travel from the kitchen to you nose? During cooking, molecules from soup and many other foods diffuse. These molecules are carried by air currents. Your nose sniffs in the molecules and sends a message to your brain. Even if only one molecule in ten million carries the odor, your nose will send a “smell” message! Amazingly, your brain can identify about ten thousand different smells.

3. How Do Materials Move Into & Out of Cells?
The cell membrane controls how materials move into or out of a cell.
Cells MUST let certain materials enter and leave the cell in order to live and function.
Oxygen (O), Water (H2O) and Particles of Food move into the cell.
Carbon dioxide (CO2) and other waste materials move out of the cell.

4. Importance of the Cell Membrane
EVERY cell is surrounded by a cell membrane!!!
Cell membrane consists of:
-- Double layer of lipid molecules (organic compounds found in living things)
-- Proteins (some with chains of carbohydrates) can be found in the layer of lipid molecules.
These molecules play an important role in helping materials move through the cell’s membrane.

5. Importance of the ell Membrane
Each cell membrane is selectively permeable.
Selectively Permeable: Some substances can cross the cell membrane while other substances cannot.
Water and Oxygen pass easily back and forth across the cell’s selectively permeable membrane.
Substances that can move into and out of a cell do so by means of one of two processes:
Passive Transport
Active Transport
Does riding a bike down hill require energy?
What happens to energy when you have to pedal back up the hill?

6. Passive Transport
Moving materials across the cell membrane sometimes requires the cell to use its own energy… other times the cell uses no energy.
Passive Transport: The movement of dissolved materials across a cell membrane WITHOUT using the cell’s energy.
**Reminder – Molecules are always moving**
Two forms of passive transport :
Diffusion
Osmosis

7. Passive Transport
Diffusion: The process by which molecules move from an area of higher concentration to an area of lower concentration. In other words… If molecules are crowded in one space (higher concentration) the molecules will move to a less crowded space (lower concentration). As particles move farther from a area of high concentration, they become spread over a greater area.

8. Passive Transport
Osmosis: The diffusion of water molecules across a selectively permeable membrane.
Cells cannot function properly without enough water.
Many cellular processes depend on Osmosis.

9. Active Transport
Molecules in cells must often move from a place of lower concentration to to a place of higher concentration. Cells MUST supply energy to do this work! (Just like pedaling a bike up hill) Active Transport: The movement of materials across a cell membrane using cellular energy.

10. Passive & Active Transport
Both diffusion and Osmosis are forms of passive transport… meaning both DO NOT use the cell’s energy.
Diffusion causes molecules to move from areas of ______________ concentration to areas of _____________ concentration.
Molecules move into and out of a cell by means of __________________ or _________________ transport.
What is different about the movement of molecules by passive transport and active transport?