The Cell in its Environment

1. The Cell in its Environment Lesson 4, Chapter 1

2. Diffusion • Diffusion is the main method by which small molecules move across the cell membrane. • A cell membrane is selectively permeable, which means that some substances can pass through the membrane while others cannot. • Cells like castles, must let things enter and leave. Let in oxygen and food molecules and let out waste products, which all pass through the cells membrane

3. Molecules are always moving, and as they move they bump in to each other. The more molecules in one area, the more collisions there will be. • Molecules move by diffusion from an area of higher concentration to an area of lower concentration.

4. Osmosis • Because cells cannot function properly without adequate water, many cellular processes depend on osmosis. • Osmosis is the diffusion of water molecules through a selectively permeable membrane

5. Active Transport • The movement of dissolved materials through a cell membrane without using cellular energy is called passive transport. • Active transport is the movement of materials through a cell membrane using cellular energy. • Active transport requires the cell to use its own energy, while passive transport does not.

6. Cells have several ways of moving materials through active transport. Transport Proteins Transport by engulfing