Chapter 1 Cell Structure and Function Section 1 The Cell In Its Environment

1. Chapter 1Cell Structure and FunctionSection 1The Cell In Its Environment

2. The Cell Membrane as Gatekeeper • The cell membrane is selectively permeable, which means some substances can pass through it while others cannot. • Usually allows oxygen, water, and carbon dioxide • Substances that can move into and out of a cell do so by one of three methods: • Diffusion, osmosis, or active transport

3. Diffusion – Molecules in Motion • Diffusion is the process by which molecules tend to move from an area of higher concentration/density to an area of lower concentration/density. • Diffusion is the main method of moving molecules into and out of cells

4. What Causes Diffusion? • Molecules are always moving. • Over time, the more molecules in an area (higher concentration) then the more they will bump into each other and spread out evenly in the area (lower concentration).

5. Osmosis – The Diffusion of Water Molecules • Osmosis is the diffusion of water molecules through a selectively permeable membrane. • Too much water or too little water can cause serious consequences for a cell, so osmosis has to happen in moderation.

6. Passive Transport • Osmosis and diffusion do not require any energy to occur because molecules naturally move from high to low, so they are easy to complete. • The movement of materials through a cell membrane without using energy is called passive transport.

7. Active Transport • If a cell needs to have materials move from low to high (unnatural), they would require energy for this “uphill battle.” • Active transport is the movement of materials through a cell membrane using energy.

8. Types of Active Transport • One method of transporting materials is when transport proteins “pick up” molecules outside of the cell and carry them in using energy.

9. Types of Active Transport • Another method of active transport is when a cell membrane surrounds, or engulfs, a particle complete and then pinches off to form a vacuole within the cell.

10. Why Are Cells So Small? • As a cell’s size increases, more of its cytoplasm is located farther from the cell membrane, slowing every process down in order for materials to move from the membrane to a part of the cell. • If it grows too large, it won’t be able to function properly. At this point, it divides into 2 new cells.