1. Chapter 1 Cell Structure and Function Section 1 The 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.