The Cell Membrane The Plasma Membrane Doublelayered membrane

The Cell Membrane

The Plasma Membrane • Double-layered membrane • (Phospholipid Bilayer) • Flexible boundary between cell and environment. • Allows nutrients to enter cell and chemical wastes to leave. • Maintains cell homeostasis by maintaining a balance in the cells environment. Hydrophilic Headwater loving Hydrophobic Tailwater fearing

Maintaining Homeostasis The plasma membrane is selectively permeable. ◦ Allows some molecules to pass through while keeping others out. Small molecules easily pass through, while large molecules cannot. ◦ Ex: Proteins and Starch cannot pass until they are digested. *Like a window screen! Cell Membrane Transport https: //www. youtube. com/watch? v=prf. MUwjobo 8

Fluid Mosaic Model The currently accepted model to describe the plasma membrane. 1. Phospholipids move within the membrane and slide past each other. 2. Transport proteins move molecules across the membrane into or out of the cell. 3. Receptor proteins are along the top of the membrane and create a mosaic, or pattern, on the membrane surface.

Proteins in the Plasma Membrane Transport proteins Receptor proteins Cell Membrane Fluid Mosaic Model https: //www. youtube. com/watch? v=Qqsf_UJcf. Bc

Barriers Oil and Water Experiment

Cellular Transport

How do molecules get into and out of the cell? Passive Transport - Molecules move freely back and forth across the cell membrane. Active Transport - Energy (ATP) is needed to move molecules across the cell membrane.

Passive Transport (Diffusion) NO ENERGY NEEDED Molecules move from high concentration low concentration. End Result: Molecules are evenly distributed on both sides of the membrane. (EQUILIBRIUM) The difference in concentration between two areas is called the concentration gradient.

Simple Diffusion Requires NO energy from the cell

Simple Diffusion Practice Down a concentration gradient. High Concentration Low Concentration

Simple Diffusion Practice High Concentration Low Concentration

Facilitated Diffusion by Transport Proteins Channel Proteins – Channel that helps substances move through the plasma membrane. NO ENERGY NEEDED

Facilitated Diffusion

Facilitated Diffusion by Transport Proteins Carrier Proteins. Transport protein that changes shape. ◦ Ex: Sodium-Potassium (Na-K) Pump NO ENERGY NEEDED

Osmosis - Diffusion of water across a selectively permeable membrane. Note: This is still diffusion! High Concentration Low Concentration

Osmosis Regulating the water flow through the plasma membrane is needed to maintaining homeostasis.

Types of Solutions Hypotonic Isotonic Hypertonic

Cells in an Isotonic Solution 1. Same amount of dissolved molecules outside and inside. 2. Same amount of water outside and inside. 3. Cell is at EQUILIBRIUM

Cells in an Hypotonic Solution 1. More dissolved molecules inside the cell. 2. Water moves into the cell. 3. The cell swells.

Cells in an Hypertonic Solution 1. More dissolved molecules outside the cell. 2. Water flows out of the cell. 3. Cells shrivel.

Active Transport Energy (ATP) NEEDED Molecules move from low concentration to high concentration. Molecules move against the concentration gradient. Carrier proteins in the cell membrane help in the transport of materials.

Active Transport Animation

Large Particles Transporting (Bulk Transport) Endocytosis: Large particles enter the cell. Particles are engulfed and enclosed by the cell’s plasma membrane. Exocytosis: Large particles exit the cell. ◦ To remove wastes.

Endocytosis

Exocytosis

Cell Membrane Transport Review Type of Transport Protein Used Direction of Movement Requires Energy Input From Cell? Classification of Transport Simple Diffusion No With concentration gradient No Passive Facilitated Diffusion Yes – channel proteins or carrier proteins With concentration gradient No Passive Yes – carrier proteins Against concentration gradient Yes Active Transport

Cell Membrane Transport Review Cell Membrane Transport http: //www. youtube. com/watch? v=kfy 92 hda. AH 0

Osmosis Example 1 If you add sugar to water, the water becomes sweeter as you add more sugar. If a strong sugar solution and a weak sugar solution are placed in direct contact, water molecules diffuse in one direction and sugar molecules diffuse in the other direction until all molecules are evenly distributed. What direction do you think the molecules moved in? ◦ High Concentration -> Low Concentration? ◦ Low Concentration -> High Concentration?

Osmosis Example 2 If 2 solutions are separated by a selectively permeable membrane that allows only water to diffuse across it, water flows to the side of the membrane where the water concentration is lower.