The Cell Membrane or Plasma Membrane

Homeostasis – Maintaining a Balance The cell/plasma membrane is selectively permeable – it will allow some things to pass through, while blocking other things. Water, nutrients in Wastes (CO2) out

Structure of the Plasma Membrane Lipid bilayer – two sheets of lipids (phospholipids). Found around the cell, the nucleus, vacuoles, mitochondria, and chloroplasts. Embedded with proteins and strengthened with cholesterol molecules.

What’s a Phospholipid? It’s a pair of fatty acid chains and a phosphate group attached to a glycerol backbone. –Polar (water-soluble) heads face out and the nonpolar fatty acids hang inside.

Membrane Proteins 1. Determine what particles can pass through the membrane. Act as markers that are recognize chemicals and molecules outside the cell ( bouncer at the door of a club)

Cellular Transport Diffusion – movement of particles from an area of high concentration to an area of low concentration. –Continues until an equilibrium is reached (no gradient). –Dynamic equilibrium – particles move freely and are evenly distributed.

2 Types of Cellular Transport 1) Passive transport 2) Active Transport

Passive transport – no energy is needed to move particles. 1) Diffusion 2) Facilitated diffusion – embedded proteins act as tunnels allowing particles to “fall” through.

Active transport – energy is needed to move particles. Carrier proteins – embedded proteins change shape to open and close passages across the membrane. 1. Endocytosis – taking something into the cell. 2. Exocytosis – expelling something from the cell.

Osmosis Diffusion of water across a selectively permeable membrane. Occurs until water is balanced on both sides of the membrane.

A Solution is -A homogeneous mixture of two or more substances (can be solids, liquids, or gases) A Solute is - A substance dissolved in another substance. A solvent is -A substance in which another substance is dissolved in.

Example Salt that is dissolved in water Solution – salt water Solute – salt Solvent - water

Cell Concentrations Hypertonic solutions – more dissolved solute. Water will leave the cell. The Cell shrinks Hypotonic solutions – less dissolved solute. Water enters the cell and the cell will swell. Isotonic solutions – the same dissolved solute. Cell is unchanged

Overcoming Osmosis Contractile vacuoles – expel excess water from bacterial cells that live in water. Turgor pressure – water pressure in a plant cell. Loss of turgor pressure causes wilting (plasmolysis).

Diffusion Demonstration Data table Temperature of water Time for food coloring to diffuse Cold water Hot water

Diffusion Demo Questions 1. What is Diffusion 2. Explain why diffusion is passive or active transport. 3. Explain what equilibrium means? (use food coloring to explain this) 4. Which beaker of water did the food coloring diffuse the fastest through and why??