3.3 Cell Membrane Key Concept: The cell membrane is a barrier that separates a cell from the external environment. Michigan Standard: 2.5h- Explain the role of cell membranes as a highly selective barrier (diffusion, osmosis and active transport)

Cell membranes are composed of two phospholipid layers. A. Cell membrane is made up of phospholipids (phosphorous + fats)

1. a polar head and two non-polar tails (likes water) (dislikes water) 3.3 Cell Membrane 1. a polar head and two non-polar tails (likes water) (dislikes water) Draw this

Draw this on the left side of your paper 3.3 Cell Membrane Draw this on the left side of your paper This represents a very small portion of a cell membrane a cell

3.3 Cell Membrane Remember a cell membrane is a 3-D structure that completely surrounds a cell (kind of like the skin of an apple)

B. Other molecules are embedded within the “bi-layer” 3.3 Cell Membrane B. Other molecules are embedded within the “bi-layer” 1. Cholesterol- for strength 2. Proteins- for moving things in and out of the cell 3. Carbohydrates- for identification

C. The cell membrane has been described by a fluid mosaic model 1. “fluid”- pieces moves around (like a soap bubble) 2. “mosaic”- made of many pieces

D. The cell membrane has the property of selective permeability 1. allows some, but not all materials to move through it 2. semipermeable or selectively permeable mean the same thing example: waterproof clothing, a window screen

3.3 Cell Membrane SKIP THIS II. Chemical signals are transmitted across the cell membrane A. Receptors help cells communicate and also help to move moleculues 1. receptor- a protein that detects a signal molecule and performs an action in response 2. “lock and key” B. Receptors are usually very specific and only react to certain molecules SKIP THIS

3.4 Diffusion and Osmosis Key Concept: Materials move across membranes because of concentration differences. Michigan Standard: 2.5h- Explain the role of cell membranes as a highly selective barrier (diffusion, osmosis and active transport)

3.4 Diffusion and Osmosis Diffusion and Osmosis are types of passive transport. Passive transport- the movement of molecules across a cell membrane without energy input from the cell Diffusion- movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration

3.4 Diffusion and Osmosis C. Concentration- number of molecules of a substances in a given volume (space/ area) + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + High or Low? High High or Low? Low

3.4 Diffusion and Osmosis D. concentration gradient- difference in concentration of a substance from one location to another 1. molecules diffuse down their concentration gradient 2. High concentration Low concentration

3.4 Diffusion and Osmosis High Concentration Equal Concentration Low Concentration + + + + + + + + + + + + + + + + + + + + + + + + + + +

3.4 Diffusion and Osmosis E. Equilibrium- equal concentrations in all areas

3.4 Diffusion and Osmosis F. Osmosis- diffusion of water molecules across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration Remember- the cell membrane is a semipermeable membrane (it lets certain things through it and keeps other things out)

3.4 Diffusion and Osmosis This is a solution. Remember- Solvent + Solute= Solution Solvent is water Solute is salt

3.4 Diffusion and Osmosis Which one has a greater concentration of solutes (salt)? Low solutes High solutes vs.

3.4 Diffusion and Osmosis Which one has a greater concentration of solvent (water)? Low solutes High solutes High water Low water vs.

3.4 Diffusion and Osmosis F. There are three types of solutions Hypertonic solutions Hypotonic solutions Isotonic solutions

3.4 Diffusion and Osmosis 1. Hypertonic solution- has a higher concentration of solutes (dissolved particles) than a cell Solution (outside of cell) Inside of cell Low concentration solutes High concentration of water High concentration solutes Low concentration of water

3.4 Diffusion and Osmosis 2. Hypotonic solution- has a lower concentration of solutes (dissolved particles) than a cell Solution (outside of cell) Inside of cell high concentration solutes low concentration of water low concentration solutes high concentration of water

3.4 Diffusion and Osmosis 3. Isotonic solution- has the same concentration of solutes (dissolved particles) as a cell Solution (outside of cell) Inside of cell equal concentration solutes equal concentration of water equal concentration solutes equal concentration of water

3.4 Diffusion and Osmosis So, what’s going to happen? Osmosis!!

3.4 Diffusion and Osmosis Hypertonic Solution But first, this cell is in what kind of a solution? Hypertonic Solution High solutes outside Low solutes inside Low water outside High water inside

3.4 Diffusion and Osmosis Remember water moves from areas of high water concentration to areas of low water concentration How will osmosis happen? Will water move into the cell or out of the cell? Out of the Cell!! The cell shrinks! Low water outside High water inside

3.4 Diffusion and Osmosis Hypotonic Solution Now, what kind of solution is this cell in? Hypotonic Solution High solutes inside Low solutes outside High water outside Low water inside

3.4 Diffusion and Osmosis Hypotonic Solution Into the cell!! Will water go into this cell or out of the cell? Hypotonic Solution Into the cell!! The cell expands! High water outside Low water inside

3.4 Diffusion and Osmosis Isotonic Solution Now, what kind of solution is this cell in? Isotonic Solution Equal water and solutes inside and outside

The cell remains the same size. 3.4 Diffusion and Osmosis Will water go into this cell or out of the cell? Isotonic Solution Both!! The cell remains the same size. Equal water and solutes inside and outside

3.4 Diffusion and Osmosis II. Some molecules diffuse through transport proteins. Some molecules cannot slip through the cell membrane very easily. Facilitated diffusion- the diffusion of molecules across a membrane through transport proteins

3.4 Diffusion and Osmosis B. Facilitated diffusion- the diffusion of molecules across a membrane through transport proteins

3.4 Diffusion and Osmosis No Enery Needed Movement of Molecules Passive Transport Active Transport Diffusion Section 3.5 Osmosis Facilitated Diffusion No Enery Needed

3.5 Active Transport, Endocytosis, and Exocytosis Key Concept: Cells use energy to transport materials that cannot diffuse across a membrane.

3.5 Active Transport, Endocytosis, and Exocytosis I. Proteins can transport materials against a concentration gradient. A. Active transport drives molecules across a membrane from a region of lower concentration to a region of high concentration. High Concentration Low Concentration

3.5 Active Transport, Endocytosis, and Exocytosis A protein uses energy to move molecules against the concentration gradient. High Concon. Low Concon.

3.5 Active Transport, Endocytosis, and Exocytosis II. Endocytosis and exocytosis transport materials across the membrane in vesicles. A. Sometimes a cell needs to move big molecules into or out of a cell with a vesicle.

3.5 Active Transport, Endocytosis, and Exocytosis B. Endocytosis- the process of taking liquids or fairly large molecules into a cell by engulfing them in a membrane. The cell membrane folds and a pocket is created The pocket pinches off and a vesicle is created The vesicle and its contents are broken down

3.5 Active Transport, Endocytosis, and Exocytosis C. Phagocytosis- a type of endocytosis in which the cell membrane engulfs large particles. “cell eating” 1. Very important process to fighting infection!

3.5 Active Transport, Endocytosis, and Exocytosis D. Exocytosis- the process of releasing substances out of a cell by the fusion of a vesicle with the cell membrane. A vesicle is created around what needs to be removed The vesicle moves to the cell membrane The vesicle fuses with the cell membrane and releases the contents

3.5 Active Transport, Endocytosis, and Exocytosis