HOMEOSTASIS and thePLASMA MEMBRANE Mrs. Neistadt BIOLOGY Adapted from Mr. Young- Thanks Mr. Young!!
Question: What happens to the helium in a balloon after a few days? Why?
Objectives Explain the function of the plasma membrane. Relate the function of the plasma membrane to the fluid mosaic model. Create a model of the plasma membrane
Homeostasis Key – BALANCE! *Homeostasis *Theequilibrium of an organism’s internal environment that maintains conditions suitable for life. Example: Human sweating • Helps body maintain its proper temperature. Organisms must be able to adjust to changes in their external environment.
Cells and Homeostasis How do cells maintain a balance? *Cells control what materials enter and leave the cell through the plasma membrane. PLASMA MEMBRANE
Plasma Membrane – Properties *The plasma membrane is selectively permeable (semipermeable). *Allows some materials to pass. Water, oxygen, carbon dioxide *Prevents others from passing. Proteins, carbohydrates • Different cells may be permeable to different chemicals or substances.
Plasma Membrane – Structure1. BILAYER (2 layers)2. Each layer made of lipid molecules3. Protein molecules embedded in bilayer
Phospholipid Bilayer POLAR blePhosphate HEAD olu Group Lipids e r-S Wat Organic compounds Glycerol Backbone Fats + Oils Non-polar Insoluble in water (Not attracted to water) FATTY ble ACIDS olu Ins Phosphate Head ater - Polar W Water-soluble (Attracted to water)
QUESTION: Most cells have a watery internal and external environment. Given this information, how might you expect the phospholipids to be arranged? OUTSIDE OUTSIDE OR INSIDE INSIDE
Do you “love” or “fear” water? Hydrophilic heads Water Loving Hydrophobic tails Water Fearing
*Fluid Mosaic Model *Phospholipid molecules may move sideways through their layer. “FLUID”
Proteins *Most of the functions of the plasma membrane are carried out by proteins. Functions: • Determine which particles can pass through membrane • Serve as enzymes (accelerate chemical reactions) • Act as markers – Help fight disease
Plasma membranes are like… Can you think of any examples that are similar to a plasma membrane? Example: Balloon lets out helium Example: Doorman to a building lets everyone out but only tenants in
What would happen… What would happen if the cell let everything in? What would happen if the cell let everything out? A balanced cell is a happy cell!!
Your turn… Draw a picture of a plasma membrane Show the bi-layer and label the parts. Refer to pgs 188 and 190 in your text Write a short summary of how the plasma membrane works (same paper) Use your new vocabulary words in your summary
Create a model of a plasma membrane: White marshmallows are the polar heads Colored marshmallows are the proteins and cholesterol Toothpicks are the non-polar tails. Label the parts of the membrane Be creative…and have fun!
Plasma Membrane – Functions NOT just a barrier surrounding the cell. 1. Selectivity 2. Molecular recognition 3. Export of wastes and cell products 4. Import of nutrients 5. Ability to change in response to environment