1. Maintaining Homeostasis
The Cell Membrane
Maintaining Homeostasis

2. Cell Membrane Function & Anatomy
One of the most important functions of the cell membrane is to regulate movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side.

3. Cell Membrane Function & Anatomy
The cell membrane of made of two layers of phospholipids.
Hydrophilic (water loving) heads are facing the inside and outside of the cell.
Hydrophobic (water fearing) fatty acid tails are oriented towards the center of the cell membrane.
Proteins shown in previous slide allow active transport and facilitated diffusion.

4. Movement of Substances Across the Cell Membrane: Types of Transport
Passive
Movement down the concentration gradient.
Expenditure of energy not required.
Simple Diffusion
Movement through lipid bilayer
Osmosis
Semipermeable membrane.
Facilitated Diffusion
Carrier or Pore Protein.
Active
Movement against the concentration gradient.
Energy (ATP) expenditure by cell.
Carrier Protein

5. Passage of Molecules In and Out of Cells
Name
Direction
Requirement
Examples
Passive Transport
Simple Diffusion
Toward lower concentration
Concentration gradient only
Lipid soluble molecules such as gases: Oxygen and Carbon Dioxide
Osmosis
Water
Facilitated Diffusion
Carrier and concentration gradient
Some sugars and amino acids: Glucose
Active Transport
Toward greater concentration
Carrier plus energy
Sugars, amino acids and ions: Sodium and Potassium
Exocytosis
Toward outside
Vesicle fuses with plasma membrane
Macromolecules: Enzymes, clumps of food, and whole cells
Endocytosis
Toward inside
Vacuole or Vesicle formation
Cells, subcellular material, macromolecules or large amounts of material

6. Let’s Permeate 1 2 3 4

7. Let’s Permeate Diffusion/Osmosis Facilitated Diffusion
Everyone move to area 1, now move back to your respective counted areas.
Facilitated Diffusion
If you are in area 2 move to an area that is an even number, all others remain where you are.
Active Transport
1 & 2 move to area 1, those in area 3 make a circle around area 1; now area 4 find someone in area 3 and ask to enter area 1.

8. Let’s Permeate
Break off into your numbered groups and use the table in slide 5 to create your own example of the transport assigned to your group in 10 minutes and then present to class:
Group 1 – Exocytosis
Group 2 – Endocytosis
Group 3 – Facilitated Diffusion
Group 4 – Active Transport
Each group should have a spokesperson for each cell membrane component or permeating component, i.e. if 5 people in the group are portraying lipid bilayer one of them should explain the role of all 5.

9. What is Homeostasis?
Definition: The process by which organisms keep internal conditions relatively constant despite changes in the external environment.
The average temperate of a human is 98.6°F regardless of the outside temperature. How does this golfer play in the frigid winter weather and still maintain a body temperature of 98.6°F?

10. Homeostasis at the Cellular Level
The cell membrane regulates what enters and exits the cell by:
Only allowing certain gases to pass through the lipid bilayer.
Requiring selective proteins for small molecules.
Requiring proteins and expenditure of energy for small molecules against the concentration gradient.