1. HOMEOSTASIS AND THE CELL MEMBRANE

2. Function of the Cell Membrane: REVIEW
Cell membrane separates the components of a cell from its environment—surrounds the cell
“Gatekeeper” of the cell—regulates the flow of materials into and out of cell—selectively permeable
Cell membrane helps cells maintain homeostasis—stable internal balance

3. Transportation through the Cell Membrane— small molecules such as H2O, CO2 and O2 move easily through the lipid bilayer – larger molecules require different mechanism
A. Passive transport – NO energy required. All molecules move from HIGH to LOW concentration
Examples:
Diffusion
Osmosis
Facilitated Diffusion

4. a. example: dye (ex: food coloring) in water
1. Diffusion -- movement of particles from a high concentration to a low concentration
a. example: dye (ex: food coloring) in water
dye diffuses down concentration gradient until equilibrium reached
concentration gradient = difference in concentration of a substance

5. b. example: blood vessel in lung tissue during respiration
Blood Lung Blood Lung
X X O O X O X O
X X O O O X O X
CO2 O CO2 and O2
high high equalized

7. c. example: sugar dissolved in water
solution – sugar water
solvent – water (dissolving substance)
solute – sugar (substance being dissolved)
solute
(sugar cube)
solution
solvent
(H2O)

8. 2. Osmosis -- diffusion of water through a selectively
2. Osmosis -- diffusion of water through a selectively permeable membrane
permeable to H2O
impermeable to salt
Water
Salt
salt water
tap water
Low Salt Concentration High Salt Concentration
High Water Concentration Low Water Concentration
= Hypotonic
= Hypertonic

9. a. hypertonic solution – high in solutes, low in solvent
hypotonic solution – low in solutes, high in solvent
isotonic solution – equilibrium has been reached

10. Ex: cell in salt water water moves into cell1.
water moves into cell
water moves in and out of cell 2.
water moves out of cell 3.

11. SALT SUCKS!! cytolysis Red Blood Cell plasmolysis Plant Cell
cell bursts – cytolysis
cell shrinks – plasmolysis (lysis = splitting)

12. b. example problem: A cell that is 80% H2O and 20% other is
b. example problem: A cell that is 80% H2O and 20% other is put into water that is 99% H2O and 1% other.
99% H2O
1% other
80% H2O
20% other
Which way will the water move?
Into cell
Which is the hypotonic solution?
Outside cell
Which is the hypertonic solution?
Inside cell

13. Think about it:
What is the big difference between diffusion and osmosis?
Can you remember an example of each?

14. 3. Facilitated diffusion – most molecules move across
3. Facilitated diffusion – most molecules move across the membrane with help from protein channels provides a larger opening for organic molecules to go through

15. a. example: glucose (food molecules)
outside of cell
inside of cell
protein channel
protein pump
Glucose molecules (high concentration)
NO ENERGY REQUIRED for FACILITATED DIFFUSION

17. Click

18. B. Active transport – energy required in form of ATP
1. Some proteins act like pumps moving molecules from LOW to HIGH concentration.

19. a. example: vitamins and minerals in soil
a. example: vitamins and minerals in soil concentrated moving into plants
= calcium ions
Outside cell
Inside cell

21. b. example:
Body cells must pump CO2 out into the surrounding blood to be carried to the lungs for exhale.
Blood is high in CO2 compared to the cells, so energy is required to move the CO2 across the cell membrane from LOW to HIGH concentration
Carbon dioxide molecules
Protein pump
outside of cell
inside of cell

22. a. Endocytosis – into cell 1. Phagocytosis – solids
2. Endocytosis/ Exocytosis – how very large molecules (food and waste) get into and out of cell
a. Endocytosis – into cell
1. Phagocytosis – solids
example: white blood cell engulfing bacteria to destroy it (immune reaction)

23. 2. Pinocytosis – liquids
example: water into cell

24. b. Exocytosis – out of cell
example: cellular waste

25. Exocytosis

26. A. Homeostasis – maintaining constant internal conditions
II. Flow Chart
A. Homeostasis – maintaining constant internal conditions
B. Cell membrane constantly working on maintaining homeostasis within the cell
ENERGY NEEDED: low to high conc.
Active Transport
Endocytosis (phagocytosis and pinocytosis)
Exocytosis
NO ENERGY NEEDED: high to low conc.
Passive Transport
Diffusion
Osmosis
Facilitated Diffusion (protein channels)

27. http://highered. mcgraw-hill