1. Homeostasis and Cellular Transport
Biology
Homeostasis and Cellular Transport

2. Homeostasis Literally means, “ inner balance”
Keeping internal conditions within healthy limits
It applies to things like body temperature and blood pressure

3. Feedback Loops or Homeostatic Mechanisms

4. Cellular Transport
Cellular transport describes how substances cross the cell membrane.
As you remember, the cell membrane controls what goes in and out of the cell.

5. Phospholipids The cell membrane is made mostly of phospholipids
They have a hydrophilic head and hydrophobic tail
Hydrophilic means water loving
Hydrophobic means water fearing

6. Phospholipid Bilayer
The cell membrane is made of two layers of phospholipids
It also contains some proteins
The hydrophilic heads face the cytoplasm and extracellular fluid, while the tails face inward

7. Types of Transport
Passive Transport – Substances cross the membrane without the use of energy (ATP is the most used energy molecule in the human body)
Active Transport – Substances cross the membrane through the use of energy, or ATP

8. Passive Transport
Diffusion - The movement of substances from an area of high concentration to an area of low concentration

9. Passive Transport Cont’d
Facilitated Diffusion – Diffusion that takes place using a membrane protein.
They can open and close when needed.

10. Osmosis
The diffusion of water.

11. Equilibrium
After diffusion or osmosis has taken place and there is an equal concentration of substances.

12. Passive Transport Summary
Passive transport usually moves things:
1. That are small
2. From high to low concentration
3. That are lipid soluble
4. Without using ATP

13. Active Transport
Movement of substances across the cell membrane that requires the use of ATP (energy).

14. Types of Active Transport
Protein Pumps – A membrane protein and ATP are used to pump substances against their concentration gradient across into or out of the cell.
Example - Na/K ATP pump
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15. Exocytosis and Endocytosis
Special vacuoles called vesicles, and ATP are used to add and remove substances from the cell.
and Exocytosis

16. Exocytosis
Substances in a vesicle are forced through the membrane using ATP and released in the fluid surrounding the cell.

17. Endocytosis
Phagocytosis – “Cell eating,” cells use ATP and a vesicle to ingest solid molecules
Pinocytosis – “Cell drinking,” cells use ATP and a vesicle to ingest liquids

18. Receptor Mediated Endocytosis
Cells ingest molecules using ATP after they bond to special receptor proteins on the cell’s surface.

19. Active Transport Summary
Active transport can move things in a wide variety of ways, but certain situations must use active transport:
1. Moving large molecules
2. Moving from low to high concentration
3. Moving things that are not lipid soluble
4. All situations must use ATP

20. Tonicity
Cells will react differently when placed into solutions with varying concentrations of substances, an idea known as tonicity.

21. Isotonic Solutions
Equal concentration of substances inside the cell and outside.
The size of the cell does not change.

22. Hypertonic Solutions
Concentration of substances is greater outside the cell than inside.
The cell shrinks as a result.

23. Hypotonic Solution
Concentration of substances is greater inside the cell than outside.
The cell swells as a result.
If the concentration is great enough, the cell will burst (aka lysis).

24. Comparison of Human Blood Cells