1. Homeostasis and Transport
Chapter 5
Homeostasis and Transport

2. What part of a cell maintains it homeostasis?
Cell Membrane is selectively permeable
Regulates what goes in and out of a cell

3. Passive transport
– movement of molecule across a cell membrane w/o energy expenditure.
Types of Passive transport
Diffusion
Osmosis
Facilitated Diffusion
Ion Channels

4. – movement of molecules from an area of [High] to an area of [low].
Diffusion
– movement of molecules from an area of [High] to an area of [low].
Concentration gradient
- No energy is required to go from High to low [ ].
Totally driven by molecules’ kinetic energy – constant motion.
Demos with Air freshener, Potassium Permangenate
The steeper the slope, the faster the rate of diffusion.
Therefore, the greater the concentration differential, the faster the rate of diffusion
Low
High

5. Movement of molecules continues until they reach Equilibrium
An increase in temperature, > the kinetic energy of the molecules therefore diffusion occurs faster.
Why sugar “melts” faster in hot water over cold
May occur across the cell membrane
Dependant on:
size of molecules
size of pores
& solubility of molecules (CO2 & O2) easily go into solution into bilipid layer.
Demo with Ammonia and phenolphthalein

6. Osmosis - [ ] means concentration
- net movement of water from [high] ---> [low] through a membrane
Direction of water movement depends on the
[ ] of solutes on 2 sides (inside the cell and outside the cell
Water Molecules move from where there is a lower solute concentration to a higher solute concentration

7. Demonstration of osmosis
What is happening to:
the water (blue)
and the dissolved substances (green and red). What is the same?
What is different?

8. Hypertonic Hypertonic Solution:
[Solute] outside the cell is higher than inside the cytosol
More dissolved particles outside of cell than inside of cell
Hyper = more;
Tonic = dissolved particles/solutes
Water moves out of cell into solution
Cell shrinks
What happens when you put salt on a slug?

9. Red Blood Cells in a normal solute concentation, freshwater and then salt

10. Elodea
Plasmolysis*
-  loss of cytoplasmic structure due to water.

11. Hypotonic

12. [Solute] concentration outside is lower than cytosol
Hypotonic Solution:
[Solute] concentration outside is lower than cytosol
Less dissolved particles outside of cell than inside of cell
Hypo = less, under
Tonic = dissolved particles/solute
Water moves into cell from solution
Cell expands(and may burst)

13. Hypotonic
Turgidity -  swollen cells due to water gain. Plant cells depend on this!
Cytolysis (bursting) may result.

14. Isotonic Solution:
Solute concentration of solution equal to that of cell
No net water movement
Most cells exists in an isotonic external environment

17. Turgor Pressure
Plasmyolysis

18. Plants usually exist in a hypotonic environment.
Cells don’t burst due to flexible & strong cell wall.
Turgor pressure – pressure exerted by water on a plant’s cell wall.

20. Part 2 of Diffusion/Osmosis lab

21. Osmosis Grape Lab Percent Change = Day 2 – Day 1 Mass x 100 Day 1 Mass
Day 1 Mass (grams)
Day 2 Mass (grams)
Difference in Mass (grams)
Percent Change
Net Movement of water
(Into grape, out of grape or no net movement)
Type of Solution
(Hypotonic, Isotonic, Hypertonic)
Distilled water
Grape Juice
Salt Water
Percent Change = Day 2 – Day 1 Mass x 100
Day 1 Mass

22. Quiz
Paramecium live in freshwater. They have a 3% salt internal environment. How do they keep from exploding in this hypotonic environment?
Contractile Vacuoles
– Organelles found in unicellular organisms that collect, then pump out excess water that enters through osmosis.
Does require energy.
Like a sump pump in your basement!

24. Contractile Vacuoles

25. Facilitated diffusion
Diffusion with assistance from Carrier proteins.
Can’t occur fast enough on their own or too large to pass through pores.
May occur into or out of cell.
Carrier proteins are specific to 1 type of molecule.
Animation

27. Steps in Facilitated Diffusion:
1. Carrier protein binds to molecule to be transported.
2. Carrier protein changes shape (shielding it from hydrophobic interior of bilipid layer).
3. Carrier protein releases molecule & goes back to its original shape.
Occurs with glucose & amino acids (that can’t pass through cell on their own).

28. Diffusion thru Ion Channels
– Na+, K+, Ca2+, & Cl- cannot pass thru the membrane.
Ions can not pass since ions aren’t soluble in lipids.
Therefore, they need ion channels to provide a small passageway for each ion.
Conditions for ion channel gates to open.
1. Stretching of cell membrane
2. Electrical signals
3. Chemicals in cytosol
or external environment.

29. Active Transport
Movement of molecules from [Low] to [High]. Energy is needed
Cell Membrane Pumps
Use Carrier Proteins and becomes cell membrane pumps
Sodium – Potassium pump - Transports Na+ and K+ up [ ] gradient
3 Na+ from cytosol bind to the carrier protein
Carrier proteins breaks ATP to ADP + P, P group binds to Carrier protein
3 Na+ are released to environment. Carrier protein changes shape.
2 K+ from outside cell bind to Carrier protein
With release of P group, K+ ions released into cytosol
Cycle repeats
Top speed – 450 Na+ & 300 K+ per second
Inside of cell membrane is now negatively charged, outside is positive. Difference is necessary for electrical impulses along nerve cells.
McGraw Hill video

31. Endocytosis and Exocytosis
Engulfing of macromolecules & food particles into the cell membrane
Animation 1
Animation 2

32. – Cells ingest external fluids, macromolecules & large particles.
Endocytosis
– Cells ingest external fluids, macromolecules & large particles.
Cell membrane surrounds material into a pouch.
Cell membrane around pouch pinches together to form a vesicle.
Vesicle may fuse with lysosome for digestion

33. 2 Types of Endocytosis
Pinocytosis (cell drinking) if solutes or fluids are involved
Phagocytosis (cell eating) if large particles or whole cells are involved
Another animation
Occurs with bacteria, viruses or phagocytes (WBC)

34. Exocytosis
– Release of vesicles thru cell membrane. May be proteins, waste materials, or indigestibles.
Vesicles fuse with membrane, release contents into environment
Proteins packaged by Golgi Apparatus into vesicles which fuse with membrane to release excess proteins
Animation

35. Vocabulary Carrier protein Diffusion Hypotonic Passive transport
Concentration gradient Equilibrium
Ion channel Plasmolysis
Contractile vacuole Facilitated Diffusion
Isotonic Turgor pressure
Cytolysis Hypertonic
Osmosis Active transport
Phagocytosis Sodium – K pump
Vesicle
Endocytosis Exocytosis
Pinocytosis Phagocytosis