1. Homeostasis & Transport
Chapter 5

2. Passive Transport
Section 5.1

3. Homeostasis
 To remain alive and function optimally, cells must maintain a biological balance with their immediate environment called _______?

4. Homeostasis?
How do cell membranes help maintain homeostasis within a cell?
By controlling what goes into and out of the cell, called semi-permeable.

5. Cell Membrane Permeability
What determines the permeability of a substance across the cell membrane?
Size
Polarity
Hydrophobic vs. hydrophilic
Charge

6. Permeability of Cell Membrane

7. Selectively Permeable
The cell membrane is described as selectively permeable because it allows some substances to pass in or out but not others.
The size, charge, and polarity of a substance determines its permeability.
The cell membrane is permeable to gases such as carbon dioxide and oxygen since gases are small.
The cell membrane is permeable to water and other small, polar molecules.

8. Passive Transport
The movement of substance across a cell membrane WITHOUT the use of energy (ATP).
Four Types:
Diffusion
Osmosis
Facilitated Diffusion
Ion Channels

9. 1. Diffusion
Movement of molecules from an area of high concentration to an area of low concentration without the help of energy.

11. Diffusion through a Membrane
Cell membrane
Solute moves DOWN concentration gradient
(HIGH to LOW)

12. Concentration Gradient
Difference in concentration of molecules across a space (or cell membrane).
“Down the gradient”
Movement from high to low concentration

13. Equilibrium
When the concentration is EQUAL throughout the space (or on each side of the cell membrane)
End of diffusion
RANDOM movement still occurs

14. Diffusion of Liquids

15. Diffusion across a membrane
Depends upon temperature, size, shape, and chemical makeup
Easy to diffuse:
Small (eg. O2 )
Nonpolar
Hard to diffuse:
Glucose
amino acids

16. Diffusion and Equilibrium

17. Main Points
Diffusion – molecules cross the cell membrane without using energy
Always moves from higher concentration to lower concentration
Ability to diffuse depends on size & type of molecule

18. 2. Osmosis WATER diffusion across a membrane quickly
“higher to lower concentration, DOWN THE GRADIENT
Hypotonic solution to hypertonic solution

19. Osmosis

20. Hypotonic Solution
The solute concentration is higher inside the cell, the water concentration is higher outside the cell.
Net movement = Water into the cell

21. Hypertonic Solution
The solute concentration is higher outside the cell, the water concentration is higher inside the cell.
Net movement = Water out of the cell

22. Isotonic Solution
The solute and water concentrations are EQUAL on both sides of the membrane.
Equilibrium

24. Osmosis in Red Blood Cells
Isotonic
Hypotonic
Hypertonic

25. Cells deal with osmosis
Cells live in isotonic environment – water moves with no problem
Freshwater organisms – freshwater outside (hypotonic environment) of the cell makes too much water go into the cells because of osmosis, cells can burst

26. hypotonic
hypertonic
isotonic
hypertonic
isotonic
hypotonic

27. Facilitated Diffusion
movement of molecules that can’t diffuse by themselves through cell membrane
Use of specific carrier proteins the assist diffusion across a membrane.
(like glucose or amino acids) THIS IS HOW GLUCOSE ENTERS CELL RAPIDLY
“Down the gradient” means
high to low concentration

28. Diffusion via ion channels
Use of membrane proteins to assist diffusion of ions across a membrane
Channel is usually specific to 1 type of ion
Some always open, some are “gated”
Common ions:
Sodium
Potassium
Chlorine
Calcium

29. Active Transport
Section 5.2

30. Active Transport
Uses energy (ATP) to move materials against the gradient
“Up the gradient”
Low to high concentration

31. 1. Sodium Potassium Pump
Transports sodium and potassium ions across the membrane up their gradients
Complete cycle 3 Na +out & 2 K+ inside cell
Low to high concentration
Uses ATP

32. 2. Endocytosis Movement of large amounts of material into the cell
Folding cell membrane to form a vesicle that will go to the lysosome for digestion
Uses ATP

33. 2 types of endocytosis 1. pinocytosis: “cell drinking”
movement of a large quantity of solutes or liquid into the cell
2. phagocytosis: “cell eating”
Movement of large solids or whole cells into the cell
Uses ATP

34. Moving the “Big Stuff”
Large molecules move materials into the cell by one of three forms of endocytosis.

35. 3. Exocytosis
The movement of a large amount of materials out of the cell
removes wastes and cell products like proteins packaged by Golgi vesicles
Vesicle fuses to the cell membrane to release contents out of the cell
Uses ATP

36. Exocytosis
Exocytic vesicle immediately after fusion with plasma membrane.

37. Passive & Active Transport
Animation