1. Cell Membrane! Diffusion and osmosis

2. The cell membrane Separates the cell from its surrounding environment
Controls movement of materials into and out of the cell
Makes it possible for cell contents to be chemically different from environment
Maintains homeostasis

4. Cell Membrane

5. Structure of cell membrane
Two layers bilayer made of lipid (fat) molecules
Hydrophilic = water loving
Hydrophobic = water hating (fear of)

6. Cell Membrane
A phosopholipid is the major lipid found in the cell membrane.
A. Each molecule has a polar head and two nonpolar tails.
1. Because of its hydrophilic nature,
the head will orient (point) toward water.
2. Because of it’s hydrophobic nature,
the tails will orient away from water.

7. CELL MEMBRANE
B. Because a cell is bathed inside and out in a watery solution, the phospholipid molecules form two layers, a lipid bilayer.
C. Cholesterol, a steroid, fits between the tails of the phosopholipid to provide support.
CHOLESTEROL

8. Proteins of the cell membrane
A. Peripheral proteins are located on the interior and exterior.

9. B. Integral proteins are embedded in the bilayer.
1. Some I.P. extend across the entire cell membrane.
2. Some I.P. protrude only on one side or the other.

10. 3. Some I.P. have carbohydrates attached which serve to:
a. hold adjoining cells together.
b. act as a site where viruses can attach.
c. site where hormones can attach.

11. 4. Some I.P. have channels or pores through which substances can pass.
5. Some I.P. bind to a substance on one side of the membrane and carry it to the other side.

12. Integral proteins Transport or move substances through membrane
Receptors are sites that bind special messenger molecules that tell cell to start or stop some chemical activity
enzymes
Bind membrane to neighbor or other cell structures

13. CELL MEMBRANE
Scientists use the term fluid mosaic model to describe the cell membrane.
Because of this fluidity, membrane proteins
and lipids can move laterally (side to side) within the bilayer.

14. THE MOVEMENT OF MOLECULES FROM AN AREA OF:
DIFFUSION
THE MOVEMENT OF MOLECULES FROM AN AREA OF:
HIGHER CONCENTRATION
TO AN AREA OF
LOWER CONCENTRATION.

15. WHAT DRIVES THE DIFFUSION PROCESS?
THE KINETIC ENERGY OF THE MOLECULES!

17. DIFFUSION AND THE CELL MEMBRANE!
SOME SUBSTANCES EASILY CROSS THE CELL MEMBRANE,
OTHERS CANNOT CROSS AT ALL.
THE CELL MEMBRANE IS:
SELECTIVELY PERMEABLE!

18. Selectively Permeable:
Some substances can pass through freely
Some can pass through only to a slight extent or at certain times
Some cannot go through at all

19. A cell cannot survive in isolation.
Nutrients and waste must pass through the cell membrane.

20. CONCENTRATION GRADIENT
THE DIFFERENCE IN CONCENTRATION OF MOLECULES ACROSS A SPACE IS CALLED:
CONCENTRATION GRADIENT
WHAT CAUSES THIS TO TAKE PLACE?

21. Concentration is most at the top of the hill

22. THE SIMPLIST TYPE OF PASSIVE TRANSPORT IS:
SOME SUBSTANCES CAN CROSS THE CELL MEMBRANE WITHOUT ANY IMPUT OF ENERGY BY THE CELL.
THE SIMPLIST TYPE OF PASSIVE TRANSPORT IS:

24. WILL MOVEMENT STILL CONTINUE?
EQUILIBRIUM
WHEN THE CONCENTRATION OF THE MOLECULES OF A SUBSTANCE IS THE SAME THROUGHOUT!
WILL MOVEMENT STILL CONTINUE?
IN WHICH DIRECTION?

25. OSMOSIS PASSIVE TRANSPORT
THE PROCESS BY WHICH WATER MOLECULES DIFFUSE ACROSS A CELL MEMBRANE FROM AN AREA OF HIGHER CONSENTRATION TO AN AREA OF LOWER CONSENTRATION!!!
PASSIVE TRANSPORT

26. HYPOTONIC DIRECTION OF OSMOSIS HYPERTONIC
DEPENDS ON THE CONCENTRATION OF THE SOLUTES ON THE TWO SIDES OF THE MEMBRANE.
HYPOTONIC
HYPERTONIC

27. Suppose you put a cell into a glass of salt water.
NaCl above normal
NaCl normal

28. Water moves out of the cell
Cell shrinks

29. Suppose you put a cell into a glass of less salt water (hypotonic)
NaCl below normal
NaCl normal

30. Water moves into cell

31. ANIMAL PLANT
If the solution is isotonic relative to the cell, then the solute concentrations are the same on both sides of the membrane and water moves equally in both directions
A hypertonic solution has increased solute, and a net movement of water outside causing the cell to shrink.
A hypotonic solution has decreased solute concentration, and a net movement of water inside the cell, causing swelling or breakage.