1. Diffusion and Osmosis

2. Functions of Cell Membrane
1. Protect cell
Control incoming and outgoing substances
Selectively permeable - allows some molecules in, others are kept out

3. Phospholipid Bilayer

4. Plasma membrane components
Phospholipid bilayer
polar
head P –
cytosol
hydrophobic molecules
hydrophilic molecules
nonpolar
tails

5. Membrane Permeability
Selective permeability
The ability of a cell membrane to control which substances and how much of them enter or leave the cell
Allows the cell to maintain a difference between its internal environment and extracellular fluid
Supplies the cell with nutrients, removes wastes, and maintains volume and pH

6. The Selectively Permeable Nature of Cell Membranes

8. Types of Membrane Proteins

9. Methods of Transport Across Membranes
1. Diffusion -passive transport – no energy expended 2. Osmosis - Passive transport of water across membrane 3. Facilitated Diffusion - Use of proteins to carry polar molecules or ions across 4. Active Transport- requires energy to transport molecules against a concentration gradient – energy is in the form of ATP

10. Concentration and Gradients
The number of molecules (or ions) of substance per unit volume of fluid
Concentration gradient
The difference in concentration between two adjacent regions
Molecules always move from a region of higher concentration to one of lower concentration

11. Diffusion
Solute molecules moving from an area of high concentration to an area of low concentration
Random motion drives diffusion
Equilibrium is reached when there is an even distribution of solute molecules
(water)

12. Diffusion

17. Osmosis Diffusion of water through a semi- permeable membrane
Semi-permeable: permeable to solvents (WATER), but not to large molecules
High [water] to low [water]
Dissolved molecules (i.e. glucose, starch) are called solutes
REMEMBER:
Water = solvent
Glucose, Starch = solutes

18. Osmosis

19. Effect of Water on Cells
Hypertonic Environment
High [solute], low [water]
Hypotonic Environment
High [water], low [solute]
Isotonic Environment
[water] = [solute]
Hypertonic
Hypotonic
Isotonic
Part 3 pg. 85

20. Osmosis in Living Cells
Cellulose in cell wall

21. Osmosis in Red Blood Cells
Isotonic
Hypotonic
Hypertonic
Observe sheep RBCs via a wet mount of the sample
Aliquot one drop the following solutions with a ½ drop of RBC to a slide
0.9% saline
10% NaCl
Distilled water
Record observation in the table on page 85
Crenation
Predictions?

23. Effect of Water on RBC

24. Osmosis in Plant Cells Plasmolysis
Hypertonic
Plasmolysis
Observe Elodea leaves via a wet mount of the sample
Aliquot two drops the following solutions with a new Elodea leaf to a slide. Incubate for 10 room temp.
10% NaCl
Distilled water
Record observation in the table on page 85
Hypotonic
Predictions?

25. Hydrostatic Pressure in Plants
Normal tomato on left – salt water gives effect (r) in 30min
Iris petal cells
Iris petal cells in wilted stage

26. Types of Transport

27. Transportation of Molecules
Passive Transport
Movement of molecules across a semi-permeable membrane
no energy required
Active Transport
Movement of molecules across a semi-permeable membrane against a concentration gradient
ENERGY – ATP
Facilitated Diffusion
Movement of molecules across a semi-permeable membrane with a protein

29. Active transport in two solutes across a membrane
FLUID OUTSIDE CELL
Phosphorylated transport protein
Active transport in two solutes across a membrane
Na+/K+ pump
Protein shape change
Transport protein
First solute 1
First solute, inside cell, binds to protein 2
ATP transfers phosphate to protein 3
Protein releases solute outside cell
Second solute 4
Second solute binds to protein 5
Phosphate detaches from protein 6
Protein releases second solute into cell
Figure 5.18

31. Exocytosis and endocytosis transport large molecules
exocytosis = vesicle fuses with the membrane and expels its contents
FLUID OUTSIDE CELL
CYTOPLASM
Figure 5.19A

32. or the membrane may fold inward, trapping material from the outside (endocytosis)
Figure 5.19B

33. Receptor-mediated endocytosis

34. Cholesterol can accumulate in the blood if membranes lack cholesterol receptors
Phospholipid outer layer
LDL PARTICLE
Receptor protein
Protein
Cholesterol
Plasma membrane
Vesicle
CYTOPLASM
Figure 5.20

35. Membrane-Crossing Mechanisms