1. Baltimore Polytechnic Institute
Ingenuity Biology
December 11th, Tuesday
Diffusion, Osmosis and Active Transport
Insong James Lee, Ph.D.

2. Diffusion, Active Transport and Osmosis
November 8th, Thursday
Learning objectives:
• Be able to explain the process of: diffusion, active transport and osmosis.
• Differentiate between diffusion and facilitated diffusion, passive and active transport, equilibrium and dynamic equilibrium.
• Understand why plants become turgid.
Diffusion, Active Transport and Osmosis

3. Diffusion, Active Transport and Osmosis
Topic slide(s)
Overview of Diffusion, Osmosis and Transport 4
Diffusion
Cell Membrane overview
Facilitated diffusion
Active transport
Osmosis

4. What does Diffusion, Active transport and Osmosis all have in common?
They all involve the movement of
molecules. These ways of moving molecules
play critical roles in living organisms

5. Diffusion
slides 6-10

6. Diffusion is a physical process that refers to the net movement of molecules from a region of high concentration to one of lower concentration. or
Semipermeable membrane

7. Concentration gradient: A gradual change in the concentration of solutes in a solution as a function of distance through a solution

8. Cell membrane
slides 9-15

9. 35 trillion cells in our bodies!
Overview of the cells need to interact with its environment.
Recall that the cell membrane acts as a boundary
between the inside of the cell and the extracellular
environment. Molecules have to move in and
out of the cell through the membrane in
order for the cell to survive and function

10. Cell membrane: Phospholipid: Phosphate Acyl chains Glucosamine
Inside of cell
outside of cell
polar head
FIGURE 11-1 Biological membranes. Viewed in cross section, all cell membranes share a characteristic trilaminar appearance. This erythrocyte was stained with osmium tetroxide and viewed with an electron microscope. The plasma membrane appears as a three-layer structure, 5 to 8 nm (50 to 80 Å) thick. The trilaminar image consists of two electron-dense layers (the osmium, bound to the inner and outer surfaces of the membrane) separated by a less dense central region.
Phospholipid:
non-polar tail
Phosphate
Acyl chains
Glucosamine
(made up of carbon
and hydrogen
atoms)

11. Cell membranes are made up of lipids and proteins
Proteins are associated with the membrane. There are different types of proteins which are associated with the membrane.

12. Diffusion: A type of passive transport
Passive transport is the movement of molecules into or out of a cell WITHOUT the use of energy by the cell.
Diffusion across the cell membrane is how small non-polar molecules get into and out of cells.
Non-polar molecules: not having partial charges, ie, dipoles

13. Example of diffusion at work in your body: how your cells get O2 and get rid of CO2
Alveoli in lung

14. Diffusion: why flatworms are flat!
Since they have no respiratory system, planarians like this have a flattened body plan to allow for fast diffusion of oxygen and carbon dioxide their cells.

15. In diffusion, (solute/solvent) molecules move (up/down) the concentration gradient from areas of (high/low) concentration to areas of (high/low) concentration
Solvent; down; high; low.
Solute; up; high; low.
Solute; down; high; low.
Solute; down; low; High.
Solute; down; high; high.

16. Facilitated diffusion slides 17-20

17. Facilitated Diffusion
Facilitated diffusion is like regular diffusion in that substances are moving from high concentration to low without the use of cell energy.
The difference is the solute molecules can’t get through the membrane alone, and travel through proteins instead.

18. The glucose will try to move to the outside of the cell.
You are informed that the concentration of glucose (a monosaccharide) outside of the cell is 5 mM. In the cytoplasm, the concentration is 0.6 mM. Which direction will the glucose tend to move to?
The glucose will try to move to the outside of the cell.
The glucose will try to move to the inside of the cell.
The glucose will not move.
5 mM
0.6 mM

19. Looking at the molecular structure of glucose below, do you think that it is polar or non-polar? If it is polar, will it cross the cell membrane easily?
Polar; No.
Polar; Yes.
Non-polar; No.
Non-polar; Yes

20. Since glucose is polar and doesn’t easily cross the cell membrane, a helper is needed. That helper is the protein, Glucose transporter; GLUT1
D-Glucose
(Conc in plasma; 4.5 to 5 mM)
FIGURE Model of glucose transport into erythrocytes by GLUT1. The transporter exists in two conformations: T1, with the glucose-binding site exposed on the outer surface of the plasma membrane, and T2, with the binding site exposed on the inner surface. Glucose transport occurs in four steps. 1 Glucose in blood plasma binds to a stereospecific site on T1; this lowers the activation energy for 2 a conformational change from glucoseout • T1 to glucosein • T2, effecting the transmembrane passage of the glucose. 3 Glucose is released from T2 into the cytoplasm, and 4 the transporter returns to the T1 conformation, ready to transport another glucose molecule.
D-Glucose
(Conc in the cell; 0.6 to 2.6 mM)

21. Active transport slides 22-31

22. Types of membrane transport
There are several types of membrane transport. The most basic is simple diffusion. All else being equal, smaller particles will diffuse more rapidly than larger particles. Also, nonpolar compounds diffuse better than polar compounds. There is also facilitated diffusion and active transport.

23. The role of the Na+ K+ ATPase in cells[
FIGURE Role of the Na+K+ ATPase in animal cells. In animal cells, this active transport system is primarily responsible for setting and maintaining the intracellular concentrations of Na+ and K+ and for generating the membrane potential. It does this by moving three Na+ out of the cell for every two K+ it moves in. The electrical potential across the plasma membrane is central to electrical signaling in neurons, and the gradient of Na+ is used to drive the uphill cotransport of solutes in many cell types.
This transporter is primarily responsible for the intracellular concentrations of Na+ and K+ and for generating the membrane potential. The electrical potential across the plasma membrane is central to electrical signaling in neurons, and the gradient of Na+ is used to drive the uphill cotransport of solutes in many cell types.

24. Dynamic Equilibrium
In a dynamic equilibrium, while the amount of reactants and products remain unchanged, the reaction continues, because the rates of the forward and backward reactions are the same. There can be some instances in equilibrium where the amounts of products and reactant remain unchanged because the reaction has stopped.

25. Osmosis slides 19-26

26. Definition of osmosis: movement of a solvent (such as water) through a semipermeable membrane (as of a living cell) into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane across a semi-permeable membrane
A hypotonic solution is any solution that has a lower osmotic pressure than another solution. In the biological fields, this generally refers to a solution that has less solute and more water than another solution
A Hypertonic solution refers to a solution with higher osmotic pressure than another solution. In other words, a hypertonic solution is one in which there is a greater concentration or number of solute particles relative
to the other solution

27. Molecules always move from areas of higher concentration to lower concentration spontaneously (passively)

28. Effects of Osmosis can be serious for a cell!
Hypotonic
Hypertonic
Isotonic
Water out
Of cell
No net change
Water into cell

29. How cells cope with hypotonic environment

30. Osmosis & Plants

31. Plant Cells & Osmosis
Plasmolysis

32. Hypotonic environment
causes turgor pressure.
Plant is healthy.
Hypertonic environment
causes wilting.
Plant is unhealthy.
Plasmolysis

33. Active Transport
Active transport processes are different from passive ones:
Energy is required.
Substances move UP their concentration gradients from lower conc. to higher.
Equilibrium is PREVENTED.

34. Endocytosis “Endo-” means in. “cyto-” means cell.
“osis” means process of.
What does endocytosis mean?
Endocytosis: the process by which cells take in large amounts of material, by folding in the cell membrane

35. Endocytosis types:
Pinocytosis: non-specific endocytosis of small amounts of extracellular fluid.
Greek: “pino-” = “drinking”

36. Endocytosis types: Phagocytosis:
the endocytosis of solid particles such as bacteria, cell debris, or other solids
Greek: “phago-” = “eating”

37. Phagocytes
Phagocytes, such as some types of white blood cells, engulf foreign cells by phagocytosis.

38. For Protists, Phagocytosis = Eating

39. Exocytosis
Exocytosis is the same process as endocytosis, except in reverse.
The stuff leaving may be:
Proteins released into the ECF
New lipids for expanding the membrane
Membrane proteins
Chemicals for communication, etc. (e.g. dopamine)

40. Exocytosis

42. Endo and Exocytosis – quick review

43. The Sodium / Potassium Pump
The Na+/K+ pump is responsible for maintaining the electrical charge of a cell
Cells are negative
Communication, e.g. neurons
Cation uptake
It is an example of a membrane pump which move specific things into or out of the cell AGAINST THEIR CONCENTRATION GRADIENT.
Since it requires energy, it is an example of ACTIVE TRANSPORT!

44. How the Na+/K+ Pump Works
Don’t forget the animation….

45. Na+/K+ Pump… Drake demonstrates…

46. Recap: Active Transport Uses ATP
Active transport is different from passive in 3 key ways (energy, up gradient, no equilibrium)
Endocytosis = cell taking in material by infolding the membrane.
Pinocytosis = “cell drinking” ECF
Phagocytosis = “cell eating” bacteria, etc.
Exocytosis = cell exporting materials in bulk.
Na+/K+ Pump =
an example of a membrane pump
moves 3 Na+ out and 2 K+ in per cycle.
Causes cells to be negatively charged.