1. Passive and Active Transport

2. What we know from the structure:
Membrane structure allows for the controlled movement of substances into and out of the cell
Living organisms demonstrate many adaptations to their membranes that allow them to survive in their environments

3. We’ve learned about the cell membrane structure:
Do all cells face the same environment?
Does the environment of a cell ever change?
Do all cells NEED the same molecules to enter and exit?

4. Expected performance:
Be able to explain the role of the cell membrane in supporting cell functions!

5. What is a key property of the Cell Membrane?
Selective Permeability!!
This property of biological membranes allows some substances to cross more easily than others.

6. How much energy will it cost the cell to MOVE molecules in or out?
It depends on HOW it enters the cell!
Which do you think does NOT “cost” the cell energy- Passive Transport or ActiveTransport?

7. PASSIVE TRANSPORT does NOT require energy!!!
However, the molecules will ALWAYS move from….
A High to a Low
concentration!

8. Diffusion
Diffusion is the net movement of particles from an area of high concentration to low concentration
The movement of individual particles is random!

9. Diffusion- Is any energy required for this process?

10. Diffusion
Diffusion can only occur when there is a gradient – a difference in concentration
This slide demonstrates a gradient of blue
When there is continuous movement but no overall change, a solution is at dynamic equilibrium

11. Watch this animation!

12. HOW DO SUBSTANCES MOVE ACROSS A MEMBRANE?

13. Osmosis
Osmosis is the diffusion of water molecules through a selectively permeable membrane from an area of high water concentration to low water concentration

14. What is inside and outside of cells?
SOLUTIONS!
THE CONCENTRATION OF THESE SOLUTIONS IS OFTEN WHAT DRIVES THE MOVEMENT OF SUBSTANCES ACROSS A MEMBRANE

15. What are the 2 parts of a solution?
Solute
Solvent

16. Naming a Solution
We can give a solution a general name by comparing the SOLUTE concentration of the SOLUTION with the SOLUTE concentration of the CELL it surrounds.

17. Isotonic
A solution with an equal solute concentration compared to inside the cell
This cell and solution are said to be in dynamic equilibrium.
3% Na
97% H2O
solution
3% Na
97% H2O
Red Blood Cell

18. Isotonic
Dynamic Equilibrium: equal amounts of water move in and out of the cell – no net change in concentration (H20 is dark blue)

19. Isotonic
Red Blood Cells in Isotonic Solution

20. Hypertonic
A solution with greater solute concentration (less water) compared to inside the cell.
5% NaCl
95% H2O
solution
3% NaCl
97% H2O
Red Blood Cell

21. Hypertonic
When concentration of dissolved substances is higher outside the cell than inside (solute is light blue)

22. Hypertonic
Water will exit the cell causing the cell to shrink

23. Hypertonic
Red Blood Cells in Hypertonic Solution

24. Hypotonic
A solution with lower solute concentration (more water) compared to inside the cell.
1% Na
99% H2O
solution
3% Na
97% H2O
Red Blood Cell

25. Hypotonic Solution
When concentration of dissolved substances (solute) is lower outside the cell than inside (solute is light blue); Water is HIGHER outside cell.

26. Hypotonic
Water will enter the cell causing the cell to expand (or explode!)
Cell will form an “O”

27. Hypotonic
Red Blood Cells in Hypotonic Solution

28. Animal Cells
Animal cells placed into a hypotonic solution will undergo HEMOLYSIS (EXPLODE).
Animal cells placed into a hypertonic solution will CRENATE (SHRIVEL).
Hemolysis
Red
Blood
Cells
Crenation

29. Plant Cells
Firmness or tension (vacuole full) that is found in plant cells (cell wall) that are in a hypotonic environment is called TURGID.
This process is called TURGOR PRESSURE.
Water
Cell
Wall
Central
Vacuole

30. Onion cell in fresh water

31. Plant Cells
When the plasma membrane pulls away from the cell wall (vacuole empty) in a hypertonic environment (loss of water) is called PLASMOLYSIS.
Water
Cell
Wall
plasma membrane

32. Onion cell in salt water

33. To do: Name the term (NO notes)!!
Diffusion of water across a selectively permeable membrane
Solution with same solute concentration (same water) as cell
Continuous movement, but no change in concentration
Solution with higher solute concentration (lower water) than cell
Random movement of ions & other particles (high-low conc)
Solution with lower solute concentration (higher water) than cell

34. This selectively permeable membrane allows only water across
Why does the column of water rise on the right side of this U – tube?

35. Transport proteins may facilitate diffusion across membranes
Many substances necessary for viability of cell do NOT freely diffuse across the lipid bilayer of the membrane
They require help of specific transport proteins
Polar molecules and ions that are impeded by the lipid bilayer diffuse with the help of transport proteins.
Teaching Tips
1. The text notes that “the greater the number of transport proteins for a particular solute present in a membrane, the faster the solute’s rate of diffusion across the membrane.” This is similar to a situation that might be more familiar to your students. The more ticket-takers present at the entrance to a stadium, the faster the rate of movement of people into the stadium.
Copyright © 2009 Pearson Education, Inc. 35

36. Transport proteins may facilitate diffusion across membranes, cont.
These Transport Proteins assist in Facilitated Diffusion:
A type of Passive transport that does NOT require energy
This means movement is ALWAYS
from High to Low concentration!

37. Transport proteins may facilitate diffusion across membranes, cont.
Some proteins transport by becoming a hydrophilic tunnel for passage
Other proteins bind passenger, change shape, and release passenger on the other side of membrane
In both situations, the protein is specific for the molecule it transports; it can be sugars, amino acids, ions, or even water
Aquaporins, the water-channel proteins, facilitate the massive amount of diffusion that occurs in plant cells and red blood cells.
Teaching Tips
1. The text notes that “the greater the number of transport proteins for a particular solute present in a membrane, the faster the solute’s rate of diffusion across the membrane.” This is similar to a situation that might be more familiar to your students. The more ticket-takers present at the entrance to a stadium, the faster the rate of movement of people into the stadium.
Copyright © 2009 Pearson Education, Inc. 37

38. Solute molecule Transport protein
Figure 5.6 Transport protein providing a channel for the diffusion of a specific solute across a membrane.
Transport
protein 38

39. Transport protein animations

40. Active Transport
The movement of molecules (small or large) across the plasma membrane in which energy (ATP) is required. NO concentration gradient required!
Examples:
1. Sodium (Na) - Potassium (K) Pump
2. Exocytosis
Endocytosis
Receptor mediated Endocytosis

41. Sodium-Potassium Pump
The mechanism that uses energy (active transport) released from splitting ATP to transport Sodium (Na+) out of and Potassium (K+) into cells.
extracellular
fluid
intracellular K+
Na+

42. Protein pumps
Some membrane proteins use energy to pump substances in and out of the cell. Molecules may move UP concentration gradient.
Sodium potassium pump animation.

43. Question:
How are large molecules transported into and out of the cell across the plasma membranes?
Answer:
Exocytosis and Endocytosis

44. Exocytosis
Cell secretes macromolecules (proteins and other biochemicals) out of (EXIT) cell.
Part of the Endomembrane System: Transport vesicles fuse with the plasma membrane.

45. Endocytosis
The energy requiring movement of particles (foreign or natural) into (ENTER) the cell.
3 types of endocytosis:
A. Phagocytosis
B. Pinocytosis
C. Receptor-mediated endocytosis

46. Endocytosis
Portion of the membrane surrounds or engulfs a large molecule. The membrane pinches off to form a vesicle (vacuole) in the cytoplasm.
Amoeba feeding

47. A. Phagocytosis
Cell eating: cells engulf particles with pseudopodia and pinches off a food vacuole.
Two examples:
1. White Blood Cell
2. Amoeba
Lysosome or
Vacuole
White Blood Cell
Bacteria

48. B. Pinocytosis
Cell drinking: droplets of extracellular fluid are absorbed into the cell by small vesicles.
Example:
1. Fungi
Liquids
Hyphae

49. Exocytosis & Endocytosis animation

50. C. Receptor-Mediated Endocytosis
Importing specific macromolecules (hormones) into the cell by the inward budding of vesicles formed from coated pits (receptors).
Hormones
Receptors
Liver Cell

51. Please copy these VOCABULARY WORDS
Please copy these VOCABULARY WORDS! Make sure you understand the definitions and you can use the terms correctly.
Concentration
Concentration gradient
Semipermeable
Passive transport
Active transport
Diffusion
Facilitated diffusion
Osmosis
Hypotonic
Isotonic
Hypertonic

52. Now define these terms! Active transport Pumps Exocytosis Vesicles
Endocytosis
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis

53. Concentration Problems In each problem below, the membrane is permeable to water only!
1. Which way will water move – into or out of the body cell? (draw an arrow!)
94% water
100% water
2. At dynamic equilibrium, the cell will ________.

54. 3. Which way will water move – into or out of the sphere
3. Which way will water move – into or out of the sphere? (draw an arrow!)
4. Is the solution in the beaker hypotonic, isotonic, or hypertonic compared to the cell? (Circle one!)

55. 5. Which way will water move – into or out of the sphere
5. Which way will water move – into or out of the sphere? (draw an arrow!)
6. What will happen to the shape / size of the sphere? What is the solution outside the cell?

56. 7. Which way will water move – into or out of the body cell
7. Which way will water move – into or out of the body cell? (draw an arrow!)
Cell
0.45 M
solute
0.35 M solute
8. What is the cell’s solute concentration after dynamic equilibrium is reached?

57. 9. Which way will water move – into or out of the body cell
9. Which way will water move – into or out of the body cell? (draw an arrow!)
cell
10. What is the cell’s water concentration after dynamic equilibrium is reached?

58. Do now!
After watching this animation, write a description of what you are seeing; use (and underline) these words in your description: Cell membrane Energy Facilitated diffusion Protein

59. Wrap-up!
How is the cell membrane structured to ensure efficiency and survival?
Explain the role of the cell membrane in supporting at least one cell function.

60. MODELLING A CELL MEMBRANE
Materials per group:
1 baggy
Water
Soluble starch solution
Iodine solution
Beaker
Twist ties for baggies
Plastic baggies are a lot like cell membranes; they are semipermeable.
Do baggies allow any of the following - water, starch, or iodine - to move through them?

61. Copy the info below into the next page of your notebook:
The relative MOLECULAR sizes of starch, iodine and water are pictured below:
Iodine
Water
Starch

62. Questions
How might the size of the molecule affect its ability to diffuse?
Does the molecule size support the results you obtained in your experiment? Explain!
List at least five improvements that can be made to the experiment you performed.
How is a plastic bag like a cell membrane? Give five reasons!
How is a plastic bag different from a cell membrane? Give five reasons!