1. Cell Boundaries and Transport
Unit 4

2. Cell Boundaries: Plasma Membrane
All cells are bordered by this thin, flexible and selectively permeable lipid bilayer barrier that has two functions
The “Bouncer” of the cell

3. Cell boundaries Two Functions of the PM:
Regulates what enters and leaves
the cell
2. Provides protection and support for the cell

4. Cell Boundaries: Cell Wall
Plants, algae, fungi and many prokaryotes have this additional barrier outside their plasma membrane. It provides additional protection and support for the cell. The wall is made of carbohydrate and protein fibers like cellulose. Cellulose is the principle component of wood and paper!
Which of the four organic compounds does a book belong to?
Carbohydrates!!!

5. Cell Limitations Recall:
A solution is a mixture of 2 or more substances
The liquid doing the dissolving is the solvent (usually water)
The solid being dissolved is the solute
The concentration is the amount of solute in the solution

6. Cell Limitations Cells are limited in their size because of 3 things:
Diffusion
Osmosis
Facilitated Diffusion
DNA
Food Requirements

7. Diffusion Does not require use of cell’s energy (passive transport)
Particles move constantly in a solution, colliding with each other. As a result they tend to spread out to areas where they are less concentrated (have more “elbow room”)
Equilibrium is reached when the concentration of solute is the same on both sides of the membrane

8. Osmosis
Does not require cell’s energy (passive transport). The water can move freely through the selectively permeable plasma membrane.
Isotonic-concentration the same on both sides
Hypertonic-solution with greater concentration of solutes
Hypotonic-solution with the lesser concentration of solutes
High Concentration Low Concentration
Video Link:

9. Osmosis and Cells
Osmosis plays an important role in maintaining homeostasis through the intake and loss of water. Osmosis exerts osmotic pressure on the hypertonic side causing a cell surrounded by fresh water to be flooded. The cell will burst (lysis) if it gains too much volume.

10. Blood cells in animals are isotonic and have roughly the same amount of dissolved materials inside the cell as surrounding the cell
Plant cells have cell walls that prevent the cell from swelling and bursting when in contact with water

11. Facilitated Diffusion
Does not require cell’s energy (passive transport)
The cell’s plasma membrane has protein channels that help larger solute molecules who wouldn’t normally be allowed in, pass through more easily.
- Red blood cells have a protein channel that facilitates the diffusion of glucose in and out
Oxygen diffusion through the blood for transport to mitochondria for cellular respiration
Video Link:

12. Active Transport
Cell’s sometimes need to move materials against a concentration gradient (low to high)
This process requires much of the cell’s daily energy
Generally carried out at PM by protein “pumps” or by processes called endocytosis and exocytosis

13. Endocytosis and Exocytosis
Endocytosis (active transport)
“Cell eating”
The PM engulfs food particles and package them in a food vacuole called a vesicle.
Pinocytosis (active transport)
“Cell drinking”
Tiny pockets form along PM and fill with water. They pinch off inside the cell
Exocytosis
The membrane of a contractile vacuole carrying waste or cellular material fuses with the PM and forces its contents outside the cell

14. Jump In: Transport and Diffusion
Complete all 3 sections. We will go over the answers as a class.

15. What kind of membrane is this?
Which direction will the water flow?
Which cell is in an isotonic, a hypertonic and a hypotonic solution? 1. 3. 2.

16. The smaller the molecule, the faster it will diffuse and most likely passive transport is used.
Which molecules do you think will diffuse across the Plasma Membrane least quickly? Why? What kind(s) of transport will be used?
Which molecule(s) do you think will diffuse across the Plasma Membrane most quickly? Why? What kind(s) of transport will be used?
What is the relationship between molecule size and the rate of diffusion?