1. Transport Across The Cell Membrane

2. Selectively Permeable
Cell Membranes act like gates allowing only certain substances in or out of the cell.

3. Selectively Permeable
The molecules are constantly in motion – because of their kinetic energy – and either move through the membrane or “bounce” off depending upon their size and charge.

4. Selectively Permeable
Size and Charge of a molecule determines if the cell membrane will let it through

5. Two Types of Cell Transport
PASSIVE VS ACTIVE

6. PASSIVE TRANSPORT
Always moves substances down a concentration gradient.
It requires no energy expenditure on the part of the cell to move these substances across the membrane.

7. 3 Kinds of Passive Transport:
Diffusion
Osmosis
Facilitated Diffusion

8. DIFFUSION
Diffusion is the movement of a solute from an area of higher concentration to an area of lower concentration. When the solute is in equal concentration throughout, it is said to be in equilibrium. The molecules will continue to move, but there will be no net movement in one direction or another

9. OSMOSIS
Water moves by osmosis through a semipermeable membrane. Water will always move from an area of high water concentration to an area of low water concentration. Water’s tendency to move is called water potential (it has the potential to move). It is said to move from an area of higher water potential to an area of lower water potential.

10. OSMOSIS
Since it is the amount of solute that determines which way water moves, we could have 3 different sets of circumstances…
a low amount of solute
a high amount of solute
an equal amount of solute on either side of the membrane. These 3 types of solutions have names

11. HYPOTONIC SOLUTIONS
Hypotonic solutions have less solute (more water) than the solution they are being compared to. Water always moves from a hypotonic solution into the solution containing the greater amount of solute.

12. HYPERTONIC SOLUTIONS
Solutions that contain a greater amount of solute (less water) than the solution they are being compared to are called hypertonic. Water always moves from a hypotonic solution into a hypertonic solution

13. ISOTONIC SOLUTIONS
When two solutions separated by a membrane contain equal amounts of solute, they are said to be isotonic to each other. Water will move back and forth between the solutions, but there will be no net movement in one direction or the other.

14. OSMOSIS
Keep in mind that to use the terms hypotonic, hypertonic, or isotonic, you must be comparing two solutions. These two solutions are on opposite sides of the plasma membrane.

15. Now let’s see what happens to a living cell placed in one of these three types of solutions. We will use a red blood cell (RBC) as an example of an animal cell.

17. Now let’s see what happens to a plant cell in our 3 types of solutions
Now let’s see what happens to a plant cell in our 3 types of solutions. Why would a plant cell behave differently than an animal cell? Do you know?

18. PLANT CELLS IN HYPOTONIC SOLUTIONS
Plant cells placed in a hypotonic solution will fill with water. They have a central vacuole that can take up to 90% of the space inside the cell. This is where the water goes. The plant will swell and the plasma membrane will push against the dead cell wall. The plant cell will not burst because of the cell wall. The rigid condition of the plant cell is known as turgor. The cell is said to be turgid

19. PLANT CELL IN HYPERTONIC SOLUTION
Plant cells placed in a hypertonic solution will lose water from their central vacuole. The shrinking of the central vacuole will cause the plasma membrane to pull away from the dead cell wall (which is immovable). This is known as plasmolysis. The cell will plasmolyze

20. PLASMOLYSIS IN ELODEA
Plasmolysis in Elodea. Note the shrinking of the cytoplasm and how the plasma membrane has pulled away from the cell wall.

21. EFFECTS OF PLASMOLYSIS IN PLANTS

22. PLANT CELL IN AN ISOTONIC SOLUTION
In an isotonic solution, water will move in and out of the plant cell. The central vacuole is not completely filled, so the cell will be flaccid or limp

23. Summarizing what we have learned

24. FACILITATED DIFFUSION
ASSISTANCE BY MEMBRANE PROTEINS: CHANNEL OR CARRIER
MOLECULES ARE MOVED DOWN THE CONCENTRATION GRADIENT FROM HIGH TO LOW CONCENTRATION

25. FACILIATED DIFFUSION

26. CARRIER PROTEIN
Alternates between two conformations, moving a solute across the membrane as the shape of the protein changes. Can move solute in either direction. Specific for certain solutes.

27. Active Transport
Requires use of a carrier protein (like facilitated diffusion)
However, Active Transport moves solutes against the concentration gradient from low to high concentration
Requires cell to expend energy in the form of ATP
Symports carry 2 different molecules in the same direction, while antiports carry two different molecules in opposite directions

29. SODIUM-POTASSIUM PUMP
The sodium-potassium (NaK) pump is the classic example of active transport. It uses an antiport carrier protein to move Na (which is INa) outside and bring K (which is Outside OK) in. The NaK pump is used in nerve conduction and muscle contraction

30. ION PUMPS Ion pumps are another example of Active Transport
H+ ions (protons) are pumped to one side of a membrane by active transport creating a proton gradient. This gives the protons potential energy
This energy can be used to do work including a type of cellular transport called co-transport

31. CO-TRANSPORT

32. BULK TRANSPORT Transport Of Large Molecules Into or Out of the Cell
Involves the use of vesicles
Endocytosis – into cell
Exocytosis – out of the cell
Cell must use ENERGY (ATP)

33. EXOCYTOSIS
Movement of large substances out of the cell
Requires ATP

34. ENDOCYTOSIS
Endocytosis is the process of bringing large molecules into the cell. There are 3 types of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis.

35. PHAGOCYTOSIS – “Cell Eating”
Phagocytes are cells that “eat” other cells. White blood cells are phagocytes that patrol the body looking for invaders, such as bacteria, to ingest. Once inside the cell, the invader is broken down into its component molecules.

36. PINOCYTOSIS – “Cell Drinking”
Pinocytosis moves liquids and smaller particles into the cell

37. RECEPTOR - MEDIATED ENDOCYTOSIS