1. Section 1 Passive Transport
Chapter 5
Objectives
Explain how an equilibrium is established as a result of diffusion.
Distinguish between diffusion and osmosis.
Explain how substances cross the cell membrane through facilitated diffusion.
Explain how ion channels assist the diffusion of ions across the cell membrane.

2. Section 1 Passive Transport
Chapter 5
Passive transport involves the movement of molecules across the cell membrane without an input of energy by the cell.
Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration
As a result of diffusion, the concentration of many types of substances eventually becomes balanced on both sides of a membrane

3. Diffusion
Concentration gradient is the difference in the concentration of molecules across a distance
Equilibrium is a state that exists when the concentration of a substance is the same throughout a space (homeostasis) Big Bang Theory
MAKE YOUR OWN ANIMATION OF EQUILIBRIUM!!!!!
High Conc. Water
Low Conc. Water
Low Conc. Solute
High Conc. Solute

4. Diffusion What does this look like on the microscopic level? Animation
Sugar molecules, initially in a high concentration at the bottom of the beaker, will move about randomly through diffusion, and eventually reach equilibrium. At equilibrium the sugar concentration will be the same throughout the beaker. Diffusion occurs naturally because of the kinetic energy the molecules possess
***Another example of diffusion would be the dispersal of ink in a beaker of water

5. Chapter 5 Diffusion cont. Section 1 Passive Transport
Remember that diffusion is movement from high concentrations to low concentrations,

6. Diffusion Diffusion Across Membranes
Molecules can diffuse across a cell membrane by dissolving in the phospholipid bilayer or by passing through pores in the membrane
Diffusion across a membrane is “simple diffusion” (only certain molecules pass through)
NO energy is expended (used up)
iodine baggy demo

7. Section 1 Passive Transport
Chapter 5
Osmosis
Osmosis is the diffusion (or passing) of water across a cell membrane.
Since water is moving from a higher to lower concentration, osmosis does not require cells to expend energy. Therefore, osmosis is the passive transport of water

8. The Direction of Osmosis
The NET direction of osmosis is determined by the relative concentrations of solute on either side of a membrane
There are specific names for solutions depending on their solute concentrations:
Hypotonic
Hypertonic
Isotonic
Remember that CYTOSOL is the soluble portion of the cytoplasm – the fluid that water or solutes flow into or out of

9. Osmosis: Hypotonic Solutions
Hypotonic (“Hypo-” is Greek for “under”)
When the concentration of solute molecules outside the cell is lower than their concentration in the cytosol (cell), the solution outside is hypotonic to the cytosol (cell)
What direction do you think water will diffuse?
Water will diffuse INTO the cell until equilibrium is established

10. Osmosis: Hypertonic Solutions
Hypertonic (“Hyper-” is Greek for “over”)
When the concentration of solute molecules outside the cell is higher than their concentration in the cytosol(cell), the solution outside is hypertonic to the cytosol (cell).
What direction do you think water will diffuse?
Water will diffuse OUT OF the cell until equilibrium is established

11. Osmosis: Isotonic Solutions
Isotonic (“Iso-” is Greek for “equal”)
When the concentration of solute molecules inside and outside the cell are equal, the solution outside is isotonic to the cytosol(cell).
What direction do you think water will diffuse?
Water will diffuse IN AND OUT AT EQUAL RATES so there is no net movement of water (it’s in equilibrium!)

12. Hypertonic, Hypotonic, Isotonic Solutions
Section 1 Passive Transport
Chapter 5
Hypertonic, Hypotonic, Isotonic Solutions
Table 5-1, pg 99

13. Chapter 5 Osmosis, continued
Section 1 Passive Transport
Chapter 5
Osmosis, continued
The cell wall of plants are strong enough to resist the pressure (turgor pressure) exerted by water in the central vacuole.
The condition of turgor pressure decreasing is called plasmolysis, and is the reason that plants wilt if they don’t receive enough water
The bursting of cells due to the increase of turgor pressure is called cytolysis

15. Facilitated Diffusion
Section 1 Passive Transport
Chapter 5
Facilitated Diffusion
Facilitated diffusion is the transport of substances through a cell membrane along a concentration gradient with the aid of carrier proteins
Carrier protein is a protein that transports substances across a cell membrane
In facilitated diffusion, a molecule binds to a carrier protein on one side of the cell membrane.
The carrier protein then changes its shape and transports the molecule down its concentration gradient to the other side of the membrane.

16. Facilitated Diffusion
Section 1 Passive Transport
Chapter 5
Facilitated Diffusion
Facilitated diffusion does not require additional energy, so it is considered passive transport
Can work in two directions, both into and out of cell depending on concentration levels
A good example of facilitated diffusion is the transport of glucose (sugar).
Pg. 101, figure 5-5

17. Facilitated Diffusion
Section 1 Passive Transport
Chapter 5
Facilitated Diffusion

18. Diffusion Through Ion Channels
Section 1 Passive Transport
Chapter 5
Diffusion Through Ion Channels
Ion channels are proteins, or groups of proteins, that provide small passageways across the cell membrane through which specific ions can diffuse.
Each type of ion channel is usually specific for one type of ion
Ex. A calcium ion channel will allow only calcium ions to pass through it
Ions diffuse by moving through gates in cell membrane: these gates may open or close in response to three kinds of stimuli: stretching of the cell membrane, electrical signals, or chemicals in cytosol or external environment

19. Section 1 Passive Transport
Chapter 5
Ion Channels

20. Section 2 Active Transport
Chapter 5
Objectives
Distinguish between passive transport and active transport.
Explain how the sodium-potassium pump operates.
Compare endocytosis and exocytosis.

21. Chapter 5 Active Transport
Section 2 Active Transport
Chapter 5
Active Transport
Active transport moves molecules across the cell membrane from an area of lower concentration to an area of higher concentration.
Unlike passive transport, active transport requires cells to expend energy (ATP).

23. Contractile vacuoles are found in paramecia and help them pump water into and out of their cell. These require energy are a type of ACTIVE transport.

24. Cell Membrane Pumps: Sodium-Potassium Pump
Some types of active transport are performed by carrier proteins called cell membrane pumps.
The sodium-potassium pump move three Na+ ions out of the cell for every two K+ ions it moves into the cytosol
ATP supplies the energy that drives the pump
Animation

25. Sodium-Potassium Pump
Section 2 Active Transport
Chapter 5
Sodium-Potassium Pump

26. Chapter 5 Movement in Vesicles
Section 2 Active Transport
Chapter 5
Movement in Vesicles
Some substances, such as macromolecules and nutrients, are too large to pass through the cell membrane by diffusion or osmosis
In endocytosis, cells ingest external materials by folding around them and forming a pouch
This is transferring molecules into the cell
The pouch then pinches off and becomes a membrane-bound organelle called a vesicle.

27. Movement in Vesicles: Endocytosis
There are two types of endocytosis:
Pinocytosis (“cell drinking”) – vesicle contains solutes or fluids
Phagocytosis (“cell eating”) – vesicle contains large particles or other cells

28. Movement in Vesicles, continued
Section 2 Active Transport
Chapter 5
Movement in Vesicles, continued
Exocytosis
In exocytosis, vesicles made by the cell fuse with the cell membrane, releasing their contents into the external environment (out of the cell).
Cells may use exocytosis to release large molecules such as proteins, waste products, or toxins that would damage the cell if they were released within the cytosol
Exocytosis involves ridding the cell of material by discharging it from sacs at the cell surface

29. Endocytosis and Exocytosis
Section 2 Active Transport
Chapter 5
Endocytosis and Exocytosis
These two types of movement are exact opposites of each other,
in and out