1. How do substances travel across cell membranes?
SB1. Students will analyze the nature of the relationships between structures and functions in living cells.
a. Explain the role of cell organelles for both prokaryotic and eukaryotic cells, including the cell membrane, in maintaining homeostasis and cell reproduction.
b. Explain how enzymes function as catalysts.
c. Identify the function of the four major macromolecules (i.e., carbohydrates, proteins,
lipids, nucleic acids).
d. Explain the impact of water on life processes (i.e., osmosis, diffusion).
How do substances travel across cell membranes?

2. The Plasma Membrane
The Gateway to the Cell

3. The Plasma Membrane Regulates What Enters and Leaves the Cell
How does it do this?

4. Structure of the Plasma Membrane
Consist of a Combination of Phospholipids, cholesterol, proteins and carbohydrates
The phospholipid bilayer allows other molecules to “float” in the membrane.

5. Membrane Proteins
Marker Proteins – like nametags to identify the cell to other cells. Works with the immune system
Transport Proteins – Move materials into and out of the cell
Receptor Proteins – Allows the cell to interact with other cells.

6. Molecular Movement Across the Plasma Membrane

7. Cell membranes are SELECTIVELY PERMEABLE
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Cell membranes are SELECTIVELY PERMEABLE
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8. Movement of Molecules Across the Cell Membrane
Passive Transport – requires no cellular energy
Active Transport – Requires cellular
energy

9. Types of Passive Transport
Diffusion –
Molecules move with a Concentration Gradient, from high concentration to low concentration.
Requires no energy
Molecules continue to move until an equilibrium is reached

10. Dynamic Equilibrium
Reached when diffusion of material into the cell equals diffusion of material out of the cell
Molecules continue to move, but the overall concentration remains the same.

11. Diffusion only works with small molecules

12. Osmosis
The Diffusion of Water Across a Selectively Permeable Membrane

13. Osmotic Pressure Gradients
In general, water moves toward the area with a higher solute concentration because it has a lower water concentration.

14. Hypertonic Solutions Solute concentration is higher outside the cell.
Water diffuses out of the cell = Cell Shrinks
Blood Cell
Plant Cell

15. Hypotonic Solutions Solute concentration is higher inside the cell.
Water diffuses into the cell = Cell Swells
Plant Cell
Blood Cell

16. Isotonic Solution
Water and dissolved substances diffuse into and out of the cell at the same rate = No Change in Cell Size
Plant Cell
Blood Cell

17. What if a cell needs to move _____ or ______ molecules that can’t get through the membrane?
LARGE
POLAR

18. Facilitated Diffusion
Diffusion with help!!
Uses Transport Proteins to move large molecule across the plasma membrane

19. Facilitated diffusion: Molecules move with the concentration gradient
Facilitated diffusion: Molecules move with the concentration gradient. Downhill !! No Energy!! Two types of transport proteins:
Channel Proteins
Carrier Proteins

20. EXAMPLES OF FACILITATED DIFFUSION IN CELLS
CARRIER PROTEINS
ION CHANNELS
AQUAPORINS (OSMOSIS)
GLUCOSE
Na+ , Cl- , Ca++ , K+
WATER

21. What if cell needs to move molecules really _______
What if cell needs to move molecules really _______? (can’t wait for it to diffuse)
FAST
Cell example:
Movement of Na + & K+ ions
required to send
nerve signals

22. Active Transport
Move molecule against the concentration gradient. Uphill!!
Known as solute or ion pumps

23. Types of Active Transport Pumps
Cellular Structure and Function
Types of Active Transport Pumps
Vesicles:
Endocytosis- Take stuff into cell
Phagocytosis- Cell Eats
Pinocytosis- Cell Drinks
Exocytosis- Dump stuff out of cell
Pumps:
Na+/K+ ATPase pump
Moves three Na+ ions out of the cell and two K+ ions into the cell

24. REVIEW