1. Ch.7-3 I Passive Transport Mechanisms
Cells

2. POINT > Define concentration gradient
POINT > Define passive transport
POINT > Describe diffusion
POINT > Describe facilitated diffusion
POINT > Define osmosis
POINT > Describe the dynamics of osmosis

3. Selectively Permeable Membrane (Semipermeable)
Some substances can pass across, others cannot
H2O
Glucose
Outside Cell
Inside Cell

4. POINT > Define concentration gradient
A concentration gradient is a difference in the concentration of solutes in a solution
High
Concentration
Low
Concentration
Moving DOWN gradient
Solutes tend to move from high to low concentration (down)

5. POINT > Define concentration gradient
Movement of solutes from low to high concentration is described as “up” the gradient or “against” the gradient
High
Concentration
Low
Concentration
Moving UP gradient
Moving DOWN gradient

6. POINT > Define passive transport
In passive transport, no cellular energy is required for the movement to occur

7. POINT > Describe diffusion
Diffusion is a type of passive transport. Solutes travel down the concentration gradient from high to low

8. POINT > Describe diffusion
Diffusion: solutes move from high concentration to low concentration
Outside Cell
Inside Cell
CO2

9. POINT > Describe diffusion
Diffusion: solutes move down the concentration gradient
Outside Cell
Inside Cell

10. WB CHECK: Which statement(s) is true about diffusion?
Solutes move down the gradient from low conc. to high conc
Solutes move up the gradient from high conc. to low conc
Solutes move down the gradient from high conc. to low conc
Solutes move up the gradient from low conc. to high conc

11. POINT > Describe diffusion
Diffusion ends up in dynamic equilibrium: The conc. of solutes is equal throughout (equilibrium) The solutes continue to move (dynamic)

12. POINT > Describe diffusion
Diffusion usually involves small, uncharged compounds (O2, CO2)
Outside Cell
Inside Cell

13. WB CHECK: Which statement(s) is true about diffusion?
Diffusion ends in dynamic equilibrium
Diffusion reverses the concentration gradient
Diffusion involves particles of all sizes
Diffusion usually involves charged particles
a and c
a-d

14. POINT > Describe facilitated diffusion
Glucose molecules
Facilitated Diffusion:
Solutes that can’t diffuse directly across membrane can pass with help from channel/transport proteins
Transport proteins only allow specific substances through
Protein channel

15. POINT > Describe facilitated diffusion
Glucose molecules
Facilitated Diffusion:
Molecules move from high conc. to low conc.
Allows large molecules & ions to pass through the membrane very quickly (Glucose, K+, Cl-, Na+)
Protein channel

16. WB CHECK: In facilitated diffusion
solutes move against the concentration gradient
only small, uncharged particles are involved
large and charged particles move up the gradient
large and charged particles move down the gradient
a and d
b and d

17. WB CHECK: Facilitated diffusion requires carbohydrates in the membrane
requires transport proteins in the cytoplasm
requires transport proteins in the membrane
requires transport proteins outside the cell
all of the above
b and c

18. POINT > Define osmosis
Osmosis is a type of facilitated diffusion Osmosis is the diffusion of water through a membrane Some cells use channel proteins called aquaporins to move water in and out quickly

19. POINT > Describe the dynamics of osmosis
During osmosis, H2O molecules move across the membrane from area of higher conc. to area of lower conc.
This occurs because the membrane is not permeable to some solute, but is permeable to water

20. POINT > Describe the dynamics of osmosis
Important Note! Water conc. & solute conc. are inversely proportional
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Higher Water Conc.
Lower Water Conc.
Lower Solute Conc.
Higher Solute Conc.

21. POINT > Describe the dynamics of osmosis
Lower Water Conc.
Na-
Na-
Higher Water Conc.
Na-
Na-
Higher Solute Conc.
Na-
Lower Solute Conc.
Na-
Na-
Na-
Na-
Na-

22. POINT > Describe the dynamics of osmosis
Outside Cell
Inside Cell
Na+

23. POINT > Describe the dynamics of osmosis
Isotonic solution: Concentration of solutes is equal on both sides of membrane

24. POINT > Describe the dynamics of osmosis
Hypertonic solution: Conc. of solute is higher compared to other side of membrane Remember: Higher solute concentration = lower water concentration

25. POINT > Describe the dynamics of osmosis
Hypotonic Solution: Conc. of solute is lower compared to other side of membrane Remember: Lower solute concentration = higher water concentration

26. POINT > Describe the dynamics of osmosis
Hypertonic & hypotonic solutions are always paired: for every hypertonic solution, the other side of the membrane must be hypotonic

27. WB CHECK: A solution that is more salty than another is isotonic
hypotonic
hypertonic
depends on the solute

28. WB CHECK: Compared to the cytoplasm, pure water is isotonic hypotonic
hypertonic

29. POINT > Describe the dynamics of osmosis
Hypotonic
Solution
Hypertonic
Solution

30. POINT > Describe the dynamics of osmosis
Hypertonic
Solution
Hypotonic
Solution
Outside Cell
Inside Cell
Na+
Na-+

31. POINT > Describe the dynamics of osmosis
Isotonic
Solutions
Outside Cell
Inside Cell
Na+

32. POINT > Describe the dynamics of osmosis
Osmotic Pressure:
Net movement of water into or out of a cell, driven by differences in solute concentration
Cytoplasm contains many dissolved solutes

33. POINT > Describe the dynamics of osmosis
Effects of Osmosis on Cells
Solution
Isotonic
Hypertonic
Hypotonic
Effect on Cell
Animal Cell
No NET
movement
Net movement
OUT of cell
Net movement
INTO cell

34. WB CHECK: The size of a cell placed in pure water would
decrease as water leaves the cell
be unchanged
increase as solutes enter the cell
increase as water enters the cell

35. Recap
Passive Transport
Diffusion
Facilitated Diffusion
Osmosis

36. Homework: Read 7.3 on Passive Transport Page 213 #1 a-c, #3 Workbook pages 101-103