1. Cell Transport
AP Biology ch 7

2. Cell Membrane Structure & Function
Fluid mosaic model

3. Cell Membrane Structures

4. Fluid Mosaic Model

5. Moving substances into/out of a cell
Cells need various molecules to function
Transporting molecules is essential to life

6. Passive Transport

7. Passive Transport Movement of substances without energy expenditure
Diffusion
Facilitated diffusion
Osmosis

8. Diffusion
Molecules moves from high concentration to low concentration (down the concentration gradient)
Biological Ex:
CO2 and O2

9. Facilitated Diffusion
Some molecules need help entering the cell
Charged or too big
Proteins help molecules w/o using energy
Biological Ex:
glucose & water

10. Osmosis
When solutes are unable follow the concentration gradient across the membrane, water responds
Biological Ex:
Salt: (Hypotonic, Hypertonic, Isotonic solutions)

11. Osmotic Solutions Hypertonic: Isotonic: Hypotonic:
Water concentration inside a cell is higher than outside the cell
Isotonic:
Water and solute concentrations in a cell are equal
Hypotonic:
Water concentration inside a cell is lower than outside the cell

12. Osmotic Images

13. Water Potential

14. Water potential = solute potential + pressure potential
One of the most confusing concepts/math in AP Bio!
Water potential:
Quantifies the potential of water to move into/out of a system
Uses math to predict movement of water in/out of plant cells
Water potential = solute potential + pressure potential
Ψ = Ψs + Ψp

15. Easiest Water Potential Story Problem
What is the water potential of distilled water in an open beaker?
Ψ = Ψs + Ψp
Ψ = 0 + 0

16. In living organisms, there are variables
Solutes:
Sucrose:
Glucose: C6H12O6
Salt: NaCl
Pressure:
Cell wall

17. Easy water potential story problem
Calculate the water potential (Ψ) of a plant cell when the solute potential (Ψs) is bars and the pressure potential (Ψp) is 0.30 bars.
Ψ = Ψs + Ψp
Ψ =

18. Easy water potential story problem
If this cell (Ψ of 0.07), is placed in a solution with a Ψ of 0.05 which direction will water move?
Since,
Water will move based upon Ψ (high Ψ  low Ψ)
And 0.07 > 0.05
Then,
Water will move out of the cell into the solution

19. Elaboration of Pressure Potential
Usually a given in the story problem:
Ex: Ψp = 4 bars
Positive Value:
Occurs when water enters a cell
Increasing internal water exerts an outward pressure on the cell wall (turgor)
Negative pressure:
Occurs when water is pulled through an opening
Xylem pulls water from the roots to the leaves for photosynthesis

20. Elaboration of Solute Potential
Rarely given in a story problem:
Always negative in a plant cell (pure water is zero)
Ψs = -iCRT
-i = ionization constant (standard value of a molecule (1-2))
How many ions form from the molecules dissolving
C = concentration (moles/liter)
More solutes, less water
R = pressure constant (.0831 liter bars/mole K)
Always .0831
T = temperature (K = (273 + C))
Increase temperature, increase molecule movement

21. Difficult plant water potential story problem
The value for Ψ in root tissue was found to be -3.3 bars. If you take the root tissue and place it in a 0.1 M solution of sucrose at 20°C in an open beaker, what is the Ψ of the solution, and in which direction would the net flow of water be? Root cell Ψ = -3.3

22. Difficult plant water potential story problem
The value for Ψ in root tissue was found to be -3.3 bars. If you take the root tissue and place it in a 0.1 M solution of sucrose at 20°C in an open beaker, what is the Ψ of the solution, and in which direction would the net flow of water be?
Beaker Ψ = Ψp + Ψs
Beaker Ψ = 0 + -iCRT
Beaker Ψ = *0.1M*0.0831*(273+20) = -2.43

23. Difficult plant water potential story problem
The value for Ψ in root tissue was found to be -3.3 bars. If you take the root tissue and place it in a 0.1 M solution of sucrose at 20°C in an open beaker, what is the Ψ of the solution, and in which direction would the net flow of water be?
Root cell Ψ = -3.3
Beaker Ψ = -2.43
Water moves from High to Low: into the cell

24. Active Transport

25. Active Transport Movement of substances with energy expenditure
Endocytosis
Exocytosis

26. Active Transport
Some carrier proteins move molecules against the concentration gradient.
Biological Ex:
Ions
Glucose
Amino Acids

27. Exocytosis Substance is contained within a vesicle
Vesicle fuses with cell membrane
Contents are expelled into environment

28. Phagocytosis (Endocytosis)
Cell approaches food particle
Pseudopodium surrounds food
Food vacuole forms

29. Pinocytosis (Endocytosis)
Cell brings in liquid using a vesicle

30. Receptor-mediated endocytosis
Receptors bind to specific molecules 30

31. Ex: Sodium/Potassium Pump
In the cytoplasm of an animal cell:
high K+ concentration
low Na+ concentration

32. Ex: Proton Pump In plants, fungi, bacteria,
H+ are pumped out of the cell

33. Cell Transport Summary