1. Transport Across Membranes
2.4

2. Transport Across Membranes
the movement of materials into and out of the cell is critical to a cell’s survival and functioning

3. Passive Transport
the movement of materials across the cell membrane without the use of chemical energy (ATP)
occurs because of diffusion

4. Diffusion
the net movement of a substance from an area of higher concentration to an area of lower concentration
dynamic equilibrium
Image from:

5. Simple Diffusion substances move across membrane unassisted
small non-polar molecules (O2, CO2, steroid hormones, some drugs) and small polar molecules (H2O, glycerol)
larger molecules and ions can not pass through membranes unassisted

6. Homework, p.97 #6
6a. How do size, polarity, and charge influence the ability of a substance to diffuse across a membrane?
6b. Which combinations of these factors require cells to use active transport to move a substance across a membrane?

7. Facilitated Diffusion
diffusion across membrane assisted by integral membrane proteins called transport proteins
channel proteins vs. carrier proteins
ions, water, amino acids, sugars, etc.

8. Image from: http://schoolworkhelper

9. Homework, p.97 #2
Facilitated diffusion is specific. What does this mean?

10. Osmosis the diffusion of water across a membrane
water follows concentration gradient (low solute concentration to high) until equilibrium

11. Homework, p.97 #1
Your biology study partner asks you a question about the concentration gradient of water. What is meant by the term “concentration gradient”? Is your study partner using the term correctly in reference to water? Explain why or why not.

12. Osmosis
direction of osmosis changes depending on type of solution surrounding the cell:
isotonic solution
hypotonic solution
hypertonic solution

13. Cell in Isotonic Solution
The Plasma Membrane
4/25/2017
Cell in Isotonic Solution
10% NaCL 90% H2O
ENVIRONMENT
CELL
NO NET MOVEMENT
10% NaCL
90% H2O
What is the direction of water movement?
equilibrium
The cell is at _______________.
copyright cmassengale 13
G. Podgorski, Biol. 1010 13

14. Cell in Hypotonic Solution
The Plasma Membrane
4/25/2017
Cell in Hypotonic Solution
10% NaCL 90% H2O
CELL
20% NaCL
80% H2O
What is the direction of water movement?
copyright cmassengale 14
G. Podgorski, Biol. 1010 14

15. Cell in Hypertonic Solution
The Plasma Membrane
4/25/2017
Cell in Hypertonic Solution
15% NaCL 85% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
What is the direction of water movement?
copyright cmassengale 15
G. Podgorski, Biol. 1010 15

16. Homework, p.97 #4
Distilled water is considered hypotonic to body cells. Explain.

17. Cells and Tonicity
Image from:

18. Red Blood Cells
Image from:

19. Homework, p.97 #3
3. A red blood cell was placed in a beaker of solution. The cell immediately began to swell and finally burst. Explain what happened, referring to the cytosol of the cell and the solution in the beaker.

20. copyright cmassengale
The Plasma Membrane
4/25/2017
isotonic
hypotonic
hypertonic
hypertonic
isotonic
hypotonic
copyright cmassengale 20
G. Podgorski, Biol. 1010 20

21. How does this impact…
…a single-celled organism living in a freshwater environment?
…a single-celled organism living in a salt-water environment?
…the roots of a plant in the spring after salt has been sprinkled during the winter?

22. More applications… Why can’t you water a plant with salt water?
Why do vegetables in the grocery store get sprayed with water periodically? (What would happen if they were sprayed with salt water?)

23. Active Transport
Image from:

24. Active Transport
the movement of materials against the concentration gradient
requires cellular energy (ATP)

25. Primary Active Transport
pumps move positively charged ions (H+, Ca2+, Na+, K+) across membranes
creates electrochemical gradient
Image from:

26. Secondary Active Transport
uses gradient established by a primary active transport pump
Image from:

27. Homework, p.97 #5
5. Compare the energy requirements of passive transport, primary active transport, and secondary active transport.

28. Homework, p.97 #7
7a. How does the concentration of a solute on the two sides of a membrane affect passive transport?
7b. How does this concentration affect primary and secondary active transport?

29. Bulk Transport
movement of larger substances across a cellular membrane
requires energy (ATP)
exocytosis & endocytosis

30. Endocytosis
Image from:

31. Exocytosis Neurotransmitters
Image from:
Neurotransmitters

32. Homework, p.97 #8
8a. What process is shown in the micrographs in Figure 13?
(8b. Draw a labelled scientific drawing of the micrographs.)

33. Credits
Slides #10, 11, 12, and 15 taken from Powerpoint presentations created by Cheryl Massengale, educator extraordinaire & creator of