1. Transport Across Membranes
2.4

2. Importance of Transport
intake of nutrients
removal of wastes
communication with environment & other cells
blocking passage of harmful substances

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
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. Image from: http://schoolworkhelper

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. Osmosis the diffusion of water across a membrane
water follows concentration gradient until equilibrium

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

10. 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 10
G. Podgorski, Biol. 1010 10

11. 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 11
G. Podgorski, Biol. 1010 11

12. 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 12
G. Podgorski, Biol. 1010 12

13. Cells and Tonicity
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14. Red Blood Cells
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15. copyright cmassengale
The Plasma Membrane
4/25/2017
isotonic
hypotonic
hypertonic
hypertonic
isotonic
hypotonic
copyright cmassengale 15
G. Podgorski, Biol. 1010 15

16. 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?

17. 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?)

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

20. Primary Active Transport
pumps move positively charged ions (H+, Ca2+, Na+, K+) across membranes
creates electrochemical gradient
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21. Secondary Active Transport
uses gradient established by a primary active transport pump
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22. Bulk Transport
movement of larger substances across a cellular membrane
requires energy (ATP)
exocytosis & endocytosis

23. Endocytosis
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24. Exocytosis Neurotransmitters
Image from:
Neurotransmitters

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