1. Chapter 3
Cells
Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Movements Through Cell Membranes
Physical (Passive) Processes
Require no cellular energy and include:
Simple diffusion
Facilitated diffusion
Osmosis
Filtration
Physiological (Active) Processes
Require cellular energy and include:
Active transport
Endocytosis
Exocytosis
Transcytosis

3. Simple Diffusion
Movement of substances from regions of higher concentration to regions of lower concentration until equilibrium is reached
Oxygen, carbon dioxide and lipid-soluble substances
Permeable membrane
Solute molecule W
ater molecule A B A B A B
(1)
(2)
(3) T
ime

4. Animation: How Diffusion Works
Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at
Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

5. Facilitated Diffusion
Diffusion across a membrane with the help of a channel or carrier molecule
Glucose and amino acids
The number of carrier molecules in the cell membrane limits the rate of this process
Region of higher
concentration
Transported
substance
Region of lower
concentration
Protein carrier
molecule
Cell
membrane

6. Animation: How Facilitated Diffusion Works
Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at
Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

7. Osmosis Special case of diffusion
Movement of water through a selectively permeable membrane from regions of higher concentration to regions of lower concentration
Water moves toward a higher concentration of solutes
Selectively
permeable
membrane
Protein molecule W
ater molecule A A B B
(1)
(2) T
ime

8. Animation: How Osmosis Works
Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at
Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

9. Osmosis and Osmotic Pressure
Osmotic Pressure – ability of osmosis to generate enough pressure to move a volume of water
Osmotic pressure increases as the concentration of nonpermeable solutes increases.
(a)
Isotonic – same osmotic pressure
Cells placed in isotonic have no net gain or loss of water.
Hypertonic – higher osmotic pressure (water loss)
Cells placed in hypertonic solution lose water.
Hypotonic – lower osmotic pressure (water gain)
Cells placed in hypotonic solution gain water.
(b)
(c)

10. Filtration
Smaller molecules are forced through porous membranes because of hydrostatic pressure
Molecules leaving blood capillaries
Blood pressure is a type of hydrostatic pressure
Capillary wall
Tissue fluid
Blood
pressure
Blood
flow
Larger molecules
Smaller molecules

11. Active Transport
Carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration
Requires energy (as much as 40% of cell’s energy supply)
Sugars, amino acids, sodium ions, potassium ions, calcium ions, hydrogen ions etc.
Carrier protein
Binding site
Region of higher
concentration
Cell membrane
Region of lower
concentration
Phospholipid
molecules
Transported
particle
(a)
Carrier protein
with altered shape
Cellular
energy
(b)

12. Active Transport: Sodium-Potassium Pump
Active transport mechanism
Creates balance by “pumping” three (3) sodium (Na+) OUT and two (2) potassium (K+) INTO the cell
3:2 ratio

13. Animation: How the Sodium-Potassium Pump Works
Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at
Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

14. Endocytosis
Cell engulfs a substance that is too large to be transported by other means by forming a vesicle around the substance
Three types:
Pinocytosis – substance is mostly water
Phagocytosis – substance is a solid
Receptor-mediated endocytosis – requires the substance to bind to a membrane-bound receptor
Cell
membrane V
esicle
Nucleus
Nucleolus

15. Endocytosis Cell membrane Particle Phagocytized particle Vesicle
Nucleus
Nucleolus
Molecules
outside cell
Receptor-ligand
combination V
esicle
Receptor
protein
Cell
membrane
Cell
membrane
indenting
Cytoplasm
(a)
(b)
(c)
(d)

16. Exocytosis Reverse of endocytosis
Substances in a vesicle fuse with cell membrane
Contents released outside the cell
Release of neurotransmitters from nerve cells
Endoplasmic
reticulum
Golgi
apparatus
Nucleus

17. Receptor-mediated endocytosis
Transcytosis
Endocytosis followed by exocytosis
Transports a substance rapidly through a cell
HIV crossing a cell layer
HIV-infected
white blood cells
Anal or
vaginal canal V
iruses bud
HIV
Receptor-mediated endocytosis
Lining of anus
or vagina
(epithelial cells)
Exocytosis
Cell
membrane
Receptor-mediated
endocytosis
Virus infects
white blood cells on
other side of lining