3. Passive Transport
Substances are allowed to cross the cell
membrane without any input of energy
Remember: The cell membrane is
“selectively permeable”
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4. Types of Passive Transport
Diffusion
Facilitated Diffusion
Osmosis
5. Diffusion
Movement of molecules from areas of
high concentration to low
How does it work?
“Kinetic energy” (energy in motion)
Concentration gradient- caused by a
difference in concentration
Diffusion results in equilibrium (all
molecules occupy the same amount of
space)
6. Facilitated Diffusion
Some molecules are helped across the
cell membrane by carrier proteins
No energy is required in this process
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7. Osmosis
The diffusion of water across the
cell membrane
The direction of osmosis depends
on the concentration of solutes
inside and outside the cell
8. Osmosis (continued)
Hypotonic- concentration of solutes
outside the cell is lower than the
concentration inside
Hypertonic- concentration outside is
higher than inside
Isotonic- concentrations inside and out
are equal
9. Direction of Osmosis
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10. Active Transport
Sometimes cells must move molecules
against the concentration gradient
This process requires energy (ATP)
and special protein “pumps”
11. Sodium-Potassium Pump
Special proteins within the membrane
that transport Na+ and K- ions
Some cells must have a higher
concentration of Na+ ions outside of
the cell and a higher concentration of
K- ions inside the cell
2 Potassiums are brought in for every 3
Sodiums removed
12. Sodium-Potassium Pump
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13. Movement In Vesicles
Some molecules are too big to be
transported across the cell membrane
by passive and active transport
Endocytosis- “cell eating”
Exocytosis- “cell pooping”
14. Endocytosis
Process by which cells ingest
macromolecules, fluids, large particles
and even other cells
These molecules are enclose in a
bubble of membrane (vesicle) that
pinches away from the cell membrane
15. Endocytosis (continued)
Pinocytosis- ingestion of small
particles and fluid
Phagocytosis- ingestion of large
molecules or other cells
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16. Exocytosis
Process by which waste and large
particles are released from the cell
A vesicle will fuse with the membrane,
releasing its contents into the extra
cellular environment
17. Endocytosis/Exocytosis
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Editor's Notes
What is meant by the word transport? Moving substances across the cell membrane
What is the cell membrane made of? Lipids make it polar--> oxygen and co2 can readily pass through Small molecules can pass through protein pores
Spray aerosol into the corner of the classroom Kinetic energy --> Particles are constantly moving and bumping into each other Start a mosh pit in the corner of the classroom In the absence of outside influence diffusion will continue until equilibrium is reached
Molecules may be too large or not soluble in lipids --> glucose
Hypotonic solutions are good Cells adapt by pumping water or solutes out of the cytosol (contractile vacuoles or solute pumps) Plants love hypotonic environments --> turgor pressure Hypertonic solutions are bad…emkay Results in the loss of water --> plasmolysis Some cells cannot adjust to changes in environment (rbc’s) --> cytolysis or “cell bursting “ may result
Macromolecules, nutrients, large quantities of small molecules
The vesicles then fuse with other membrane bound organelles within the cell
Phagocytosis can be used to ingest bacteria or viruses that invade the body! Pic --> white blood cell ingestng bacteria
