1. Transport Across the Cell Membrane
SBI4U1

2. Cell Membrane Semi-permeable phospholipid bilayer
Glucose, amino acids, and lipids can enter the cell
Some other molecules, such as ions cannot readily pass through the cell membrane

3. Types of Transport Passive Active No energy High to low concentration
Follows con’c gradient
Active
Requires energy
Low to high concentration
Against con’c gradient

4. Passive Transport: Diffusion
Natural movement of molecules from high[con’c] to low [con’c]
Continues until equilibrium is reached
Factors that affect diffusion rate:
Molecule Size: ↑ size = ↓rate of diffusion
Molecule Polarity: small polar molecules diffuse slower than non-polar molecules
Molecule/Ion Charge: cannot diffuse w/ a charge

6. Passive Transport: Osmosis
The movement of H2O an area of high [con’c ] to an area of lower [con’c ]
If a cell has too much H2O  cell swells
If a cell has too little H2O  cell shrinks

7. Hypertonic Sol’n (hyper = more than)
Sol’n w/ higher [con’c]
Hypotonic Sol’n (hypo = less than)
Sol’n w/ lower [con’c]
Isotonic Sol’n (iso – same)
Same osmotic concentration/equilibrium

8. Less solutes inside
More solutes outside
H2O leaves
Cell shrivels (crenation)
More solutes inside
Less solutes outside
H2O enters
Cell bursts (lysis)
No net movement of
H2O

9. Passive Transport: Facilitated Diffusion
Movement of molecules or ions across a membrane via channel proteins and carrier proteins
Channel Proteins
Non-polar hydrophilic hole inside through which molecules/ions pass through
Uses [con’c] gradient
E.g. Na+ ions and K+ ions

10. For ions and small polar molecules E.g. Glucose
Carrier Proteins
Bind to specific molecules, transport them across membrane, then release
For ions and small polar molecules
E.g. Glucose

11. Active Transport Against the conc’ gradient
Requires energy: adenosine triphosphate (ATP)
ATP is derived from adenosine nucleotide

13. Primary Active Transport
Direct use of ATP
E.g. Sodium-potassium pump
Transports Na+ ions out and K+ ions into the cell
**Use textbook to review steps

15. Secondary Active Transport
Indirect use of ATP
Result of ion pump is an electric potential across the membrane
One side; + and one side
[] gradient builds up w/ ions creating electrochemical gradient
E.g. Hydrogen-sucrose pump
**Use textbook to review steps

17. Membrane-Assisted Transport
Macromolecules are too large to cross the cell membrane
Requires energy
Two forms: endocytosis and exocytosis
Endocytosis
Cell engulfs material by folding cell membrane around it and pinching it off

18. Phagocytosis
Endocytosis of solid particles
Pinocytosis
Endocytosis of liquid particles

19. Exocytosis
Macromolecules leave cell
Vesicles with waste material fuse w/ cell membrane
Empty contents to extracellular environment
Vesicles becomes part of cell membrane
E.g. In humans specialized glands secrete sebum, an oily substance that lubricate skin, hair, and eyes

20. Review the Cellular Transport Summary Table in your textbook.