1. TRANSPORT OF
MATERIALACROSS
THE CELL

2. PROCESS OF TRANSPORT ACROSS THE PLASMA
MEMBRANE
•Motion of substances in and out of the cell
• Cell membranes are Selectively permeable
• Two Types of Transport Mechanisms:
1. Passive Transport
2. Active Transport

3. Membrane transport
•Passive transport is movement of molecules
through the membrane in which no energy is
required from the cell
• Active transport requires energy expenditure by
the cell

4. 1. Passive Transport
•Passive transport is movement of molecules through the
membrane in which no energy is required from the cell.
• Molecules move in response to a concentration gradient.
- A concentration gradient is a difference between the
concentration on one side of the membrane and that on the
other side.
• Passive transport mechanisms only movement substances
along the concentration gradient.

5. 1. Passive Transport
•Passive transport mechanisms only movement
substances along the concentration gradient:
- Substances move from an area of high
concentration to an area of low concentration

6. 1. Passive Transport
•Mechanisms of Passive Transport:
1. Diffusion
- movement of solute molecules from high solute
concentration to low solute concentration
2. Osmosis
- movement of solvent water from high solvent
concentration to low solvent concentration

7. Diffusion
• Diffusion is movement of solute molecules from high
concentration to low concentration.

8. Diffusion
•There are two types of diffusion
1. Simple Diffusion
2. Facilitated Diffusion

9. 1.Simple Diffusion
•Substances pass directly through the cell
membrane
• The cell membrane has limited permeability
to small polar molecules, water, and ions
• The motion of water across the membrane is
known as osmosis

10. •The rate (molecules/s) of simple
diffusion depends on the degree of
concentration gradient
• As the gradient reaches equilibrium,
diffusion slows
• At equilibrium, substances pass in and
out of the membrane at equal rates

11. 2.Facilitated Diffusion
•Substances must pass through
transported proteins to get through the
cell membrane.
• The cell membrane is selectively
permeable.
•Carrier proteins bind to the molecule
that they transport across the
membrane.

12. 2.Facilitated Diffusion
•Selective permeability: integral membrane proteins
allow the cell to be selective about what passes through
the membrane.
- Channel proteins have a polar interior allowing
polar molecules to pass through.
- Carrier proteins bind to a specific molecule to
facilitate its passage.

13. ion channels

14. Carrier Proteins
• Carrier proteins bind to a specific molecule to
facilitate its passage.

15. Osmosis
•Osmotic concentration is
determined by the
concentration of all solutes in
solution.

16. 16
2. Active Transport
Active transport
• Requires energy – ATP is used directly or indirectly to fuel active
transport
• Able to moves substances against the concentration gradient - from
low to high concentration
- allows cells to store concentrated substances
• Requires the use of carrier proteins

17. Active transport

18. Fig. 5.15-2

19. Fig. 5.15-3

20. 20
Bulk Transport
• Bulk transport of substances is accomplished by
1. Endocytosis – movement of substances into the cell
2. Exocytosis – movement of materials out of the cell

21. 21
Bulk Transport
• Endocytosis occurs when the plasma membrane
envelops food particles and liquids.
1. phagocytosis – the cell takes in particulate
matter
2. pinocytosis – the cell takes in only fluid
3. receptor-mediated endocytosis – specific
molecules are taken in after they bind to a receptor

22. 22

23. 23