1. Cell Transport
Chapter 4

2. Cells and Homeostasis How do cells maintain homeostasis? Chapter 4
Section 1 Passive Transport
Cells and Homeostasis
How do cells maintain homeostasis?
Cell membrane controls the movement of substances in and out of the cell
2 Types of transport:
Active: Requires energy
Passive: Does not require energy

3. passive transport: Chapter 4 concentration gradient:
Section 1 Passive Transport
passive transport:
Movement across the cell membrane that does not require energy from the cell
concentration gradient:
difference in the concentration of a substance
Equilibrium:
condition in which the concentration of a substance is equal throughout a space.
TREND towards EQUILIBRIUM

4. Chapter 4
Section 1 Passive Transport
Diffusion
movement of a substance from an area of high concentration to an area of lower concentration
What causes this?
random motion of particles of the substance
Many molecules and ions dissolved in the cytoplasm and in the fluid outside cells, enter or leave cells by diffusion

5. Chapter 4
Section 1 Passive Transport
Diffusion

6. Diffusion Example Chapter 4 Section 1 Passive Transport
Because of diffusion, food coloring (blue) will gradually move through uncolored gelatin (yellow), as shown in the beakers below.

7. Chapter 4
Section 1 Passive Transport
Osmosis
The diffusion of water through a selectively permeable membrane (What is this?)
involves the movement of a substance—water—down its concentration gradient (remember what this is!)
passive transport

8. Osmosis 3 possibilities for the direction of water movement: Chapter 4
Section 1 Passive Transport
Osmosis
3 possibilities for the direction of water movement:
Water moves out.
water diffuses out of the cell
cell shrinks
solution that causes a cell to shrink due to osmosis is a hypertonic solution.
No net water movement.
solution that produces no change in cell volume because of osmosis is called an isotonic solution
Water moves in
water diffuses into the cell
cell swells.
A solution that causes a cell to swell because of osmosis is called a hypotonic solution

9. Hypertonic, Hypotonic, and Isotonic Solutions
Chapter 4
Section 1 Passive Transport
Hypertonic, Hypotonic, and Isotonic Solutions

10. Cell Membrane is a barrier How do water and other substances cross it?
Chapter 4
Section 1 Passive Transport
Cell Membrane is a barrier How do water and other substances cross it?
Ion Channels
transport protein with a polar pore through which ions can pass.
spans the thickness of the cell membrane.
ion that enters the pore can cross the cell membrane without contacting the nonpolar interior of the lipid bilayer.

11. Chapter 4
Section 1 Passive Transport
Ion Channels

12. Chapter 4
Section 1 Passive Transport
******* Influence on Ion Transport:
movement of a charged particle is influenced by the particle’s electrical charge.
positively charged ion located outside the cell is more likely to diffuse into the cell, where the charge is negative.
negatively charged ion located inside the cell is more likely to diffuse out of the cell.

13. Facilitated Diffusion
Chapter 4
Section 1 Passive Transport
Facilitated Diffusion
transport specific substances—such as amino acids and sugars—down their concentration gradient that transport is called facilitated diffusion
How is this accomplished?
carrier proteins: can bind to a specific substance on one side of the cell membrane, carry the substance across the cell membrane, and release it on the other side.

14. Facilitated Diffusion
Chapter 4
Section 1 Passive Transport
Facilitated Diffusion

15. Movement Against a Concentration Gradient
Chapter 4
Section 2 Active Transport
Movement Against a Concentration Gradient
active transport
transport of a substance across the cell membrane against its concentration gradient
requires the cell to use energy
WHY?
Most often, the energy is ATP.

16. Sodium-Potassium Pump
Chapter 4
Section 2 Active Transport
Sodium-Potassium Pump
One of the most important membrane pumps in animal cells
transports three sodium ions, Na+, out of a cell and two potassium ions, K+, into the cell during a complete cycle
Na+/K+ Pump Animation

17. Sodium-Potassium Pump
Chapter 4
Section 2 Active Transport
Sodium-Potassium Pump
4 steps:
3 sodium ions inside the cell bind
The pump changes shape, transporting the three sodium ions across the cell membrane and releasing them outside the cell.
Two potassium ions outside the cell bind to the pump.
The two potassium ions are transported across the cell membrane and are released inside the cell.

18. Sodium-Potassium Pump
Chapter 4
Section 2 Active Transport
Sodium-Potassium Pump

19. Movement in Vesicles Chapter 4
Section 2 Active Transport
Movement in Vesicles
VERY VERY large substances moveve across the cell membrane by vesicles.
Examples: proteins and polysaccharides
Endocytosis: movement of a substance into a cell by a vesicle
Exocytosis: movement of a substance by a vesicle to the outside of a cell
Khan Academy Endocytosis and Exocytosis

20. Endocytosis Phagocytosis:
Pinocytosis:
“Cell drinking”
Material that the cell takes in is liquid
“Cell eating”
Material that the cell takes
in may include particulate,
digested particles or other
fragments of organic matter

21. Endocytosis and Exocytosis
Chapter 4
Section 2 Active Transport
Endocytosis and Exocytosis

22. Endocytosis and Exocytosis
Chapter 4
Section 2 Active Transport
Endocytosis and Exocytosis

23. Membrane Receptor Proteins
Chapter 4
Section 2 Active Transport
Membrane Receptor Proteins
Cells can receive the messages carried by certain signal molecules because the cell membrane contains specialized proteins, called receptor proteins, that bind these signal molecules.
receptor protein: protein that binds to a specific signal molecule, enabling the cell to respond to the signal molecule.

24. Chapter 4
Section 2 Active Transport
Functions of Receptor Proteins
Changes in Permeability The binding of a signal molecule to the receptor protein causes an ion channel to open, allowing specific ions to cross the cell membrane.
Second Messengers The receptor protein may cause the formation of a second messenger inside the cell. The second messenger acts as a signal molecule and amplifies the signal of the first messenger—that is, the original signal molecule.
Enzyme action The receptor protein may act as an enzyme. When a signal molecule binds to the receptor protein, the receptor protein may speed up chemical reactions inside the cell.

25. Changes in Permeability
Chapter 4
Section 2 Active Transport
Changes in Permeability

26. Chapter 4
Section 2 Active Transport
Second Messengers