1. Chapter 8 Cell Transport
Section 1 ~ Cell Membrane
Section 2 ~ Movements in and out of the cell
Section 3 ~ Cell Communication

2. Homeostasis
Homeostasis is the maintenance of stable internal conditions in a changing environment. Individual cells, as well as organisms, must maintain homeostasis in order to live.
One way that a cell maintains homeostasis is by controlling the movement of substances across the cell membrane. Cells are suspended in a fluid environment. Even the cell membrane is fluid. It is made up of a “sea” of lipids in which proteins float.

3. By allowing some materials but not others to enter the cell, the cell membrane acts as a gatekeeper.
The cell membrane also 1) provides structural support to the cytoplasm, 2) recognizes foreign material, and 3) communicates with other cells, all of which contribute to maintaining homeostasis.

4. Cell Membrane Surrounds cells Gives shape to animal cells
Inside cell wall of plant cells

5. Cell Membrane Made of: 1) Lipid (wax) bilayer 2) Protein channels
It is
Semi-permeable

6. Semi-permeable: Semi= “some” substances may pass
Selective on what gets in or goes out
Based upon size & solubility
H20 flows
Salt remains

7. -cytosis Exocytosis- endocytosis- When substances when substances
exit out of the cell enter into the cell

8. Cell Membrane

9. Membrane Proteins
Various proteins can be found in the cell membrane. Some proteins face inside the cell, and some face outside. Other proteins may stretch across the lipid bilayer and face both inside and outside.
Proteins are made of amino acids. Some amino acids are polar, and others are nonpolar.
The attraction and repulsion of polar(partial opposite charge at opposite ends) and nonpolar parts of the protein to water help hold the protein in the membrane.

10. Types of Proteins
Proteins in the cell membrane include: 1) cell-surface markers, 2) receptor proteins, 3) enzymes, and 4) transport proteins.
Cell-surface markers act like a name tag. A unique chain of sugars acts as a marker to identify each type of cell.
Receptor proteins enable a cell to sense its surroundings by binding to certain substances outside the cell. When this happens, it causes changes inside the cell.

11. Many specialized proteins called enzymes in the cell membrane help with important biochemical reactions inside the cell.
Many substances that the cell needs cannot pass through the lipid bilayer. Transport proteins aid the movement of these substances into and out of the cell (movement into or out of the cell is known as Cellular Transport).

12. The movement of materials in and out of cells
Cellular Transport
The movement of materials in and out of cells

13. Solution Concentration:
Like density =
# molecules per
volume of container
Low or High Concentration
* * * * *
* * * * * * * * * * * * * * *
High Conc.
* *
Low Conc.

14. 2 types of Passive Transport 1st ~Diffusion
Diffusion is the movement of molecules:
from High Concentration to Low Concentration
(like water flowing from high ground to low ground)
Before
After

15. Diffusion of gases……. O2
High
CO2
CO2
High
Conc.

16. 2nd passive Transport ~ Osmosis
Movement of water from high concentration to low concentration
Across a semi-permeable membrane
Special case of diffusion water only

17. Equilibrium H2O H2O H2O on both sides of membrane Osmosis stops
“Equi” =Equal concentrations
on both sides of membrane
Osmosis stops
Called an Isotonic Solution
cell stays same size
H2O H2O H2O

18. In Osmosis….only H2O (water) moves
Therefore focus on the water concentration:
1% Salt solution
Water is high concentration
Salt is Low
Like traveling downhill!
10% Salt Solution
Water is low
concentration
Salt is High

19. Concentration Gradient
* *
* * * *

20. Passive Transport Diffusion or Osmosis Going with the gradient
No ATP energy required
High Conc. To Low Conc.
* * * * * * * * * *

21. Active Transport Against the gradient Requires ATP
Low to High Concentrations
Salt returning to blood in kidneys
Like riding a bike uphill!!!
Going against the flow.
* * * * * * * * * * *

22. Active or Passive Transport?
Which requires ATP energy?
Which goes with the concentration gradient?
Which goes against the gradient?

23. Plasmolysis Cell membranes shrink or expand
Dependent on salt concen-trations

24. Hypotonic or Hypertonic Solutions?
Tap
Water
Hypotonic = “under” or low salt outside, relative to cell
Hypertonic = “over” or high salt relative to cell
Salt water
inside cell

25. Sea water organism in fresh water……………….
Tap
Water
Hypotonic Solution =
Low salt concentration outside the cell
High Water concentration outside
Water moves?
Inside
Cell Swells and increases!
Salt Water
Inside Cell
Low Water
H20

26. Fresh water organism in salt water………….
Hypertonic Solution
Water moves?
Out of the cell
Cell shrinks
Salt Water
High salt
Low water
Fresh water
Inside cell=
High Water
H20

27. Plants cells bulge, not burst!
Animal cells can burst.
Why can they burst, but not plant cells?
Or Cell Membranes Shrink
Answer:
Plant cells have a rigid cell wall which animal cells don’t!!!

28. Paramecium (1 celled organisms) have water pumps to pump out excess water! (called contractile vacuoles)

29. Cellular Transport What substances move ? How do they move?
What is the membrane structure?
What is passive versus active transport?

30. Sending Signals, continued
Cells communicate and coordinate activity by sending chemical signals that carry information to other cells.
A signaling cell produces a signal, often a molecule, that is detected by the target cell.
Typically, target cells have specific proteins that recognize and respond to the signal.

31. Sending Signals, continued
Neighboring cells can communicate through direct contact between their membranes.
Nerve cells also signal information to distant locations in the body, but their signals are not widely distributed.
While most signal molecules originate within the body, some signals come from outside. For example, light has a great effect on the action of hormones in plants. The length of day determines when some plants flower.

32. Receiving Signals
A target cell is bombarded by hundreds of signals. But it recognizes and responds only to the few signals that are important for its function.
This response to some signals, but not to others, is made possible by receptor proteins, such as the ones in the cell’s membrane.
A receptor protein binds specific substances, such as signal molecules.

33. Receiving Signals, continued
The outer part of the receptor protein is folded into a unique shape, called the binding site. A receptor protein binds only to signals that match the specific shape of its binding site.
Only the “right” shape can fit into the receptor protein while the “wrong” shape have no effect on that particular receptor protein.
A cell may also have receptor proteins that bind to molecules in its environment.

34. Binding Site of Receptor Proteins

35. Receiving Signals, continued
Receptor proteins enable a cell to respond to its environment.
Once it binds the signal molecule, the receptor protein changes its shape in the membrane.
This change in shape relays information into the cytoplasm of the target cell.

36. Responding to Signals, continued
Some receptor proteins are enzymes or they activate enzymes in the cell membrane. Enzymes trigger chemical reactions in the cell.
Binding of a signal molecule outside the cell may cause a second messenger to form. The second messenger acts as a signal molecule within the cell and causes changes in the cytoplasm and nucleus.

37. Second Messengers of Receptor Proteins