1. Chapter 4 Cells and their Environment
Mrs. Cook
Biology

2. Cell Structure Cont. Cell Membrane - primarily made of lipids
- makes a barrier that separates the outside of the cell from the inside of the cell
- it allows only certain substances in the environment to pass through, “selectively permeable”
Lipid Bi-layer
-phosolipids are arranged in a double layer
-non-polar tails make up the interior of the bi-layer.
- “Hydrophobic”
-polar heads make up the outside of the bilayer.
- “Hydrophilic”

3. Cell Structure cont.
Phospholipid bi-layer contains several types of Membrane Proteins
1. Marker Proteins- attached to carbohydrate on cell surface and advertise cell type- heart cell, liver cell, etc.
2. Receptor Proteins- recognize and bind to substances outside the cell. Ex: hormones
3. Enzyme- assist in chemical reactions inside the cell.
4. Transport Proteins- move substances into and out of the cell.

5. Fluid Mosaic Model http://www.youtube.com/watch?v=Rl5EmUQdkuI

6. Homeostasis

7. Homeostasis
Your body responds to external conditions to maintain a stable internal condition.
When an organisms adjusts internally to changing external conditions they are maintaining Homeostasis.
How cells maintain homeostasis is by controlling movement of substances across their cell membrane.
Water
CO2 O2
Na+ K+

8. Homeostasis
Either by transporting substances using energy- called active transport.
Or with out the use of energy- called passive transport.

9. Passive Transport
When substances enter or leave a cell without the use of any energy.
1st type of Passive Transport is Diffusion-
-is the movement of molecules from an area of higher concentration to an area of lower concentration

11. Passive Transport- Diffusion cont
This difference in the concentration of molecules across a distance is called a concentration gradient
Is driven by the molecules’ kinetic energy. Molecules are constantly in motion because they have kinetic energy.
Moving from an area of high to low is called “moving down” the concentration gradient
Like swimming with the current

12. Passive Transport- Diffusion cont
Diffusion will eventually cause the molecules to be in equilibrium when the concentration of molecules will be equal throughout the space they share.
Diffusion across a membrane, if molecules are small enough to pass is call simple diffusion.

14. Passive Transport- Osmosis
2nd Type of Passive Transport is Osmosis-
-Is the diffusion of water molecules
Osmosis is the passive transport of water!
The direction of Osmosis does NOT REQUIRE ENERGY!!

15. Passive Transport- Osmosis
Solute- A substance dissolved in another substance creating a solution.
Solvent- as substance that dissolves a solute, can be a liquid or a gas- is usually water.
Example:
- sugar dissolved in water
Sugar is the solute
Water is the solvent
- salt water
Salt is the solute

16. Passive Transport- Osmosis
The cell membrane
Remember it is selectively permeable! This means it is only going to allow certain substances in and out of the cell.
Water can move by passive transport in and out of the cell depending on the concentration of solute either inside or outside the cell.

18. Passive Transport- Osmosis cont.
When the concentration of solute molecules outside the cell is LOWER than the concentration in the cytosol, the solutions outside is HYPOTONIC to the cytosol; water will diffusion into the cell until equilibrium is reached.
Sugar and water inside the cell
Water outside the cell.
Water moves into the cell

20. Passive Transport- Osmosis cont.
When the concentration of the solute molecules outside the cell is HIGHER than the concentration in the cytsol, the solution outside is HYPERTONIC to the cytosol; water will diffuse out of the cell until equilibrium is reached.
Sugar and water outside the cell
Water inside the cell.
Water moves out of the cell

21. http://www.youtube.com/watch?v=Ym1rvwP-po4 Hypertonic RBCs

22. Passive Transport- Osmosis cont.
When the concentration of solutes outside and inside the cell are EQUAL, the outside solution is said to be ISTOTONIC to the cytosol and there is no net movement of water molecules.
Sugar and water outside the cell
Sugar and water inside the cell
Water moves in and out of the cell

24. How Cells Deal with Osmosis
Many animals live in hypotonic environments. If they take in too much water their plasma membrane could burst!
To deal with this they have an adaptation called a contractile vacuole.
Contractile Vacuoles are organelles, which remove water by pumping it out of the cell. This pumping is different than osmosis or diffusion because it does require ENERGY from the cell.

27. How Cells Deal with Osmosis
Some animals cells do not have contractile vacuoles, such as red blood cells. If they take in too much water they will eventually burst.
The bursting of cells is called cytolysis.
Which solution will cause cytolysis?

29. How Cells Deal with Osmosis
Plant cells have cell walls strong enough to resist the water pressure, called TURGOR PRESSURE.
When Plants are in HYPERTONIC environments and lose water they also lose their Turgor Pressure and wilt. This process is called plasmolysis.

32. 3rd Type of Passive Transport is Facilitated Diffusion
When molecules CAN NOT MOVE through cell membranes even when there is a concentration gradient they go through FACILITATED DIFFUSION.
The molecules are assisted through the membrane through proteins called carrier proteins.
Carrier proteins still move molecules from an area of high to low concentrations and therefore do not use energy.
Carrier proteins are used to transport specific substances such as amino acids and sugars.

33. Facilitated Diffusion occurs in 4 steps
1. A molecule binds to a carrier protein on one side of the cell membrane.
2. The carrier protein changes shape, shielding the molecule from the interior of the membrane.
3. The molecule is released on the other side of the membrane.
4. The carrier protein then returns to its original shape.

34. Step 1.
Step 4
Step 2
Step 3

38. Diffusion through Ion Channels
Another type of transport involves membrane proteins known as ION CHANNELS.
They transport ions such as sodium (Na+), potassium (K+), calcium (Ca+), and Chloride (Cl-) from areas of HIGH to LOW concentrations.
Ion Channels are for specific ions
Some are always open and others have “GATES” that open or close.

39. Active Transport
When energy is required to move substances into or out of the cell.
Uses energy molecule ATP (adenosine triphosphate)
Molecules are moving from LOW to HIGH concentrations or “UP” (or “against”) their concentration gradients.
- like swimming against the current

40. Active Transport- Sodium-Potassium Pump
Active transport in animal cells involving a carrier protein
Transports Na+ ions and K+ ions up their concentration gradients because higher concentrations are needed.

41. Active Transport- Sodium-Potassium Pump
Creates an electrical gradient across the cell membrane
Outside becomes positively charged and inside becomes negatively charged
This is important for sending electrical signals by nerve cells.

42. Active Transport- Sodium-Potassium Pump
FOUR STEPS to active transport
1. THREE sodium ions inside the cell bind to the sodium-potassium pump. ATP is used for energy and loses a phosphate to become ADP (adenosine diphosphate.

43. Active Transport- Sodium-Potassium Pump
2. The pump changes shape, transporting the three sodium ions across the cell membrane.

44. Active Transport- Sodium-Potassium Pump
3. Two potassium ions, K+, bind to the pump and are transported across the cell membrane.

45. Active Transport- Sodium-Potassium Pump
4. The phosphate group and the two potassium ions are released inside the cell.

46. Active Transport- Sodium-Potassium Pump
Pump transports Na+ out of the cell
3 Na+ bind to the pump 4 3
2 K+ bind to the pump
K+ realeased into the cell

49. Movement in Vesicles
Many substances, such as proteins and polysaccharides, are too big to be transported by carrier proteins.
These substances are moved across the cell membrane by vesicles.

50. Movement in Vesicles- Endocytosis
Is the process by which cells ingest external fluid, macromolecules and large particles, including other cells.
Uses vesicles to move their particles into the cell
Two Types of Endocytosis:
1. Pinocytosis: involves the transport of solutes or fluids.
2. Phagocytosis: involves the transport of large particles or whole cells.

51. A vesicle is formed around the particles
The particles are carried across the membrane and into the cell
Particles to be transported into the cell

52. Movement in Vesicles- Exocytosis
Is the process by which a substance is released from the cell though a vesicle
Is basically the reverse of endocytosis
May be used to release large molecules such as proteins, waste products, or toxins that would damage the cell if released in the cytosol.

53. The molecules are released from the cell
A vesicle is formed around the molecules
The vesicle attached to the cell membrane

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