1. CHAPTER 5 The Working Cell
Modules 5.10 – 5.21

2. CELL MEMBRANE STRUCTURE AND FUNCTION
Cell membranes controls entry and exit of materials into the cell
Membranes are selectively permeable or semipermeable (some substances can pass throught it, while others cannot).  
Cytoplasm
Figure 5.10

3. Your teacher will draw this on the board for you to copy.
The cell membrane has 2 major components:
1. A double layer of phospholipids (lipid bilayer)
2. Protein molecules that serve as channels, pumps or receptors for communication.
Your teacher will draw this on the board for you to copy.

4. Draw this diagram of the cell membrane:
Hydrophobic
↵tails fatty acid
↵Phosphate Head
phospholipid

5. 5.11 Membrane phospholipids form a bilayer
Phospholipids are the main structural components of membranes
They each have a hydrophilic head and two hydrophobic tails
Head
Symbol
Tails
Figure 5.11A

6. In water, phospholipids form a stable bilayer
The heads face outward and the tails face inward
Water
Hydrophilic heads
Hydrophobic tails
Water
Figure 5.11B

7. The plasma membrane of an animal cell
Glycoprotein
Carbohydrate (of glycoprotein)
Fibers of the extracellular matrix
Glycolipid
Phospholipid
Cholesterol
Microfilaments of the cytoskeleton
Proteins
CYTOPLASM
Figure 5.12

8. 5.13 Proteins make the membrane a mosaic of function
Proteins that serve as channels
Others transport substances across the membrane
Figure 5.13
Transport

9. Cell membrane structure

10. STOP for demonstration

11. Your cells can move some substances across their membranes using NO ENERGY!

14. Background Information on Diffusion
- Diffusion is a process where molecules move from a region of higher concentration to a region of lower concentration.
- The difference in concentration on either side of a membrane is known as a concentration gradient.

15. Background Information on Diffusion
- Diffusion of water molecules across a membrane is known as osmosis.
- Diffusion will occur until an equilibrium is reached. (some will move each direction in equal amounts)

16. 5.14 Passive transport is diffusion across a membrane
In passive transport, substances diffuse through membranes without work by the cell
They spread from areas of high concentration to areas of lower concentration
Molecule of dye
Membrane
EQUILIBRIUM
EQUILIBRIUM
Figure 5.14A & B

17. Many membrane proteins are enzymes
Some proteins function as receptors for chemical messages from other cells
The binding of a messenger to a receptor may trigger signal transduction
Messenger molecule
Receptor
Activated molecule
Figure 5.13
Enzyme activity
Signal transduction

18. Transport Across the Cell Membrane
The cell uses 2 types of transport:
1. Passive transport
- Passive transport requires NO ENERGY use by the cell. Substances move along a concentration gradient.

19. 1. Passive transport continued…
a. Molecules may be moved through a process called simple diffusion.
- Examples:
Water,
oxygen,
carbon dioxide, lipid soluble molecules

20. 1. Passive transport continued…
b. Facilitated diffusion
- Uses carrier proteins to transport molecules that are not lipid soluble
- Examples: glucose, some ions – sodium, potassium

21. Link to illustrate passive transport
Link to illustrate passive transport

22. 2. Active Transport
- This transport requires the cell to USE ENERGY
- Examples: large compounds OR when molecules are moved against the concentration gradient.

23. 2. Active Transport
2 types of Active Transport
Protein Pumps – carry molecules across the membrane against the concentration gradient (moleculer transport) neuron animation

24. 2. Active Transport
b. Bulk Transport
- This is where large amounts of molecules are carried across. There are 3 types of this.

25. 2. Active Transport
b. Bulk Transport
1. Endocytosis – cell membrane brings materials into the cell by infoldings of the membrane which can form vacuoles.
2 Forms:
Phagocytosis – ameba undissolved materials
Ex: Ameba eating food
Pinocytosis – dissolved materials

26. or the membrane may fold inward, trapping material from the outside (endocytosis)
Figure 5.19B

27. Material bound to receptor proteins
Three kinds of endocytosis
Pseudopod of amoeba
Food being ingested
Plasma membrane
Material bound to receptor proteins
PIT
Cytoplasm
Figure 5.19C

28. 2. Active Transport
b. Large quantity Transport
2. Exocytosis – removes material from the cell through outpinchings of the cell membrane. Ex: wastes
3. Contractile Vacuole - Used for removing excess water from a cell. Ex: a freshwater paramecium contractile vacuole video

29. 5.19 Exocytosis and endocytosis transport large molecules
To move large molecules or particles through a membrane
a vesicle may fuse with the membrane and expel its contents (exocytosis)
FLUID OUTSIDE CELL
CYTOPLASM
Figure 5.19A

30. Link to illustrate active transport
Link to illustrate active transport

31. What will happen to a plant or animal cell when placed in fresh or salt water?

32. Background Information
Hypertonic – Solution that has a higher concentration of Solute than a surrounding solution
Hypotonic – Solution that has a lower concentration of solute than a surrounding Solution
Isotonic – Two solutions have the same solute concentrations

33. - water is more highly concentrated outside the cell
FRESH WATER
Animal Cell Plant Cell
- water is more highly concentrated outside the cell
- water will enter the cell
100% H20
SAME, but plant w/cell wall
Cell85%H20

34. Red blood cell will explode.
(called CYTOLYSIS)
Plant Cell will NOT explode because the cell wall prohibits it. (becomes TURGID)

35. - water is more highly concentrated inside the cell
SALT WATER
Animal cell Plant Cell
- water is more highly concentrated inside the cell
- water will exit the cell
80% H20
20% salt
SAME, but plant w/cell wall
Cell85%H20

36. - Plant cell will lose water.
Animal Cell will lose water and shrink (becomes CRENATE)
- The cell membrane will pull away from the cell wall – (this is called PLASMOLYSIS.)

37. osmosis Red blood cell in isotonic environment
Red blood cell in hypertonic solution
cytolysis and crenation in red blood cells
osmosis

38. 5.15 Osmosis is the passive transport of water
Hypotonic solution
Hypertonic solution
In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration
Selectively permeable membrane
Solute molecule
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
Water molecule
Selectively permeable membrane
Solute molecule with cluster of water molecules
NET FLOW OF WATER
Figure 5.15

39. 5.16 Water balance between cells and their surroundings is crucial to organisms
Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution
The control of water balance (osmoregulation) is essential for organisms
ISOTONIC SOLUTION
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
ANIMAL CELL
(1) Normal
(2) Lysing
(3) Shriveled
Plasma membrane
PLANT CELL
Figure 5.16
(4) Flaccid
(5) Turgid
(6) Shriveled

40. 5.17 Transport proteins facilitate diffusion across membranes
Small nonpolar molecules diffuse freely through the phospholipid bilayer
Many other kinds of molecules pass through selective protein pores by facilitated diffusion
Solute molecule
Transport protein
Figure 5.17