Chapter 3

1
Chapter 3 Sections 3, 4, 5

• Movement through the membrane

2
In or Out?

• How is a window screen similar to
• a cell membrane?
• 1. What are some things that can pass through a
  window screen?
• 2. What are some things that cannot pass through
  a window screen? Why is it important to keep
  these things from moving through the screen?
• 3. The cell is surrounded by a cell membrane,
  which regulates what enters and leaves the cell.
  Why is it important to regulate what moves into
  and out of a cell?

3
Cell Membrane - function

• Regulates what enters and leaves the cell

4
Cell Membrane - function

• Regulates what enters and leaves the cell
• Provides protection and support

5
Cell Membrane - function

• Regulates what enters and leaves the cell
• Provides protection and support
• The cell takes in food and water and eliminates
  wastes through the cell membrane

6
Cell membrane - structure

• Lipid bilayer- tough, flexible structure that
  forms a strong barrier between cell and
  surroundings

7
Cell membrane - structure
Cell membrane
Lipid bilayer
8
Cell membrane - structure

• Lipid bilayer- tough, flexible structure that
  forms a strong barrier between cell and
  surroundings
• Protein molecules run through the lipid
  bilayer some form channels and pumps

9
Cell membrane - structure
Proteins
Cell membrane
Protein channel
Lipid bilayer
10
Cell membrane - structure

• Lipid bilayer- tough, flexible structure that
  forms a strong barrier between cell and
  surroundings
• Protein molecules run through the lipid
  bilayer some form channels and pumps
• Carbohydrate molecules chains attached to outer
  surface of protein ID markers

11
Cell membrane - structure
Carbohydrate chains
Proteins
Cell membrane
Protein channel
Lipid bilayer
12
Cell basics

• Every living cell contains a liquid interior and
  is surrounded by liquid

13
Cell basics

• Every living cell contains a liquid interior and
  is surrounded by liquid
• The cytoplasm of a cell is a solution of many
  different substances in water.

14
Cell basics

• Every living cell contains a liquid interior and
  is surrounded by liquid
• The cytoplasm of a cell is a solution of many
  different substances in water.
• Solute substance dissolved in liquid
• Cells may have different solutes in different
  concentrations

15
Diffusion

• In a solution, molecules move constantly
• They collide with one another and tend to spread
  out randomly through space

16
Diffusion

• In a solution, molecules move constantly
• They collide with one another and tend to spread
  out randomly through space
• This movement results in molecules moving from
  areas of high concentration to areas of low
  concentration (diffusion)

17
Diffusion

• In a solution, molecules move constantly
• They collide with one another and tend to spread
  out randomly through space
• This movement results in molecules moving from
  areas of high concentration to areas of low
  concentration (diffusion)
• Eventually the system reaches equilibrium

18
Diffusion

• In a solution, molecules move constantly
• They collide with one another and tend to spread
  out randomly through space
• This movement results in molecules moving from
  areas of high concentration to areas of low
  concentration (diffusion)
• Eventually the system reaches equilibrium
• Causes many substances to cross membrane

19
Diffusion

• In a solution, molecules move constantly
• They collide with one another and tend to spread
  out randomly through space
• This movement results in molecules moving from
  areas of high concentration to areas of low
  concentration (diffusion)
• Eventually the system reaches equilibrium
• Causes many substances to cross membrane
• Requires NO energy

20
Selectively permeable

• Not all substances can cross biological membranes

21
Selectively permeable

• Not all substances can cross biological membranes
• Permeable substances that are able to diffuse
  across a membrane
• Impermeable - substances that cannot cross
  membrane

22
Selectively permeable

• Not all substances can cross biological membranes
• Permeable substances that are able to diffuse
  across a membrane
• Impermeable - substances that cannot cross
  membrane
• Selectively permeable membrane that allows only
  certain things to cross it

23
Osmosis

• Diffusion of water through a selectively
  permeable membrane

24
Osmosis

• Diffusion of water through a selectively
  permeable membrane
• Water will move across a membrane until an
  equilibrium is reached
• Isotonic same strength - equal

25
Osmosis

• Diffusion of water through a selectively
  permeable membrane
• Water will move across a membrane until an
  equilibrium is reached
• Isotonic same strength - equal
• Hypertonic above strength - concentrated
• Hypotonic- below strength - diluted

26
Osmosis
Water molecules
Cell membrane
Sugar molecules
27
Osmosis

• The membrane is
• Permeable to water
• Impermeable to sugar
• What will happen to the concentration of sugar
  and water?

28
Osmosis
High Concentration of Water
Water molecules
Cell membrane
Sugar molecules
29
Osmosis
High Concentration of Water
Water molecules
Cell membrane
Low Concentration of Water
Sugar molecules
30
Osmosis

• The membrane is
• Permeable to water
• Impermeable to sugar
• What will happen to the concentration of sugar
  and water?
• Water will diffuse across the membrane until both
  sides are isotonic.

31
Osmotic Pressure

• Pressure that results on the hypertonic side of
  selectively permeable membrane

32
Osmotic Pressure

• Pressure that results on the hypertonic side of
  selectively permeable membrane
• Most cells are hypertonic to freshwater because
  of salts, sugars, proteins and other molecules
  that fill them
• Therefore water would flow ____ the cell.

33
Osmotic Pressure

• Pressure that results on the hypertonic side of
  selectively permeable membrane
• Most cells are hypertonic to freshwater because
  of salts, sugars, proteins and other molecules
  that fill them
• Therefore water would flow into the cell.

34
Osmotic Pressure

• Pressure that results on the hypertonic side of
  selectively permeable membrane
• Most cells are hypertonic to freshwater because
  of salts, sugars, proteins and other molecules
  that fill them
• Therefore water would flow into the cell.
• The volume of the cell would then ________.

35
Osmotic Pressure

• Pressure that results on the hypertonic side of
  selectively permeable membrane
• Most cells are hypertonic to freshwater because
  of salts, sugars, proteins and other molecules
  that fill them
• Therefore water would flow into the cell.
• The volume of the cell would then increase.

36
Osmotic Pressure

• Pressure that results on the hypertonic side of
  selectively permeable membrane
• Most cells are hypertonic to freshwater because
  of salts, sugars, proteins and other molecules
  that fill them
• Therefore water would flow into the cell.
• The volume of the cell would then increase and
  possibly _____.

37
Osmotic Pressure

• Pressure that results on the hypertonic side of
  selectively permeable membrane
• Most cells are hypertonic to freshwater because
  of salts, sugars, proteins and other molecules
  that fill them
• Therefore water would flow into the cell.
• The volume of the cell would then increase and
  possibly burst.

38
Osmotic Pressure

• However, cells of most large organisms are not in
  danger of bursting.
• Instead of being surrounded by a hypotonic
  solution of freshwater, they are instead
  surrounded by an ________ solution.

39
Osmotic Pressure

• However, cells of most large organisms are not in
  danger of bursting.
• Instead of being surrounded by a hypotonic
  solution of freshwater, they are instead
  surrounded by an isotonic solution.

40
Osmotic Pressure

• What about the cells of organisms that do come in
  contact with freshwater?
• Plants and bacteria
• Some single celled organisms

41
Osmotic Pressure

• What about the cells of organisms that do come in
  contact with freshwater?
• Plants and bacteria
• Tough cell walls generally prevent the cells from
  expanding
• Some single celled organisms

42
Osmotic Pressure

• What about the cells of organisms that do come in
  contact with freshwater?
• Plants and bacteria
• Tough cell walls generally prevent the cells from
  expanding
• Some single celled organisms
• Structure called a contractile vacuole
  continuously pumps out excess water

43
Osmotic Pressure

• Look at Figure 3-23 on page 86
• What happens when a cell is put in an isotonic
  solution?
• What happens when a cell is put in a hypotonic
  solution?
• What happens when a cell is put in a hypertonic
  solution?

44
Osmotic Pressure

• Look at Figure 3-23 on page 86
• What happens when a cell is put in an isotonic
  solution?

45
Osmotic Pressure

• Look at Figure 3-23 on page 86- What happens
  when a cell is put in a hypotonic solution?

46
Osmotic Pressure

• Look at Figure 3-23 on page 86
• What happens when a cell is put in a hypertonic
  solution?

47
Crossing the membrane

• Some molecules, including alcohol, water, and
  small lipids can move through the lipid bilayer
  and diffuse directly across the cell membrane.
• How do other molecules diffuse across the cell
  membrane?

48
Facilitated Diffusion

• Facilitate to help or assist

49
Facilitated Diffusion

• Facilitate to help or assist
• Facilitated diffusion when protein channels of
  cell membrane help certain molecules across the
  membrane
• Example

50
Facilitated Diffusion

• Facilitate to help or assist
• Facilitated diffusion when protein channels of
  cell membrane help certain molecules across the
  membrane
• Example specific protein in RBC allows glucose
  to cross membrane in or out

51
Facilitated Diffusion

• Facilitate to help or assist
• Facilitated diffusion when protein channels of
  cell membrane help certain molecules across the
  membrane
• Example specific protein in RBC allows glucose
  to cross membrane in or out
• The movement results from diffusion and therefore
  requires NO energy

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• Diffusion molecules move from ____
  concentration to ___ concentration.

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• Diffusion molecules move from high
  concentration to low concentration.

55

• Diffusion molecules move from high
  concentration to low concentration.
• Not all molecules move across a membrane from
  high to low concentrations

56
Active Transport

• Materials move across a membrane from low
  concentration to high concentration

57
Active Transport

• Materials move across a membrane from low
  concentration to high concentration
• Requires the input of Energy from the cell

58
Active Transport

• Materials move across a membrane from low
  concentration to high concentration
• Requires the input of Energy from the cell
• For small molecules it is often compared to a pump

59
Active Transport

• Materials move across a membrane from low
  concentration to high concentration
• Requires the input of Energy from the cell
• For small molecules it is often compared to a
  pump
• where the protein acts as the pump

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Active Transport
Cell membrane
Cell membrane
61
Active Transport
Low concentration
Cell membrane
High concentration
Cell membrane
62
Active Transport
Molecule to be carried
Low concentration
Cell membrane
High concentration
Low concentration
Cell membrane
High concentration
63
Active Transport
Molecule to be carried
Low concentration
Cell membrane
High concentration
Low concentration
Cell membrane
High concentration
Molecule is carried
64
Active Transport

• Why cant large molecules be pumped through the
  proteins?

65
Active Transport

• Why cant large molecules be pumped through the
  proteins?
• How do they get inside the cell then?

66
Active Transport

• Why cant large molecules be pumped through the
  proteins?
• How do they get inside the cell then?
• Through movements of the cell membrane

67
Active Transport

• Endocytosis -

68
Active Transport

• Endocytosis process of taking material into the
  cell by engulfing movements of the cell membrane

69
Active Transport

• Endocytosis process of taking material into the
  cell by engulfing movements of the cell
  membrane
• eventually forms vacuole inside cell that is
  separate from initial cell membrane

70
Active Transport

• Endocytosis process of taking material into the
  cell by engulfing movements of the cell
  membrane
• eventually forms vacuole inside cell that is
  separate from initial cell membrane
• Phagocytosis form of endocytosis where large
  solid particles are taken into cell

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Active Transport

• Exocytosis -

73
Active Transport

• Exocytosis process where the removal of large
  amounts of material from a cell occurs

74
Active Transport

• Exocytosis process where the removal of large
  amounts of material from a cell occurs
• How?

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Active Transport

• Exocytosis process where the removal of large
  amounts of material from a cell occurs
• How?
• The membrane of the vacuole surrounding the
  material fuses with the cell membrane and
  releases contents outside cell