1. Chapter 5
Cell Membrane

2. Homeostasis
 Maintenance of stable internal
conditions (“inside different from
outside”)
 Cell membrane controls movements
of substances

3. Structure of the Membrane
 Mainly a lipid
bilayer
 Hydrophilic
phospholipid
“heads” point out
and in
 Hydrophobic
phospholipid
“tails” point
towards interior

4. Structure of the Membrane
 Membrane
contains steroid
cholesterol
 Fluidity increases
with increasing
temperatures
 Cholesterol also
helps prevent
freezing

5. Structure of the Membrane
 Only small, non-
charged
molecules can
pass through
the membrane
 Examples:
 Oxygen
 Carbon Dioxide

6. Structure of the Membrane
 Proteins
embedded in
membranes
have many
functions
1. Cell-surface
markers act as
“ID” tags

7. Structure of the Membrane
2. Receptor
proteins receive
signals from out
of the cell
3. Enzymes cause
chemical
reactions to
occur

8. Structure of the Membrane
4. Transport proteins move substances
across membrane

9. Other Important Terms
 “Peripheral
Proteins” lie
on only one
side of the
membrane
 “Integral
Proteins” pass
completely
through

10. SOLUTES AND
SOLVENTS
Chapter 5

11. Important Terms
 Solute: type of molecule dissolved in
another type of substance; that substance
is called a…
 Solvent: substance that dissolves the
solute

12. Examples
 Put one
tablespoon of
sugar into a
glass of water
and stir.
 Solute = sugar
 Solvent = water

13. Examples
 Fish use gills to extract oxygen dissolved in
seawater
 Solute = oxygen
 Solvent = water

14. CONCENTRATION
 Concentration refers to how
much of some substance
(solute) is present, compared to
another substance (solvent).

15. CONCENTRATION
EXAMPLES
 High solute
concentration: lots
of sugar dissolved in
a relatively small
amount of water
 Low solute
concentration: little
sugar dissolved in a
relatively high
amount of water

16. REMEMBER!
 Solutes can be many different
kinds of molecules (sugars,
gases, nutrients, proteins, and
lipids)
 Solvents can vary as well
(solids, liquids, or gases), but
are usually H2O

17. DIFFUSION

18. Diffusion
 Diffusion is the process by
which solute passes through
pores in a cell membrane
 Diffusion also occurs within one
area (no membrane) as solute
travels from one area of space
to another

19. Diffusion
 Molecules ALWAYS diffuse in
both directions at once (into and
out of a cell)
 NET FLOW OF SOLUTES IS
ALWAYS FROM AREAS OF
HIGHER CONCENTRATION
TO AREAS OF LOWER
CONCENTATION!

22. Diffusion
 Molecules
diffuse through
a solvent
 Example:
aromas

23. Types of Diffusion
 “Simple
Diffusion”
 Directly through
membrane  “Facilitated
Diffusion”
 Done by
specific carrier
proteins in
membrane

24. OSMOSIS

25. Osmosis
 Osmosis is the process by which
WATER passes through a cell
membrane
 Water molecules always flow in both
directions at once (into and out of a
cell)
 NET FLOW OF WATER IS ALWAYS
FROM AREAS OF LOWER SOLUTE
CONCENTRATION TO AREAS OF
HIGHER SOLUTE CONCENTRATION

27. Osmosis: Net Flow of Water
 Hypotonic solution – Lower than cell’s
solute concentration
 Hypertonic solution – Higher than…
 Isotonic – The same as…

28. Results of Osmosis
 Plant cells in hypotonic
environment experience “turgor
pressure” due to cell wall
 In a hypertonic environment,
plasmolysis (wilting) occurs

29. Important Terms
• Equilibrium
• Concentration Gradient
• Diffusion
• Osmosis
• Concentration of a substance is
the same throughout
• Difference in concentration
across a membrane
• Process by which molecules
move from areas of high to low
solute concentration
• Transport of water across a
membrane from areas of low
solute concentration to high
solute concentration

30. CELLULAR
TRANSPORT

32. Cellular Transport
 Passive Transport
 Movement across a
membrane without
using energy (ex.:
simple diffusion,
facilitated diffusion,
and osmosis)
 Active Transport
 Movement across a
membrane using
energy

33. Cellular Transport
 Passive transport
allows flow of
molecules down
concentration
gradient
 Active transport
uses energy to
force molecules
against
concentration
gradient

34. Passive Transport

35. Active Transport

36. Other Important Terms
 Homeostasis
 Stable internal
conditions of a
living thing
 This is another
characteristic of all
living things
 Living things
actively keep their
“insides” different
than their
“outsides”

37. Cellular Transport
Passive Transport
Diffusion Osmosis
Active Transport
Example:
Sodium/Potassium
Pump
Maintain
Homeostasis by…

38. Sodium/Potassium
Ion Pump

39. Sodium/Potassium Ion Pump
 Sodium = Na+
 Potassium = K+
 Ions are electrically charged atoms

40. Sodium/Potassium Ion Pump
 Pump is a protein in the membrane of cells.
 Example of ACTIVE TRANSPORT (pumps
AGAINST the concentration gradient)

41. Sodium/Potassium Ion Pump
 Pumps 3 Na+ ions
out of the cell and 2
K+ ions into the cell.
(Uses ATP, a
molecule with lots of
stored energy)
 750 ions transported
per second
 High concentrations
of Na+ and K+ build
on opposite sides of
cell membrane

42. Importance of Na+/K+ Pump
 Electrical signal
sent through
neuron when gated
ion channels open
and Na+ and K+ are
able to rapidly
diffuse across
membrane (which
is passive
transport)

43. Chapter 5 / 8
Test Review

44. Terms to Know:
 Solute
 Solvent
 Concentration
 Homeostasis
 Hydrophilic
 Hydrophobic
 Concentration
gradient
 Diffusion
 Osmosis
 Equilibrium
 Active Transport
 Passive
Transport
 Net flow
 ATP
 Na+/K+ Pump

45. Concepts to Study
 What is the structure of the cell
membrane?
 Which way do solutes travel during
diffusion?
 Which way does water travel during
osmosis?
 The egg lab and the dialysis bag lab

46. Example Question 1
 If the environment surrounding a
cell has a higher solute
concentration than the cell (and
the membrane is permeable to
the solute), describe two things
that may occur.

47. Example Questions 2-3
 A cell is placed in pure water.
What would you expect to
happen to the mass of the cell?
 A cell is placed in water with the
same solute concentration as
inside the cell. What is this
called? Which way will solutes
flow?

48. Example Question 4
 Oxygen moves into an area
where there is already a very
high concentration of oxygen.
Does this process require
energy or not? Explain.