BIOLOGY FORM 4 CHAPTER 3 - MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE

1. BIOLOGY FORM 4
CHAPTER 3
MOVEMENT OF SUBSTANCES ACROSS
THE PLASMA MEMBRANE

2. SUBTOPICS
3.1 - Movement of Substances Across the
Plasma Membrane
3.2 – Understanding the Movement of
Substances Across the Plasma
Membrane in Everyday Life
3.3 – Appreciating the Movement of
Substances Across the Plasma
Membrane

3. LEARNING OUTCOMES
• To state the substances required by living cells
• To state the substances that have to be
eliminated from cells
• To explain the necessity for movement of
substances across the plasma membrane
• To describe the structure of the plasma
membrane
• To describe the permeability of the plasma
membrane

5. Substances to be eliminate from the cells
• Water
• Nutrient
– Glucose
– Amino acid
– Mineral
– Fatty acid
– Vitamin
• Urea
• Toxin

7. NECESSITY FOR MOVEMENT OF SUBSTANCES
ACROSS THE PLASMA MEMBRANE
 To provide nutrients for metabolism & growth;
 To supply oxygen for respiration;
 To regulate solute concentration & suitable pH for
maintaining a stable internal environment for optimal
enzymatic activities
 To maintain an ion concentration gradient required
for nerve & muscle cell activities;
 To secrete useful substances, for example, digestive
enzymes & hormones;
 To eliminate toxic waste products such as urea &
carbon dioxide

8. PLASMA MEMBRANE

9. Functions of the plasma membrane:
1. Boundary- barrier to environment.
Saparates the contents of the cells
from their external environment.
2. Regulates what enters and leaves
the cell.
3. Provides protection.

10. The plasma membrane of a cell
can be thought of as a gatekeeper:
allowing only specific substances in or out
passing messages from the external
environment to the cell’s interior

11. Which term is better to describe a
plasma membrane?
semi-permeable
Only allows certain substances to pass through

12. The general structure of membranes
is know as the: fluid mosaic model
Fluid
refers to the
phospholipid
bilayer
Mosaic
refers to the
proteins
The phospholipid bilayer is like a “lake” in
which a variety of proteins “float”.

13. This model is referred to as the ‘fluid mosaic
model’ because the components are free to
move independently of each other.
Surface view
4.6

14. The main components of the plasma
membrane are:
Protein
Side view
Phospholipid
4.6

15. Outer & inner membrane
surfaces differ.

16. Let us explain how
a bilayer forms

17. Structure of a phospholipid
molecule
Hydrophilic head
(phosphate)
Hydrophobic tail
(fatty acid)
What happens when a thin layer of phospholipid
molecules is spread over the surface of water?

18. 4.6

19. 4.6

20. 4.6
They arrange themselves
into a single layer

21. 4.6
A spherical
micelle

22. Two layers form: a bilayer
4.6
phospholipid bilayers like this are the basic
structure of plasma membranes

23. Phospholipids can move within the
membrane
The phospholipid bilayer is flexible, and the
interior is fluid, allowing lateral movement of
molecules

24. Proteins can move within the Plasma Membrane
Side view
Surface view

25. Let us have a look at
PROTEINS

26. PROTEINS
 There are proteins on the outer & inner surfaces of
the plasma membrane.
 Some proteins penetrate partially through the
membrane, others penetrate completely.

27. Transport Proteins
2 types:
1. Channel/pore proteins are embedded in the cell
membrane & have a pore for materials to cross
2. Carrier proteins can change shape to move
material from one side of the membrane to the
other
CHANNEL/PORE PROTEINS CARRIER PROTEINS

28. The phospholipid bilayer only allows CERTAIN
materials to cross.
polar
head
nonpolar
tails
hydrophobic
molecules
hydrophilic
molecules
1. Small non-polar molecules – O2 & CO2
2. Lipid-soluble substances – vitamins ADEK, steroids &
alcohols
3. Water molecules (small amount)

29. The phospholipid bilayer does not
polar
head
allow all materials to cross
nonpolar
tails
hydrophobic
molecules
hydrophilic
molecules cytosol
BUT hydrophilic molecules STILL
get through. How?

30. Nonpolar, hydrophobic
solutes Polar, ionised,
hydrophilic
solutes

31. Charged molecules & ions can
enter a cell. How can this be?
Move
through a
protein.
Big & polar
molecules (glucose,
amino acid),
charged ions
~~cannot cross and
need help of
TRANSPORT
PROTEIN

32. Which substances can/cannot pass
through the phospholipid bilayer?
Small
amounts.

33. Explain why organic solvents such as
alcohol, ether and chloroform penetrate
membranes more readily than water.
Alcohol, ether & chloroform are non-polar
Water is polar: repelled by non-polar portions

34. Recall concept on “Cell
surface membrane” which is
found in all living cells
 Partially-permeable
membrane that forms a
boundary between the
cytoplasm of the cell
and the outside.
 Controls the passage of
substances (small
molecules) entering
and exiting the cell

35. MOVEMENT THROUGH THE
PLASMA MEMBRANE

36. LEARNING OUTCOMES
 To explain the movement of substances across the
plasma membrane through the process of passive
transport
 To explain the movement of water molecules
across the plasma membrane by osmosis,
 To explain the movement of substances across the
plasma membrane through the process of active
transport,
 To explain the process of passive transport in living
organisms using examples

37. PASSIVE

40. PASSIVE TRANSPORT
ACTIVE TRANSPORT
Cell uses ATP
high
Weeee!!!
low
Cell does not use ATP: substances
just diffuse through the membrane
high
low
This is
going to
be hard
work!!

43. DIFFUSION
is the movement of molecules or ions
from a region of high concentration to
region of low concentration down a
CONCENTRATION gradient

44. Describing the process of DIFFUSION
Molecules (possess
kinetic/movement energy)
moving down a
concentration gradient
Difference in
concentration
between two regions
is called
Region A Region B

47. 51
Diffusion of Liquids

48. Diffusion
• Water, carbon dioxide and other small
uncharged particles

54. The rate of diffusion depends on
1. The steepness of the
diffusion gradient
 the steeper the
gradient, the faster
the rate of diffusion
faster slower
It is an advantage for cells to maintain steep
diffusion gradients if rapid transport is required.
How is such a gradient kept in the gut?

55. Blood carries away the digested
food

56. In windy conditions, air outside
leaves becomes drier
Water diffuses faster through the stomata

58. At a higher temperature the particles have more kinetic
energy and are moving around faster. Therefore in a given
time more diffusion will occur.

60. The surface area of the second cell is much bigger than the first cell
due to the folded membrane. The volume of the cells is very similar.
Therefore the second cell has a much larger surface area to volume
ratio and it increases the rate of diffusion.

61. The larger the surface area of a membrane
through which diffusion is taking place, the faster
the diffusion

62. Surface Area
• As the rate of diffusion relies on the surface
area.
• The parts of organisms that rely on diffusion
therefore tend to have a large surface area.

63. Rate of diffusion decreases rapidly with
distance
 diffusion is effective over very short
distances
Squamous epithelial cells
line:
 Alveoli
 Capillary walls

64. EXAMPLE OF DIFFUSION

65. Diffusion in lungs
 The cells of your lungs exchange oxygen and
carbon dioxide through diffusion.

66. A single air sac 21
blood supply to air sac
air breathed
in and out
diffusion of
oxygen
diffusion of
carbon dioxide O2
CO2
0.03 mm

67. Diffusion in root hair cells
 Plant cells such as root hair cells also take in
oxygen and remove carbon dioxide through diffusion.

68. Leaf
O2 and CO2 diffuse
into the spaces between cells
the ‘veins’
bring water
O2 and CO2
diffuse through
pores in the
epidermis
In a thin leaf, the
diffusion distance
is short
26

69. Diffusion of O2 & water vapour
through stomata

70. FACILITATED DIFFUSION

71. Two types of diffusion
Simple diffusion:
small molecules cross
the lipid bilayer
Facilitated diffusion:
substances cross the
bilayer aided by:
 channel or
 carrier proteins

72. Difference between
channel & carrier proteins:
Channel proteins
fixed shape
Carrier proteins
undergo rapid changes
in shape
Extracellular space
Intracellular space

73. Down or Against a concentration
gradient?
Simple & Facilitated
Diffusion:
Active
transport:

74. Which substances enter by
facilitated diffusion?
 those that cannot diffuse through the
phospholipid bilayer such as:
1. Large particles:
 glucose
 amino acids
 proteins
2. Some ions:
 Na+ ions
 Cl- ions

75. Facilitated diffusion can occur
through a:
Non-specific
transporter
Specific
transporter

76. Carrier proteins:
 substance to be transported is bound to a
membrane protein

77. Why does the rate of uptake reach
a maximum in facilitated diffusion?
Carriers are saturated.
Simple
diffusion
Facilitated
diffusion

78. Facilitated diffusion has three
essential characteristics:
 it is:
1. Specific
2. Passive
3. Saturates

79. 85
Facilitated Diffusion
Molecules will randomly move through
the pores in Channel Proteins.

80. 86
Facilitated Diffusion
• Some Carrier
proteins do not
extend through
the membrane.
• They bond and
drag molecules
through the lipid
bilayer and
release them on
the opposite side.

81. 87
Carrier Proteins
• Other carrier
proteins
change shape
to move
materials
across the cell
membrane

82. Define:
Simple diffusion:
The passive transport of substances
across the plasma membrane
Facilitated diffusion:
The passive transport of substances
across the plasma membrane with
the help of transport proteins such
as the channel protein and the
carrier protein

83. EXAMPLES OF
FACILITATED DIFFUSION

84. OSMOSIS

85. Osmosis
 is the passage of water molecules from a
region of their high concentration to a
region of their low concentration through a
partially permeable membrane

86. Water continues to flow until:
equilibrium is
reached

88. Three terms are used to compare
the solute concentrations of two
solutions separated by a membrane:
Isotonic
Hypotonic
Hypertonic

89. Isotonic solutions
[same concentration]

90. Hypotonic
solution
Hypertonic
solution
[lower conc. of
solute]
[higher conc.
of solute]

91. Water molecules always move from
from HYPOTONIC solution to
HYPERTONIC solution
HYPO  HYPER

92. Osmosis
Partially
permeable
membrane
High Water
Concentration
means the
solution is
Hypotonic
Loses water by
Water
molecules
Solute molecules
cannot pass
through the
partially
permeable
membrane
There is a net movement of water molecules towards the
less concentrated side (in terms of water molecules) until
water concentrations equalize.
osmosis
Low water
concentration
means the
solution is
Hypertonic
Gains water by
osmosis
HYPO
HYPER

94. ISOTONIC

95. HYPERTONIC

96. HYPOTONIC

97. Osmosis in Animal Cells

98. isotonic
solution
Crenated cells haemolysis
hypertonic
solution
10 microns
hypotonic
solution
equal movement of water
into and out of cells
net water movement
out of cells
net water movement
into cells

99. Name the solutions
Osmosis in Red Blood Cells
Isotonic Hypotonic Hypertonic

100. Plant cells in a hypotonic solution:
Water enters the cell and
fills the vacuole.
The plasma membrane
pushes against the cell
wall making the cell very
inflexible.
Cells in this state are
TURGID.

101. Plant cells in a hypertonic solution:
The cell loses water and goes
FLACCID.
REASON:
 the vacuole becomes flaccid
 the cytoplasm stops pushing against
the cell wall
This state is called PLASMOLYSIS.
A cell at this stage is said to be plasmolysed.

102. HYPOTONIC ISOTONIC HYPERTONIC

103. Why is it that
plant cells do
not burst?
Presence of a
cell wall.

105. 115
hypotonic hypertonic isotonic
hypertonic isotonic hypotonic

108. Hypertonic Isotonic Hypotonic
Plasmolysed Flaccid Turgid
PLANT
CELLS

111. Onion epidermal cells were
placed in a 1M sucrose solution.
What fills the space
between the cell wall
and the protoplast?
Sucrose solution

112. (1) wilting
(2) recovering
(1) Wilting. Pant is short of water. The leaf
cells are no longer turgid and the leaves curl
up and droop.
(2 3) Recovered. Water is once more
available. The leaf cells take up water by
osmosis and become turgid. The leaves are
now firm and are held horizontally.
Woody plants such as trees and shrubs do
not collapse when they wilt but their leaves
become limp.
(3) recovered

113. Importance of Turgor pressure
• Helps to support the soft tissues of plants so
that they remain firm.
• Absence of turgor in cells results in plant cells
becoming flaccid (soft)  plant will wilt.
• Causes the opening and closing of the
stomata.
• Causes the opening and closing of flowers.

114. Potato strips were first placed in either
a hypotonic or a hypertonic solution,
than in water. Why did potato
strips P float & Q sink?
PLASMOLYSED
TURGID

117. Osmosis demo
• The membrane contains
strong sugar solution.
• The membrane is stood
in a weak sugar solution.
• Soon liquid starts to rise
up the tube.
• Why?

118. Osmosis demo
• Water molecules can
diffuse through the
membrane from the
weak solution to the
strong one.
• Sugar molecules can
not diffuse through
because they are too
big.

119. HYPERTONIC
HYPOTONIC

128. Visking tubing
0.5%
Sugar
solution
0.1%
Sugar
solution

129. Visking tubing
0.5%
Sugar
solution
0.1%
Sugar
solution
Water moves from a dilute solution to a more concentrated
one across the partially permeable cell membrane.

130. Amoeba has a cytoplasm that is
hypertonic to the pond water in which it
lives
What does this lead to?
Net flow of water by osmosis over the
entire plasma membrane.

131. What is the role of the
contractile vacuole?
Expels excess water from the cell

132. Amoeba may also adjust the quantity of
dissolved substances in the cytoplasm
Amoeba actively pumps out ions.
How does this help in the contractile vacuole
working more efficiently?
Less water enters and so the
contractile vacuole can cope
with the water to be pumped
out.

137. Why the use of
excess fertilizer caused
wilting in plant?

138. Wilting of Plants
• Problems can arise if chemical fertilisers
are added in excess to the soil.
• The soil solutions becomes hypertonic to
the cell sap of the root hair cells.
• Water moves out of the plant by osmosis.
• When flaccidity spreads throughout the
plant, wilting occurs.

139. Explain these preservation process

140. Preservation of Food
• Food can be preserved by using salt or
sugar.
• When salt or sugar is added to the food, it
creates a hypotonic condition for the
microorganisms that spoil the food.
• Water passes out from the
microorganisms into the concentrated
solution. This results in slower growth of
the microorganisms or even death.

141. ACTIVE TRANSPORT

142. Active Transport
Problem:
• Diffusion is very slow
• moves substances down a concentration gradient.
• Many substances are needed by organisms in
larger amounts
• need to be accumulated in cells against the
concentration gradient.
• Energy needed to move the needed substances
across the cell membrane  ACTIVE TRANSPORT

143. Active Transport
Active transport occurs using channel proteins.

146. Movement of substances by active
transport is usually in
one direction only.
What about in
diffusion?
Direction is reversible in
diffusion.

148. ATP supplies the energy for active
transport. What is the use of energy?
The carrier proteins need energy to
keep changing shape.

151. EXAMPLES OF
ACTIVE TRANSPORT

152. 168
Sodium-Potassium Pump
in plasma membrane of neurones
3 Na+ pumped in for every 2 K+ pumped
out; creates a membrane potential

153. Active transport in small
intestine

154. Active transport in root hair
cells

155. LEARNING OUTCOMES
• To explain the process of active transport in
living organisms using examples,
• To compare and contrast passive transport &
active transport.

156. Remember the Examples
 Examples of diffusion:
= gaseous exchange between the alveolus & the blood
capillaries, blood capillaries & body cells
 Examples of osmosis:
Absorption of water from soil solution by plant root hairs
Reabsorption of water by kidney tubules
 Examples of facilitated diffusion :
- transportation of glucose, amino acids & mineral ions across
the membrane of the vilus at the ileum & body cells.
 Example of active transport :
- absorption of potassium ions from pond water by algae Nitella sp.,
- the intake of mineral ions by the plant root hairs,
- Na+/ K+ protein pumps in the plasma membrane of neurones

157. MOVEMENT OF SUBSTANCE ACROSS
PLASMA MEMBRANE
Passive
transport
•Movement of substance
from concentration to
concentration
•Move DOWN their
concentration gradient
•DOES NOT require energy
Simple
diffusion
Osmosis
Facilitated
diffusion
Active
transport
•Movement of substance
from concentration to
concentration
•Move AGAINST their
concentration gradient
•Requires energy

158. Movement of Substances Into or Out of Cells
Processes
Diffusion Osmosis
Similarities
• Energy not required
• Movement of substances down
a concentration gradient
• Refers only to water molecules
• Takes place across a partially
permeable membrane
• Refers to any substance,
gaseous or liquid
• Membrane is not required
Differences

159. Molecule to
be carried
Section 7-3
Energy
Molecule
being carried
Figure 7-19 Active Transport
ACTIVE
TRANSPORT
•Against
concentration gradient
•Requires energy
•Carrier protein
Low concentration
High
concentration

160. Facilitated Diffusion Facilitated Diffusion
•Across gradient
•High to low
•No energy required
•Protein channel
High
Concentration
Low
Concentration
Cell
Membrane
Glucose
molecules
Protein
channel
Section 7-3

161. COMPARISON BETWEEN PASSIVE & ACTIVE TRANSPORT
PASSIVE
TRANSPORT
SIMILARITIES ACTIVE
TRANSPORT
DIFFERENCES
Concentration gradient
Cellular energy
Outcome of the
process
Occurs in
Name of process
Examples

162. COMPARISON BETWEEN PASSIVE & ACTIVE TRANSPORT
PASSIVE
TRANSPORT
SIMILARITIES ACTIVE
TRANSPORT
Transport of substances across the plasma membrane
Need a difference of concentration gradient between extracellular environment
& the cell
DIFFERENCES
Follow Concentration
gradient
Against
Does not expend energy Cellular energy Need to expend energy
Until an equilibrium is
reached
Outcome of the
process
Depends on the cells
requirement (no need to
reach an equilibrium)
Non-living & living
organisms
Occurs in Living organisms only
Simple diffusion, osmosis,
facilitated diffusion
Name of process Active transport
Examples

171. THE END
I CONTROL
who
enters!!

173. Solutions Observation Discussion Condition
Hypotonic
solution
• Water diffuses into
the cell by osmosis.
• The cell swell up
and eventually
burst
The condition is
known as
haemolysis.
Isotonic
solution
• Water diffuses into
and out of the cell
at equal rates.
• No net movement of
water.
The cell retain
their normal
shape.
Hypertonic
solution
• Water diffuses out
of the cell by
osmosis.
• The cell shrinks.
The red blood
cell is said to
have undrgone
creanation.

174. Solutions Observation Discussion
Condition of
cell
Hypotonic
solution
• Water diffuses into
the large central
vacuole by osmosis.
• The large central
vacuole expands,
causing the cell to
swell.
The cell is said
to be turgid
Isotonic
solution
• Water diffuses into
and out of the cell at
equal rates.
The cell retain
their normal
shape
Hypertonic
solution
• Water diffuses out of the
large central vacuole by
osmosis.
• Both the vacuole and
cytoplasm lose water to
surroundings and shrink.
• The plasma membrane
pulls away from the cell
This condition is
called
plasmolysis.
The plant cell
becomes flaccid
and less turgid.

175. ACTIVITIES

176. Cell Membrane Structure
Sketch and label a phospholipid coloring the heads red
and the tails blue.
Hydrophilic
Hydrophobic
Hydrophilic

177. List 4 functions of the cell or
plasma membrane:
a. Boundary- barrier to environment
b. Provides protection & support
c. Regulates what enters and leaves cells
d. Maintains homeostasis

178. Correctly color code and identify the
name for each part of the cell
membrane.
A-Phospholipid bilayer
B-Integral protein
C-Peripheral protein
E-Cholesterol
F-Fatty acid tails
G-Phosphate heads
H-Glycoprotein
I-Glycolipids

179. Match the cell membrane structure or its
function with the correct letter from the cell
membrane diagram.
G-Attracts water
I-Helps maintain
flexibility of
membrane
E-Involved in cell-to-cell
recognition
F-Repels water
A-Make up the bilayer
B-Help transport
certain materials
across the cell
membrane

180. Define:
• Isotonic- equal solutes in solution and cell
– Equal movement of water in and out
• Hypertonic- greater solutes in solution when
compared to the cell
– Causes water to be drawn out of cell & shrink
• Hypotonic- lower solute in solution when
compared to the cell
– Causes water to enter cell and swell

181. Match with osmotic condition
• A- Isotonic
– solution in which the solute concentration is the
same
– condition that animal cells require
• B- Hypertonic
– plant cell loses turgor pressure (Plasmolysis)
– solution with a higher solute concentration
• C-Hypotonic
– solution with a lower solute concentration
– condition plant cells require
– red blood cell bursts (cytolysis)
– plant cell with good turgor pressure
– solution with a high water concentration

182. Label the tonicity for each
solution (isotonic, hypotonic, or
hypertonic):
Hypotonic Isotonic Hypertonic

183. Label the tonicity for each
solution (isotonic, hypotonic, or
hypertonic):
Hypotonic Isotonic Hypertonic

184. How can the rate of diffusion be
affected?
1. Temperature
 Increase in temp. increases rate
2. Size of particles
 Small sizes diffuse faster than large ones
3. Thickness of the barrier
 Thicker walls, slower rate
4. Concentration gradient
 Greater concentration gradient, faster rate
5. Surface area
 Increase S.A., increase rate

185. How does osmosis affects cells?