2. CHAPTER 3 :
MOVEMENT OF
SUBSTANCES ACROSS THE
PLASMA MEMBRANE
3. SUBSTOPICS
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
4. 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. 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;
6. To secrete useful substances, for
example, digestive enzymes &
hormones;
To eliminate toxic waste products
such as urea & carbon dioxide
7. Substances can move into or out
of a cell by :
Passive transport
Simple diffusion
Osmosis
Facilitated diffusion
Active transport
8. Movement of substances across
the plasma membrane would
depend on :
Selectivity of the partially
permeable membrane;
The difference in concentration
between the cell & extracellular
fluid
11. Structure of the Plasma
Membrane
All cells are covered by a thin plasma
membrane.
It separates the cell contents from the
surrounding
1972, S.J. Singer & G.L. Nicolson
proposed the fluid-mosaic model of
plasma membrane.
12. The plasma membrane is dynamic &
fluid. The phospholipid molecules can
move thus giving the membrane its
fluidity & flexibility
The proteins are scattered in the
membrane giving it a mosaic
appearance
Thickness : 7.0 – 8.0 nm.
13. Structure of the Plasma
Membrane
The membrane consists of
a phospholipid bilayer (2
molecules thick)
The polar hydrophilic heads
– outer layer face
outwards, chemically
attracted to the watery
surrounding
The non-polar hydrophobic
hydrocarbon fatty acid tails
– face inwards, away from
water.
14. Structure of the Plasma
Membrane
There are proteins on the outer & inner
surfaces of the plasma membrane.
Some proteins penetrate partially
through the membrane, others
penetrate completely.
The phospholipid bilayer is permeable
to diffusion of small uncharged
molecules such as O2 & CO2.
15. Structure of the Plasma
Membrane
Two types of transport protein :
Channel / pore proteins – have pore to facilitate
diffusion of particular ions / molecules across the PM.
Some carrier proteins – have binding sites that bind to
specific molecules such as glucose @ amino acids
alter their shape to facilitate the diffusion of solutes.
Other carrier proteins – function in active transport
an energized carrier protein actively pumps the solute
across the cell membrane against the concentration
gradient.
16.
17. Structure of the Plasma
Membrane
Cholesterol molecules stabilise the
structure of PM.
18. MECHANISM OF
MOVEMENT OF
SUBSTANCES ACROSS
THE PLASMA MEMBRANE
PERMEABILITY
A semipermeable @ partially permeable
membrane = selectively permeable to small
molecules such as water & glucose.
Does not permit large molecule to move through
it.
Examples : egg membrane, plasma membrane
of living cells & cellaphone membrane of the
Visking tubing.
19. MECHANISM OF
MOVEMENT OF
SUBSTANCES ACROSS
THE PLASMA MEMBRANE
A permeable membrane – permeable to the
many solvent (water) & solute molecules
diffusion can occur.
Example : cellulose cell wall of plant cell
An impermeable membrane – not allow
substances to diffuse through it.
Example : the impermeable polythene
membrane.
20. 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
21. PASSIVE
TRANSPORT
The movement of particles (molecules/ions)
within a gas or liquid across the plasma
membrane from a region of higher
concentration to a region of lower
concentration & does not require expenditure
of energy from ATP.
The substances move down their concentration
gradient through different ways :
Phospholipid bilayer
Pore protein/ channel protein
Carrier protein
24. SIMPLE DIFFUSION
The net movement of molecules / ions
from a region of higher
concentration to a region of lower
concentration until an equilibrium
is reached.
Substances :
Small non-polar molecules – O2 & CO2
Lipid-soluble substances – vitamins ADEK,
steroids & alcohols
Water molecules
25. SIMPLE DIFFUSION
The bigger the concentration gradient
the faster the rate of diffusion.
These substances will diffuse down the
concentration gradient if there is a
concentration gradient. (until an
equilibrium is reached).
Examples : gaseous exchange between
the alveolus & the blood capillaries,
blood capillaries & body cells.
26.
27.
28.
29.
30. osmosis
The diffusion of water molecules (solvent) from
a region of higher water concentration (diluted
solution) to a region of lower water
concentration (concentrated solution) through a
semi-permeable membrane until an equilibrium
is reached.
A special type of diffusion.
Examples :
Absorption of water from soil solution by plant root
hairs
Reabsorption of water by kidney tubules
31.
32. FACILITATED DIFFUSION
The movement of molecules / ions down
their concentration gradient assisted by
transport proteins (channel protein / pore
protein) across the plasma membrane
without using energy.
The transport proteins facilitate & increase
the rate of diffusion across the plasma
membrane.
Not require energy
33. FACILITATED DIFFUSION
The rate of facilitated diffusion depends on the
number of transport protein molecules in the
membrane & how fast they can move their
specific solute.
Only allows small charged molecules such as
mineral ions to pass through the pore protein.
Carrier protein : allows larger uncharged
polar molecules – glucose & amino acids to
cross the membrane.
34.
35. THE MECHANISM
The solute moves to the binding site of
the specific carrier protein.
The solute binds to the carrier protein
at the binding site & triggers the
carrier protein to change its shape.
The carrier protein changes its shape
& moves the solute across the
membrane.
The carrier protein returns back to its
original shape.
36. FACILITATED DIFFUSION
The solutes can be transported by
carrier proteins in either direction but
the net movement is always down the
concentration gradient.
Examples : the transportation of
glucose, amino acids & mineral ions
across the membrane of the vilus at the
ileum & body cells.
37. ACTIVE
TRANSPORT
The movement of substances across the
plasma membrane from a region of low
concentration to a region of high
concentration (against the concentration
gradient) by using metabolic energy.
The substances move across a membrane
against the concentration gradient, using
metabolic energy
Perform by a specific protein embedded in the
plasma membrane.
38. ACTIVE
TRANSPORT
Require energy to change the shape of the
protein such that the substance can be
pumped across the membrane.
Example : absorption of potassium ions from
pond water by algae Nitella sp. against a
concentration gradient, the intake of mineral
ions by the plant root hairs, Na+/ K+ protein
pumps in the plasma membrane of neurones
transport Na+ & K+ against their
concentration gradients.
41. LEARNING OUTCOMES
To explain the process of active transport
in living organisms using examples,
To compare and contrast passive
transport & active transport.
42. COMPARISON BETWEEN PASSIVE & ACTIVE
TRANSPORT
PASSIVE SIMILARITIES ACTIVE
TRANSPORT TRANSPORT
DIFFERENCES
Concentration gradient
Cellular energy
Outcome of the
process
Occurs in
Name of process
Examples
43. COMPARISON BETWEEN PASSIVE & ACTIVE
TRANSPORT
PASSIVE SIMILARITIES ACTIVE
TRANSPORT TRANSPORT
Transport of substances across the plasma membrane
Need a difference of concentration gradient between extracellular environment
& the cell
DIFFERENCES
Follow Concentration Against
gradient
Does not expend energy Cellular energy Need to expend energy
Until an equilibrium is Outcome of the Depends on the cells
reached process requirement (no need to
reach an equilibrium)
Non-living & living Occurs in Living organisms only
organisms
Simple diffusion, osmosis, Name of process Active transport
facilitated diffusion
Examples
