MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE

1. MOVEMENT OF SUBSTANCES ACROSS THE
PLASMA MEMBRANE

2. Subtopics
2
01
02
03Movement of Substances
Across the Plasma Membrane Understanding the Movement
of Substances Across the
Plasma Membrane in Everyday
Life
Appreciating the
Movement of Substances
Across the Plasma
Membrane

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

4. NECESSITY FOR MOVEMENT OF SUBSTANCES
ACROSS THE PLASMA MEMBRANE
To………
provide nutrients for
metabolism & growth
supply oxygen for
respiration
regulate solute concentration &
suitable pH for maintaining a
stable internal environment for
optimal enzymatic activities
maintain an ion
concentration gradient
required for nerve &
muscle cell activities
eliminate toxic
waste products
such as urea &
carbon dioxide
secrete useful substances,
for example, digestive
enzymes & hormones4

5. SUBSTANCES CAN MOVE INTO OR OUT
OF A CELL BY :
5
PASSIVE
TRANSPORT
ACTIVE
TRANSPORT
Simple
diffusion
Osmosis
Facilitated
diffusion

7. 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

9. 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
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

10. The membrane consists of a phospholipid bilayer (2 molecules thick)
The non-polar hydrophobic hydrocarbon fatty
acid tails – face inwards, away from water
The polar hydrophilic heads – outer layer
face outwards, chemically attracted to the
watery surrounding
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 & CO

16. Channel /
pore
proteins
Other
carrier
proteins
Some
carrier
proteins
2 TYPES OF
TRANSPORT
PROTEIN
16
have pore to
facilitate diffusion
of particular ions /
molecules across
the PM
have binding sites
that bind to specific
molecules such as
glucose @ amino
acids  alter their
shape to facilitate the
diffusion of solutes
function in active transport  an energized carrier protein actively
pumps the solute across the cell membrane against the
concentration gradient.

18. Cholesterol molecules
stabilise the structure of
PLASMA MEMBRANE

19. selectively permeable to small
molecules such as water &
glucose
MECHANISM OF MOVEMENT OF SUBSTANCES
ACROSS THE PLASMA MEMBRANE
MECHANISM
19
semipermeableDoes not permit large
molecule to move
through it
egg membrane,
plasma membrane of
living cells &
cellaphone
membrane of the
Visking tubing
permeable to the many
solvent (water) & solute
molecules
permeable
membrane
Example : cellulose cell wall of plant cell
impermeable
membrane
not allow substances to diffuse through it
Example : the impermeable polythene membrane

20. LEARNING OUTCOMES
20
03
04
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. 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

25. OSMOSIS
SIMPLE
DIFFUSION
FACILITATED
DIFFUSION

26. 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
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 ,eg:
O2 & CO2
Water
molecules
SIMPLE DIFFUSION
26
Lipid-soluble
substances,eg:
vitamins ADEK,
steroids &
alcohols

29. OSMOSIS
OSMOSIS
A special type of diffusion
Examples
Absorption of water from
soil solution by plant root
hairs
Reabsorption of water by kidney
tubules
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
29

31. 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
31
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

33. THE MECHANISM
33
The solute
moves to the
binding site of
the specific
carrier protein
The carrier
protein returns
back to its
original shape
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
01
02
03
04

34. 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

35. 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
Require energy (ATP) 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 neurons transport Na+ & K+
against their concentration
gradients
35

37. SODIUM-POTASSIUM PUMP

38. PASSIVE TRANSPORT SIMILARITIES ACTIVE TRANSPORT
o Transport of substances across the plasma membrane
o 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