Diffusion, Osmosis & Active Transport

SOLVENT: a liquid in which a substance is dissolved in (H2O is the UNIVERSAL SOLVENT)

SOLUTE: particles/molecules that are dissolved in the solvent

SOLUTION: the mixture of dissolved particles in the solvent

HYPERTONIC: A highly concentrated solution (high solute)
- water molecules will diffuse OUT OF cells in a hypertonic solution

HYPOTONIC: A low concentrated solution (low solute)
- water molecules will diffuse INTO cells in hypotonic solution

ISOTONIC: A solution with the same concentration as its surrounding
- water molecules will NEITHER move into or out of cells in an isotonic solution
(concentration inside and outside the cell are equal)
•
SEMI-PERMEABLE MEMBRANE: A membrane that separates two areas (eg. Inside/outside of an animal
cell) that allows certain substances through but not others. May be selectively permeable according to
size, charge, polarity of the substances.
• Diffusion is the net movement of molecules from a
region of high concentration to a region of low
concentration
• Diffusion occurs DOWN a
concentration gradient
• It DOES NOT require energy
• It will occur naturally until
EQUILIBRIUM is reached
(concentration gradient levels
out)
• The rate of diffusion can be
increased via:
 Increase in concentration
gradient
 Increase in heat
 Smaller molecules
 Medium the molecules are
moving through is a gas
•
Facilitated diffusion is a type of diffusion and
works in the same way where the particles
move from high to low concentration without
the need of any energy
•
The difference is that facilitated diffusion is
across cell membranes and involves assistance
by channel proteins or carrier proteins (see
right)
•
Speeds up the rate of diffusion of particular
molecules
•
Substances moved by facilitated diffusion
usually cannot diffuse by dissolving in the lipid
bilayer
•
Large polar and non-polar molecules need
carrier proteins to move through the membrane
(eg. Glucose)
Active transport is the net movement of molecules
from a region of low concentration to a region of
high concentration
• Active transport occurs
UP/AGAINST a
concentration gradient
• It is ENERGY
REQUIRING
• Active transport often involves
channel proteins, carrier proteins or
gated channels
• It has many important roles to play
in cellular processes such as
Glucose transport into cells
Waste products out of cells
Potassium/Sodium concentration in
nerve cells
• The energy required for Active
Transport to occur generally comes
from ATP generated during
Cellular Respiration
• Osmosis is the net movement
of WATER molecules from a
region of high concentration
to a region of low
concentration across a semipermeable membrane
• Osmosis DOES NOT require
energy
• The more concentrated a
solution the more dissolved
particles in that solution and
therefore the lower the amount
of water molecules present
• This is the opposite in less
concentrated solutions
• Therefore water will naturally
move across a membrane from
a concentrated solution to a
dilute solution until equilibrium is
reached (See left)
• VIDEO – OSMOSIS THE
BASICS
OSMOTIC PRESSURE: refers to the pressure
required to prevent osmosis occurring. Dilute solutions
are said to have low osmotic pressure as water is less
likely to move into them
• An animal cell will react
differently depending on the
concentration of the solution it is
in
• Hypotonic solutions cause water
to enter the cell and swell, it
can potentially cause the cell to
burst
• Isotonic solutions cause no
change
• Hypertonic solutions cause water
to move out of the cell and the
cell to shrivel
• Plant cells react in a similar
fashion to animal cells when
placed in different
concentrated media
• The difference is that plant
cells have a cellulose CELL
WALL which is not effected by
water movement
• When in a hypotonic solution
the membrane swells out to
the cell wall causing the cell to
become TURGID. The cell does
not burst.
• When in a hypertonic solution
the cell membrane shrivels
away from the cell wall
causing the cell to become
FLACCID. This process is called
PLASMOLYSIS.
•
4 methods by which substances (eg. Oxygen, Carbon Dioxide, Water, Amino acids, Fatty acids, Sugars, Vitamins, Mineral ions, hormones etc) move across
cell membranes
 DIFFUSION
 FACILITATED DIFFUSION
 OSMOSIS
 ACTIVE TRANSPORT
•
The cell membrane is selectively permeable
 some particles are small enough to fit through pores in the membrane
 some are helped through
 large molecules restricted
 molecules such as water, carbon dioxide, oxygen can pass through easily
 glucose and ions can move through channels with the assistance of transport proteins
PROCESS
DEFINITION
PART OF THE CELL
INVOLVED
PASSIVE/
ACTIVE
EG. OF MATERIAL
MOVED
DIFFUSION
Movement of particles from a region of HIGH
concentration to a region of LOW concentration
Cell Membrane, various
organelles
Passive
Carbon dioxide, Oxygen,
Ethanol, Glycerol
FACILITATED
DIFFUSION
Same as diffusion but aided by attachment to a
specific carrier molecule (IONOPHORE) to pass
across a membrane. May involve transport
proteins or channel proteins
Cell membrane (Carrier
proteins, Channel proteins)
Passive or
Active
Simple sugars, amino acids,
nucleotides, charged ions
OSMOSIS
Net movement of WATER molecules from a
region of HIGH concentration to a LOW
concentration through a semi-permeable
membrane
Cell membrane, various
organelles
Passive
Water
ACTIVE
TRANSPORT
Movement of particles against a concentration
gradient from a region of LOW concentration to
a region of HIGH concentration
Cell membrane (Carrier
proteins)
Active
Glucose, some ions
ENDOCYTOSIS
The movement of solids or liquids into the cell
Cell membrane, vesicles
Mostly passive
Various usually large particles
such as digestive enzymes,
hormones, toxins
EXOCYTOSIS
The movement of solids or liquids out of the cell
(usually via vesicles)
Cell membrane, vesicles
Mostly passive
Various usually large particles
such as digestive enzymes,
hormones, toxins
PINOCYTOSIS
Endocytosis involving the movement of LIQUIDS
into the cell
Cell membrane, vesicles
Mostly passive
Liquids
PHAGOCYTOSIS
Endocytosis involving the movement of foreign
material (mostly solids) into the cell for diigestion
Cell membrane, vesicles
Mostly passive
Solids (usually foreign matter
such as bacteria
BULK TRANSPORT
VIDEO: CRASH COURSE
CELL MEMBRANES &
TRANSPORT
• FUNCTION:
Acts as a SELECTIVE BARRIER between the inside of the cell and external fluid
 Regulates the transfer of substances into and out of the cell. Supplying nutrients and removing wastes
 Utilises the processes of DIFFUSION & ACTIVE TRANSPORT
 Width is usually 7 – 10 nm
• PHOSPHOLIPID BILAYER
HYDROPHOBIC tails form a non-polar hydrophobic interior
(VERY INSOLUBLE IN WATER – NON-POLAR)
HYDROPHILIC ends face the aqueous medium and are polar
(VERY SOLUBLE IN WATER)
•
The hydrophobic head tends to dissolve in water and the hydrophobic tails are repelled and force inward
forming a PHOSPHOLIPID BILAYER
•
Phospholipids are capable of sideways movement
•
Specialised protein molecules are also embedded in a ‘mosaic’ pattern
•
Proteins and lipids can flip around in the membrane
- protein molecules in the membrane have particular functions and can carry a sugar molecule
(GLYCOPROTEIN)
•
Glycoproteins are often receptors/marker molecules important in cell recognition
•
The lipid structure gives it the property of being flexible and able to repair itself
•
Allows it to change shape and for vesicles to be pinched off from them or fuse to it
PERMEABLE SUBSTANCES
Small hydrophobic molecules
 Oxygen, Carbon Dioxide, Nitrogen
Small uncharged polar molecules
 Water, Glycerol, Ethanol
NON-PERMEABLE SUBSTANCES
Ions
 Na+, H+, K+, Mg+, Cl-, HCO3Larger uncharged molecules
 Amino acids, Nucleotides, Glucose
• PHOSPHOLIPIDS:
The bilayer structure means the non-polar tails act as a barrier for ions and
watersoluble substances
• CHOLESTEROL:
Help regulate the fluidity of the membrane preventing it from becoming
too rigid. Mechanical stability so membranes don’t break easily
• PROTEINS:
Transport Proteins: provide hydrophilic channels for ions & polar
molecules. Specific for the molecule being transported. Some are
enzymes which may catalyse reactions. Can be gated or non-gated.
Gated are important for Ca+, Na+ & K+ and muscle/nerve operation
Cell Adhesion Proteins: attach adjacent cells to one another
Hormone Binding Proteins: allow hormones to bind to them
and a signal is transmitted to inside of the cell
Cell Recognition Proteins: allows the cell to be recognised as
‘self’ or ‘foreign’ and act as markers
• GLYCOLIPIDS & GLYCOPROTEINS:
Carbohydrate chains are often attached to the lipids and proteins of the
outer membrane. These are known as glycolipids and glycoproteins.
Project out into watery fluids surrounding the cell where they form
hydrogen bonds with water. They help stabilise the membrane
structure. Can act as receptor molecules for hormones or
neurotransmitters. Are the basis for cell ANTIGENS.
*may be called glycocalyx
CELL MEMBRANE
and PROTEINS
Structure and Function of Plasma Membranes
Which of the following is a function of plasma membranes?
A) Organizing cellular processes
B) Regulating transportation of materials in and out of a cell
C) Communicating directly with the cell nucleus
D) Producing proteins and hormones
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Structure and Function of Plasma Membranes
Which of the following is a function of plasma membranes?
A) Organizing cellular processes
B) Regulating transportation of materials in and out of a cell
C) Communicating directly with the cell nucleus
D) Producing proteins and hormones
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Structure and Function of Plasma Membranes
Which of the following statements best describes the lipid bilayer plasma
membrane?
A) The interior and exterior surfaces of the membrane are hydrophobic and the
middle is hydrophilic
B) The interior and exterior surfaces of the membrane are hydrophilic and the
middle is hydrophobic
C) The interior surface and the middle of the membrane are hydrophobic and the
exterior is hydrophilic
D) The exterior surface and the middle of the membrane are hydrophobic and
the interior is hydrophilic
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Structure and Function of Plasma Membranes
Which of the following statements best describes the lipid bilayer plasma
membrane?
A) The interior and exterior surfaces of the membrane are hydrophobic and the
middle is hydrophilic
B) The interior and exterior surfaces of the membrane are hydrophilic and the
middle is hydrophobic
C) The interior surface and the middle of the membrane are hydrophobic and the
exterior is hydrophilic
D) The exterior surface and the middle of the membrane are hydrophobic and
the interior is hydrophilic
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Structure and Function of Plasma Membranes
What does the term 'mosaic' refer to in the fluid mosaic model of the
plasma membrane?
A) The heterogeneous composition of phospholipids, cholesterol, proteins, and
carbohydrates
B) The array of colors seen when the plasma membrane is viewed with a
microscope
C) That scientists had to put together pieces from various models to make one to
fit
D) The different sizes of plasma membranes that exist in nature
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Structure and Function of Plasma Membranes
What does the term 'mosaic' refer to in the fluid mosaic model of the
plasma membrane?
A) The heterogeneous composition of phospholipids, cholesterol, proteins, and
carbohydrates
B) The array of colors seen when the plasma membrane is viewed with a
microscope
C) That scientists had to put together pieces from various models to make one to
fit
D) The different sizes of plasma membranes that exist in nature
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Structure and Function of Plasma Membranes
What role does cholesterol play in plasma membrane fluidity?
A) Cholesterol has a detrimental role in membrane fluidity.
B) Cholesterol extends the range of temperature in which the membrane is fluid
and functional.
C) Cholesterol acts like a magnet pulling proteins around the membrane.
D) Cholesterol forces out the unsaturated fatty acids that 'kink' from the
membrane.
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Structure and Function of Plasma Membranes
What role does cholesterol play in plasma membrane fluidity?
A) Cholesterol has a detrimental role in membrane fluidity.
B) Cholesterol extends the range of temperature in which the membrane is fluid
and functional.
C) Cholesterol acts like a magnet pulling proteins around the membrane.
D) Cholesterol forces out the unsaturated fatty acids that 'kink' from the
membrane.
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