Transcript active transport

All cells have a plasma membrane. This outermost,
double-layered membrane separates a cell’s interior
from its surroundings. The plasma membrane is selectively
permeable.
Plant, fungal,
eubacterial, algal and
archaebacterial cells
also have a cell wall,
which helps to give the
cell its structure, and
protect it from
osmotic pressure.
Animal cells, and most
protists don’t have a cell
wall.
There are many ways in
which a material can
pass through the cell
membrane.
One such method is
simple diffusion.
Diffusion is simply the
movement of particles
(molecules) from a region of
higher concentration to a
region of lower
Thus, particles travel from compartment
concentration.
A to B, given the concentration gradient.
Another way that molecules can move through
a membrane is through osmosis.
• Osmosis is simply the diffusion of water
molecules across a selectively permeable
membrane
• The plasma membrane is responsible for
maintaining homeostasis within the cell by
allowing water in when the cell needs water
and allowing water out,
when it doesn’t
The movement of water is
influenced by the presence or
absence of dissolved solute in
solution, so again, it’s about
concentration gradient.
What types of cells have cell walls?
What types of cells don’t typically have cell
walls?
Movement of particles from a region of high
concentration towards low concentration is
referred to as???
What is another name given to the diffusion of
water?
What causes water molecules to diffuse in a
given direction?
solute
SPM
Tonicity is a measure of the osmotic pressure
gradient of two solutions separated by a
semipermeable membrane.
So it could be referring to a cell in a solution…or a solution
surrounding a cell.
In other words…tonicity is about perspective.
There are three different classifications of tonicity.
• Hypertonicity
• Hypotonicity
• Isotonicity
Isotonic solutions occur when the
concentration of dissolved substances in the
solution outside the cell is the same as the
concentration of dissolved substances inside
the cell.
Osmosis still
occurs, but it
flows into and
out of the cell
at the same
rate.
In a hypotonic solution, the concentration of
dissolved substances is lower in the solution
outside the cell than the concentration inside the
cell.
Osmosis will
occur, and
water will
flow into the
cell,
sometimes
What type of pressure is
until the cell
increasing in this plant cell?
Turgor Pressure
bursts.
When cells are placed in a hypertonic solution,
one which contains more dissolved particles than
are within the cell, water will flow out of the cell.
Due to
osmosis,
cells will
shrivel up
and
shrink as
they lose Is the turgor pressure low or high
water.
in this plant cell? LOW
In the image to the right, in
which direction will the water
flow?
Why?
What will happen to these red blood cells,
when they are placed in a hypotonic solution?
What do I mean when I say “tonicity” is all
about relativity?
When cells are placed in isotonic solutions, in
which direction will the water move?
• Steepness of concentration gradient
Molecules will appear to move faster out of a region of higher
concentration than a region of lower concentration.
• Molecular size
Smaller molecules move faster than larger molecules
• Temperature
Heat energy causes molecules to move faster than in colder
adjoining regions
• Electric or pressure gradients present
Dissolved ions can create a potential difference where positive ions
are attracted to negative areas, and pressure can also cause a
gradient “pushing” molecules from one region to another
When the net movement of molecules remains nearly
uniform in two adjoining regions, it is known as
dynamic equilibrium.
Substances can diffuse passively across a membrane
by two processes: simple diffusion through the
phospholipid bilayer and facilitated diffusion through
either channel proteins or by means of a carrier
protein.
Because no energy is required by
the cell to accomplish this
movement, it is referred to as
passive transport. All it needs to
move, is a concentration gradient.
Substances such as water,
oxygen, and carbon dioxide,
can cross the cell membrane
without any input of energy
by the cell.
Explain how concentration gradient can affect
the diffusion rates of molecules.
What other factors may influence diffusion
rates?
What is dynamic equilibrium?
Name three molecules that can move through
the plasma membrane via passive transport.
How is simple diffusion different from
facilitated diffusion, if they’re both passive
mechanisms of cellular transport?
A cell can also move particles from a region of lower
concentration to a region of higher concentration if it
needs to, but it must extend energy to do so.
 Movement of materials through a membrane against
a concentration gradient is called active transport
and requires energy output from the cell.
The energy required for
this active transport comes
from the ATP molecule,
dropping off an Pi , and
transforming into an ADP.
Passive Transporters:
• movement requiring no energy
output by the cell.
Examples: Vacuoles in plant and
animal cells; nerve and muscle
cells with sodium, calcium,
potassium, and chloride ion
channels.
Active Transporters:
• movement requiring energy
output by the cell.
Examples: Movement of
particles against the
concentration gradient, like the
calcium “pump” which helps keep
the concentration of calcium
inside a cell at least a thousand
times lower than it is outside a
cell.
All cellular membranes are made primarily of phospholipids,
organized as a double layer.
• This lipid bilayer gives cells protection
against the haphazard movement of water,
and water-soluble substances.
• The structure of the plasma membrane is
sometimes referred to as the fluid mosaic
model. This “fluidity is achieved with the
help of the cholesterol molecules within.
Phosphate heads are hydrophilic
Phosphate
Lipid
Lipid tails are hydrophobic
• Receptor proteins within the plasma membrane receive
chemical signals that trigger changes in cell activities. The
endocrine system is linked to the plasma membrane through
the work of hormones.
•Transport proteins are also within the plasma
membrane and form channels through which water
soluble substances can cross.
• Recognition
proteins help
identify a cell as
being of a
certain type.
• Adhesion proteins help cells of the same type
locate, stick together, and remain in the proper tissues
In some instances
(cardiac tissue), this
channel forms a gapjunction between
cells so that
electrical signals can
flow quickly and all
cells can contract
together as a
functional unit.
By what name did
• Communication proteins form channels the surface features
that match up across the plasma
of plant cells that
membranes of two cells, and allow signals require these
and substances to flow rapidly between communication
their cytoplasm.
proteins go by?
Why do cells need to accomplish active
transport?
How is fluidity of the plasma membrane
accomplished?
Describe why some cells would need to form
channels linking one cell to another?
Give examples of where communication
proteins forming gap-junctions and
plasmodesmata form.