Transcript Cellular Transport - Northwest ISD Moodle

Cellular Transport
Lesson Objectives
• Explain the processes of diffusion,
facilitated diffusion, and active transport
• Predict the effect of a hypotonic,
hypertonic, or isotonic solution on a cell
• Discuss how large particles enter and exit
cells
Main Idea
• Cellular transport moves substances
within the cell and moves substances into
and out of the cell.
Diffusion
• Molecules and ions dissolved in water are in
constant motion, moving randomly.
• The net movement of particles (caused by the
random motion) from an area of high
concentration (many particles) to low
concentration (few particles) is called diffusion.
• Net movement will occur until the concentration
in all regions are the same, which is dynamic
equilibrium.
Diffusion
• The amount of substance in a particular
area is called concentration.
• There must be a concentration gradient,
a difference between concentrations
across a membrane, for cellular transport
to occur.
Diffusion
• All types of diffusion are passive transport
mechanisms because no energy is
needed.
• Three main factors that affect the rate of
diffusion:
– Concentration
– Temperature
– Pressure
Facilitated Diffusion
• Many molecules needed by cells are polar
and cannot pass through the plasma
membrane, so an alternate route is
needed.
• Channels are made out of proteins that
form a polar interior that is “friendly” to the
molecules.
• Carrier proteins help substances diffuse by
changing shape as the diffusion process
occurs to help move the particle through
the membrane.
Osmosis
• Water is a universal solvent.
• The molecules dissolved into the solvent
are called solutes.
• The net movement of water across a
membrane by diffusion is called osmosis.
• 3 types of solution:
– Isotonic
– Hypertonic
– hypotonic
Osmosis
• When a cell is in a solution that has the
same concentration of water and solutes
(ex. Ions, sugars, proteins, etc.) as its
cytoplasm, the cell is said to be in an
isotonic solution.
• The cell is in equilibrium with the solution.
Osmosis
• If a cell is in a solution that has a lower
concentration of solute, the cell is in a
hypotonic solution.
• There is more water on the outside of the
cell than the inside, so water moves into
the cell.
• Causes swelling as the vacuoles in the cell
fill with water
Osmosis
• When a cell is placed in a hypertonic
solution, the concentration of the solute
outside the cell is higher than inside.
• Net movement of water is out of the cell.
• Vacuoles are emptied of water, causing
cells to shrink.
Osmosis
Active Transport
• Sometimes substances must move from
an area of low concentration to high
concentration.
• The movement of substances across the
plasma membrane against a concentration
gradient is called active transport.
• Requires energy!
• Helps maintain homeostasis
Active Transport
• Occurs with the aid of carrier proteins, called
pumps
• Endocytosis is a process by which a cell
surrounds and takes in material from its
environment.
–
–
–
–
Does not pass directly through the membrane
Engulfed
Phagocytosis – eating of the particle
Pinocytosis – drinking of the substances
• Exocytosis is the expulsion or secretion of
materials from a cell.
– used to expel wastes and secrete hormones
Active Transport
Sodium Potassium Pump
• 1. Protein in the membrane binds intracellular
sodium ions.
• 2. ATP attaches to protein with bound sodium
ions.
• 3. The breakdown of ATP causes shape change
in the protein, allowing sodium ions to leave.
• 4. Extracellular potassium ions bind to exposed
sites.
Sodium Potassium Pump
• 5. Binding of potassium causes release of
phosphate from protein.
• 6. Phosphate release changes protein
back to its original shape, and potassium
ions move into the cell.
Sodium Potassium Pump
Coupled Transport
• Many molecules are cotransported into
cells up their concentration gradients by
coupling their movement to that of sodium
ions or protons moving down their
concentration gradients.