Download A simple rule of diffusion

Homeostasis & Cell Transport
• Passive Transport
– Diffusion aka Simple Diffusion
– Osmosis
– Facilitate Diffusion
• *No energy required
• Active Transport
– Cell Membrane Pumps
– Endocytosis and Exocytosis
• *Requires energy
Passive transport is diffusion across
a membrane
• What is diffusion or simple diffusion?
– Movement of molecules from an area of HIGH concentration to
LOW concentration.
– Driven entirely by kinetic energy the molecules possess.
Molecules are in constant motion.
• Think about when you open a bottle of perfume…The
bottle has a high concentration of perfume the air has a
_____ concentration. So the molecules in the perfume
want to go???
• A simple rule of diffusion: a substance will diffuse from
where it is more concentrated to where it is less
concentrated. To put it another way, any substance will
diffuse down its concentration gradient.
More Diffusion…
• When does diffusion stop?
– When the concentration of the molecules of a
substance is the same throughout a space
called?
• What types of molecules can move into a
cell by diffusion?
– Oxygen and carbon dioxide because they
dissolve in lipids.
More Diffusion…
• Is diffusion regulated?
– Is the cell membrane selective?
– What kind of molecules are going to diffuse
across a cell membrane?
• Size and type of the molecule…the smaller the
better!
• Chemical nature of the membrane…if they dissolve
in lipids!
Osmosis is the passive transport of
water
• What is osmosis?
– The process by which water molecules diffuse across a
cell membrane from an area of higher concentration to
an area of lower concentration.
• How does osmosis affect a cell?
– Under HYPERTONIC conditions? – H2O out
– Under HYPOTONIC conditions? – H2O in
– Under ISOTONIC conditions? – H2O same
• Remember…where salt goes water will follow!!!
More osmosis…
• How do cells deal with osmosis?
– Vertebrate animals living on land and most
living in the sea…cells function in an isotonic
external environment – NO PROBLEM when
balancing movement of water.
– Unicellular freshwater organisms…cells
function in hypotonic environments – Water
CONSTANTLY diffuses into these organisms.
• How do they get rid of this excess water that enters
by osmosis?
– Contractile Vacuole
More osmosis…
– How do plant cells deal with osmosis? Remember they
live in hypotonic environments…
• Turgor pressure – if pressure against the cell walls is so
great…water will be pushed out of the cell.
– In a hypertonic environment…water leaves plant cells
by osmosis.
• The cells shrink away from the cell walls and turgor pressure is
lost…this is called plasmolysis.
– Changes to a cell’s environment can create
problems…Human Red Bloods Cells
• Cytolysis – hypotonic environment…cells burst!!!
Facilitated Diffusion
• What is facilitated diffusion?
• How is this different from simple diffusion?
– How does the selectivity compare?
• MORE selective than simple diffusion…molecules
are assisted by specific proteins in the membrane.
• What are carrier proteins?
• Example…How does glucose, a molecule that many
cells need for their energy, get into the cell?
• Must diffuse down its concentration
gradient!!!
What did we learn?
• Diffusion is SLOOOOOOWWWW!!!
• Osmosis is the diffusion of water.
• Hypertonic, hypotonic, isotonic (remember
where salt goes water will follow).
• Facilitated diffusion uses carrier proteins to
help large molecules across the cell
membrane.
Active Transport
• What is active transport?
• How is it different than passive transport?
– Where does the energy come from to drive active transport?
• What are cell membrane pumps?
• What kind of proteins do they use?
• An example of a cell membrane pump…
– Sodium-Potassium pump…the mother of all pumps
– How does the Sodium-Potassium Pump work?
• Exchanges sodium (Na+) for potassium (K+) across the cell membrane
of animal cells.
Other types of active transport…
• What is Endocytosis?
– What are the two types of endocytosis?
– What does pinocytosis involve?
– What does phagocytosis involve?
• What is Exocytosis?
What did we learn today?
• Active transport uses ATP (it’s energy
currency) to move molecules from low to
high concentration.
• Cell membrane pumps ex. SodiumPotassium Pump.
• Endocytosis and Exocytosis