Download A simple rule of diffusion

The Cell :
The Basic Unit of Life
Leeuwenhoek
What is he
known for?
Developed the
first microscope.
This is Leeuwenhoek’s
first microscope.
Englishman
Robert Hooke
First to use
the word:
“Cells.”
Unfortunately, he was
looking at cork cells
which aren’t living
structures but the remains
of living cells
Robert Brown
in 1833,
Scottish
Scientist who
discovered
the nucleus
of cells
Matthias Schleiden Theodor Schwann
“First to see
plant cells”
“First to see
animal cells”
“The Cell Theory”
•All living things are
made of cells
•Cells are the basic
units of structure
and function in
living things
•All cells come from
preexisting cells
Rudolph Virchow
E.coli bacterial cells
Bacteria
on diesel
waste
Amoeba
Green alga
cells
Blood Cells
Platelet
(piece of a
cell)
surrounded
by red blood
cells
Epithelial cells:
Found in skin, hair, nails,
lining of organs
Skeletal muscle
Cardiac Muscle cells
Mammalian Nerve Cell
Prokaryotic cells vs.
Eukaryotic cells
Cells with no nucleus vs.
Cells with a true nucleus
Cell size is
limited by
surface area
to volume
ratio.
Typical
Animal
Cell with
Structures
Typical
plant cell
w/structures
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