Cell Transport notes
Transcript Cell Transport notes
Membranes and Homeostasis
• Facilitated Diffusion
• Molecular Transport
• Bulk Transport (Endocytosis and Exocytosis)
regulates what enters and
leaves the cell, and also protects and
supports the cell
• Consist of phosphate “head” water loving
• 2 fatty acid “tails” water fearing
• Forms a bilayer with heads facing out and tails
• “float” and move along the lipids
• Form channels and pumps that help to move
materials across the membrane
• Usually attach to proteins
• Act like chemical “ID cards”; allow cells to
recognize one another.
• Proteins literally float among the lipids
• So many different molecules make up the cell
membrane; it looks like a mosaic (a kind of art
that involves bits and pieces of different colors
• Only some things can enter the cell membrane,
other things cannot.
• Things that are too large or too strongly charged
will have difficulty entering, or will not be able
to enter at all
living things want to maintain
homeostasis, relatively constant internal
physical and chemical conditions.
To stay in balance, molecules in the cell
will move across the cell membrane until
equilibrium is reached.
is passive transport?
• The movement of molecules from high
concentration to low concentration
• Requires no energy (ATP)
• Molecules move with the concentration gradient
• Eventually equilibrium is reached (but
molecules keep moving!)
of Passive Transport:
• Facilitated diffusion
• The process by which particles move from an
area of high concentration to low concentration.
• How small, nonpolar molecules move across the
• For example, O2 and CO2
• Molecules that cannot directly diffuse across the
membrane because of size, charge, or polarity
pass through special protein channels.
• For example, molecules like starch are too large,
and require proteins to diffuse into the cell.
• The facilitated diffusion of water across a
selectively permeable membrane through
proteins called aquaporins.
• Water will move based on its concentration in
solution (solute + solvent):
Solute concentration is lower inside cell (solvent
concentration is higher inside cell) ;Water goes out
Causes plasmolysis in plant cells
• Isotonic Solution
Equal concentration of solvent inside and outside of
cell; water goes in and out
Cell’s volume remains the same; equilibrium
Solute concentration is greater inside the cell (solvent
concentration is lower inside the cell); water goes in
Cell swells and may lyse
Causes cytolysis in animal cells
is active transport?
• The movement of molecules from low to high
• Requires energy (ATP)
• Molecules move against the concentration
of active transport:
• Molecular transport
• Bulk transport
• For example, sodium/potassium pump
• Small molecules and ions like sodium (Na+) and
potassium (K+) are carried across membrane
• Moves larger molecules and even solid clumps
• Involves the formation of a vesicle
Bulk Transport: Endocytosis
• Movement of large molecules or particles into
the cell. The cell membrane folds in, taking in
materials, and forms a vesicle to bring the
contents into the cell.
“cell eating” solid, can be food particles
“cell drinking” liquid particles
• The vesicle carrying molecules or particles fuses
with the cell membrane, forcing the contents out
of the cell.