Cell Membrane Review
Functions
– Provides boundary for cell
– Selectively Permeable: only allows
certain things to pass through. “Picky”
Ex: Window screen
– Maintains homeostasis: balance
within the cells
Cell Membrane
Structure vs. Function
– Membrane is a phospholipid bilayer
– Phospholipids: two sided molecule with a
head that loves (hydrophilic) and a tail
that repels (hydrophobic) water
– Embedded Proteins: “club bouncers”
Decide who goes in & out
Markers for recognition
TYPES OF TRANSPORT
Passive Transport:
-Uses No Energy
-Movement from high concentration to low
concentration
Active Transport:
–
–
Requires Energy (ATP)
Usually against the concentration gradient
(from low concentration to high concentration)
Passive Transport
Diffusion = movement of molecules from
high concentration to low concentration
Passive Transport
Osmosis =
movement (or
diffusion) of
water from
area of high
concentration
to low
concentration
Higher Concentration
of Water
Lower Concentration
of Water
(Water molecules)
(Sugar molecules)
HYPO/HYPER/ISO
HYPOTONIC:
•Concentration is lower outside cell than inside cell
•HYPOTONIC means “below strength”
•Water will move INTO cell causing it to SWELL
•Cells could rupture if the cell takes in too much water
•This increases pressure inside of cell (TURGOR
PRESSURE)
HYPERTONIC:
•Concentration is higher outside the cell, lower
inside cell
•HYPERTONIC means “above strength”
•H2O rushes OUT of cell causing it to shrivel
•Can result in PLASMOLYSIS in plants which
causes wilting
ISOTONIC:
Concentration outside the cell is the
same as the inside of the cell
ISO- means “equal to” or “same”
Movement into cell = movement out
of cell; cell does not change.
Passive Transport
Facilitated Diffusion = proteins are used to
help larger molecules (like sugar) cross the
membrane. Facilitated means “assisted”. Still
passive. No energy required.
Active Transport
Movement against the concentration gradient.
Molecules will move from an area of low
concentration to an area of high
concentration.
Requires energy in the form of ATP
(Adenosine Triphosphate) and protein pumps
Active Transport
Endocytosis = the process by which cells take in
particles; into the cell
– Pinocytosis = drinking action, used for small
particles or water
– Phagocytosis = devouring action, used for large
particles like food
Exocytosis = the process by which cells
remove wastes and large particles; exit the
cell