Transcript Plasma Membrane

Plasma membrane
Cell membrane
Phospholipid bilayer
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
Cell membranes are mosaics of
different molecules combined.
Selective permeability
• The plasma
membrane enables
only certain
molecules to enter or
exit the cell.
• Why is this important?
Selective transport
1. Diffusion
2. Facilitated diffusion
3. Active transport
Chemicals usually move across the cell
membrane from areas of higher to
lower concentration.
1. Diffusion: simple
movement from
HL
2. Osmosis: water
diffusion
3. Facilitated or
passive diffusion:
movement of
chemicals through
proteins from H-L
Glucose
molecules
High
Concentration
Cell
Membrane
Low
Concentration
Protein
channel
Diffusion video
Click on image to play video.
Diffusion across a membrane
Osmosis
• Water diffusion from higher to lower
concentration
• When solutions of varying water
concentrations are found across a
membrane, the solutions are given names.
– Hypertonic
– Hypotonic
– Isotonic
Osmosis across a membrane
Achieving equilibrium
Osmosis video
Click on image to play video.
Solutions
• Hypertonic solutions have less water than
the solution across the membrane.
• Hypotonic solutions have more water
than the solution across the membrane.
• Isotonic solutions have the same water
concentration as the solution across the
membrane.
Cells in various solutions
Hypotonic
LYSE
Isotonic
NORMAL
Hypertonic
animal
PLASMOLYZE
Plant,
fungus,
algae,
bacteria
TURGID
FLACCID
Channel vs. Carrier Proteins
Molecule to
be carried
Active transport
• Moving chemicals in and
out of a cell, past the
plasma membrane, using
energy and a carrier
protein
• Chemicals move from
areas of lower
concentration to areas of
higher concentration.
Energy
Molecule
being carried
Active transport video
Click on image to play video.
Example of active transport
Exporting and importing materials
Click on image to play video.
Surface to volume ratio
• Because materials must be transported
across cell membranes, maximizing the
amount of membrane surface area
increases cellular activity.
• This is why larger organisms are
multicellular.
Comparing surface area to volume
• Surface area: 6 mm x
6 mm x 6 sides = 216
mm2
• Volume: 216 mm3
• S/T = 1
• Surface area: 3 mm x
3 mm x 6 sides x 8
cubes = 432 mm2
• Volume = 216 mm3
• S/T = 2