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Cell Transport
Maintaining Balance
• Homeostasis – process of
maintaining the cell’s internal
environment
• Cannot tolerate great change
• Boundary between cell and the
environment
• What provides this?
Plasma Membrane
• Fluid Mosaic Model
• Selective Permeability
• Phospholipid bilayer
– Hydrophobic; Fatty Acid Tail
– Polar Head; Hydrophilic
• Cholesterol
– Provides stability
• Transport Proteins
• Carbohydrates
• Other Proteins
– Cell recognition (immune
system)
Recall Following Terms
• Solution
• Diffusion
• Concentration gradient
• Results in uniform concentration
Osmosis
• Cells try to reach equilibrium
• Diffusion of water across a
selectively permeable membrane;
3 results
– Isotonic
– Hypertonic
Tonicity
– Hypotonic
Isotonic
• Solute concentration of solution
equal to that of cell
• No net water movement
Hypertonic
• Solute concentration of solution
higher than cell
• More dissolved particles outside
of cell than inside of cell
• Hyper = more (think hyperactive);
Tonic = dissolved particles
• Water moves out of cell into
solution
• Cell shrinks
Hypotonic
• Solute concentration of solution
lower than cell
• Less dissolved particles outside
of cell
• Hypo = less, under (think
hypodermic, hypothermia); Tonic
= dissolved particles
• Water moves into cell from
solution
• Cell expands (and may burst)
Active vs. Passive
• Active vs. Passive Transport
• Passive requires no energy from
the cell
• Active requires cells to use
energy, usually ATP
Passive Transport
• Have to move with the
concentration gradient
• Diffusion
• Osmosis
• Facilitated Diffusion- involves use
of transport proteins but still
follow rule of diffusion
Active Transport
• Movement of materials against
concentration gradient
• Transport proteins
• Endocytosis – cell takes in
material
• Exocytosis – expulsion or
secretion of materials from cell
Pinocytosis Phagocytosis