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Pretest• What is the job of the plasma membrane?
• What is semi-permeable?
• What is the difference between active transport and passive transport?
• What is osmosis?
• What will happen to a cell when placed in a hypertonic solution? Hypotonic solution?
• What are examples of each?
The plasma membrane maintains homeostasis for the cell
It is selectively permeable:
It controls what goes into and out of the cell
Two forms of transport across the membrane:
Passive TransportNo energy needed
• WITH the gradient (high to low)
• Examples:
– Diffusion– Osmosis
Active Transport• ENERGY used
• AGAINST the gradient
• Examples:
– Endocytosis– Exocytosis
Plasma Membrane Structure
Two key components of the membrane:
phospholipids
proteins
Crossing the Plasma Membrane: Passive Transport
Energy?Direction?Examples?
Passive Transport: Diffusion
• The phospholipids line up to form a double membrane
• Small, uncharged particles are able to pass right between the phospholipids
• This is called simple diffusion
Passive Transport: Diffusion
• There are also proteins embedded between the phospholipids.
• These proteins function as gates, allowing larger or charged molecules to get in/out of the cell
• Only molecules which are “recognized” are allowed thru these proteins
• This is facilitated diffusion
Passive transport: Diffusion
Lower Concentration
Higher Concentration
Molecules collide – pass thru membrane
Concentration gradient:
Passive Transport: Osmosis
• The movement of water• Water moves TOWARDS the molecules
• Think of it as “water wants to dissolve stuff”
• Which way will water move in each case?
Passive Transport: Osmosis
HYPERtonic ISOtonic HYPOtonic
The effect of osmosis on animal cells
Cytolysis
What do plant cells have outside of the cell membrane
that animal cells do not have?
What difference will this make with osmosis?
Effect of osmosis on plant cells
Flaccid - Turgiddue to plasmolysis - cell shrinks from cell wall
Passive transport: osmosis
Osmosis
Which way will water move?
Hypertonic or Hypotonic?
Active Transport:Which direction?
Energy Used?Examples?
Crossing the Plasma Membrane
Figure 3.8
Active transport
AGAINST the gradient
requires energy
Active Transport• Endocytosis
– Pino-
– Phago-
• Exocytosis
Figure 3.9
Ion pumps: Thru a protein, but using energy
Crossing the Plasma Membrane
Passive Transport Active Transport
Crossing the Plasma Membrane
Passive Transport
• No energy needed
• WITH the gradient
• Diffusion
• Osmosis
Active Transport
• ENERGY used
• AGAINST the gradient
• Can be through a protein
• Endocytosis
• Exocytosis
Post test• What is the job of the plasma membrane?
• What is semi-permeable?
• What is the difference between active transport and passive transport?
• What is osmosis?
• What will happen to a cell when placed in a hypertonic solution? Hypotonic solution?
• What are examples of each?