Cell Transport Ch. 7.3 & 7.4

Copyright © by Holt, Rinehart and Winston. All rights reserved.Copyright © by Holt, Rinehart and Winston. All rights reserved.

Cell Transport

Ch. 7.3 & 7.4

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Copyright © by Holt, Rinehart and Winston. All rights reserved.

Plasma Membrane

Membrane Lipids• Cell

membranes consist of a phospholipid bilayer

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Plasma Membrane

Membrane Proteins• Cell membranes often contain proteins

embedded within the phospholipid bilayer.

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Plasma Membrane

Fluid Mosaic Model• the phospholipid bilayer behaves like a

fluid more than it behaves like a solid.

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Diffusion

• Diffusion– the movement of a substance from an area of high

concentration to an area of lower concentration – caused by the random motion of particles of the

substance

Chapter 4

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Copyright © by Holt, Rinehart and Winston. All rights reserved. 6


passive transport– movement across the cell membrane that does not

require energy

• concentration gradient– A difference in the concentration of a substance, across

a space

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Equilibriumequilibrium

the concentration of a substance is equal throughout a

space

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Some substances move across the cell membrane

without any use of energy by the cell.

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Simple Passive Diffusion

• Many substances enter or leave cells by diffusing across the cell membrane.

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Osmosis• osmosis

– the diffusion of water through a selectively permeable membrane

– determined by solute concentration on both sides of the cell

Chapter 4

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Osmosis is a type of passive transport

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Copyright © by Holt, Rinehart and Winston. All rights reserved.Copyright © by Holt, Rinehart and Winston. All rights reserved.

There are three possibilities for the direction of water movement:

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Osmosis

Hypertonic solution– solute concentration

outside the cell is HIGHER THAN the cytosol

– there is a NET movement of water out of the cell.

– the cell shrinks.

Chapter 4

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OsmosisHypotonic solution

– solute concentration outside the cell is LOWER THAN the cytosol

– there is a NET movement of water into the cell.

– the cell swells.

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Isotonic solution

– the solute concentration outside the cell is EQUAL TO the cytosol

– there is no NET movement of water.

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Osmosis


Compare

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Facilitated Diffusion

• Passive transport across the membrane using an embedded protein

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Carrier proteins

bind to a specific substance on one side of the cell membrane,

carry the substance across the cell membrane, and release it on

the other side.


• Ion channel

–a transport protein with a polar pore through which ions can pass.

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Movement Against a Concentration Gradient

• active transport– the transport of a substance across the cell

membrane against its concentration gradient. Energy is required.

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Comparing Active and Passive Transport

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Movement in Vesicles

• endocytosis – The movement of larger substances across the cell

membrane by vesicles.

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exocytosis

the movement of a substance by a vesicle to the

outside of a cell

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Documents

Cell Transport Ch. 7.3 & 7.4