CH 8: Cellular Transport

Diffusion and Osmosis

What is diffusion? - the movement of molecules from regions of

high concentration to regions of low concentration, “down” a concentration gradient.

What is osmosis? – The diffusion of water across a selectively

permeable membrane

Why do we need to regulate osmosis? – To maintain homeostasis because the plasma

membrane is naturally permeable to water

Osmosis

How long does water diffuse in a solution? - Until it has reached equilibrium (even distribution)

What controls osmosis? – The concentration gradient

What is a concentration gradient? – The unequal distribution of particles

Types of Solutions: Isotonic Remember: Salt Sucks!!!

"ISO" means the same

Definition: When the concentration of water is the same inside and outside the cell so a cell remains the same.

Both animal and plant cells retain normal shape and pressure

Types of Solutions: Hypotonic

• The prefix "HYPO" means less-Less water inside the cell than outside so water will move into the cell.

• Definition: When the concentration of water is lower inside the cell than outside the cell so the cell swells

• What happens: The cell swells up • Animal Cell- swell until they burst • Plant Cell- swell beyond their normal size as

pressure increases; this pressure is called turgor pressure. The plasma membrane presses against the cell wall and makes the cell more firm (why grocers mist fruits at the market)

Types of Solution: Hypotonic

Types of Solution: Hypertonic• The prefix "HYPER" means more

-More water inside the cell than outside so the water leaves the cell.

• Definition: When the concentration of water is higher inside the cell than outside the cell so the cell shrivels

• What happens: Cell shrivels up • Animal cell- shrivels up • Plant cell – loses pressure as the plasma

membrane shrinks away from the cell wall; the plant wilts = plasmolysis

Types of Solutionhttp://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

Red Blood Cells in SolutionBurst---------------Swollen----------Normal-----------------Plasmolysis---------

• http://www.wiley.com/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm

• http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html

Passive Transport: No Energy Required

• Passive Transport -the movement of the movement of particles across a membrane that goes particles across a membrane that goes with the concentration gradient…high with the concentration gradient…high concentrationconcentration low concentration…and low concentration…and energy is not requiredenergy is not required

• What do materials need to cross the plasma membrane? Transport proteinsTransport proteins

• What is this process called? Facilitated diffusion Facilitated diffusion

Types of Transport Proteins

• Channel Proteins- form channels that allow specific molecules to flow through.

• Carrier Proteins - change shape to allow a substance to pass through the plasma membrane.

Active Transport: Requires Energy

• Active Transport – Movement of particles Movement of particles through a membrane against a through a membrane against a concentration gradient…low concentration gradient…low concentrationconcentration high concentration… high concentration…Energy Energy is requiredis required

• How does active transport occur?

A carrier protein binds with the substance A carrier protein binds with the substance to be transported. The protein changes to be transported. The protein changes shape so that the particle can be released shape so that the particle can be released into the cell--like the opening of a door. into the cell--like the opening of a door.

Type ofTransport

TransportProtein Used?

Direction of Movement

Requiresenergy from

the cell?

Classification of transport

SimpleDiffusion

No WithConcentration

Gradient

No Passive

FacilitatedDiffusion

Yes- channel protein or carrier protein

WithConcentration

Gradient

No Passive

ActiveTransport

Yes- carrier protein

AgainstConcentration

Gradient

Yes Active

Passive Transport vs. Active Transport

Transport of Large Particles

• Endocytosis- The process by which a cell surrounds and takes in material from its environment

• Explain the process of endocytosis- the material is engulfed and enclosed by a portion of the cells plasma membrane.

Exocytosis

• Exocytosis- the expels or secretes materials from a cell.

Transport of Large Particles

• Phagocytosis- the engulfing and ingesting of solid particles- “cell eating”

• Pinocytosis- the ingestion of fluid into a cell- “cell drinking”

http://www.researchandteaching.bio.uci.edu/lectureprojects.html