Cell Transport

Ch. 9: Cell Transport Passive Transport Targets

Distinguish between diffusion & osmosis Define equilibrium & explain how it is

established Explain what is meant by a concentration

gradient Explain how substances cross the cell

membrane through facilitated diffusion Explain how ion channels assist the diffusion

of ions across the cell membrane

Concentration how much of a given substance there is

mixed with another substance

Kinetic Motion All particles of matter are in

constant (random) motion Molecules travels in a straight

line until they hit something, bounce off, and travel in a new direction

Molecules move down the concentration gradient from an area more concentrated to an area less concentrated

Concentration Gradient Difference in concentration of a substance

across a space

Types of Cellular Transport

Passive Transport cell doesn’t use energy

1. Diffusion2. Facilitated Diffusion3. Osmosis

Active Transportcell does use energy

1. Protein Pumps2. Endocytosis3. Exocytosis

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This is gonna

be hard work!!

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Weeee!!!

• Animations of Active Transport

& Passive Transport

Passive Transport Diffusion

- Movement of molecules from an area of higher concentration to an area of lower concentration

- Driven entirely by the kinetic motion of molecules

- Continues until the concentration of molecules is the same throughout the space they occupy

Factors Affecting Diffusion Rate

Equilibrium Exists when the concentration of the molecules

of a substance is the same throughout a space Random motion of molecules continues so

equilibrium is maintained (no concentrated gradient)

Diffusion Across Membranesright guard commercial

Cell membranes are selectively permeable Phospholipid bilayer (non-polar)

Diffusion depends on size, type of molecule, & chemical nature of molecule

3. Structure of cell membrane

Lipid Bilayer -2 layers of phospholipidsa. Phosphate head is polar (water loving)

b. Fatty acid tails non-polar (water fearing)

c. Proteins embedded in membrane

About Cell Membranes (continued)

Phospholipid

Lipid Bilayer

Diffusion Across Membranes Non-polar molecules

(O2 & CO2) can dissolve in lipid bilayer and thus pass through by diffusion

Very small insoluble molecules may pass through membrane pores by diffusion

Large or Polar substances move through membrane with help from transport proteins as do ions

Osmosis Osmosis Diffusion of water molecules

through a cell membrane from an area of higher water molecule concentration to an area of lower concentration

Quick Fact! Process of osmosis was first

described in 1748 by French scientist Abbé Jean Antoine Nollet. He observed that water spontaneously diffused through a pig bladder membrane into alcohol!

Direction of Osmosis Depends upon the relative

concentration of solutes on the two sides of the membrane

Osmotic Potential The tendency of water to move

across a membrane into a solution

The lower the solute concentration, the higher the osmotic potential

Isotonic Solution A solution in which the concentration of

dissolved substances is the same as the concentration inside the cell; therefore, the concentration of water is the same on both sides of the plasma membrane

Diffusion of water in = water out

Turgor Pressure Pressure that exists inside a cell

Hypotonic Solution A solution in which the concentration

of a dissolved substance is lower than the concentration inside the cell; therefore, the concentration of water is greater outside the cell than inside the cell

Water diffuses into the cell & the cell swells-Turgor Pressure increases

Cytolysis – cell bursts Plant v. Animal

Osmosis (Cell in Hypotonic Solution

Hypertonic Solution A solution in which the concentration of

dissolved substances is higher than the concentration inside the cell; the concentration of water is greater in the cell than outside Result: water moves out of the cell & the

turgor pressure decreases & the cell shrivels

Plasmolysis – loss of water pressure in a cell

Osmosis (Cell in Hypertonic Environment)

Click for animation

How Cells Deal with Osmosis Example: Paramecia (freshwater protozoan)

Live in a hypotonic environment Water constantly diffuse into them Contractile vacuoles (organelle) removes the excess

water A common remedy for a sore throat is to gargle

with salt water. Using the concept of osmosis, explain how this remedy might work.

Quick Fact! Wooden drawers in cabinets absorb water from the

air on humid days causing the wood to swell & hard to open!

Osmotic Pressure Pressure required to stop osmosis in a

solution- Pressure that builds up as water diffuses into

a cell- If a physical barrier prevents expansion of

a hypertonic solution as water moves in by osmosis, a buildup of pressure is created as water continues to flow in- As pressure ↑, the net flow of water molecules will

slow (stops in plants due to cell wall – turgor pressure)

Reverse Osmosis The movement of

water particles from an area of lower concentration to an area of higher concentration with the

Addition of pressure

Facilitated Diffusion Used for molecules that cannot

diffuse rapidly across the membrane (size, polarity)

Molecules are assisted by membrane proteins

2 Types Carriers & Channels Move down the concentration

gradient (High [ ] to low [ ]) no energy is used by cell

Facilitated Diffusion Molecule binds to carrier protein Protein changes shape shielding molecule

from lipids as it crosses Molecule is released to cell interior Carrier protein returns to original shape

Accelerates glucose movement Carrier proteins are specific to the

molecules they carry

Facilitated Diffusion

Carriers Channels

Diffusion through Ion Channels Membrane proteins Passageway through membrane for ions to

pass through (Na+, Ca2+, Cl-) Each ion channel is specific to one type of ion Some channels are always open, others have

gates Gates open in response to stimuli

1. Stretching of cell membrane2. Electrical signals3. Chemical signals

Ion Channels

Active Transport Differentiate between active & passive

transport

Compare & contrast endocytosis & exocytosis

Active Transport Movement of materials up a

concentration gradient, from an area of low concentration to an area of higher concentration

Requires cell to use energy Uses carrier proteins [ ] = Concentration

Active Transport Endocytosis &

Exocytosis Transport of

macromolecules & food particles too large to pass to pass through cell membrane

Endocytosis Process by which cells ingest large

materials by surrounding them with the cell membrane forming a pouch

Pouch pinches off from membrane & forms a vesicle

Endocytosis Types:

Pinocytosis Transports solutes or fluids

(cell drinking)

Endocytosis Phagocytosis

Ingestion large particles or whole cells (cell eating) Many unicellular organisms feed this way Used to ingest bacteria & viruses Cells called phagocytes – allows lysosomes to fuse with vesicles

containing bacteria & viruses to destroy them

Exocytosis Reverse of endocytosis Cell excretion Vesicles in cytoplasm fuse with cell membrane to

release contents to external environment Releases proteins packaged in Golgi apparatus

ENDOCYTOSIS/EXOCYTOSIS

Kidspiration by: Riedell