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
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