Transcript Cell Transport - Madison Public Schools

Cell Transport
Facilitated Diffusion
Cells in their Environment
Active Transport
Passive Transport
1.
Diffusion- movement of molecules from an area
of high concentration to an area of low
2.
Osmosis- process by which water molecules
diffuse across a cell membrane from an area of
high concentration to an area of low
3.
Facilitated Diffusion- used for molecules that
cannot readily diffuse through cell membranes,
even when there is a concentration gradient…
Facilitated Diffusion

Facilitated Diffusion- carrier proteins in the
cell membrane assist molecules that cannot readily
diffuse across the cell membrane
 Molecules cannot diffuse because:


May be not soluble in lipids
May be too large to pass through
Carrier proteins move molecules from a
higher to lower concentration, so no energy
is required… so it is PASSIVE TRANSPORT!
 http://www.northland.cc.mn.us/biology/Biolo
gy1111/animations/active1.swf

Example of Facilitated Diffusion
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Example= Glucose
Cells depend on glucose for energy


glucose molecules are too large to diffuse by simple
diffusion
When glucose levels in cell are lower than outside
the cell, carrier proteins transport glucose in
Cells in Hypotonic/ Hypertonic Environments
Cells exposed to an isotonic environment
usually have no trouble keeping the
movement of water across the membrane in
balance.
 It is more difficult for cells in a
hypotonic/hypertonic environment

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Contractile Vacuoles
Turgor Pressure
Plasmolysis
Cytolysis
Contractile Vacuoles
Unicellular freshwater organisms that live in
a hypotonic environment use contractile
vacuoles to rid excess water
 Contractile Vacuoles- organelles that
collect excess water and then contract to
pump the water out of the cell


Pumping action requires cell to expend energy, it
is not a form of passive transport
Cytolysis

Red Blood Cells-
Lose their normal shape when exposed
to an environment that is not isotonic


Hypertonic environment = water leaves/ cells
shrink and shrivel
Hypotonic environment = water diffuses into cell/
cells swell and burst  Cytolysis
Cytolysis – bursting of cells
Turgor Pressure


Most plant cells live in hypotonic environment- water moves into
plant cells by osmosis
Cells fill as they swell with water until cell membrane is pressed
against cell wall
Cell wall resists pressure exerted by water
 Turgor Pressure- the pressure that water
molecules exert against cell wall

Plasmolysis

Plasmolysis- cells are in a hypertonic
environment and water leaves through
osmosis. Cells shrink away from the cell
walls (turgor pressure is lost)

This is the reason plants wilt if they don’t
receive enough water
Active Transport

Active Transport- movement of
materials from an area of lower
concentration to an area of higher
concentration. Requires a cell to expend
energy.
1.
Endocytosis
1.
2.
2.
3.
Pinocytosis
Phagocytosis
Exocytosis
Sodium-Potassium Pumps
Endocytosis

Endocytosis- process by which cells ingest
external fluid, macromolecules, and large
particles


1.
Pinocytosis- transport of solutes/ fluids
1.
2.
External materials are enclosed by a portion of the cells
membrane- folds into itself/ forms a pouch
Pouch pinches off and becomes a vesicle
http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/pinocyt.html
Phagocytosis- movement of large particles
1.
http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/phagocyt.html
Exocytosis

Exocytosis- process by which a substance is
released from the cell through a vesicle
(reverse of endocytosis)
 Vesicles release their contents to the cell’s external environment

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Ex: large molecules such as proteins, waste products, toxins
http://www.coolschool.ca/lor/BI12/unit4/U04L05/exocytosis.html
Sodium-Potassium Pumps

Sodium-Potassium pump – moves
substance (ions) from lower to higher
concentration/ require energy
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Energy needed for active transport is supplied
directly or indirectly by ATP
http://highered.mcgraw-hill.com/olc/dl/120068/bio03.swf