Embed Size (px)
Citation preview
Chapter 5Homeostasis and Transport
Homeostasis & TransportBIG IDEAS:Cell Membranes help organisms maintain homeostasis by controlling what substances enter and leave the cell.
Some substances can cross the cell membrane without any energy input from the cell.
Some substances require a cell to expend energy to enter or leave the cell.
For cells to remain alive, a certain combination of chemicals must be able to be present inside its cell membrane.
The cell membrane is one of the structures that helps maintain this special environment inside and outside the cell.
How Materials Enter and Leave CellsHow does the cell move materials into and out of a cell?
One way molecules of a substance get into and out of a cell is by a process known as passive transport
Passive transport is the diffusion or movement of molecules across a cell membrane. It does NOT REQUIRE any ENERGY input from the cell.
The Cell MembraneThe cell membrane is Selectively Permeable.
Meaning, it allows the passage of some substances and blocks other or not required substances.
The Cell MembraneThis selectively permeable membrane only allows certain things in/out of the cell.• Made of protein and
lipids• BILAYER-two layers; the
head of the molecules face outward while the tails face inwards.
PHOSPHOLIPID-molecule that makes up the cell membrane. Has two parts.1. The phosphate head (hydrophilic – water loving)2. Two lipid tails (hydrophobic – water hating)
Molecules diffuse or move from an area of higher concentration to an area of lower concentration. THEY MOVE DOWN A CONCENTRATION GRADIENT!
Passive transportSubstances crossing the cell membrane without any input of energy by the cell – move down their concentration gradientTypes:•Simple Diffusion•Osmosis•Facilitated Diffusion•Ion Channels
http://www.youtube.com/watch?v=JShwXBWGMyY
DOWN A CONCENTRATION GRADIENT.
?? Concentration Gradient= a gradient results from an unequal distribution of dissolved molecules across the cell membrane. When this happens, solutes downconcentration gradient.
This kind of movement is called diffusion.
Diffusion Stops when…Molecules reach EQUILIBRIUMThe concentration of the molecules is the same throughout a space.No more diffusion! But molecules keep moving.EXAMPLE: food coloring, cookie smell in your house, etc.
DiffusionThe simplest type of passive transport is diffusion. Diffusion is the natural movement of molecules from an area of high concentration to an area of low concentration.
Molecules naturally intermingle as a result of their kinetic energy of random motion.
Diffusion
Diffusion
Diffusion Across a Cell Membrane
REMENBER - The cell membrane is Selectively Permeable. There are tiny pores or holes in it that allow some molecules to diffuse into the cell.
For example, oxygen molecules diffuse into your blood stream through the membranes of cells in your lungs.
http://videos.howstuffworks.com/hsw/23424-cell-diffusion-across-the-cell-membrane-video.htm
OsmosisA cell is made up mostly of water and dissolved substances. Water can move into or out of a cell through the cell membrane. The diffusion of water through a cell membrane is called osmosis.
Osmosis takes place through passive
transport.
Osmosis maintains the balance of water inside and outside the cell.
Question??If there is more salt outside of the cell, will water move into the cell or out of the cell??
OsmosisThe direction that water moves depends on the amount of dissolved substances inside and outside of a cell. If there are more dissolved substances inside the cell, water will move into the cell and vise-versa.Water will move to where there is LESS WATER.
Water goes where it aint !!
http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf
Example of Osmosis
3 Types of Environments
The net movement of water, or osmosis, depends on the type of environment the cell is in.Three types of environments:1.Isotonic2.Hypertonic 3.Hypotonic
1. Isotonic:
Concentration of water is equal inside and outside of the cell.• Water will diffuse into and out
of the cell at an equal rate• No net movement of water. • Cell stays the same.
2. HypertonicMore water inside the cell, less outside.More solutes outside the cell than INSIDE the cell.• Water moves out of the cell until
equilibrium is reached.• Net movement of water is out of
the cell. • Can cause the cell to shrink or
shrivel.• Crenation in animal cells• Plasmolysis in plant cells
3. Hypotonic
More water outside the cell, less inside the cell.
More solutes inside, less solutes OUTSIDE the cell.
• Net movement of water into the cell.• Can cause cell to burst.• CYTOLYSIS-cells take in so much water that they burst.
Osmosis in Plants Remember
Plant cells store waterin vacuoles.
http://www.kscience.co.uk/animations/turgor.htm
FYI - Plants whose cells do not have enough water appear dry and may droop.
However, once the plant receiveswater, its cells may absorb the water through osmosis.
Once water is absorbed into itscells, the plant swells.
It will probably stand upstraight and appear healthy. This is referred to as “Turgor” and is determined by osmosis.
DRAWOsmosis in Plant
CellsPlant CellCell Wall Vacuole Cytoplasm
Cell Membrane
The Cell absorbs water …But the cell wall stops by osmosis… the cell from expanding
Plant cell membranes can be seen pulling away from their cell wall, in a process called plasmolysis, as their cells lose water.
DRAW Cells in 3 Types of
Solution!
cytolysiscrenation
plasmolysis
Remember:
SALT SUCKS!!!Wherever there is more solute (i.e. salt, sugar), that is where water will be pulled to
WATER WILL MOVE TO WHERE IT AINT!!
Do NowRespond to the following in your journal:
Why do supermarkets have sprinkler systems set up in their produce section? Explain.
Like diffusion, molecules are still moving from an area of higher concentration to an area of lower concentration.
Facilitated Diffusion
Facilitated Diffusion:Facilitated diffusion is the form of passive transport in which carrier proteins embedded in the cell membrane help or facilitate the movement across it.
It does not require the cell to use any energy.
Like diffusion, molecules are still moving from an area of higher concentration to an area of lower concentration.
Ion ChannelsSome ions are important for cell functions (Na+, K+, Ca2+ and Cl-)Since they are charged and hydrophilic, they can’t get across the lipid bilayer.
Ion channels – specific membrane proteins that help ions get across c ell membrane – some are always open, some are gated and require a stimuli to open.
• EXAMPLE: impulse from nerve travels to muscle cell-causes some gated channels to open.
• It does not require the cell to use any energy.
Active Transport
Active Transport: Movement through the cell membrane thatis the opposite of diffusion. Molecules of certain substances move through the cell membrane from an area that is less crowded to an area that is more crowded is called ACTIVE TRANSPORT.
•Energy is needed to move these materials across the cell membrane - Molecules move AGAINST the concentration gradient!!
http://www.youtube.com/watch?v=STzOiRqzzL4&feature=related
Most plants get water and minerals they need from their roots.Minerals enter the root by active transport.
Active transport is also needed to move certain waste materials out of a cell.
Types of Active Transport
• Cell Membrane Pumps
• Endocytosis
• Exocytosis
Cell Membrane Pumps
Carrier proteins also help out in active transport and work against the concentration gradient:Low HighSimilar to facilitated diffusion, but a cell’s energy is required.
SODIUM (Na+)/Potassium (K+)
Pump
Uses a special carrier molecule.• K+ (potassium) goes
into the cell.• Na+ (sodium) leaves
the cellUses energy from the cell
Passive vs. Active Transport
High ConcentrationLow Concentration
Passive Transport
Active Transport
High Concentration
Low Concentration
Endocytosis & Exocytosis Cells have two processes of moving large particles across the cell membrane:Endocytosis and Exocytosis
Endocytosis is the process by which the cell Membrane wraps around the large particle, forms a vesicle, and pulls it inside the cell. Once inside, the vesicle releases the particle.
2 Ways:1. Pinocytosis-movement of solute or fluid into the
cell.2. Phagocytosis-movement of large food particles or
entire microorganisms into the cell.
Endocytosis & Exocytosis Exocytosis is exact opposite.
When the cell wants to get rid of a large particle, it encloses the particle inside a vesicle. The vesicle fuses with the cell membrane and the cell can then release the particle.
http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/interactivemedia/activities/load.html?7&G
Endocytosis & Exocytosis
