Download - Osmosis and Diffusion
Homeostasis Maintenance of stable internal
conditions (“inside different from outside”)
Cell membrane controls movements of substances
Structure of the Membrane
Mainly a lipid bilayer
Hydrophilic phospholipid “heads” point out and in
Hydrophobic phospholipid “tails” point towards interior
Structure of the Membrane
Membrane contains steroid cholesterol
Fluidity increases with increasing temperatures
Cholesterol also helps prevent freezing
Structure of the Membrane
Only small, non-charged molecules can pass through the membrane
Examples: Oxygen Carbon Dioxide
Structure of the Membrane
Proteins embedded in membranes have many functions
1. Cell-surface markers act as “ID” tags
Structure of the Membrane
2. Receptor proteins receive signals from out of the cell
3. Enzymes cause chemical reactions to occur
Other Important Terms “Peripheral
Proteins” lie on only one side of the membrane
“Integral Proteins” pass completely through
Important Terms
Solute: type of molecule dissolved in another type of substance; that substance is called a…
Solvent: substance that dissolves the solute
CONCENTRATION
Concentration refers to how much of some substance is present, compared to another substance.
CONCENTRATION EXAMPLES
High solute concentration: lots of sugar dissolved in a relatively small amount of water
Low solute concentration: little sugar dissolved in a relatively high amount of water
REMEMBER!
Solutes can be many different kinds of molecules (sugars, gases, nutrients, proteins, and lipids)
Solvents can vary as well (solids, liquids, or gases), but are usually H2O
Diffusion
Diffusion is the process by which solute passes through pores in a cell membrane
Diffusion also occurs within one area (no membrane) as solute travels from one area of space to another
Diffusion
Molecules ALWAYS diffuse in both directions at once (into and out of a cell)
NET FLOW OF SOLUTES IS ALWAYS FROM AREAS OF HIGHER CONCENTRATION TO AREAS OF LOWER CONCENTATION!
Types of Diffusion
“Simple Diffusion”
Directly through membrane “Facilitated
Diffusion”
Done by specific carrier proteins in membrane
Osmosis Osmosis is the process by which
WATER passes through a cell membrane
Water molecules always flow in both directions at once (into and out of a cell)
NET FLOW OF WATER IS ALWAYS FROM AREAS OF LOWER SOLUTE CONCENTRATION TO AREAS OF HIGHER SOLUTE CONCENTRATION
Osmosis: Net Flow of Water Hypotonic solution – Lower than
cell’s solute concentration
Hypertonic solution – Higher than…
Isotonic – The same as…
Results of Osmosis Plant cells in hypotonic environment
experience “turgor pressure” due to cell wall
In a hypertonic environment, plasmolysis (wilting) occurs
Important Terms• Equilibrium
• Concentration Gradient
• Diffusion
• Osmosis
• Concentration of a substance is the same throughout
• Difference in concentration across a membrane
• Process by which molecules move from areas of high to low concentration
• Transport of water across a membrane
Cellular Transport Passive Transport
Movement across a membrane without using energy (ex.: simple diffusion, facilitated diffusion, and osmosis)
Active Transport Movement across a
membrane using energy
Cellular Transport
Passive transport allows flow of molecules down concentration gradient
Active transport uses energy to force molecules against concentration gradient
Other Important Terms
Homeostasis Stable internal
conditions of a living thing
This is another characteristic of all living things
Living things actively keep their “insides” different than their “outsides”
Cellular Transport
Maintain Homeostasis by…
Passive Transport
Diffusion Osmosis
Active TransportExample:
Sodium/Potassium Pump
Sodium/Potassium Ion Pump
Pump is a protein in the membrane of cells.
Example of ACTIVE TRANSPORT (pumps AGAINST the concentration gradient)
Sodium/Potassium Ion Pump
Pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell. (Uses ATP, a molecule with lots of stored energy)
750 ions transported per second
High concentrations of Na+ and K+ build on opposite sides of cell membrane
Importance of Na+/K+ Pump
Electrical signal sent through neuron when gated ion channels open and Na+ and K+ are able to rapidly diffuse across membrane (which is passive transport)
Terms to Know:
Solute Solvent Concentration Homeostasis Hydrophilic Hydrophobic Concentration
gradient
Diffusion Osmosis Equilibrium Active Transport Passive
Transport Net flow ATP Na+/K+ Pump
Concepts to Study
What is the structure of the cell membrane?
Which way do solutes travel during diffusion?
Which way does water travel during osmosis?
The egg lab and the dialysis bag lab