osmosis and diffusion

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Cell Processes

Chapter 5Cell Membrane

HomeostasisMaintenance of stable internal conditions (inside different from outside)

Cell membrane controls movements of substances

Structure of the MembraneMainly a lipid bilayer

Hydrophilic phospholipid heads point out and in

Hydrophobic phospholipid tails point towards interior

Structure of the MembraneMembrane contains steroid cholesterol

Fluidity increases with increasing temperatures

Cholesterol also helps prevent freezing

Structure of the MembraneOnly small, non-charged molecules can pass through the membrane

Examples:OxygenCarbon Dioxide

Structure of the MembraneProteins embedded in membranes have many functions

Cell-surface markers act as ID tags

Structure of the MembraneReceptor proteins receive signals from out of the cell

Enzymes cause chemical reactions to occur

Structure of the MembraneTransport proteins move substances across membrane

Other Important TermsPeripheral Proteins lie on only one side of the membrane

Integral Proteins pass completely through

SOLUTES AND SOLVENTSChapter 5

Important TermsSolute: type of molecule dissolved in another type of substance; that substance is called a

Solvent: substance that dissolves the solute

ExamplesPut one tablespoon of sugar into a glass of water and stir.

Solute = sugar

Solvent = water

ExamplesFish use gills to extract oxygen dissolved in seawater

Solute = oxygen

Solvent = water

CONCENTRATIONConcentration refers to how much of some substance is present, compared to another substance.

CONCENTRATION EXAMPLESHigh 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

DiffusionDiffusion 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

DiffusionMolecules 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!

DiffusionMolecules diffuse through a solvent

Example: aromas

Types of DiffusionSimple Diffusion

Directly through membraneFacilitated Diffusion

Done by specific carrier proteins in membrane

OSMOSIS

OsmosisOsmosis 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 WaterHypotonic solution Lower than cells solute concentration

Hypertonic solution Higher than

Isotonic The same as

Results of OsmosisPlant cells in hypotonic environment experience turgor pressure due to cell wall

In a hypertonic environment, plasmolysis (wilting) occurs

Important TermsEquilibrium

Concentration Gradient

Diffusion

OsmosisConcentration 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

Cellular TransportPassive TransportMovement across a membrane without using energy (ex.: simple diffusion, facilitated diffusion, and osmosis)

Active TransportMovement across a membrane using energy

Cellular TransportPassive transport allows flow of molecules down concentration gradientActive transport uses energy to force molecules against concentration gradient

Active Transport

Passive Transport

Other Important TermsHomeostasisStable internal conditions of a living thing

This is another characteristic of all living things

Living things actively keep their insides different than their outsides

Sodium/PotassiumIon Pump

Sodium/Potassium Ion PumpSodium = Na+Potassium = K+

Ions are electrically charged atoms

Sodium/Potassium Ion PumpPump is a protein in the membrane of cells.

Example of ACTIVE TRANSPORT (pumps AGAINST the concentration gradient)

Sodium/Potassium Ion PumpPumps 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+ PumpElectrical signal sent through neuron when gated ion channels open and Na+ and K+ are able to rapidly diffuse across membrane (which is passive transport)

Chapter 5 / 8Test Review

Terms to Know:SoluteSolventConcentrationHomeostasisHydrophilicHydrophobicConcentration gradient

DiffusionOsmosisEquilibriumActive TransportPassive TransportNet flowATPNa+/K+ Pump

Concepts to StudyWhat 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

Example QuestionsA cell is placed in pure water. What would you expect to happen to the mass of the cell?

A cell is placed in water with the same solute concentration as inside the cell. What is this called? Which way will solutes flow?