OSMOSIS and DIFFUSION

Molecules are always moving Molecules move randomly and bump into each other and other barriers

Concentration gradient Concentration Gradient - change in the concentration of a substance from one area to another.

Diffusion Molecules in solution tend to slowly spread apart over time. This is diffusion.

Diffusion MOVEMENT OF LIQUID OR GAS MOLECULES from high concentration to a low concentration until the substance is evenly spread out. IMPORTANCE: lets food and oxygen into a cell waste products such as carbon dioxide out of the cell

Diffusion [High] [Low] concentrated, high energy molecules diffuse, low energy molecules

Diffusion continues until equilibrium is reached. Equal distribution of molecules throughout the space. This is why food coloring moves throughout a beaker of water why odors smell strong at first and then disappear over time. Equilibrium, a result of diffusion, shows the uniform distribution of molecules of different substances over time as indicated in the above diagram.

Definition of Osmosis Osmosis is the movement of water molecules, from a region of high water concentration to a region of low water concentration ACROSS A SELECTIVELY PERMEABLE MEMBRANE. LEARN THIS !!!!

Selectively Permeable? A selectively permeable membrane is a membrane with holes in it small enough for WATER to go through it easily. Big molecules like starch, proteins and carbs can not fit through easily Remember!! A membrane controls what goes in and out of the cell. Permeable means it allows substances to go through it. See next slide…

Model of a Selectively Permeable Membrane Water Starch Small molecules, such as water can pass through it. Large molecules like starch can not pass through the membrane Diagram shows the net flow of water

Osmosis

Over time molecules will move across the membrane until the concentration of solutes is equal on both sides. This type of solution is called ISOTONIC.

Cells in an isotonic solution = concentrations Conc. Inside = conc. Outside Happens @ same rate Cell retains normal size/shape pressure H2O H2O Water Molecule Dissolved Molecule

Cells in an isotonic solution

PASSIVE TRANSPORT occurs without expenditure of energy NO ENERGY IS USED BY THE CELL move using their own kinetic energy Particles go DOWN OR WITH their concentration gradient. Diffusion and osmosis are PT allows cells to get water, oxygen and other small molecules that they need allows the cell to get rid of waste such as carbon dioxide.

Passive Transport by proteins Passive transport of materials across the membrane using transport proteins is called facilitated diffusion. Channel proteins Plasma membrane Concentration gradient

Passive Transport by proteins Some transport proteins, called channel proteins, form channels that allow specific molecules to flow through.

Active Transport against a concentration gradient requires energy from the cell. Cellular energy Carrier proteins Plasma membrane Concentration gradient Cellular energy

Active vs. Passive Transport Passive Transport – does not require energy. Particles move from high to low concentration. Active Transport – does require energy because molecules are moving from low to high concentration

Transport of Large Particles Endocytosis Exocytosis Endocytosis Exocytosis

Endocytosis too large to pass through the cell membrane. The cell membrane can surround a large particle located outside the cell. 1. The membrane forms a sac around the particle. 2. Then the sac opens inside the cell.

Exocytosis Large particle leave the cell in sacs too. Inside the cell, a sac forms around large waste particles. 1. The sac moves to the membrane and then opens outside the cell. 2. Waste particle move OUTSIDE the cell.

Cells in a hypotonic solution hypotonic solution: dilute solution thus low solute concentration In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell. H2O H2O Water Molecule Dissolved Molecule

Cells in a hypotonic solution Plant cells swell beyond their normal size as pressure increases. (plants prefer this –it makes the leaves firm)

Cells in a hypertonic solution concentrated solution, thus a high solute concentration In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink H2O H2O Water Molecule Dissolved Molecule

Cells in a hypertonic solution Plant cells lose pressure as the plasma membrane shrinks away from the cell wall. PLASMOLYSIS

Cytoplasm is a solution of water and solids (solutes dissolved in the water). Water moves into and out of cells because of the different concentrations of the solutes. Different kinds of cells react differently depending on the solution they are in. Below are examples of red blood cells in different types of solutions and shows what happened to the red blood cells.

Animal Cells in different solutions A red blood cell in pure water, water will move into the cell and the cell will BURST (there is no cell wall to prevent this happening) In a strong salt/sugar solution water will move out and the cell will SHRINK (the cell in described as CRENATED)

PLANT CELLS Hypotonic Solution Hypertonic Solution Turgor Pressure builds in the cell and causes osmosis to stop because of the rigid cell wall. Plants will wilt when cells lose water through osmosis.

Plant Cell in different solutions In pure water – water will move in swelling the vacuole which pushes out against the cell wall. The plant cell is described as TURGID. The cell does not burst because of the cell wall. Plant cell placed in pure water Water moves Into the cell

Plant Cell in Strong Sugar Solution In a strong salt or sugar solution – water will move out of the vacuole causing it to shrink. The cytoplasm can also shrink away from the cell wall. The plant cell is described as Plasmolysed or Flaccid. Strong Sugar/Salt Solution

As viewed under the microscope ELODEA CELLS As viewed under the microscope

THE END