Lab 7: Diffusion and Osmosis PDF

Preview

Summary

These are for the lab class, not lecture, and covers diffusion and osmosis as well as tonicity in animal and plant cells....

Description

Lab 7: Diffusion and Osmosis

Solute: Substance dissolving Solvent: Liquid the solute dissolves in Solution: Solute dissolved in solvent

Diffusion  







Net movement of molecules or atoms from a region of high concentration to a region of low concentration The ability of the cell membrane to allow some substances to pass through more easily than others is called selective permeability. This only allows simpler substances to pass through rather than larger ones. Rate of diffusion can change with variables such as: o Temperature  Increase of temperature: Increased rate of diffusion o Size  Smaller molecules diffuse faster o Concentration  Greater difference in concentration: increased rate of diffusion When the cell increases in size, the volume increases faster than the surface area, because volume is cubed where surface area is squared. When there is more volume and less surface area, diffusion takes longer and is less effective. By reducing cell size, cells are greatly increasing the surface area to volume ratio which makes diffusion/osmosis much more effective. Cellular concentrations of ions, nutrients, salts, can occur much more quickly and efficiently. The ability to use the gradient, and then re-establish the gradient for the next ‘job’ is important.

Phenolphthalein   

Acid/base indicator White = Base or neutral Pink = Alkaline

Osmosis  

Simple diffusion of water If the barrier separating two solutions is permeable, diffusion and osmosis will occur until a state of equilibrium is reached.

 

Equilibrium: The concentrations of solvent and solute are equal on both sides of the membrane. Water will move to the concentration with the highest concentration o Think – Water is greedy!

Tonicity  

Describes the ability of a solution to cause a cell to gain or lose water. There are 3 different types of tonicity: o Hypertonic  “Hyper-” prefix meaning “excessive”  Higher solute concentration o Hypotonic  “Hypo-” prefix meaning “under”  Lower solute concentration o Isotonic  “Iso-“prefix meaning “equal”  Equal solute concentration

Animal Cells vs. Plant Cells in different tonicities 





Hypertonic solution o Animal Cell: Crenation (deflated) o Plant Cell: Plasmolysis (deflated) Isotonic Solution o Animal Cell: Normal o Plant Cell: Flaccid Hypotonic solution: o Animal Cell: Lysis (bursting) o Plant Cell: Turgid (swollen - normal)...