Osmosis

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Advanced Placement Biology
®

AP Biology

Lab 1

281
EDVO-Kit # Storage:

Principles & Practice of Diffusion & Osmosis
Store entire experiment at room temperature.

EXPERIMENT OBJECTIVE
The objective of this experiment is to develop an understanding of the molecular basis of diffusion and osmosis and its physiological importance. Students will analyze how solute size and concentration affect diffusion across semi-permeable membranes and how these processes affect water potential. Students will also calculate water potential of plant cells.

EDVOTEK, Inc. • 1-800-EDVOTEK • www.edvotek.com

EVT 080423AM

2
AP
Biology

EDVO-Kit # 281

Principles & Practice of Diffusion and Osmosis

Table of Contents
Lab #

1
Experiment Components Experiment Requirements Background Information Experiment Procedures Experiment Overview PART A. Diffusion and Dialysis PART B. Osmosis PART C. Water Potential PART D. Onion Cell Plasmolysis Study Questions Instructor's Guidelines Notes to the Instructor Pre-Lab Preparations Experiment Results and Analysis Study Questions and Answers Material Safety Data Sheets

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10 11 12 16 20 21

23 24 26 29 31

Advanced Placement (AP) Program is a registered trademark of the College Entrance Examination Board. These laboratory materials have been prepared by EDVOTEK, Inc. which bears sole responsibility for their contents.

EVT 080423AM

1-800-EDVOTEK • www.edvotek.com

EDVO-Kit # 281

Principles & Practice of Diffusion and Osmosis

3

AP

Experiment Components

Biology

Lab #

This experiment is designed for 10 lab groups

Contents A B C D E Orange Indicator Dye, low molecular weight Blue/green dye, high molecular weight 1M Sucrose and 1M NaCl Powdered sucrose NaCl Dialysis tubing

Store entire experiment at room temperature.

1

Requirements
All components are intended for educational research only. They are not to be used for diagnostic or drug purposes, nor administered to or consumed by humans or animals. EDVOTEK, The Biotechnology Education Company, and InstaStain are registered trademarks of EDVOTEK, Inc. • Beakers* (300 to 400ml) 20 for Part A 50 for Part B 16 for Part C 1ml, 5ml, and 10ml pipets Graph paper Scales Distilled or deionized water Thermometers (10) Potatoes (4) Cork borers, or small kitchen knives Onion Microscope Slides Coverslips *Beakers can be substituted with clear disposable plastic cups.

• • • • • • • • • • •

EDVOTEK - The Biotechnology Education Company ® 1-800-EDVOTEK • www.edvotek.com FAX: (301) 340-0582 • email: edvotek@aol.com

EVT 080423AM

4

EDVO-Kit # 281

Principles & Practice of Diffusion and Osmosis

AP
Biology

Principles & Practice of Diffusion and Osmosis

Lab #

1
-

DIFFUSION
Diffusion is the net flow of molecules from a region of high concentration to a region of low concentration. This difference in concentration of a substance across space is called a concentration gradient. Diffusion is due to the random movement of particles. This phenomenon was first observed by Robert Brown in 1827 and is called Brownian movement. All objects in motion have kinetic energy, or energy of motion. Particles of matter move in straight lines until they collide with other particles. After colliding, the particles rebound, move off in straight lines until the next collision. There is no loss of energy. Diffusion will continue until there is no concentration gradient (Figure 1). In diffusion, molecules move randomly colliding with one another until they become evenly distributed. For example, if one puts a teaspoon of a purple dye, potassium permanganate, into a beaker of water, then the dye molecules, or solute (dissolved molecules), will collide randomly with the water molecules, or solvent. These random collisions within the solution will scatter the molecules of solute and solvent until they are evenly mixed. However, the molecules still continue to collide with each other and...
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