Biol 1440, Principles of Biology I

Cellular Processes
Diffusion  across cell membranes

Principle

 Diffusion is the process used for the passive transport of nutrients, water, and wastes into and out of cells.

Diffusion is the net movement of matter along a concentration or energy gradient.

Objectives

 The overall objectives are:

1. Investigate the factors that effect the rates on diffusion  on solutes (dialysis).

2. Investigate the role of membrane structure can play in permeability.

3. Learn to use a data acquisition system and couple it to data analysis.

4.  Learn how to store and retrieve data.

Research Questions
  • What factors affect the rate of diffusion?

What would occur with regards to how a solute (ion) and water would move across the cell membrane by diffusion, if:

  • the solute concentration is greater in the cytoplasm than in the environment surrounding the cell?
    How would the conductivity of the environment change?
  • the water concentration is less in the cytoplasm than in the environment surrounding the cell?
    How would the weight and size of the cell change?

Do the solutes and water diffuse in the same direction?

Readings

 

 

Know the Essentials                        LAB INTRO

Diffusion Tutorial: simple compared to facilitated diffusion

Practice Quiz

Internet
Experimental Set-up using a Conductivity Probe

Students need
  • DATA COLLECTION TABLES for Directed Investigations
  • graph paper
  • metric ruler
  • calculator
Computer Use  NEVER USE THE LAB COMPUTER FOR ANY PURPOSE OTHER THAN THOSE ASSOCIATED WITH THE LAB INVESTIGATION UNLESS BY PERMISSION!!

Students found misusing the computers will be subject to being DROPPED from the course IMMEDIATELY !

Directed Investigation 1.
Finding the maximum rate of diffusion

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Directed Investigation 2
Does concentration have an effect on the rate of diffusion?

 

 

 

 

 

 

 

 

 

 

 

 Objectives
 1. Investigate the responses of an artificial cell to changes in its salt status by creating different concentration gradients across a artificial cell membrane.

2. Learn to use  Loggerpro 3® a data acquisition system.

3. Use a conductivity probe to measure salts in solution with the data acquisition .

This investigation is designed to allow the student to make key observations about the processes of diffusion. From these observations, your lab group will design an experiment to test a hypothesis about what can happen to cells from changes in their cytosol or in their environment.

Cellular responses to solute (salt) changes

What will happen to conductivity of your simulated cell cytosol, if the concentration of a salt changes in the cell's environment?

Will equilibrium be reached or will the cell continue to take up salt?

Procedure

1.  Measure the conductivity of the environmental solution (NaCl) & the simulated cytosol (distilled water).

2. Fill the each side of the chamber with the appropriate solution using the syringe.

3. Monitor the change in conductivity for 5 min (300sec) using LoggerPro.

4.  Analyze the rate of diffusion overtime in five 20sec blocks to the end of the collection period and find the maximum rate of diffusion.  Enter your data into a Data Collection Table.  

For example, find the rate between 0 and 60 sec (when the graph starts to increase, then a 20 sec interval between 60-120 sec, and so on.  The fifth 20 sec interval will be between 240-300 sec.

Treatment

Salt Conc., M

 Rate of Diffusion (conductivity),
µS/cm/sec
Max Rate of Diffusion,
µS/cm/sec 
1st 20
sec		 2nd 20
sec		 3rd 20
sec		 4th 20
sec		 5th 20
sec

 

            

Questions
1.  Is the rate of change constant?  Measure five 20sec increments and graph it as a function of time and rate of diffusion.
2.  Which timeframe gives you the maximum rate of diffusion?
3.  Was equilibrium reached?  How would you know if it was?

Experimental Design
What would you predict changing concentration will have on the rate of difffusion?

  • If you double the concentration, would the rate of diffusion double?  remain the same?  decrease by half?

Researchable Question
Does concentration have an effect on the rate of diffusion?

Construct a hypothesis and design an experiment to test your hypothesis

Your class will select four salt concentrations as treatments to test your hypothesis.  In your dilution table, C1 = 1.2M NaCl (1M= 58g/mole), V2=60mL

  • What would be a suitable control treatment?  

Independent variable= salt concentration, units = M
Dependent variable = conductivity of the solution, unit of conductivity = microSiemens/cm (µS/cm). 

Lab groups will measure the rate of diffusion for each concentration and enter their results in a class data collection table.

Treatments, NaCl conc., M

Diffusion Rate, µS/sec
R1 R2 R3 R4 R5 R6 Avg
               
               
               
               

Results
Lab groups will construct a Figure of the results.  You will store your data in your lab groups folder.

Your lab instructor will show you how to store your data.
Relevance to Biology Relevance of your investigation.
Diabetes mellitus results in a failure of the cells of the body to take up glucose even though the blood has high levels. The excess glucose is excreted in the urine, which is a diagnostic test for diabetes. High blood glucose leads to damage of kidneys and eyes among other organs. Could glucose in the blood be affecting diffusion and osmosis in certain organs like the kidneys or the eyes?

Cystic fibrosis and cholera both affect how salts and water move across cell membranes. Cystic fibrosis results in a mucous, composed of protein and other substances, lining the tissues of the lungs, salivary glands, pancreas, and small intestine.

Hypothermia and fever have adverse effects on the human body.  Thus, temperature could affect diffusion and osmosis, especially when you consider sweating from a fever.