PACT Due Dates

Osmosis in Carrots (Rashida Madraswala)

Title: Osmosis in Carrots(Rashida Madraswala)

Principle(s) Investigated: Cells maintain homeostasis by controlling the movement of substances across their membrane. Osmosis is the movement of water down its concentration gradient. Solutions when compared to each other can be defined as hypertonic, hypotonic or isotonic.

Standards:  Biology

1a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings. 


Materials: Sodium Chloride(grocery store)

                  Baby Carrots(grocery store)

                  Distilled Water(grocery store)

                  Plastic Cups(grocery store)

                  Digital Balance (Ward's Scientific)

                  Graduated Cylinder or Beaker for measuring volume (Ward's Scientific)

                  

Procedure: Introduction: Living cells must move materials in and out. One of the ways materials can get into or out of cells is through diffusion. Diffusion is the movement of a substance from an area of high concentration to an area of low concentration. Osmosis is a special case of diffusion: the diffusion of water across a membrane. 

Think of when someone has a sore throat. A common home remedy is to gargle with salt water. Use the concept of osmosis to explain why this remedy works.

(Answer should mention that a sore throat is the result of swollen throat tissues. Salt water has a lower concentration of water than the tissues and the water moves out of the tissues by osmosis. This should decrease the swelling and the pain associated with it.)

In the following lab, you will observe and measure osmosis in a carrot. Predict what will happen to the carrots after they have sat in each of the 4 different solutions.

Directions:

1. Weigh 4 carrots and record the weight of each carrot in the data table below. Place each one in one of the four solutions, noting which carrot is in which solution.

 Salt Concentration          Initial Mass
(Weight of carrot before)
 Final Mass (Weight of carrot after)  change in mass

 % change in mass
 0 M
Distilled Water
       
 0.4 M        
 0.8 M        
 1.0 M        

2. Wait 25 minutes. Remove the carrots and blot them dry. Remember which one came from which solution. Record the weight of each after in the table above.

3. Calculate the % change in mass. 

change in mass = (final mass - initial mass)/initial mass

% change in mass = change in mass x 100

4. Graph the data. Determine what variable goes on the X-axis and what variable goes on the Y-axis.

Student prior knowledge: Students need to know about the permeability of membranes to water. Students need to know the difference in concentrations(molarity) of various solutions and the concept of concentration gradients.

Explanation: Students will be able to visualize what happens when cells are put into hypertonic and hypotonic solutions. They should see that carrots will swell when they are placed in solutions that are hypotonic and will shrink when they are placed in solutions that are hypertonic. If they encounter an isotonic solution, they should see no % change in mass. 


Questions & Answers: 1. Why did you graph the percent change in mass and not simply the change in mass?

Answer: Since we are using different carrots for each solution, they will have different initial mass. Therefore, when comparing across solutions we need to examine the percent change to equalize for the variability of initial mass.

2. List and explain three sources of error in this lab. 

Answer:  1. Improperly made solutions. If the solutions are not as described then the graph may not show a clear relationship. 2. Mixing up the carrots. If the carrots were switched, the data would not be accurate. 3. Forgetting to dry the carrots before weighing would add excess weight not attributed to osmosis. 

3. Which solution was hypertonic to the carrot cells? Which solution was hypotonic?

Answer: This will depend on the experimental results. Mathematically, any percent change in mass greater than 100% will be hypotonic and any percent change in mass less than 100% will be hypertonic.


Applications to Everyday Life: 1.Gargling with salt water to relieve sore throat. Explanation given in procedure above.

2. Preservation of Foods. Salt solutions are used to preserve vegetables. The high salt concentrations are hypertonic to bacterial cells and kill them before they can spoil the food.
 
3.

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made. 

Google Docs for entering data and graphing.

References: Lab activity adapted from Mrs. Turner-Graham, El Camino Real HS

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Norman Herr,
Oct 10, 2011, 8:25 PM
ĉ
Norman Herr,
Oct 10, 2011, 8:25 PM
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