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Materials move into and out of cells through either passive transport or active transport. Passive transport includes diffusion and osmosis. Molecules tend to move from crowded to less crowded, in order to achieve a balance, or homeostasis. The cell membrane is selectively permeable, which allows the movement of substances, especially oxygen, water, food molecules, carbon dioxide, and waste products, into or out of the cell.

Diffusion – The movement of particles from a region of higher concentration to a region of lower concentration. In other words, they spread out.
Osmosis – The diffusion of water through a membrane. In osmosis, however, the water will move in the opposite direction as the diffusing particles. In other words, when particles diffuse into a cell, water will move out of that cell to make room. If the particles diffuse out of a cell, water will move into that cell.

 

Problem:

How can carrots demonstrate the process of osmosis?

 

Materials:

  • Two 400 mL beakers
  • String
  • Measuring tape or meter stick
  • Salt
  • Distilled water
  • Balance scale
  • Carrots
 
Safety concerns: iconicon Be sure to keep all glassware and chemical safety rules. As with all science lab activities, the most important safety rule is to follow all teacher directions.
 

Procedures:

  1. Fill the two beakers with equal amounts of water.
  2. Add 15 g. salt to one beaker and label it "Salt Water."
  3. Label the other beaker "Fresh Water."
  4. Cut a carrot in half. Tightly tie a piece of string about two centimeters below the cut end of both pieces.
  5. Place one carrot half (cut end down) in the "Salt Water" beaker. Place the other carrot with cut end down in the "Fresh Water" beaker. Allow carrots to remain undisturbed for 24 hours. At the conclusion of the 24 hour period, remove the carrots and observe them and the tightness of the strings. Record your data.
 

Analysis:

  1. In which kind of water did the thread become tighter around the carrot?
  2. In which kind of water did the carrot gain mass?
  3. Did the carrot cells gain water in fresh water or salt water?
  4. In which kind of water did the carrot cells lose water?
    • What evidence supports your conclusion?
  5. In which kind of water did the carrot cells gain water?
    • What evidence did you use to determine this?
  6. In which carrot was the direction of osmosis inward? How do you know?
  7. If your lettuce is wilting in your fridge what could you do to get it fresh again?

Review science safety rules here.

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Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE 7th grade science core.


Updated October 24, 2008 by: Glen Westbroek

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