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Title: Honey, I “Shrunk” the Carrot

Author(s): Carol Ann Drane, Lois Eppich, and Mary Lee Ruch

Grade Suitability: 3, 4, 5, 6, 7, 8

Scope: Science, Math, and Reading

Sequence: Life Sciences

Length: 2 class periods

Background:

Osmosis is the diffusion of water through a membrane. A carrot is made up of tiny units called cells that are surrounded by cell membranes. The cell membrane keeps cell parts inside and protected. While this membrane stops most things, water can pass through it.

Water moves through cell membranes towards higher concentrations of dissolved chemicals. When the carrot is soaking in salt water (a hypertonic solution) the water found in the carrot's cell will move into the salty water to equalize the amount of water inside and outside the cells' membranes. As more and more of the cells lose water, the carrot becomes soft and flexible.

When the carrot is placed in the fresh water (hypertonic solution), the reverse happens. The fresh water around the carrot will move into the carrot's cells. The string will appear to tighten around the carrot as the carrot swells with water.

Objectives:

The students will be able to :

  1. The learner will understand the process of osmosis.
  2. The student will use a scale to measure the weight of a carrot before and after soaking in a solution.
  3. The students will make observations and predictions based on current knowledge.

Materials:

  • Two beakers
  • String
  • Ruler
  • Salt
  • Carrot – pre-sliced in half lengthwise
  • Paper and pencil
  • Microscope
  • Balance Scale

Setting:
The activity may occur in the classroom in small cooperative groups.

Activity Description:

  1. Fill two beakers with equal amounts of water.
  2. Add 4 teaspoons salt to one beaker and label it “Salt Water.”
  3. Determine the mass of each of the two pieces if carrot and record that data.
  4. Cut a carrot in half. Tightly tie a piece of string mid way on each carrot pieces.
  5. Place one carrot half in the “Salt Water” beaker. Place the other carrot in the “Fresh Water” beaker. Allow carrots to remain undisturbed for 24 hours.
  6. Form a hypothesis.
  7. Remove carrots and observe them and the tightness of the strings. Record data.
  8. Determine the mass of each piece of carrot and record the data.

    Sample Data Sheet

     

    Original Mass

    24- Hr. Mass

    Difference in Mass (+/-)

    Observation of String

     

    Carrot Piece #1

    Freshwater

     

     

     

     

    Carrot Piece #2

    Saltwater

     

     

     

     

Extensions:

  1. Use different vegetables in the solution.
  2. Use dye in the solution.
  3. Relate osmosis to humans and why we need to keep ourselves hydrated.
  4. Use a microscope to view and draw the cells before and after soaking.

Evaluation:

  1. Did the thread become loose in fresh water or salt water?
  2. Did the thread become tight in fresh water or salt water?
  3. Did the carrot develop a soft texture in fresh water or salt water?
  4. Did the carrot develop a firm texture in fresh water or salt water?
  5. In which type of water did the carrot cells increase due to turgor pressure (fresh water or salt water?) YOU MUST HAVE A MICROSCOPE TO ANSWER THIS QUESTION.
  6. In which type of water did the carrot cells decrease in cell size (fresh water or salt water?)
  7. Was there a loss of water by cells in fresh water or salt water?
  8. Did the cells gain water in either fresh water or salt water?

Optional Higher Level Questions:

  1. What was the purpose of tying thread around each carrot?
  2. In which kind of water did the carrot cells lose water?
  3. What evidence supports your conclusion?
  4. In which kind of water did the carrot cells gain water?
  5. What evidence did you use to draw this conclusion?
  6. What do you think would happen to human blood cells if they were placed in a beaker of salt water?

Ocean Science Literacy Standards:
5d  -  Ocean biology provides many unique examples of life cycles, adaptations and important relationships among organisms (such as symbiosis, predator-prey dynamics and energy transfer) that do not occur on land.

5f  -  Ocean habitats are defined by environmental factors. Due to interactions of abiotic factors such as salinity, temperature, oxygen, pH, light, nutrients, pressure, substrate and circulation, ocean life is not evenly distributed temporally or spatially, i.e., it is “patchy”. Some regions of the ocean support more diverse and abundant life than anywhere on Earth, while much of the ocean is considered a desert.

National Science Education Standards:
Overall  -  Unifying concepts and processes in science

A  -  Science as inquiry

B  -  Physical science

C  -  Life science

D  -  Earth and space science

References: