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Principle(s) Investigated: Osmosis, Diffusion, Cell Membranes, Gradients, Hypotonic, Hypertonic
Standards :Biology/ Life Sciences
1a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.
Materials:
Grocery Store
- Egg (raw)
- Vinegar
- Cornstarch
- Water
- Celery
- Containers- Plastic Cups
Procedure:
In Class
Celery
1. From the front of the classroom grab four pieces of celery and two cups for each group of two.
Label one cup water and it with water
Label the other cup salt water and fill the cup with salt water
2. Weight each piece of celery and record this data in the document below. Note be sure to remember which celery goes with which weight.
3. Place two
pieces of celery in each cup.
4. Wait 15 minutes then remove the celery and pat it dry and reweigh the celery recording the weights in the document below
Color Dye
1. Take a cup and fill it up with water.
2. Add three drops of die to the water and watch the reaction
3. Record your observations in the data table below
Osmosis and Diffusion Data Table
At Home
Egg
1. Place an egg in a cup and fill the cup with vinegar until it covers the egg. The egg will float so some of the egg may still be exposed.
2. Wait about 24 hours until the eggshell has dissolved. This will create a naked egg.
3. Once the eggshell has dissolved remove the egg from the vinegar, gently rub the egg to remove remaining remnants and rinse the egg off.
4. If you have a scale weigh the egg now and record the weight.
5. Place the egg in cornstarch for at least two hours and record the weight. If you can try to record the egg during this time and play it back in fast mode to see the change in the egg.
Note you may want to check on the cornstarch every few hours to remove the excess water.
6. After a period longer than two hours remove the egg and pat it dry and record the new weight.
7. Now place the egg in water and wait at least two more hours. Again record this time if you can but if not then take pictures at each stage and compare it to a typical egg.
8. After at least four hours, remove the egg and pat it dry. Then weigh the egg again.
Throughout this whole process write observations and at the end make some conclusion about what you think has occurred.
The eggs broke on their way to class so this will be the replacement demonstration
Dialysis tubing
Materials
Dialysis tubing- science catalog
Water-sink
Iodine-CVS
Corn Syrup- Grocery Store
Procedures
1. Cut off a piece of dialysis tubing about 5 inches
2. Place the dialysis tubing in water for about 10 minutes
3. Tie one side of the tubing and add corn syrup till it is about 3/4 full
4. Tie the other side in a knot
5. Fill a beaker about 3/4 of the way full and add iodine until the water has a gold hint to it.
6. Place the filled dialysis tubing into the beaker and wait 15-20 minutes
7. Record observations at the end of the experiment
Student prior knowledge:
The students need to be able to think critically but no other prior knowledge is necessary in order to participate in this lab experiment. In the beginning of the lab I review what we will be going over and demonstrating so no prior knowledge is necessary
Explanation
The process of osmosis and diffusion are often times confusing for students and can be hard to visualize. By giving the students an activity where they can see and compare the two concepts. The students will hopefully better understand the concept
Osmosis
Osmosis is the process of molecules moving across a semipermeable membrane and this occurs because the concentrations are different. One side might have a high salt concentration and the other side a lower salt concentration, to have each side be in equilibrium either the salt or water could move across the membrane depending on the type of membrane. Often times, water is able to pass through and other molecules are not so the liquid will become higher in the side with the high concentration of salt and the other side the fluid level will decrease. See the figure below
This process will continue until the two sides reach equilirbrium. No energy is used during simple osmosis.
This process of osmosis is very important because our cells have a specific concentration of molecules it must maintain in order to keep the cell functioning. Let’s look at a red blood cell; if the cell is place in a very low concentration solution then water will enter the cell causing the cell to be lysed. This occurs when the cell is in a hypotonic solution or a solution with a low concentration in relation to the cell. If the inside of the cell and the area surrounding the cell are both at similar concentrations then the cell will continue to function normally and the amount of water going into the cell is the same amount entering the cell. If the red blood cell is placed in a solution that has a high concentration of molecules then the water will diffuse out of the cell into the outside solution causing the cell to shrivel. This occurs when the cell is in a hypertonic solution or high concentration of molecules.
Diffusion
Diffusion is the process of molecules moving from an area of high concentration to an area of low concentration. The particles may be contained and once they are released they spread out over time and the mixture will eventually reach an equilibrium. Equilibrium is when the particles are at a constant concentration throughout the mixture.
Questions & Answers:
1. How is the egg comparable to a red blood cell?
The egg has a semi permeable membrane that allows water to enter and exit the egg to reach equilibrium
2. Does diffusion occur during the process of osmosis?
Yes during osmosis a substance is moving from a high concentration down to a lower concentration
3.How do fish deal with osmosis because the salt water has a high concentration of salt than does the fishes body.
The fish must continuously drink water and the fish filters out the salt so the body can stay at homeostasis.
Applications to Everyday Life:
Fragrance- When you spray a fragrance into the air, the fragrance drifts into other rooms and spreads to other areas until the concentration of the fragrance is throughout the whole area. This is an example of diffusion.
Circulatory System- The circulatory system uses osmosis and diffusion for exchanging oxygen and carbon dioxide in the capillary veins. The concentration of oxygen is very high in the capillaries and the carbon dioxide concentration is high in the cells. The cells and capillaries have semipermeable membranes allowing specific substances to pass through; these include oxygen and carbon dioxide. As the blood goes through the capillaries the oxygen goes down it's concentration gradient into the cells and the carbon dioxide passes through the capillaries into the blood
Salt on a Slug- When I was little my parents showed me a cool trick that if I put salt on slug they would die. This death occurs because slugs have a semipermeable membrane and they need to keep their body at homeostasis with lots of water inside their bodies. When salt is on their skin is causes the water to leave the slugs body causing the slugs to lose water and eventually shrivel up and die.
Pruny Fingers and Toes- When you are in the pool, bathtub or spa for too long your fingers and toes eventually become wrinkly. Your body does not have as high of a concentration of water as the spa, pool or bathtub. This difference in water concentrations and that your skin is semipermeable allows water to go into your skin to try and even the concentrations. The wrinkly look is actually due to the increase in water in your skin rather than a decrease, which many people think.
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