EIS 19: Membrane Transport
Activity 1: Naked Egg (3 day)
These experiments take a few days to really see the full effect. We recommend that you set them up and continue working on this course on your normal schedule while periodically keeping an eye on what the experiment is doing. You can then come back to it when the experiment is done to do your analysis questions.
A chicken egg, if unfertilized (so, if it’s sold for you to eat, and isn’t growing into a chicken) is a single cell. It is the largest easily-obtainable single cell out there! (Other, bigger eggs would be other examples of macroscopic cells). This makes it really great to use as a model to see what would happen inside of our own cells under different conditions!
As a cell, a chicken egg is surrounded by a semipermeable cell membrane. It will allow water to pass through, but will not allow salts to pass through (when not “living”). (Think about why this is: how is most salt transport different from most water transport?) This will allow us to see osmosis at work. In order to do this, we must first dissolve the shell around the egg, which we can do by putting the egg in vinegar for a couple of days. This makes it naked!
This video gives a good overview of the basic idea of this experiment (which you can also try if you like), but ours is set up just a little bit differently, so be sure to read the details.
A chicken egg, if unfertilized (so, if it’s sold for you to eat, and isn’t growing into a chicken) is a single cell. It is the largest easily-obtainable single cell out there! (Other, bigger eggs would be other examples of macroscopic cells). This makes it really great to use as a model to see what would happen inside of our own cells under different conditions!
As a cell, a chicken egg is surrounded by a semipermeable cell membrane. It will allow water to pass through, but will not allow salts to pass through (when not “living”). (Think about why this is: how is most salt transport different from most water transport?) This will allow us to see osmosis at work. In order to do this, we must first dissolve the shell around the egg, which we can do by putting the egg in vinegar for a couple of days. This makes it naked!
This video gives a good overview of the basic idea of this experiment (which you can also try if you like), but ours is set up just a little bit differently, so be sure to read the details.
Materials
Day 1:
Day 3:
- 2 eggs
- Enough distilled white vinegar (this is “normal” vinegar) to cover both eggs completely.
- 2 clear containers/cups/glasses, one for each egg
Day 3:
- Enough salt water to cover egg #1. You can make this by adding roughly 1 teaspoon of salt to 1 cup of water.
- Enough distilled water to cover egg #2. If you do not have this and cannot easily acquire it, doing this experiment with regular water will still show you some cool differences between salt water and regular water: but the effect is more pronounced with distilled water.
Procedure
- On day 1, put one egg in each of your two cups/containers and cover each completely with vinegar (this should take roughly ½ cup each).
- Let sit for 2 days at room temperature. You should notice the egg shell dissolving over this period. If the egg shell is not completely dissolved after 2 days, you can let it sit longer.
- On day 3, gently pour out the vinegar from each cup.
- Wash each egg once with regular or distilled water. By wash, we mean gently pour water into the container near the egg (do not pour directly over the egg, as it is fragile) and then pour out the water.
- Gently pour salt water into container #1, being careful not to pour it too vigorously or directly over the egg, as the egg is fragile.
- Gently pour distilled (or regular, if you don’t have distilled) water into container #2, as in step 5.
- Let sit for 1 day at room temperature and observe the effects that take place over that time period. You may start to see some changes pretty quickly.
We’d love to see your experiments at work! If you have an Instagram and the permission of your relevant responsible adult, share a photo or video with us @kast_edu, #NakedEggKASTEdu.
Activity 2: Osmosis in Red Blood Cells
This activity can be done in the virtual lab at this site, or, if you have access to a microscope, it can be done IRL.
It is important that our bodies maintain a constant internal environment. This ensures that every cell in our body can have the resources that it needs to thrive. You can compare this idea to maintaining a large city or advanced civilization: While some unicellular organisms, like pond amoebae, are well-equipped to survive certain changes in the external environment and scarcity of nutrients, not unlike hunter-gatherers, in order for a large, complex, multicellular organism to function, those resources need to be in abundant local supply so that the cells can work together instead of competing for scarce resources.
Aside from just resources, it’s important that the body’s levels of salt and water stay the same. When you’ve finished with your egg activity, you’ll see just what happens to cells when the levels of salt and water change in the external environment. You may already be able to guess: If the water is saltier than the cell, where will water move by osmosis? If the water is less salty than the cell, where will water move then? (Assume that the salts can’t cross the membrane—they often require active transport—, but water can, since this is passive transport).
We’ll see that same idea again in this activity. Here are some helpful vocabulary terms to know:
Option 1: Complete the virtual lab online at this site. Put each cell type into each solution, and note your observations. What happens to the cell? Why do you think this is? How do cell types differ?
Option 2: If you have access to a microscope and you’re not squeamish, you can do this activity IRL!
It is important that our bodies maintain a constant internal environment. This ensures that every cell in our body can have the resources that it needs to thrive. You can compare this idea to maintaining a large city or advanced civilization: While some unicellular organisms, like pond amoebae, are well-equipped to survive certain changes in the external environment and scarcity of nutrients, not unlike hunter-gatherers, in order for a large, complex, multicellular organism to function, those resources need to be in abundant local supply so that the cells can work together instead of competing for scarce resources.
Aside from just resources, it’s important that the body’s levels of salt and water stay the same. When you’ve finished with your egg activity, you’ll see just what happens to cells when the levels of salt and water change in the external environment. You may already be able to guess: If the water is saltier than the cell, where will water move by osmosis? If the water is less salty than the cell, where will water move then? (Assume that the salts can’t cross the membrane—they often require active transport—, but water can, since this is passive transport).
We’ll see that same idea again in this activity. Here are some helpful vocabulary terms to know:
- Hypotonic: The surrounding solution is less concentrated than the cell.
- Hypertonic: The surrounding solution is more concentrated than the cell.
- Isotonic: The surrounding solution and the cell are the same concentration.
Option 1: Complete the virtual lab online at this site. Put each cell type into each solution, and note your observations. What happens to the cell? Why do you think this is? How do cell types differ?
Option 2: If you have access to a microscope and you’re not squeamish, you can do this activity IRL!
Materials
- A microscope.
- Salty water. This can be made by adding roughly a tablespoon of salt to a cup of water.
- Distilled water. Distilled water works best, but you should also be able to see differences between the two groups if you use regular tap water.
- Glass slides and coverslips.
- A lancet (this comes with certain microscope sets, or may also be found if you or someone in your family has diabetes and checks their blood sugars by finger stick) or a sanitized needle (such as a sewing needle or pin that has been cleaned with rubbing alcohol).
- Rubbing alcohol or an alcohol wipe. This is recommended, but is not absolutely mandatory if you wash your hands immediately before the experiment rather than sanitizing with alcohol.
- Cotton/gauze/a paper towel/a bandaid.
- An eyedropper/plastic pipet is helpful. A syringe or very small measuring spoons will also work.
Procedure
- Sanitize your finger tip with rubbing alcohol/an alcohol wipe. Prick your finger with the lancet or a freshly sanitized needle/pin. This should be just enough to draw blood. We recommend pricking the finger on the finger pad, mostly toward the side of your finger (but still in an area where you can see your fingerprint), as you are more likely to get enough blood from one attempt there. This video will show you proper finger prick technique (if you don’t have a lancet device, click here for an alternative. It’s the same process as shown from 2:15 onward—you just don’t have to worry about priming the lancet device)
- Smear 2 slides using the blood from your finger tip. One effective way to do this is to squeeze a drop of blood onto the center of the slide and scrape a coverslip over it to create a very thin layer. Another, somewhat less effective but generally adequate way to do this is to smear your fingertip (the spot with the blood) across the slide.
- Stop the bleeding on your finger with the cotton/gauze/a paper towel/a bandaid. Hold direct pressure over the bleeding. It shouldn’t take more than 10-30 seconds to stop bleeding.
- Find your blood under the microscope. If you have staining supplies and want to stain the blood, you can do this (follow the instructions provided with your staining supplies). But, you should be able to find clear outlines of cells even if you don’t do any staining.
- While looking under the microscope, put a small drop of salt water over your blood (you may find it easier to see if you then put a coverslip over this to make a thin layer). What changes do you observe in the cells?
- Repeat step 5 using distilled water (or regular water if you don’t have distilled).
- Record your observations.
If you’re having fun or observe something cool, we want to see it! If you have an Instagram and the permission of your relevant responsible adult, share a photo or video with us @eons_learning, #FingerPrickEons.