Make sure you’ve completed the How to Use a Microscope and also the Wet Mount activities before you start here!
If your critter is hard to see, you can use a dye to bring out the cell structure and make it easier to view. There are lots of different types of stains, depending on what you’re looking at.
The procedure is simple, although kids will probably stain not only their specimens, but the table and their fingers, too. Protect your surfaces with a plastic tablecloth and use gloves if you want to.
We’re going to use an iodine stain, which is used in chemistry as an indicator (it turns dark blue) for starch. This makes iodine a good choice when looking at plants. You can also use Lugol’s Stain, which also reacts with starch and will turn your specimen black to make the cell nuclei visible. Methylene blue is a good choice for looking at animal cells, blood, and tissues.
In addition to your specimen, you’ll need to get out your slides, microscope, cover slips, eye dropper, tweezers, iodine (you can use regular, non-clear iodine from the drug store), and a scrap of onion. If you can find an elodea leaf, add it to your pile (check with your local garden store). Here’s what you do:
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Download Student Worksheet & Exercises
1. Fill a container with water and add a small piece of elodea leaf and onion. You’ll want the onion to be a thin slice, no more than a quarter of an inch thick.
2. Practice making a wet mount first. Put a fresh slide on the table. Using tweezers, pull off a thin layer of onion (use a layer from the middle, not the top) and place it on your slide. Gently stretch out the wrinkles (use a toothpick or tweezers) and add a small drop of water and cover with a cover slip. Take a peek at what your specimen looks like on low power – do you notice it’s hard to see much? Draw what you see in your notebook.
3. Now increase the power and look again. Draw a new sketch in your notebook.
4. Now we’re going to highlight the cell structure using iodine. Lugol’s is also iodine, but the regular brown stuff from the drug store works, too. Grab a bottle of the one you’re going to use.
5. To stain the specimen, we’re going to add the stain to one side of the cover slip and wick away the water from the other side. Use a folded piece of tissue paper and touch it lightly to one side of the cover slip as you add a single drop of stain to the other side. When the stain has flowed through the entire specimen, take a peek and draw what you see in a a fresh circle.
6. Do the same thing with the elodea leaf. And anything else plant-based from your backyard. Or refrigerator. Draw what you see and don’t forget to label it with a title and power of magnification!
Exercises
- Why do we use a wet mount slide?
- Give one example of a specimen that would use a wet mount slide?
- How do you prepare a wet mount slide?
- Why do we stain specimens?
- Give one example of a specimen that would use a stain.
- What type of stain can we use (give at least one example).
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Each brown dot is the nucleus of a onion cell.
what are the little brown dots?
Dish detergent or ethyl alcohol should do the trick. The slide covers are harder to clean since they are so thin. If the slides are old and dirty, soak them in warm water with detergent overnight, and then wipe them clean with a towel. Wrap the slides in paper until you’re ready to use them again.
This may seem like a silly question. but what is the best way to clean the slides after using them? Just soap and water or do we have to do anything special? What about the slide covers. Do we just throw those away?
I’ll have my team connect with you right away!
Hello!
I am having the same problem as Eric Christiansen. Thanks, Laura
We’ll check into this right away, and if there’s an issue with your account my team will get right back to you! Sorry for the trouble.
We are also having difficulty completing the 7th grade activities for the Life Science unit.
You simply request to get access, and poof! It should happen automatically. I’ll check those particular posts to see if there’s a glitch somewhere. Check back soon and let me know if it’s still an issue.If there are any others, let me know as well. Make sure you log out, then log back in when you check back. Thanks!
I am having similar difficulties in that I’m blocked from the ‘how to use a microscope’ and ”wet mount’ activities. I would very much like to be able to progress through the curriculum for my 7th grader. What do I need to do? Thanks, Christina
Hi, I am trying to navigate the site and preplan my lessons. My problem is that in looking at the 7th grade activities, in order to do the experiments for the Life Science unit, we are to have completed the How to Use a Microscope and Wet Mount activities. However, when I attempt to access those, I get the ‘sorry this is in 9-12th grade content’ message. Again, I am in Life Sciences section under 7th grade level. Please help! 🙂 Thanks, Ramona