Getting out the microscopes is one of the best parts of teaching biology. I love hearing the ooh's and aah's when they finally get the specimen into focus. But if you've taught biology before you know it can also be one of the most exhausting units- constantly running around the room because "Mrs, I just don't see anything!" or they end up drawing dust, air bubbles, or their eyelashes. After a decade of tweaking my microscope unit, I've come up with some tips to help save your sanity.
1. Don't get them out until it makes sense.
While it may be tempting to get microscopes out the first week of school, it just doesn't make sense. If you aren't going to use them regularly until later in the year, why are you teaching them the names of the microscope parts in week 1? They will forget the information and you will find yourself reteaching. Hold off until you get to cells (or whichever unit you need them regularly).
2. Make sure they know the names of all the microscope parts.
It can be really frustrating when you are trying to help a student, tell them to adjust the fine focus, and they look at you like you are speaking another language. Because of this I don't let students start using the microscope until they can tell me the names of all the parts. We take notes on it and I give them a short quiz at the beginning of the unit. If you want to check out the worksheets I use for teaching parts of the microscope, click here.
3. Try a virtual lab first
Virtual labs are a way to provide students extra practice on the methods of using a microscope before getting out the real deal. Extra practice never hurts, especially for your SPED or ELL students who would really benefit from some visual practice.
For practice going through the process of using a microscope, check out this activity from Brainpop. (This site is great for middle school). For some higher level practice, check out this site from University of Delaware.
4. If your scopes have a single ocular, teach them which eye to use.
The microscopes in my room have a single ocular lens, so students often ask me which eye to use. This video shows an easy and quick way to teach them which of their eyes is dominant.
5. Start with prepared slides.
I always begin with prepared slides. I put 4 different prepared slides at each lab group, and have students practice focusing and drawing. The first day of prepared slides you will hear a lot of "I don't see anything!" but eventually they get the hang of it. Not all of your students are going to be great artists, but I make sure they know when they turn in their drawings they must a) be drawn to scale, and b) be neat. No scribbles allowed. I should be able to look at the drawing and easily tell what slide it is. I use these lab templates for prepared slides. Don't have access to prepared slides? You can make your own! Check out this blog post on how to easily make a classroom set.
6. Encourage peer help
There is only 1 of you and 30 students. It is physically impossible for you to be running around helping every single student. One day when I was about to rip my hair out I made this poster and hung it up on the whiteboard. Students were not able to call me over for help unless they had checked all of these items off the list. Most of the time their neighbor can help them resolve the issue before you need to be called over. If they still needed help after going down the checklist, then they could call me over. It has helped greatly! You can download this for free in my TpT store here.
7. After they have mastered prepared slides, then move on to wet mounts
Wet mounts can be much more exciting than prepared slides because you can have students look at their own cells (if your school allows you to do a cheek cell swab) or watch microorganisms swimming around. Protists are an absolute blast to watch, but students need to have mastered focusing the microscope and scanning relatively quickly in order to see the protozoa zooming around. You don't have to spend money ordering protists from a supply company, you can easily get your own culture going. Check out this blog post on how to set up a hay infusion. During this lab, I allow students to take pictures or videos with their phones. It takes a steady hand, but they can line up their smart phones with the ocular and get a decent video.
It can be really frustrating when the bell is about to ring and students try to walk out of the classroom without cleaning up. General microscope clean up procedures should include:
a) Removing your slide and returning it to where the teacher directs
b) Turn the objective to low power
c) Turning off the light
d) Putting the dust cover back on
e) If you are putting microscopes away for the day, unplugging and winding the cord around the arm.
I have this poster hanging on my microscope cabinet- it is a freebie from my friend Bethany Lau. You can find it in her TpT store.
I hope these tips help your microscope unit run more smoothly! Have fun!
Air pollution is a topic that fits into almost all science content areas. Teach biology? You teach the water and carbon cycles. Environmental science? Climate change and smog. Earth and space science? Layers of the atmosphere and ozone. Chemistry? Water + CO2 = carbonic acid. (Side note: My students recently tested the pH of different water sources, and were blown away that the pH of our rainwater sample was 5.4). I think it is telling that our air and atmosphere are woven into so many different sciences. Air is vital, so let's talk about it with our students!
I recently did a mini unit with my students on urban ecology. We were learning about the effects of urbanization on ecosystems, and pollution and urban heat islands came up in our discussions. (You can read my blog post about urban heat islands here). Here in Phoenix it is relatively easy to see how polluted our air is, all you have to do is drive up a hill and you will see the layer of haze that sits over our city of 1.6 million people. We discussed the health effects of air pollution and I wanted my students to have a visual of what they were breathing in. You can buy fancy (and expensive) sensors that will give you data readings of all the particles in the air, but I found an easy way for students to see the particulate matter floating around.
You will need:
This lab is super easy. All you have to do is have students smear a thin layer of petroleum jelly across the center of a glass microscope slide with a clean cotton swab. If you want your students to have quantitative data at the end of the experiment, gridded slides are ideal (See image). No worries if you only have plain slides.
Students got to choose where they wanted to leave their vasaline-covered slide for 24 hours. I had some students leave the slides in the classroom and others left their slides outside. (Tip: I had students set them in a petri dish and label them with their initials so we could track them down easier the next day. Also, if students choose to leave them outside, find a location on your school campus where they won't get disturbed). In the next 24 hours, any particulate matter floating around will land on the slide and stick to the petroleum jelly. If you want easier cleanup, you can also try putting a piece of double sided tape on the slide instead.
The next day, students retrieved their slides and viewed them under the microscope. I had them switch slides with their neighbors so they could compare indoor vs. outdoor slides. As you can see from our results pictured below, there was generally a lot more particulate matter on the outdoor slides. I had students draw what they observed and do a little math to calculate the particle deposition rate. If you are interested in checking out the lab write up, click here.
Remember when I said there was generally more particulate matter outside than inside? Are you ready to be completely grossed out? I had a student that decided to hang his slide from the ceiling by the classroom air vent... and this is the image that ensued. Can you say "time to change the air filter?"
I hope your students enjoy this lab as much as mine did! It was definitely eye opening for them to see the microscopic matter going into their lungs.
Ordering class sets of prepared slides can be pricey. Want a fun and free way to make your own? All you need are some slides, clear tape, and some animal hair samples. Put a few pieces of hair on a slide and carefully cover it with clear tape. A couple tips:
(Below: Left image is human hair, Right image is cat hair)
Another way to get some unusual hair samples is by checking with your local game and fish department. In Arizona our Game and Fish department has skull and pelt boxes that they loan to schools for free. I had borrowed the skull box for my ecology unit and had my students compare skulls of different animals. While I had the box, I also plucked a hair or two off the pelts and made prepared slides. It was fun to look at mountain lion, bear, and coyote hair in addition to the everyday pets.
Have you made prepared slides for specimens other than hair? I'd love to hear about it! Leave it in the comments!
I'm excited to share with you an EASY PEASY way for students to see osmosis in plant cells! In the past, I always used elodea leaves for this lab. Elodea can be hard to find at pet stores and is a little temperamental to keep alive. This year I decided to use onion skin from a purple onion and we got awesome results!
I used this lab BEFORE I taught any vocabulary such as osmosis, equilibrium, hypertonic, hypotonic, or isotonic. I wanted students to visually see what happens to cells in fresh water vs. salt water before I threw any vocabulary at them. Students were really excited to see the cells change within a matter of 60 seconds. Here are a few tips when doing this lab for the first time:
1. You cannot use the dry layers of the onion skin. You need to use the very top of the purple fleshy layer. It can be a little bit tricky to get a specimen that is thin enough, so I decided to do it myself and hand each kid a piece. I took metal tweezers, gently pushed them under the purple layer, and slid the tweezers out so a small flap of onion skin was loose. I peeled it off, handed it to each kid, and they set up their own wet mounts. No dye needed!
2. Have students make drawings using fresh water first. After they finished their drawing, they switched to salt water. To do this they do not need a new piece of onion, just leave it directly on the slide. Add a drop or two of salt water directly to the slide, no need to pre-soak the onion. Make sure your salt water solution is pretty saturated.
3. Tell students to wait at least 2 minutes before drawing the salt water image, because sometimes it takes a little time for the cytoplasm to shrivel up. Below are images of the onion cells in fresh water (left) and salt water (right) on 100x magnification. We had a discussion on whether or not the cell wall shriveled as well. Students automatically said yes, because the cell wall is almost transparent and harder to see. Once I told them to switch to high power (400x) they were able to see the cell wall more clearly and realize that the cell walls were still intact, while the membrane and cytoplasm shriveled.
Tomorrow we are going to follow up with the discussion of what happened and why. Students will take notes on osmosis and we will relate it to real world situations such as: Why can't I drink salt water if I'm stranded on a boat in the ocean? Why is my contact lens solution saline instead of pure water? Why do grocery stores spray the produce with water? If you want a quick worksheet to use as a formative assessment to follow this lesson, check out my tonicity and osmosis worksheet in my TpT store HERE.
I hope your students enjoy the lab as much as mine did! Other than having my classroom smell like onion for a day, it was a total win! Want more ideas? Check out this blog post that has 10 resources for teaching cell membranes!
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As fun as prepared slides are, students always LOVE looking at living organisms under the microscope. I generally order mixed protist specimens from Wards or Carolina Biological, but this year I didn't get an order put in on time (if your district is like mine it often takes months to get things ordered and delivered...) Since I didn't have anything for my students to look at, I decided to make a hay infusion. It turned out great for what I needed.
Overall, here are the pros and cons of doing a hay infusion:
Before using the hay infusion, have your students practice using the microscope with prepared slides. If students are comfortable with how to focus and scan, it makes it much easier when they are looking for things that are swimming around. We began the class with learning how to set up a wet mount slide using an elodea leaf. Once they got the hang of it, they cleaned their slide and took a sample of the pond water.
Here is a video I took under 40x magnification:
and 100x magnification:
Although there weren't a variety of species to see, students were still pretty excited to see them swimming around. I wasn't able to identify which type of protists we had- if you had honors or AP students it might be fun to give them a protist dichotomous key and see if they can figure out which species they find. Overall it was a success and didn't cost me a cent!