Microscope slide with fly antenna mounted in nail polish.
I’m really beginning to like the idea of giving students the option of putting together their own, individual, slide collections. So, to practice mounting slides with nail polish, I tried to make a start on my own permanent slide collection. It was partially successful.
Procedure
The subject fly. 30x magnification under the stereoscope.
To start, I found a dead fly near the window. It had been dead for a while and so I assumed it was pretty well dried. Carefully, under the stereoscope, I pulled off the appendages — antenna, wings, legs — for mounting. The fly itself was too big to mount, as were the major body parts, but as I was dismembering it the head, thorax, and abdomen came apart. In fact, the head broke into a few pieces as well, including one of the compound eyes, which I thought would be worth trying to mount even though it was somewhat thicker than the other parts.
I started with the antenna. The procedure I tried to follow is simple. Place a small drop of nail polish on the slide and then put the sample on the nail polish drop. Next place a drop of nail polish on the coverslip, flip it upside down and put the two drops together. The weight of the coverslip will flatten nail polish out into a thin layer. You then put small drops of nail polish at each corner of the coverslip. The polish will seep in between the slide an coverslip by capillary action until the entire underside of the slip is saturated.
Since the antenna was so small, I actually broke a cover slip into quarters to make them, I hoped, easier to manage. The slides were then left to dry overnight.
The initial results were, as I have mentioned, mixed. Bubbles encroached on a number of the specimens, particularly the thicker ones, like the rear legs, but for the most part, the specimens were clearly visible, with a minimum of obstructions to the view.
Antenna
Antenna at 40x magnification:
Fly’s antenna at 40x magnification. Mounted on slide in nail polish: Strengthener, Nail Hardener. Notice the air bubble encroaching on the sample from the bottom.
Antenna at 100x magnification:
Fly antenna tip at 100x.
Antenna tip at 400x:
Fly antenna tip at 400x.
Legs
Of the four leg slides I made, three had serious problems with bubbles, and the one that did not was missing the end segment of the leg. Part of the problem with the bubbles may have been that it took me a while to get the legs onto the nail polish drops, which allowed the drops time to evaporate. This could have resulted in a more viscous drop by the time I added the coverslips, which would not have lain down quite as flat, leaving space for the bubbles to come in. Another possibility is that the thickness of the legs made the glass coverslip tip up toward one side.
Fly front leg:
Fly front leg 100x.
Middle leg: Fly’s middle leg. 100x magnification.
The tip of the middle leg is inside the nail polish. Fly middle leg’s tip. 400x.
Rear leg: The tip of the rear leg is in air pocket while the rest is not. 100x magnification.
Rear Wing
The last appendages I mounted were the two small, rear wings. They were very thin and I placed them both under the same full sized slide. It worked quite well.
Rear wing at 40x:
Fly rear wing at 40x.
Rear wing at 100x:
Fly rear wing at 100x. Click and zoom for more detail.
OnlineUniversities.com has compiled an interesting list of ways what we’ve learned from neuroscience is being used to rethink school and the classroom.
From 9 Signs That Neuroscience Has Entered the Classroom via OnlineUniversities.com.
Much of the list consists of simpler, practical things that are straightforward (if not easy) to implement: like starting school later (for the adolescents), emphasizing more group work, and stressing the importance of the emotion (positive affect).
But the article also points out some of the newer technology based approaches, such as interactive “cognitive tutoring”.
The radishes did well this year. Planted in containers on March 29th (in St. Louis, USA), they were harvested one month later. The short, early season means that they’re a workable crop for school. Students can plant, harvest, and consume them all within a semester.
The CDC’s Fruit and Vegetable of the Month website has a little history, some information about the varieties, nutritional information, recipes, and more information about radishes. The University of Illinois Extension also has information about planting and growing.
NutritionData.self.com has some very nice graphical representations of the nutritional value of the food (although their serving size is 1 cup of slices, which seems a bit much).
These sites, however, focus on the radish bulbs, and not on the fact that the leaves are edible. Radish Leaf Pesto is quite good.
Harvested radishes. Both the red bulbs and the green leaves are edible. You'll note that radishes also spot a long tap-root.
I told my two (elementary aged) kids that if they didn’t behave Santa would fill their stockings with coal. They were so excited. Since the coals we use on the grill can’t melt metal, they were hoping some real coal would burn hotter. They want to make rings.
Energy cannot be either created or destroyed, just changed from one form to another. That is one of the fundamental insights into the way the universe works. In physics it’s referred to as the Law of Conservation of Energy, and is the basic starting point for solving a lot of physical problems. One great example is calculating the average temperature of the Earth, based on the balance between the amount of energy it receives from the Sun, versus the amount of energy it radiates into space.
The Temperature of Radiation
Anything with a temperature that’s not at absolute zero is giving off energy. You right now are radiating heat. Since temperature is a way of measuring the amount of energy in an object (it’s part of its internal energy), when you give off heat energy it lowers your body temperature. The equation that links the amount of radiation to the temperature is called the Stefan-Boltzman Law:
where:
ER = energy radiated (W/m-2)
T = temperature (in Kelvin)
s = constant (5.67 x 10-8 W m-2 K-4)
Now if we know the surface area of the Earth (and assume the entire area is radiating energy), we can calculate how much energy is given off if we know the average global temperature (the radius of the Earth = 6371 km ). But the temperature is what we’re trying to find, so instead we’re going to have to figure out the amount of energy the Earth radiates. And for this, fortunately, we have the conservation of energy law.
Energy Balance for the Earth
Simply put, the amount of energy the Earth radiates has to be equal to the amount of energy gets from the Sun. If the Earth got more energy than it radiated the temperature would go up, if it got less the temperature would go down. Seen from space, the average temperature of the Earth from year to year stays about the same; global warming is actually a different issue.
So the energy radiated (ER) must be equal to the energy absorbed (EA) by the Earth.
Now we just have to figure out the amount of solar energy that’s absorbed.
Incoming Solar Radiation
The Sun delivers 1367 Watts of energy for every square meter it hits directly on the Earth (1367 W/m-2). Not all of it is absorbed though, but since the energy in solar radiation can’t just disappear, we can account for it simply:
Some if the light energy just bounces off back into space. On average, the Earth reflects about 30% of the light. The term for the fraction reflected is albedo.
What’s not reflected is absorbed.
So now, if we know how many square meters of sunlight hit the Earth, we can calculate the total energy absorbed by the Earth.
The solar energy absorbed (incoming minus reflected) equals the outgoing radiation.
With this information, some algebra, a little geometry (area of a circle and surface area of a sphere) and the ability to convert units (km to m and celcius to kelvin), a student in high-school physics should be able to calculate the Earth’s average temperature. Students who grow up in non-metric societies might want to convert their final answer into Fahrenheit so they and their peers can get a better feel for the numbers.
What they should find is that their result is much lower than that actual average surface temperature of the globe of 15 deg. Celcius. That’s because of how the atmosphere traps heat near the surface because of the greenhouse effect. However, if you look at the average global temperature at the top of the atmosphere, it should be very close to your result.
They also should be able to point out a lot of the flaws in the model above, but these all (hopefully) come from the assumptions we make to simplify the problem to make it tractable. Simplifications are what scientists do. This energy balance model is very basic, but it’s the place to start. In fact, these basic principles are at the core of energy balance models of the Earth’s climate system (Budyko, 1969 is an early example). The evolution of today’s more complex models come from the systematic refinement of each of our simplifications.
Advanced Work
If students do all the algebra for this project first, and then plug in the numbers they should end up with an equation relating temperature to a number of things. This is essentially a model of the temperature of the Earth and what scientists would do with a model like this is change the parameters a bit to see what would happen in different scenarios.
Feedback
Global climate change might result in less snow in the polar latitudes, which would decrease the albedo of the earth by a few percent. How would that change the average global temperature?
Alternatively, there could be more snow due to increased evaporation from the oceans, which would mean an increase in albedo …
This would be a good chance to talk about systems and feedback since these two scenarios would result in different types of feedback, one positive and one negative (I’m not saying which is which).
Technology / Programming
Setting up an Excel spreadsheet with all the numbers in it would give practice with Excel, make it easier for the student to see the result of small changes, and even to graph changes. They could try varying albedo or the solar constant by 1% through 5% to see if changes are linear or not (though they should be able to tell this from the equation).
A small program could be written to simulate time. This is a steady-state model, but you could assume a certain percent change per year and see how that unfolds. This would probably be easier as an Excel spreadsheet, but the programming would be useful practice.
Of course this could also be the jumping off point for a lot of research into climate change, but that would be a much bigger project.
References
Yochanan Kushnir has a page/lecture that treats this type of zero-dimesional, energy balance model in a little more detail.
Razib Kahn has a fascinating interview with Milford Wolpoff, one of the main scientists behind the research that argues that humans are not all part of a single family tree, descended from a single ancestor who moved out of Africa about 200,000 years ago.
This section focuses on the theory, and has a nice explanation of what mitochondrial DNA is (and why it’s important):
It gives an excellent perspective on how science works, and how scientists work (scientists are people too with all the problems that entails).
The entire thing is a bit dense, but it’s one of the better discussions I’ve seen describing the process of science in action, with little hints at all the challenges that arise from personality conflicts and competing theories.
