Biology: You must be this small to ride this ride

What does the cell membrane have in common with filters, sifters, and colanders? All of the above are SEMI-PERMEABLE, meaning some substances can pass through them, while others can't.

In this week's experiment we used dialysis tubing (thin layer of material that contains various sized holes) to model the cell membrane. We tied off the dialysis tubing with string to create a bag that we filled with corn starch solution and glucose solution. First we submerged the bag in a jar of water and tested the surrounding water for the presence of glucose using glucose strips. Then we replaced the water with iodine. We waited a few minutes to see if there was a color change in either the bag or the jar. Iodine turns black upon contact with starch, so a color change inside or outside the bag would demonstrate which molecules had traveled through the bag. Check out the picture, and see if you can guess which molecule, starch or iodine can travel through the bag. Hint: Bigger ISN'T better.

General Science: Pond water: More than meets the eye

This week the kids hunted for microorganisms in a sample of pond water taken from Robert and Karen Clements' pond (thanks once again for your annual donation of pond scum!).

To get a sense of what we were looking for, we started off by watching a few short video clips of different microorganisms. Then the kids prepared their slides, making sure to get a sample of pond water that was nice and goopy. After hunting around a bit, the kids turned up some interesting single-celled organisms and even a worm or two. Believe me when I tell you, these 2 mm guys are pretty alarming swimming around eating algae magnified 100x!

Biology: 10,000 Microns under the Sea

This week the kids hunted for microorganisms in a sample of pond water taken from Robert and Karen Clements' pond (thanks once again for your annual donation of pond scum!).

The kids turned up some interesting single-celled organisms and even a worm or two. Believe me when I tell you, these 2 mm guys are pretty alarming swimming around eating algae magnified 100x!

The kids used what they learned last week to estimate the sizes of the different organisms.

General Science: The Right Stuff

This week the kids had to design a spacesuit that could withstand the intensely high temperatures one might find on Venus. Lacking the funding to actually travel to Venus and not wanting to violate the Helsinki Declaration (ethical principles for research on human subjects), we used ice-pops instead of people and hot water instead of Venus. The kids made spacesuits using one of three available materials: tin foil, cotton balls, and bubble wrap. Each of the subjects was then placed in a plastic bag and then then submerged in hot water for 1 minute. Afterward, the kids opened up each ice-pop and measured how much of it had melted by pouring the liquid from each one into a graduated cylinder.

Physics: Good Vibrations

This week we talked about what a sound is and experimented with sounds produced by different materials. The kids made oboe-like straws, plucked rubber bands of different widths and lengths across shoe boxes, bounced wooden sticks off the side of tables, and struck glasses filled with water (looks like wine, but it's just food coloring, I promise!), noting in each case how different changes affected the pitch. Finally, the kids used their observations to created their own instruments, and then we had a concert!

Biology: How small is small?

This week we learned a technique for measuring specimens under the microscope. The kids measured the lengths of ants and even actual cells. You can be sure we weren't measuring in meters or even centimeters. The kids got some practice with micrometers, 1000 of which make a millimeter.

How did we do this? Using a ruler, the kids measured the field of view. Then they converted this number to micrometers (so much easier to work with when you're measuring cells and such). They estimated how many times a specimen would fit within the field of view, did some simple math and came up with a measurement that was within 100 micrometers (.1mm of the accepted answer). Not bad for a day's work!

Physics: What color is it really?

This week we did 3 mini-experiments to investigate how we perceive color. The first was with spinning color wheels. The kids compared the patterns of the discs when still to the patterns they saw when the discs were spun. The second mini-experiment involved looking at magazine pictures under the microscope and comparing the images seen with the naked eye to the colors seen at greater magnification. The third was simply giving each kid some red, blue, and yellow paint and letting them go wild...well on paper anyway.

When we physically combine red, blue, and yellow paints in different proportions we can create an enormous range of colors. Similarly the human brain will combine colors that your eyes see when those 2 colors are seen in rapid succession, as in the case of the spinning color wheels or when they are placed very close together, as revealed by a microscopic examination of pictures from a magazine. What is especially cool about the magazine pictures is that no matter what color you "see," when examined under the microscope you realize that the image is made up of just 3 colors: magenta, cyan, and yellow (aka red, blue, and yellow). By producing images that include different ratios of the primary colors, you can get just about any color.

General Science: Iodine the indicator

This week the kids learned how to use an INDICATOR, a compound that changes color when it comes in contact with a particular substance. The kids were given around 10 different foods to test using iodine, an indicator that changes from orange to black on contact with starch. As they made their way through the food samples (testing them, not eating them), they were able to refine guesses about what starches have in common. Finally, we concluded that starches come from plants and are how plants store simple sugars.

Afterward we discussed how simple sugars are connected by chemical bonds to make complex sugars and conversely, how the chemical bonds within complex sugars are broken to produce simple sugars. Try chewing on a cracker for a few minutes (works best with unsalted ones), and you'll notice a sweet taste in your mouth that results from your saliva breaking down the starch into simple sugars.

Biology: Planting Day

Today was planting day! Before planting our daffodil bulbs we compared them to other bulbs, measured their circumference and weight, and then dissected them to get a sense of what's going on inside. After learning that the bulb provides food for the growing flower bud, we decided to see whether bulb weight affects flower growth. We grouped the remaining bulbs (the ones we hadn't yet dissected) by weight and planted them in 3 separated areas. Over the next few months, we'll observe and measure their growth. Stay tuned...