Cells, up close and personal

This week we continued our investigations with microscopes. Having already gotten some experience last week with the ins and outs of using one, we focused on cells. The kids got a chance to compare plant and animal cells by extracting human cheek cells (sounds much more painful than it actually is) and onion cells (a little smelly, but otherwise no tears). We talked about how animal cells are more "blob-like," and how plant cells have a rigid exterior, which makes them look like boxes or bricks. 

Afterward the kids looked at other specimens under the microscope including: a mosquito (the wings are really interesting up close), a spider (much hairier than you'd think) , a louse (even scarier magnified 100X), a blade of grass, and various leaves.

Biology: Birds and the Beans

This week we took what we learned about genetics one step further. We asked the question: if individuals with one version of a trait have an advantage over individuals with other versions of the trait, what happens to the distribution of this trait in the population over time?

To understand this concept, we carried out the following exercise. We started off with 50 red beans and 50 white beans, representing the parent generation. The beans were spread out over the white floor. A kid/bird from each group would hunt for 75 beans, and then the 25 remaining survivors would reproduce, having 3 offspring, each one the same color as the parent. The kids repeated the simulation 2 more times, and then observed the long-term effects of living in this particular environment on the frequency of red and white beans in the population.

Over time, the frequency of red and white beans changed, with white beans outnumbering reds. Put another way, the population evolved. The white environment gave white beans an advantage in helping them camouflage, so white beans were in effect "selected by nature" (that's why they call it natural selection). Whites out-performed reds, causing them to be more successful, which in biology means having more baby beans, and over time the frequency of each trait changed. We wrapped up by discussing how things may have turned out differently if our bean population was living on the red sidewalk or the green grass.

Biology: Genetics of Blood Types

This week we continued learning about genetics. Once again we carried out a simulation. However, there were a couple key differences from last week:

• Last week "parents" produced 1 child with a lot of different traits, and this week "parents" produced MANY kids, focusing only on a single trait.
• Last week we looked at made up traits, such as star- vs blast-shaped eyes, while this week we looked at a genuine example: ABO blood types in human genetics.
• Because we had such a large sample size of offspring, we were able to compare the distribution of the different genotypes and phenotypes to what we would predict based on chance alone.
  

Biology: Genetics with a smile

This week the kids carried out a simulation in which they explored how traits are passed down from one generation to the next in the strange but cheerful species, commonly known as "Smileys." The kids flipped coins to see which genes the Smileys would pass on to their offspring. Afterward we compared and contrasted Smiley and human patterns of inheritance. The following statements hold true for both species:

• Each individual caries 2 versions of each trait, one from mom and one from dad.
• Each individual passes 1 version of each trait to an offspring.
• The offspring's phenotype (what he looks like) is the combined result of the 2 versions he got from mom and dad - sometimes, but not always following the rules of dominance.
  

Biology: Owl Pellets

Over the last 2 weeks we dissected owl pellets. Owls are really interesting for many reasons.

• Owls can turn their heads as much as 270 degrees.
• They're nocturnal.
• Many species of owls have special flight feathers adapted for silent flight.

and my personal favorite, although not for the fainted-hearted...

• They consume their prey whole, and then regurgitate the undigested fur and bones in a compact pellet that can be dissected.

Still there?  Well, if you can stomach the dissection, (Truth be told, it's more of a in your head gross than an actual gross) this is just about one of the coolest labs you can do!

The first step was to remove all the bones from the pellet.  Next the kids classified the bones, putting each type in a different compartment of an egg carton (is there any craft or science project that isn't vastly improved by the use of egg cartons?!).  Finally the kids used pictures of intact skeletons to identify and reconstruct the prey skeletons they had discovered.  Awesome!

Biology: What are bones made of?

Over the last 2 weeks we have been investigating bones. We tested the effects of heat and acidic solutions on chicken bones. After placing bones in the oven, the kids observed that they became more brittle. On the other hand, bones soaking in vinegar lose their rigidity and become flexible. What do these two experiments demonstrate about the main components of bone? Bone is made up of collagen, a protein that gives bones flexibility, and calcium phosphate, a mineral that gives bone its strength. Heat destroys the protein, and vinegar dissolves the calcium phosphate through an acid-base reaction.

After these experiments, we reviewed the bones in the human skeleton and then did some comparative anatomy as we tried to identify various animal bones.

Biology: Acids and Bases

This week we started a new topic:  acids and bases.  First we used litmus paper and pH paper to classify different household liquids.  Then we boiled up some purple cabbage. Cabbage broth has the interesting property of indicating for acids and bases.

The kids added cabbage juice to the different liquids and observed the results. They recorded the color changes and using the pH values, ordered the cups according to where they fall on the scale. They observed that cabbage juice indicates strong acids with pinks, weak acids with purples, neutrals with blues, weak bases with greens, and strong bases with yellows. Finally they were given an unknown liquid, and using their cabbage-pH scale they guessed its pH.

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Biology: Homeostasis...the final verdict

We spent this past lesson analyzing our data using Excel. Each kid entered and analyzed one of the 5 sets of data we collected. Then we discussed our results. Most of our results fit in with what we know about how the body maintains homeostasis. Following exercise our heart rate and breathing rates increased in order to bring in more oxygen and sugar, and at the same time rid our cells of accumulating waste products.

Our data on body temperature were somewhat contradictory. While on average body temperature decreased, subjects sweated more and their skin color reddened over time, both of which are ways our body regulates increasing body temperature. We all agreed that measuring body temperature is difficult and subject to a lot of error. But there's hope...

Following our analysis we read an article about the CorTemp temperature pill that can record body temperature and heart rate data continuously and wirelessly transmit this data to an external device for graphing and archiving. The pill has seen many applications in the real world for athletics, for the military, for monitoring of animal vitals, and my personal favorite...for helping food companies test exactly how much heat a hot dog can tolerate before it becomes overdone.

Biology: Homeostasis, new and improved

After 2 weeks of brainstorming, trying out mini-experiments, and working out the logistical details of how to simultaneously measure a whole bunch of different things within a short period of time, we finally carried out our new and improved homeostasis experiment. Each kid ran for 6 minutes, while the rest of the crew made observations of body temperature, skin color, perspiration level, heart rate, and breathing rate. We'll analyze our results next week.

Biology: Homeostasis

This week the kids completed their experiment on the effects of different physical activities on body temperature. The results were quite surprising. After performing activities, subjects' body temperature stayed the same or went down. Afterward we discussed sources of error and decided that there were some design issues we wanted to change. Most importantly the kids wondered whether carrying out an activity for one minute would be enough time to produce a measurable change. The kids spent the rest of the class planning out a more extended experiment in which subjects will perform 10 minutes of physical activity and the kids will observe a number of physiological changes in addition to body temperature, such as heart rate, skin color, and amount of sweating. Next week they will carry out this experiment.

Biology: Feeling hot hot hot!

This week we talked about homeostasis, the idea that our bodies need to keep things inside more or less the same despite an-ever changing outside environment. Our cells need a certain amount of oxygen, water, and energy in order to function. Furthermore, they can only carry out their metabolic processes within a particular range of temperatures. When we are in situations that challenge the status quo,the body must do something to compensate.

This week the kids designed and ran experiments to determine the effects of exercise on body temperature. Next week they will analyze their data and present their findings.

Biology: Why are cells so small?

I've been getting some push back from the kids on all the tiny stuff we've been studying: microscopes, cells, chemistry, etc. So before we move on to bigger and better things, I thought we should at least address one last itsy bitsy, but not unimportant question: Why are cells so darn small? Even elephants, whales, and oak trees, big as they are, are made of of tiny cells, the same size as the unicellular organisms we found in drops of pond water.

To answer this question we looked at potatoes. The potatoes represented cells, and we submerged these potato cells in iodine, which stood for oxygen, food, waste or whatever stuff needed to be moved in or out of the cell. We cut up potatoes into 2 different-sized cubes: teeny tiny (c. 0.5 cm3) and large (c. 5 cm3). We placed these in a jar of iodine and waited. After about 20 minutes, we removed the potatoes, now black after reacting with the iodine, and sliced them in half. The idea was to see how far the iodine penetrated the potato (Picture shows similar experiment done with agar cubes absorbing phenolphthalein). In both teeny tiny and large potatoes the iodine moved less than a millimeter in. However, the big difference was when we considered what percentage of the potato had been exposed to the iodine.

We discussed how the surface area of cell is a limit on how much stuff can be moved in and out of a cell, while the volume of the cell determines the demand on imports (food, O2, etc) and exports (waste products). In large cells, there is simply too much volume for the surface area to handle, and the cell cannot move stuff in and out of the cell fast enough to meet the cell's needs.

Biology: Measuring tiny things

This week we learned a technique for measuring the length of tiny things. The kids measured a louse (for the uninitiated that's singular for lice), onion cells, and a human hair. This activity gave new meaning to the question: Do you have thick hair or thin hair?

So what unit do you use when you're measuring something so small? Meters, centimeters, millimeters? At this scale we're talkin' microns, 1000 of which make a millimeter. Using a ruler, the kids measured the field of view. Then they converted this number to microns. After examining a specimen, they estimated how many times it would fit within the field of view, did some simple math, and came up with a measurement that was within 2.5% of the accepted value. Not bad for a day's work!

Biology: You must be this SMALL to go on 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.

Biology: Sensational Skin

This week we investigated a type of cell called the sensory receptor. These receptors are found in our skin and allow us to feel pressure, pain, heat, and cold. The kids made pressure probes (see photo), which were used to test 4 different areas of the body: fingertip, forearm, cheek, and calf. The idea was to GENTLY poke these areas with the probe, gradually increasing the distance between the 2 toothpicks until the subject could feel 2 distinct sensations. The area with the smallest 2-point discrimination was the area that was most sensitive and was assumed to contain the highest number of sensory receptors for pressure. The kids were surprised to find quite a great deal of variation. Subjects could distinguish 2 distinct sensations at an average of 2.5 mm on their fingertips, while the 2-point discrimination was much larger for the calf and forearm - as much as 10-15 mm.

Biology: Testing for organic compounds

This week we discussed organic compounds. First we dispelled any myths about organic compounds being any healthier than regular old compounds. Likewise, if someone tries to charge you more money for an organic compound, don't fall for it! In chemistry, organic means relating to living things and containing lots of carbon atoms.

We used chemical and physical tests to find out whether the 6 foods in question (water, chicken soup, sucrose (table sugar and water), egg, margarine, and bread crumbs solution) contain proteins, fats, or carbohydrates (starches or glucose).

Biology: Carbon

This week we talked about carbon and how its atomic structure gives it so much versatility in forming chemical bonds with other elements. Using the latest in electron microscopy we were able to produce this incredible image of an actual ethane molecule.

Next time we meet we'll investigate the major carbon-containing macromolecules that make up all living things.

Biology: 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 water flea. What's cool about this little guy is that being transparent means you can WATCH its heart beat!

Biology: Etrog vs Lemon

This week we studied etrogs from a biological perspective. First we classified them as citrus, a type of flowering plant and talked about the role flowers play in helping plants reproduce. Etrog trivia: What part of the flower is the pitom?

Then we asked the question: What's the difference between an etrog and a lemon? The kids started off by making some external observations: shape, color, volume, and weight, and then they opened them up and looked inside. They noted differences in the relative proportions of peel and fruit as well as differences in the volume of juice. They took the pH of each fruit and congratulated themselves on a job well-done to the tune of a tall glass of lemonade. Etrogade, we learned is pretty tough to make given how little juice each fruit contains.

Biology: "Newly discovered planet may have water on its surface" ....so what?

Just about a year ago a team of astronomers announced the discovery of an extrasolar planet, called Gliese 581g*. What's neat about Gliese 581g is that it may have liquid water on its surface.  When scientists search for water in space, they're looking for just one thing: life.

What makes water so special, and why do we think it's essential for life? These were some of the questions we set out to explore on day 1 of Biology. We started off by observing water's amazing ability to dissolve other substances. The kids prepared strips of filter paper, each one with a different marker color. After placing them in a bowl of water, we watched as the water traveled up the papers and dissolved the inks, revealing surprising bands of different colors.

We talked a bit about the chemical structure of water and how this structure allows water to dissolve substances easily and in doing so helps along the important chemical reactions necessary to sustain life.

*http://en.wikipedia.org/wiki/Gliese_Catalogue_of_Nearby_Stars