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Elodea nuttallii: Image courtesy of Christopher Fischer.Summary
Students often believe that only animals “breathe”, but all things exchange gases with their environment. It’s just that the process is not so obvious in plants. Elodea is a very common water plant that can be found in aquarium stores. As photosynthesis occurs, oxygen is produced as a by-product. Elodea releases bubbles of oxygen as it photosynthesizes. In fact, the number or volume of bubbles in a certain amount of time can be used as a rough measure of photosynthetic rate.
Submitted by irene on Sat, 2006-07-29 13:08.
These experiments use a bell jar (or any other very large, clear, glass jar) to determine the identity of the gas produced by plants. It mirrors the famous experiments of Joseph Priestley and Jan Ingenhousz from the 1700’s that first demonstrated the existence of oxygen and its importance to plants and animals.
In 1771 and 1772, Priestly conducted a series of experiments using a bell jar. It was known that a candle placed in a sealed bell jar would eventually burn out and could not be relighted while still in the jar. Priestly discovered that a plant can survive indefinitely within a jar. Thus, he tried placing a plant into the jar with the burning candle. The candle went out as before and could not be relit right away. Priestly waited several days and tried again. The candle could be relit! The plant had restored the air inside the jar! (Do not try the next series of experiments since it harms animals!) Next priestly investigated what would happen to animals. He found that a mouse placed inside a sealed jar will eventually collapse. However, a mouse can survive in a sealed jar with a plant since the plant restores the air. Priestly was the first to demonstrate that oxygen is necessary for fire and animals but that given time, plants can create oxygen, allowing fires to burn and animals to breathe.
Submitted by irene on Sat, 2006-07-29 13:14.
Blow through a straw into bluish liquid and watch it turn green then yellow before your eyes. Put some plants into the yellow liquid, leave it in a sunny window, come back the next day and the liquid is green. What if you leave the plants in the dark? What if you put some pond snails in? What if you put both pond snails and plants? What’s going on?
The liquid is bromthymol blue (BTB) a non-toxic acid-base indicator that can be used to indirectly measure levels of dissolved carbon dioxide (CO2). The amount of CO2 in a solution changes the pH. An increase in CO2 makes a solution more acidic (the pH gets lower). A decrease in CO2 makes a solution more basic (the pH gets higher). The reason for this is that carbon dioxide that is dissolved in water is in equilibrium with carbonic acid (H2CO3).
CO2 + H2O ↔ H2CO3
In any solution, while the majority of CO2 stays as CO2, some of it is converted to H2CO3, turning the solution slightly acidic. If CO2 is added to the water, the level of H2CO3 will rise and the solution will become more acidic. If CO2 is removed from the water, the amount of H2CO3 falls and the solution becomes more basic. Thus, acid-base indicators such as BTB can indirectly measure the amount of CO2 in a solution.
For more than you ever wanted to know about carbonic acid, see the Wikipedia article on carbonic acid. For the example lesson plans developed by Bob Culler through Access Excellence at the National Health Museum. For a great time lapse video showing BTB color changes using elodea and snails, see Activity C13 from Addison-Wesley’s Science 10 curriculum.
- Bromthymol blue (BTB can be ordered from any science supply company such as Flinn Scientific $9 for 1 liter 0.04% BTB solution).
- Several 2 liter soda bottles
- Test tubes
- 500 ml beakers or disposable plastic or paper cups
- Water (since the pH of tap water varies, you may wish to use distilled water for your master BTB solution)
- Drinking straws
- Plastic wrap
- Pond snails
- Before the lesson, the teacher should mix a master BTB solution in one or more 2 liter soda bottles. For each 2 liter bottle, mix 120 ml 0.04% BTB with 1800 ml water. The end result should be a medium blue master BTB solution, dilute enough to be safe for plants and snails but dark enough to see the color changes.
- Pour 200 ml diluted BTB in a beaker or cup.
- Take a deep breath then blow bubbles in the BTB solution through a drinking straw. What happened? Why?
- Set up a test tube rack with 3 tubes. In tube #1 put unbubbled BTB solution (blue). In tube #2 put bubbled BTB solution (yellow). Tubes #1 and #2 will be your comparison tubes. In tube #3 you have a choice of what to do. Choose one option from each of the following columns:
|bubbled BTB (yellow)
||spring of Elodea
||Sunny window/bright light
|unbubbled BTB (blue)
||5 pond snails
||Dark closet/drak heavy cloth
||both Elodea and 5 pond snails
- Make a hypothesis about what will happen to your tube.
- After 24 hours, check the color of your tube. What happened? Why?
Submitted by irene on Sat, 2006-07-29 13:28.
Bubbling Yeast: Thanks to Ellen Loehman for creating this image.Yeast are a single celled fungi that are a great model organism for studying respiration in the classroom. The species Saccharomyces cerevisiae is commonly used for leavening bread and fermenting beer but other species such as Candida albicans are known to cause infections in humans (vaginal yeast infections and diaper rash being the most common). In this investigation, students fill the bulb of a disposable pipet (eyedropper) with yeast, then submerge the pipet in a test tube of water. They can then measure the rate of respiration by counting the number of bubbles of carbon dioxide gas that emerge from the tip of the pipet in a certain length of time. By varying the temperature and the nutrient source, students can discover what variables affect the rate of respiration in yeast. By submerging the pipet in bromthymol blue (see Colorful Respiration activity), students can identify the gas being produced as carbon dioxide.
Submitted by irene on Sat, 2006-07-29 13:35.
Raising trout from eggs to fry in the classroom is a fabulous way for students to observe and study the life cycle of vertebrates and simultaneously learn about threatened species in local watersheds. Many states have programs where teachers and students raise trout in their classrooms in partnership with the Department of Fish and Wildlife for later release into a designated lake, creek or river. Described here is information for teachers on how to partner with state agencies, fish hatcheries, and local fly-fisher groups to raise rainbow trout in the classroom. A worksheet for the trout release field trip is provided. Best of all, many Trout in the Classroom Programs are fully supported by local fly-fisher groups and the California Department of Fish and Game (such as the California program that I participated in), and thus there is no materials cost to the teacher beyond the costs of organizing the trout release field trip at the end of the project.
Submitted by irene on Thu, 2006-08-03 08:45.
What drives the motion of the Earth’s tectonic plates? Partly, it is convection, the process by which heat energy is transferred by currents in a liquid or gas. Convection currents within the mantle carry tectonic plates along with the slowly moving mantle like giant rafts carried along by a current in a river. To help students understand this idea, soapy water in a pie pan is heated from below and convections currents can be observed forming and moving in the soapy water. Several prelude demonstrations help students recognize that hot things rise and cold things sink.
Submitted by irene on Wed, 2006-08-09 08:56.
In response to a question on ways to teach electron configuration to students, here's a model I used with my 8th graders. We had been using beans to represent and build 2D models of atoms (green lentils = electrons, white beans = protons, black beans = neutrons). I made a handout for them to help them understand the idea of where electrons like to go when they are added (download it at the bottom of this page).
Submitted by irene on Sun, 2007-02-04 13:25.
When I suddenly fall ill, or otherwise don't want to take 10 hours to plan a sub lesson, I usually go online to http://puzzlemaker.school.discovery.com/ and plug in some vocab words for some puzzles (they have some pre-made banks of words also!)
I make four puzzles using the exact same list of words. I usually start them with the word search (even non-readers can do this!) then go on to word scramble, then crossword. This because they need to know the words pretty well by the time they get to the crossword - also, the word search has the word bank on it.
Submitted by csgreen on Sat, 2007-03-10 20:05.
Please click "Add Child Page" to recommend videos to show in a science classroom. Please include the following info: (and attach study guide please if you have it!)
- Distributor (PBS, National Geographic, etc.)
- Where found (Berkeley Unified Digital Library, Explo Library, Blockbuster, Netflix, Etc.)
- Science Concept Targeted (DNA ethics, volcanoes, Bad Science)
Submitted by csgreen on Sat, 2007-03-10 20:16.