This lab will demonstrate the circadian phototaxis of Chlamydomonas. Some strains of Chlamydomonas (ex. strain 124mt-) show a phototactic response which is controlled by a circadian clock. About a week before the lab, you will need to entrain 3 cultures of Chlamydomonas in a 12 hr.light / 12 hr.dark cycle and another 3 cultures in a 12 hr.dark / 12 hr.light cycle. After 7 days of incubation and entrainment, the students will put the cells in a mini-phototaxis chamber (instructions for assembling are below). The phototaxis chamber consists of 2 small lights glued to a microscope slide with wires connected to a DPDT switch and a 3-volt battery source. The microscope's illuminator is covered with a piece of red cellophane. To demonstrate phototaxis, a drop of cells from the L/D batch is added to the slide with a coverslip and spacer added. One of the lamps is turned on. The "diurnal" cells will swim toward the light. If the opposite light is turned on, the cells will swim in the opposite direction. To demonstrate the circadian nature of the phototactic response, cells from the D/L culture can be put on a slide at the same time of day as the L/D culture. The D/L cells will not swim to the light because they are at the trough of their circadian cycle whereas the L/D are at the peak. This activity works well as a demonstration and is particularly effective with a video microscope.
(This lab is the idea of Dr. Anthony Moss at Auburn Univ.)
For a more detailed description of the lab, click on the hand.
Start growing your garden variety lima beans about two weeks before the lab date. The plants, after two to three weeks of growth, exhibit nice large vertical leaf movements and are fairly hardy. The plant leaves are attached by rubber cement, to a string and pulley system that is hooked up to a mechanical recording device. The recorder shows a distinct up and down leaf movement. One significant problem with the plant is that it is continually growing and when the plant gets to a certain size it no longer has easily recordable movement. When originally planting the beans, due to this problem, it may be wise to stagger their planting dates by a few days to have a continuous supply of plants at the correct size. The mechanical drum also has some small problems. The fountain pen has to be cleaned daily in order to keep it running. The materials and directions needed for making the drum are listed in a link.
For more information on the set up of the plants, click on the hand.
For more information on making the mechanical drum, click on the hand.
This lab is designed around the idea that a cockroach exhibits circadian rhythms in terms of activity levels. A small cockroach race track can be made out of Tygon tubing. Embedded in the tubing is an infrared LED and infrared phototransistor. In other words, when the roach is active it will break an infrared beam (that is does not detect) as it actively circles the tubing.
Two means of counting activity levels were developed. The first is by ordering a photogate kit from Vernier software company (an education software company that mainly designs things for physics teachers) that hooks up to an Apple IIe computer. Why such an archaic computer? All schools have these computers. The IBM could probably be easily adapted as well. The pre-Power MacIntosh, however, seems to present some problems. An interface card is required and the card is beyond the price of most high school teacher budgets.
A program was written to record and keep track of the roach activity.
The second method of activity recording is a strictly mechanical device. The recorder is a simple circuit where every time the infrared beam is broken it causes a relay arm to move. When the mechanical recorder is hooked up to the drum designed for the plant experiment, a simple and inexpensive means of recording activity is available. The rough instructions for building the circuit are in the link. The directions are designed for a person who knows nothing about circuitry, however be warned that it does require at least an hour to build the device. This may be a perfect for a student looking for a science fair project. There are other possible mechanical devices using an infared beam available. Try the physics teacher!! The only difficulty with some of these devices is that they do not quantify the activity as it relates to time of day. However that can be compensated for a little bit by just resetting the counter at designated times.
NOTE: A teacher has tried this in the classroom already and found that it was a good activity for a group of students to work on. This is a good lab because it teaches the students how science is not always a "cookbook" process--the experiment requires tinkering and several hypotheses may be made before an experiment works.
For more detailed information on the cockroach set-up, click on the hand.
For more detailed information on the mechanical event recorder,
click on the hand.
For more detailed information on the Apple IIe event recorder, click on the hand.
This lab will demonstrate the circadian rhythm of conidiation in Neurospora crassa . Neurospora with the band mutation (available from the Fungal Genetics Stock Center) will grow across an agar surface at a constant rate and produce bands of differentiating aerial hyphae which are distinct from the surface hyphae on either side. The cycle recurs approximately every 22 hours. Neurospora can be grown in a race tube or large Petri dish. Because of the problems associated with making race tubes, we grew Neurospora in Petri dishes. The agar used to grow the mutated Neurospora is a recipe that is very specific for allowing the fungus to grow in such a way that the bands appear. We tried a commercially prepared agar which did not give good results. In fact, our fungus even outgrew the dish within a few days. The teacher should be aware of the proper safe procedures for handling fungal spores. We would recommend this lab as a demonstration so that students are not involved with handling the fungi.
For a detailed description of this lab, click on the hand.
(This lab was designed by Dr. Jennifer J. Loros and Dr. Jay C. Dunlap of Dept. of Biochemistry of Dartmouth Medical School.)
This lab will demonstrate the circadian eclosion of fruit flies (Drosophila pseudoobscura ). The teacher should obtain a culture of Drosophila two weeks before the experiment. The flies should be placed in fresh media in 4 culture bottles. Entrain them during growth in light/dark cycles until pupae have formed. After the entrainment, place 1 bottle in constant light, one in constant darkness, one in a warm room, and one in a cold room.
The students should shake eclosed adults from the bottles into a funnel leading to the jar with oil at various times throughout the day (the work may be done by several classes and the data shared.) They should count the flies trapped in the oil for the samples kept under different conditions and graph the data. This lab should serve to demonstrate that rhythms are endogenous and temperature compensated.
(This lab is the idea of Dr. Paul Hardin at Texas A & M.)