Biology in Daphnia
Teachers Information. qxd
Teacher/Lecturer A1. 21L PRIMARY
Activity 1 . 21 Truly does caffeine influence heart rate?
• • To investigate the result of caffeine on the heart rate of Daphnia (water fleas). To highlight trial and error and examinative assessment objectives.
Any student proven to suffer from photosensitive epilepsy needs to be warned just before a stroboscopic light can be used. Flickering lights in the range 5–30 Hertz are thought to trigger seizures in hypersensitive individuals.
Paperwork on the procedure
The student bed sheet that occurs with this activity guides pupils through organizing and writing up this investigation. After students plan the analysis their strategies can then be talked about with the group. To support significantly less able students, or to assist with the business of practical work for a big group, students could be provided the functional procedure by the end of these records (see page 3). It provides basic summarize and will have to be read by simply students before beginning the practical with decisions and modifications made since appropriate. The method is for a simple experiment; more able pupils could complete a more complex research using serial dilutions, with several Daphnia used each and every concentration. Remember that high concentrations of caffeine can be fatal for Daphnia. The Daphnia hearts happen to be fairly very easily seen yet counting the number of beats could be difficult. Keeping track of is easier if each heart beat is registered by tapping a pen on a piece of paper and checking up the pad marks after the specified time. In addition , chilling the Daphnia before the test may help sluggish their heartrate. An ICam above the eye-piece of the microscopic lense to project an image of the slide onto a large screen may also help with counting. Engender, in the Log of Natural Education (1997) 31, pp. 253–255, gives a method by using a stroboscope to freeze the motion. Utilization of the stroboscope may conquer the problems of counting quicker heart costs. However , we would not suggest this method. Setting the light sources and strobe is challenging. It is very challenging to freeze the motion and viewing which has a strobe lumination can cause vision strain and dizziness. An easier approach should be to count the pace at which the legs beat. This rate is proportional to the level at which the heart beats. A dissecting microscope with a source of light under the level works well for this kind of experiment. In order to avoid the Daphnia from overheating while on the microscope turn off the microscopic lense light between observations and use a warmth sink – a tooth cavity tile stuffed with iced normal water placed on the microscope within the slide. Using pond water/Daphnia culture option is recommended for the control group and to melt the caffeine as this may give more valid outcomes and be less stressful towards the Daphnia. In distilled normal water the heartrate may rise due to deficiency of oxygen.
Edexcel practical elements created simply by Salters-Nuffield Advanced Biology, ©University of You are able to Science Education Group.
Teachers Guideline. qxd
Teacher/Lecturer A1. 21L CORE
Activity 1 . 21 Truly does caffeine have an effect on heart rate?
In the trial with the experiment caffeine was used in 0. 1% and 0. 5% w/v with no unwell effect. By 1% the Daphnia ceased swimming following 5 minutes. It is strongly recommended that a ‘blind' study is performed. This means that anybody counting the heart rate is definitely unaware whether or not the Daphnia is in normal water with or perhaps without caffeine. It has been proven that viewer expectations effect the result. It is difficult to acquire clear-cut comes from this research and significant differences among treatments is probably not found. The sets of results under indicate the kinds of benefits that can be anticipated. It should be impressed upon college students that it is not important if they do not get dissimilarities between treatments. Indeed, the experiment delivers plenty of possibility to evaluate seriously the technique used and really target attention for the experimental...