Protozoa- Exceeding the Speed Limit
AUSTRALIAN CURRICULUM ALIGNMENT:
Classification helps organise the diverse group of organisms
- Classifying using hierarchical systems such as kingdom, phylum, class, order, family, genus, species
Many protozoans are fast moving. Ciliates are particularly fast and often difficult to look at under a microscope. In order to observe and study these organisms, biologists have to ‘slow’ them down. There are two popular methods that can be used. Both methods involve protozoan samples being placed on a slide with a viscous solution added. Thick (viscous) solutions, such as Methyl cellulose or Protoslo, are effective in restricting the movement of the organisms’ cilia and flagella.
Methyl cellulose reacts when mixed with water; the grey/white powder swells and transforms to develop a viscous solution; similar to the consistency of syrup. A dilute solution of 3% makes it difficult for microscopic organisms to move but maintains their osmotic balance so that the organisms are not harmed. Methyl cellulose solution maintains the natural appearance and behaviour of organisms, whilst slowing the movement. Protoslo can also be used - this comes in a dropper bottle ready for use, no mixing required.
METHOD- STUDENT ACTIVITY:
- Make a circular ring of the methyl cellulose solution in the centre of a clean microscope slide using a plastic pipette.
- Place a sample of the organism culture in the centre of the methyl cellulose ring using a pipette.
- Partially mix the methyl cellulose and culture by gently pressing a coverslip over the microscope slide.
- Using your microscope, observe how the organisms behave immersed in the methyl cellulose.
- * If using Protoslo, simply add 1-2 drops directly onto the culture sample on the slide, and place a coverslip over the top.
OBSERVATION AND RESULTS
Using the diameter measurement of the microscope field students can calculate the protozoan’s speed in km/ph; using a stopwatch to time the ciliate crossing the microscope field. Students will find the organisms move surprisingly fast and will be able to compare the time it takes an organism to move the same distance through a methylcellulose/Protoslo solution.
- 45 mins
- Wear appropriate personal protective equipment (PPE).
- Know and follow all regulatory guidelines for the disposal of laboratory wastes.