Chlamydomonas Phototaxis Lab

• Materials Needed:
  
  • Chlamydomonas culture, strain CC-124mt- (see instructions below)
    
  • microscope
  • cover slip
  • cover slip spacers
  • 1 small piece of red cellophane to cover the microscope's lamp
  • heavy black plastic trash bag
  • 1 mini-phototaxis chamber (see instructions below)
  
  
• Materials for building the mini-phototaxis chamber
  
  
  • 1 microscope slide
  • 2 pre-focus lamps (Radio Shack 272-1124) (also called 222 lamps)
  • 2 AA batteries
  • 1 AA battery holder (Radio Shack 270-382 A)
  • 1 9-volt battery clip (Radio Shack 270-325)
  • 1 center-off DPDT toggle switch (Radio Shack 275-1545 or similar)
  • 100 cm 2-conductor wire (Radio Shack speaker wire is good)
  • 1 plastic container such as what yogurt comes in (select a brand with a sturdy lid)
  
  
• Additional supplies for building the apparatus
  
  • High heat hot glue gun
  • Soldering iron
  • Needle-nose pliers
  • Wire strippers
  
  
• Building the apparatus:
  
  • 1. Put the batteries in the battery holder, making sure the positive and negative terminals are positioned correctly (look on the plastic for + and - indicators). With this series arrangement, you will be delivering 3 volts to each bulb.

  • 2. Snap on the battery clip to the top of the holder. Solder one wire to each of the 2 middle terminals on the toggle switch. The toggle switch can be oriented in either direction.

  • 3. Cut your 2-conductor wire into 2 50 cm strips. Separate the 4 ends of the wires about 2cm. Using your wire strippers, strip away approximately .5 cm of plastic from each wire.

  • 4. Take one end of one wire and place the exposed wires into the end terminals of your toggle switch. Solder in place.

  • 5. Take one end of the other wire and place the exposed wires into the other end terminals of your toggle switch. Solder in place.
  • 6. The exposed ends of the 2 wires should now be individually soldered onto your 2 lights.

  • 7. Use your hot glue gun to glue one light to each end of a clean microscope slide. The lights should be lying on their sides, facing the interior of the slide. The glue must be very hot for the bulbs to stick to the slide. Notice that the toggle switch is moved to the left, the right bulb comes on and vice versa.

  • 8. Your apparatus is now ready to use, but you will want to put the batteries and switch in the plastic container. Put a 1 cm (diameter) hole in the bottom of the yogurt container (I used the soldering gun to melt the hole since plastic is hard to drill.) The top of the switch can be unscrewed at the nut. Insert the switch in the yogurt container and then tighten the nut. The battery holder can then rest on the inside top of the yogurt container. You will have to make holes for the wires to escape. Close the lid on the yogurt container.

Chlamydomonas culture

		Chlamydomonas Genetics Center
		Duke University
		Department of Biology
		Box 90338
		Durham, NC 27708-0338
		USA

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