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How to Observe a Stagnant Pond Water Slide and Distinguish Viable Life Forms

One of the most interesting environments to examine with a microscope is stagnant pond water. This type of water is easy to collect and offers a great variety of microscopic organisms. Although a drop of stagnant water contains many organisms, it's often difficult to determine living organisms from other matter, such as plant debris. Use a few basic microscopy techniques to distinguish viable life forms in a drop of stagnant pond water.

Things You'll Need

Jar
Screwdriver
Eye dropper
Microscope slides
Biological microscope
Pencil
Paper

Instructions

- 1
  
  Any source of stagnant water can be used.
  
  Collect fresh pond water samples. Microbial organisms have short lives and, if cut off from their oxygen supply, they die. Collect a small amount of stagnant pond water in a jar. Use a screwdriver to punch holes in the top of the lid. This provides oxygen for the microbes. Keep the sample away from direct sunlight.
- 2
  
  Use an eye dropper to transfer the pond water to the slide.
  
  Prepare the slide. Use an eye dropper to transfer the stagnant pond water to the slide. Fill the eye dropper to the halfway point. Squeeze two drops of pond water onto the slide. Do not use a glass slip cover. The absence of a slip cover creates an environment similar to the pond, providing room for many of the larger organisms to move around.
- 3
  
  Use the lowest-powered eyepiece.
  
  Set up the microscope. Turn on the microscope's bulb or position the mirror so the microscope's stage is lit up. Position the lowest power eyepiece in the turret. Use the lowest power lens because it provides the widest field of view. Look through the eyepiece and focus the lens. If the microscope has an adjustable light source or condenser, set it at a level that lets the smallest amount of light through the stage while maintaining visibility.
- 4
  Determine non-living life forms. Stagnant pond water contains debris from its surroundings. Most of this debris is in the form of plant matter. Most debris are asymmetrical in shape. Debris appear to float in place. Using a pencil and paper, draw the positions of these debris.
- 5
  
  Always make drawings of any microorganisms seen.
  
  Look for fast-moving organisms. Many microscopic organisms, such as Chlamydomonas or Ciliates, can be seen moving freely through the pond water. Make a drawing of their shape and any noticeable details. The pond water will start to evaporate because of the heat generated by the microscope's lamp. This causes stationary debris to look like it's moving. Actually,, the debris is being pulled toward the edges of the sample as it evaporates. Do not confuse this action with those of a living microorganism.
- 6
  Identify the non-motile life forms. Most life forms in stagnant pond water are slow-moving or non-motile organisms such as Diatoms. Non-motile organisms, such as some forms of algae, remain stationary. Look for a nucleus, which will appear as a round dot either in the middle of the organism or at one end of its body. Many of these organisms will have symmetric shapes.

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