LIBERTY SCIENCE CENTER
INVESTIGATION AND IDENTIFICATION OF MARINE PLANKTON
OBJECTIVES
To study live plankton using a microscope
To distinguish between phytoplankton (autotrophs) and zooplankton (heterotrophs)
To learn to identify organisms using a biological key
MATERIALS
Compound (or digital) light microscopes
Microscope slides and cover slips
Eye droppers or disposable pipettes
100mL beakers
Live plankton samples – collected and refrigerated (Alternative – use freshwater plankton.)
Marine plankton handouts and/or plankton identification books
2-3% solution of methyl cellulose (or any other viscous solution for immobilizing live plankton,
optional)
PROCEDURE
You may want to have multiple plankton identification worksheets per student available. If you like, ask
students to identify at least a certain number (5, 7, 10 – based on how much time you have) of
organisms.
1) Prepare a wet mount slide by adding one drop of water from the sample to a clean microscope
slide. Be sure that there is some visible material in the drop of water. Add a cover slip.
2) View under low power (100x). When you find an interesting organism, keep it in view. Use a
higher power lens if necessary for smaller forms. If fast-moving organisms are difficult to view,
add a drop of methyl cellulose solution.
3) Sketch each organism found in the plankton sample on the accompanying chart and add
information about its identification, manner of acquiring nutrition, and whether it spends its life
as a planktonic organism (holoplankton) or is a larval form of a larger animal (meroplankton).
Optional: In addition to having students freely explore the plankton sample, set up a few microscopes as
stations with pre-chosen organisms for them to observe or draw. Have students rotate through the
stations throughout the lesson.
SAFETY CONSIDERATION
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Have a broken glass receptacle ready in case of broken slides. Use plastic cover slips if possible. Have
students wear gloves when handling the plankton sample and wash hands after the lesson; samples will
contain bacteria as well as plankton.
QUESTIONS
1) Which types, autotrophs or heterotrophs, do you find more of in your sample? Do you believe
this is the same in nature? Why or why not?
2) What organism or organisms were most abundant in your sample?
3) What do you think determines how much plankton there is in the water?
4) Why is phytoplankton particularly important to a healthy and productive aquatic environment?
5) What types of structures do zooplankton use for locomotion?
6) How many kingdoms are represented in the sample? List them.
7) Explain why it is challenging to classify planktonic organisms. Use examples from your
observations.
EXTENSION
Phytoplankton are eaten by zooplankton (such as krill), or by small invertebrate filter feeders
(such as mussels and clams). These are fed upon by larger invertebrates, fish, and marine mammals.
Have students choose a favorite marine animal and research what it eats. They should then draw the
food chain or web showing what their animal eats, what that food source consumes itself, and so on.
How many of your diagrams begin with phytoplankton?
BACKGROUND
Plankton presents a fascinating, and initially, confusing miniaturized tableau of life in water.
Microorganisms present a seemingly infinite contrast of form, function, evolutionary design, and motion
which will be sure to captivate students. Here are so many new things to see and an extraordinary new
world to explore.
Identification of marine plankton can be challenging as there are many changes that occur from
the egg to larval forms to the adult in most multi-cellular species. In addition, many of the unicellular
forms take on both plant and animal characteristics. For example, there are diatoms which contain
chlorophyll yet can move under their own power. There are also some planktonic animals, such as
foraminifera, that contain photosynthetic symbionts.
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A 2-3% solution of methyl cellulose (available from most biological supply houses) should slow
down the activity of most plankton for better observation.
There are numerous biological keys for identification listed in the resources section.
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