Chapter 9

By Eugene F. Provenzo, Jr. and Cory A. Buxton

Life in a Drop of Water







Florida Sunshine State Standards Benchmark
SC.A. 2.2.1Materials may be made of parts too small to be seen without magnification.
SC.F. 1.2.3Living things are different but share similar structures.
SC.G. 1.2.7Variations in light, water, temperature, and soil content are largely responsible for the existence of different kinds of organisms and populations.




Microscopic Aquatic Life


You know that many organisms live in the water – fish, dolphins, whales, seaweed, or manatees might come to mind. Most of the organisms that live in the water, however, are too small to see with the naked eye, and we generally do not think about them. Plankton are microscopic, single-celled aquatic organisms with limited swimming abilities. They are classified into two groups: phytoplankton (plants) and zooplankton (animals). Phytoplankton are very important to other larger aquatic organisms as well as to people. They are the basis of nearly all aquatic food chains and also produce about 80% of the oxygen we breathe. Phytoplankton, like all plants, make their own food through photosynthesis.






Phytoplankton occur in many shapes, including disks, rods, chains, and spines. There are three major types of phytoplankton: diatoms, dinoflagellates, and coccolithophores. Diatoms float and usually live where the waves and currents push them around. Dinoflagellates are plankton with two tails (flagella) that beat to push the organism around. Coccolithophores are spherical and covered with chalky discs that shed off the organism and sink to the ocean floor.

Zooplankton are floating or weakly swimming animals that rely on water currents to move. They are usually larger than phytoplankton, ranging from microscopic creatures like rotifers to easily visible jellyfish. Zooplankton are also an important part of aquatic food chains. Some zooplankton are primary consumers, eating phytoplankton, and others are secondary consumers, feeding on other zooplankton. Zooplankton are the favorite food of many marine animals such as fish and baleen whales.

Is it possible for you to see phytoplankton or zooplankton? In the following activity, you will use your naked eye, a magnifying glass, and a microscope to find out.




Activity: What’s in a Drop of Water?


Find out what organisms you can see in a sample of water


Materials Needed


  • three water sample jars
  • samples of fresh and salt water
  • a permanent marker
  • magnifying glass or hand lens
  • microscope
  • petri dishes, baby food jars, or other small clear or white colored glass containers
  • microscope slides and cover slips
  • copy of Life in a Drop of Water Activity Worksheet on page 57


Follow these steps:


  1. Choose a location or locations to collect your samples. Ideally, collect a fresh water sample from a stream, another from a pond or lake, and a saltwater sample from the ocean.

          Note: It may be necessary for the teacher to collect samples in advance of this activity or ask students to bring water samples from the surrounding area.      
  2. Collect 1-liter samples from each water location. When collecting, dip your container into the water at the water’s edge making sure to get any algae or plant life present. Quickly remove the container to ensure that most of your organisms do not escape.
  3. Use a permanent marker to write the location and date for each sample on each “water sample” container.
  5. Bring samples back to the classroom for observation.
  7. With your naked eye, observe, sketch, describe and count the type and number of visible organisms found in each sample. Record your data in the naked eye column of the worksheet. The samples can be transferred to a petri dish, baby food jar, or other shallow clear or white container. Containers can also be placed on a white sheet of paper for easier viewing.
  9. Next, observe the water samples using a magnifying glass or hand lens. Again, sketch, describe, and count the type and number of visible organisms found in each sample, recording your data in the magnifying glass column of the worksheet.
  11. Finally, observe the water samples using the microscope. Again, sketch, describe, and count the type and number of visible organisms found in each sample, recording your data in the microscope column of the worksheet.
  13. Discuss your observations in groups and as a class.
  15. Create a graph to compare and analyze your collected data.




Have students review the following summary questions:


  1. What types of animals did you find in the pond water?
  3. Did the type of water sample change the number and kinds of organisms found? Why or why not?
  5. Would you expect to find the same organisms in each sample all year round? How could you test your prediction experimentally?




Exploring One Water

Look at the following clip of mosquitoes spreading the malaria infection to humans.




Mosquito Larvae





Consider the Following Poem


“Eventually, all things merge into one, and a river runs through it. The river was cut by the world’s great flood and runs over rocks from the basement of time. On some of the rocks are timeless raindrops. Under the rocks are the words, and some of the words are theirs. I am haunted by waters.” —Norman Maclean, A River Runs Through It, 1989



Extension Activities


Elementary School Students


Some of the most beautiful scientific drawings ever created are the work of the German scientist Ernst Haeckel (1834-1919). Many of them are of microscopic animals found in seawater such as Radiolarians. Have students go online and collect a portfolio of his work, finding out who Haeckel was and what were the subjects of his illustrations.





Have students create a slide show using Power Point™ or a bulletin board display of Ernst Haeckel’s drawings of microscopic sea life.



Middle School Students


Microscopic sea animals such as Radiolarians and various other planktons have the same shapes and structures as soap bubbles made with soap bubble frames. Have students construct a square soap bubble frame using pipe cleaners or light-weight wire. When dipped in a soap solution, the bubble formed assumes the same shape as certain types of Radiolarians. Why does this happen? A soap bubble is a minimal surface. It takes the most physically efficient form possible—free standing, this is a sphere. When stretched on a square frame this shape is a trapezoid bubble with a square bubble in the center. A triangular frame gives a triangular trapezoid.






A video recording with instructions for completing this activity can be referenced at the One Water curriculum website.


Have students compare these shapes with the following drawings of Radiolarians made by Ernst Haeckel. Have them try to conclude why these shapes are the same. (The Radiolarian’s skeleton takes the most energy efficient shape possible, the same as a soap bubble).







Have students create a slide show on Power Point™ of Radiolarians as compared to soap bubble frames.



Secondary School Students



Plate 71 from Ernst Haeckel’s Kunstformen der Natur (1904), showing Radiolarians of the order Stephoidea.


The architect Peter Stevens in his book Patterns in Nature has shown that the stress lines found in rocks, dried mud, and even the cracked surface of an ancient Chinese vase follow the most efficient and stable lines of stress possible. In general, when most elastic substances are placed under stress, they will fracture into hexagonal shapes, meeting one another at angles of approximately 120 degrees. Individual snowflakes and the cells of plants and animals assume this basic hexagonal form. The cells in the eye of a common housefly take on these hexagonal shapes. Even the shells of tortoises have hexagonal configurations that repeat the shapes and forms that soap bubbles can take. As discussed above, the skeletons of the tiny sea creatures, Radiolarians, are remarkably similar in form to soap bubbles formed with differently shaped wire frames. Have students go online to research and write a 3 to 4 page double-spaced paper outlining how patterns are found in nature, even among the smallest animals and plants found in fresh water ponds or the ocean.





Have students create a Point Point™ presentation, a website or short film on patterns found in nature. Keywords that will help them on Internet searches include Darcy Wentworth Thompson, On Growth and Form, and Fibonaccian sequences.