BIOLOGY • CLASSIFICATION OF MARINE ORGANISMS

Title: Using a Dichotomous Key in the Identification of Seagrasses

(Classification of Marine Organisms)

Grade Level (s): 6 - 7

Introduction: Biologists identify organisms by physiological and structural characteristics. Thousands of years ago, people formed simple classification systems by grouping living organisms by similar characteristics. The science of classification of organisms into orderly groups by characteristics and evolutionary history is termed taxonomy. In the fourth century B. C., the Greek philosopher Aristotle classified all living things as plants or animals. He grouped animals as either land, water or air dwellers and plants by their stem differences. In the eighteenth century, Swedish scientist Carolus Linnaeus developed a system of classification of living things by similarities in form and structure. Prior to Linnaeus, biologists realized that Aristotle's classification system was inadequate and common terms may not describe species accurately from one locale to another. For example, Portuguese man-of-wars are not specifically found in Portugal, nor are they men. The common term for the jellyfish is not even accurate since they are not fish. Linnaeus is credited for two-part names, or binomial system for identifying organisms. A species is a group of similar offspring that can reproduce living, fertile young, and is named by the genus and species identifier. The genus is capitalized and appears first in the species name and both names are written together in Italics or underlined. For example, humans belong to the genus, Homo, and the species identifier sapiens. The species name for humans is therefore, Homo sapiens. A species name may be descriptive of the organism, as in the amoeba Chaos chaos which is constantly changing its shape. In some instances, names are given to honor a person. For example, Linnaeus's favorite species of northern region flower, Linnaea borealis. Borealis means northern. One method of sorting and identifying organisms in the field is the use of a dichotomous key that uses pairs of descriptions to identify an object.

Students will learn that there are many different species of seagrasses, even though the name implies that they are all the same. Seagrasses are a diverse group of marine flowering plants with true roots, leaves and stems. The students will use a dichotomous key to identify the species name of several Florida marine seagrasses.

Learner Objectives:

• Students will understand that living things are sorted for convenience and identification
  
  
• Students design and use a dichotomous guide based on structural characteristics of an organism

Sunshine State Standards Correlation: Science: SC.G.1.3.3

Competency-based Curriculum Correlation: Science: Sci.M/J1 II-A; Sci.M/J II-A, Sci.M/J1 I-A, Sci.M/J2 I-A

Materials

Field Guide Seagrass Identification Key
Seagrass Sketches
Scissors
Glue/tape

Activity Procedures:

1. Ask students to look around the classroom and give suggestions as to how they would group students for a dynamic water snorkeling activity. The end groups, however, will need to be limited to two snorkeling buddy members. (Students may initially start by dividing groups by sex, then hair color, etc.)
   
   
2. Explain the importance of using classification systems in science, especially biology. Introduce a dichotomous key as a means of identifying species.
   
   
3. Inform students that they are about to embark on a voyage and they have to find the area that is diverse in seagrasses where there will be an abundance of fish to view on their snorkeling trip.
   
   
4. Divide class into cooperative learning groups of three or four students.
   
   
5. Give groups a copy of the seagrass field guide with identification key.
   
   
6. Students are to use the field guides to identify the different types of seagrass they will observe on their adventure.
   
   
7. Students should cut and paste the seagrass sketch beside the identified name.
   
   
8. Groups should exchange their final products and decide if other groups have accurately identified seagrasses. They should be sure to include feedback if there is disagreement with the other groups' final products.

Assessment:

1. Students create a dichotomous key of marine fish. (Some common Florida marine fish pictures are attached.)
   
   
2. Visit a local beach and use the field guide identification key to name the seagrasses observed.
   
   
3. Drag a collecting net along a side of the boat to gather and identify marine samplings of floating seagrasses. This can be constructed by using pantyhose and wire hangers.
   
   
4. Make a dichotomous key for catches that are not seagrass.

Activity Extensions:

1. Seagrasses are important for the maintenance of life in the ocean. They provide food and shelter for a large number of marine organisms. Think about the last time you walked through or saw a bed of seagrass near the ocean shore. Write an essay describing the importance of seagrasses to the existence of marine life. (Language Arts)
   
   
2. Describe the impact to the economy if hotel developers were not allowed to build their properties on the beach in order to preserve seagrasses in the water. (Social Studies)

Vocabulary: classification, taxonomy, species, dichotomous key, binomial

References:

Florida Fish and Wildlife Conservation Commission - Bureau of Protected Species. Identification of Florida's Seagrasses. [Online] Available
http://www.state.fl.us/fwc/psm/habitat/grassid.htm

Johnson, G. B. (1995). Evolution and Natural Selection . In K. Harris, L. Jegerlehner, K. Timp, J. Leland (Eds.), The Living World (pp. 171-196) Dubuque, Iowa: Wm. C. Brown Publishers

Odyssey Expeditions. [Online] Available
http://www.odysseyexpeditions.org/fish.asp