Education on a Halfshell

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Education on the Halfshell:
Writing a Descriptive Essay

By: Cassie Zanca

Download the entire lesson (PDF FILE: 458K)

Lesson Goal

The students will learn how to write and use a descriptive essay as a means of identifying an organism or object.

Lesson Objective

The student will write a descriptive essay on a seashell.

Background Information

Below you will find a short, descriptive essay on Polinices duplicatus. This is just an example of how a descriptive essay could appear.

The shell’s scientific name is Polinices duplicatus. It can be commonly found in the shallow waters of Galveston Bay and the Gulf of Mexico. This particular shell was once the home and a source of protection of a snail. It belongs to the mollusk class gastropoda. It is also a univalve, which means that the shell consists of a single valve or piece.

The size of this shell is 3.5 cm long and 4 cm wide. It weighs 22 grams. The shell is round. and has an array of colors that include shades of brown, very light purple, orange and tan. It has a very smooth texture. This shell is right-handed, which means the shell coils to the right. It has a hollow interior and the bottom of the shell is white with one round brown spot.

Which of the shells below was just described?

   A B
C D
(For Answer, see bottom of the page)

The example above is a style of writing called technical or descriptive writing. Descriptive writing is "writing that paints a colorful picture of a person, a place, a thing, or an idea using concrete, vivid details." To write effectively, one should keep some things in mind. The use of details and the organization of these details into significant patterns are great descriptive techniques. In the example above, details such as quantitative and qualitative descriptions help the reader select the right shell.

Another technique used by writers is organizing details in order of importance, from the least important to the most important. In the example above, the details described would require students to have researched the topic beforehand. The description includes details that require readers to experiment by measuring and weighing to help them figure out the correct shell. Finally, the last descriptions are qualitative characteristics, such as color, that the reader can use to identify the shell being described.

Topical sentences are vital to an effective description. One can place a topical sentence at either the beginning or the end of a paragraph, depending on the outcome one is trying to achieve. The example above has the topical sentence at the end of the paragraph. Everything in the paragraph might seem awkward the first time one reads it until one gets to the last sentence. The final sentence is the culmination of all details, allowing the reader to understand the purpose of the description.

It is important not to overwrite. Keep descriptions short and simple, and use words with which people are familiar. A thesaurus is a great resource for descriptive writing. One should also use quantitative descriptions, which is a description using measurements. In the description of the above shell, such quantitative information as the length, width, and weight of the shell is provided. Another excellent technique is to use qualitative descriptions. Qualitative descriptions are those that describe special qualities. In the example above, colors, texture, and shape are qualitative descriptions. These guidelines will enable one’s writing to be effective.

Teacher Preparation

In this activity, individual student will choose, an oyster shell about which to write a descriptive essay. Each student is to choose a different shell or picture (see the website). Additional materials, such as rulers, color cards from paint stores, triple beam balances, etc., may be valuable for writing preparation.

After students are finished writing their essays, it will be necessary to match each essay with the shell described. Therefore, while students are writing their essays, label ziplock bags with numbers. When students are finished with their shells, place them in the numbered bags, noting in your gradebook the bag number that holds each student’s shell. This will allow you to later distribute student descriptive essays and see if they can be used to correctly identify a particular shell. Don’t let a student see the number of the ziplock bag that you place their shell in, since this will give them unfair advantage in picking out their shell.

Option 1. Give the students’ original essays back to them. Place the ziplock bags in a central location so that as students read their essays, they can choose potential matches from the stack of shells. If the student cannot identify their own shell, then the essay should be rewritten to reflect a more accurate description.

Option 2. Randomly distribute the essays to the students ensuring that no student receives his or her own paper. Place the ziplock bags in a central location so that as students read their assigned descriptive essays, they can choose potential matches from the stack of shells. If an essay is written correctly, the shell can be identified.

Blackline masters
     BM 1: Descriptive Essay Instruction Sheet & Observation Form (PDF, 96K)

Alternative Assessments

Given a descriptive essay, have the students draw to scale the object of the essay.

Given a written descriptive essay, have the student make an analogy to another object that possesses some of the same characteristics. Example: essay on how the elbow works would be similar to a description of a simple lever device.

Create a concept map from student descriptions.

Answer Key(s)
No answer key is necessary. See TEACHER PREPARATION for the way to check for accuracy.

Extension Ideas

Using several descriptive essays, such as an oyster, crawfish, redfish, and etc., write one scene for a play that take part in a marsh.

Use the decriptive essays written in class along with other art work to create a mural.

Resources and web links

Timme, Stephen, 1991, Association for Biology Laboratory Education website, How to Construct and Use a Dichotomous Key, accessed 02/16/01, http://www.zoo.utoronto.ca/able/volumes/vol-12/7-timme/7-timme.htm

Description: An excellent web-based activity on the construction and use of a dichotomous key that also describes the use of a dichotomous key in the field and provides a key for prairie plants.

Frontier High School, Red Rock, OK, The Dichotomous Key, accessed 02/16/01, http://pc65.frontier.osrhe.edu/hs/science/hbotkey.htm

Description: Provides instructions on the two methods of constructing a dichotomous key as well as several online dichotomous keys. Grade level: High School.

Detka, Jon , California State University at Monteray Bay, Designing and Using a Dichotomous Key, accessed 02/16/01, http://www.monterey.edu/students/Students_D-H/detkajon/world/ron/dichotdesign.html

Description: Students first construct a simple dichotomous key and then use a basic key to identify some of the native plants and the most unwanted invasive weeds of California. Grade level: 3-5.

Santa Cruz Productions, Wastewater Filamentous Bacteria Dichotomous Key, accessed 02/16/01, http://home1.gte.net/vsjslsk1/gramstainflowchart.htm

Description: A completely web-based dichotomous key designed to assist students in identifying wastewater bacteria.