Studying Living Organisms

Barbara J. Errington

The Endosymbiotic Theory, OR Eukaryotic and Prokaryotic Feast
Woodrow Wilson Biology Institute

Target age or
ability group:
Biology I.
Class time
One fifty-minute class period.
Materials and equipment: Cultures of prokaryotes and eukaryotes for each lab group
Prepared slides of prokaryotes and eukaryotes
Materials for wet mounts

Teacher demonstration
one light-colored balloon and one dark- colored balloon
ribbon about five inches long

Summary of activity: This exercise is designed to help achieve an understanding of the Hardy-Weinberg Equilibrium without recourse to algebra. Since population geneticists frequently express themselves using algebra, many of their ideas, such as the Hardy-Weinberg Equilibrium, are not accessible to students for whom algebraic thinking is difficult. After participating in this activity, students gain a feeling for the significance of the Hardy-Weinberg Equilibrium without using algebra. The teacher can decide whether this exercise should serve as the entire lesson, or as an introduction to a more rigorous algebraic discussion. Such extensions of the exercise are suggested.
Prior knowledge, concepts or vocabulary necessary to complete activity: Students should have experience with microscopic techniques. They should be familiar with the following terms: prokaryote, eukaryote, heterotroph, autotroph, chemotroph, mitochondria, and chloroplast.

Teacher Instructions

1.Begin the activity with a discussion of some differences between prokaryotes and eukaryotes. Show slides of prokaryotic cells, such as various kinds of bacteria, and a range of eukaryotic cells, such as algae and protozoa. Discuss the similarities and differences. Ask students to suggest ways in which eukaryotes may have evolved from prokaryotes. Use the responses as a springboard for further exploration.

2.Demonstrate the endosymbiotic theory as follows:

  • Place the ribbon, which will represent a single strand of DNA, inside one of the balloons.
  • Place this balloon inside the second balloon and blow both of them up at the same time.

3. Produce a diagram of a prokaryotic and a eukaryotic cell. Copy and distribute to students, and make an overhead transparency of the diagram. Remind students that eukaryotes are organisms with membrane-bound organelles.

Ask, "What may have developed from a prokaryote ingesting a chemotroph?" A mitochondrion. "Why?" Some event may have occurred to keep the chemotrophic organism alive inside the prokaryote.

4.Ask, "Why is the organism taken into a membrane-bound organelle or vacuole?" To protect its own DNA from being digested by the enzymes necessary for it to digest the other organism.

5.Ask, "What may have developed from a prokaryote ingesting an autotroph?" A chloroplast. Remind students that a chloroplast is also a membrane-bound organelle.

6. Explain that the mitochondria and the chloroplast are both important in explaining the endosymbiotic theory. This theory proposes that mitochondria and chloroplasts originated by forming an association with a nucleus-containing host cell. Restate theories studied today. Remind students that none have been proven. Effect closure by asking students to think about the theories, what they can explain, and what they cannot explain.

Post Lab

1.Ask students to present their group findings that will lead to a class discussion.

2.Review answers to questions.

Acknowledgment: Adapted from an activity written by Elizabeth Moore, Lessons and Experiments in Wetland Science, The University of Southwestern Louisiana, Lafayette, LA, 1993.

The Endosymbiotic Theory, OR
Eukaryotic and Prokaryotic Feast

The endosymbiotic theory explains one manner in which the origin of organelles may have evolved. In this lab, various prokaryotic and eukaryotic organisms will be examined and cellular change and linkage which support the endosymbiotic theory will be identified.


To identify differences between prokaryotes and eukaryotes
To identify organelles in the evolution of a prokaryote to a eukaryote
To gain skill in microscopic techniques

Materials And Equipment

Cultures of prokaryotes and eukaryotes for each lab group
Prepared slides of prokaryotes and eukaryotes
Materials for wet mounts


Prepare drawings and descriptions of both wet mounts and prepared slides. View each under the microscope noting differences observed between prokaryotes and eukaryotes.

Endosymbiotic Theory Data Sheet




Problem: What are the structural differences between prokaryotes and eukaryotes?

Background Information(from pre-lab and notes)



Data(Place descriptions here, attach drawings):


Questions (answer on separate sheet of paper)

1.What suggestions can you make for future lab studies in this area?

2.How can you apply what you have discovered?

On to Comparative Embryology
Using Japanese Medaka Fish

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