Lesson: Interactions Between Microscopic Populations
Glencoe Biology: The Dynamics of Life
Unit 2, Chapter 2, Section 2.1 and 2.2
Context of Lesson
At this point in the curriculum students have had a growing exposure to scientific inquiry. Students are
beginning their exploration of ecology, hopefully linking ideas they learned in previous units. In this
lesson students will work in groups of four to explore the different interactions between two
microorganisms. This is a modified version of the Glencoe BioLab in Chapter 2 “How can one population
affect another?” However, in this version students are more active in their inquiring into the interactions
and a variety of interactions could potentially be observed. Also, the time frame for this investigation
differs from the version in the book.
Main goals/ Objectives
As a result of performing this investigation, students will be able to:
 Make observations about organisms using the microscope
 Develop a hypothesis from their observations
 Design an experiment to test their hypothesis
 Collect qualitative and quantitative data
 Speculate about variables affecting organism behavior
Nature of Science: Integrated Theme


Explain that scientists’ background knowledge and creativity influence their doing inquiry so
they may have different observations and interpretations of the same phenomena.
Explain that scientific knowledge should be based on empirical data.
Scientific Inquiry: Integrated Theme


Explain that inquiry procedures are guided by the question asked
Explain that research conclusions must be consistent with the data collected
General Alignment to Standards
State Goal 11: Understand the processes of scientific inquiry and technological design to
investigate questions, conduct experiments and solve problems
A. Know and apply the concepts, principles and processes of scientific inquiry.
 ILS 11.A.4a Formulate hypothesis referencing prior research and knowledge
 ILS 11.A.4c Collect, organize and analyze data accurately and precisely
State Goal 12: Understand the fundamental concepts, principles and interconnections of the life,
physical and earth/space sciences.
B. Know and apply concepts that describe how living things interact with each other and
with their environment.
 ILS 12.B.4a Compare physical, ecological and behavioral factors that
influence interactions and interdependence of organisms.
 ILS 12.B.4b Simulate and analyze factors that influence the size and stability
of populations within ecosystems (e.g., birth rate, death rate, predation,
migration patterns).
Interactions Between Microscopic Populations
PSAE Goals
STANDARD 11A – SCIENTIFIC INQUIRY
 11.11.01 Understand and follow procedures relating to scientific investigations,
including understanding the design and procedures used to test a hypothesis, organizing
and analyzing data accurately and precisely, producing and interpreting data tables and
graphs, performing appropriate calculations, applying basic statistical methods to the
data, identifying appropriate conclusions, making predictions and evaluating competing
models.
 11.11.02 Distinguish among the following: observing, drawing a conclusion based on
observation, forming a hypothesis, conducting an experiment, organizing data,
comparing data.
STANDARD 12 B- ENVIRONMENT AND INTERACTION OF LIVING THINGS
 12.11.36 Understand the effects upon the population of a species caused by various
ecological factors, particularly (a) the presence of another species with competitive
feeding habits, (b) the presence (or absence) of and number of predators, (c) the
abundance or scarcity of food sources.
Materials
Microscopes (OR Dissecting scopes OR hand lenses)
Microscope slides
Cover slips
Culture of Didinium
Culture of Paramecium
Methyl cellulose (optional)
Beakers or jars
Eyedroppers or pipettes for capturing the organisms
Student lesson of the investigation (included)
Notes for the Teacher
When preparing for this lesson the microorganisms should be ordered 1 week before the start of the
lesson. Following the directions for care of the organisms (sent with the organisms) they should stay
alive from 1-2 weeks. A larger culture could be started with the remaining organisms, again see the
directions included with the organisms. Teachers may want students to add methyl cellulose to their
wet-mount preparations to slow the protozoans.
Facilitation (2 class periods, however, presentations may extend to a third day)
It is important the teacher NOT tell students that these two organisms have a predator/prey
relationship. Students should be able to observe these interactions and come to that conclusion on their
own.
Interactions Between Microscopic Populations
Day 1 Bell Ringer
Didinium and Paramecium (5 minutes)
Students are asked to categorize whether these organisms are Eukaryotes or Prokaryotes and give their
reasons. Distribute the investigation to the students and instruct them to read the investigation
thoroughly.
Lesson (35 minutes)
Review the investigation with the students. Make sure to tell them they will be expected to write a
complete report of their work. They may use their laboratory notebooks or the accompanying handout
to prepare their written report. The teacher will collect their work for evaluation later. A Laboratory
Report Guide is included as an attachment to this lesson and can be used to guide student thinking.
Also included is a student handout in which students can record their observations.
Assist students in setting up their microscopes (or dissecting scopes or hand lenses) and making
observations. It takes some skill for students to set up a wet mount preparation. Students should be
cautioned not to break the cover slip by bringing down the lens too fast as they attempt to focus the
microscope. The teacher should move from group to group, monitoring progress and asking questions
about what they are observing.
Discuss the following points regarding the Nature of Science and Scientific Inquiry with students as they
prepare to formulate their hypotheses for homework on Day 1.

Scientists’ background knowledge and creativity influence their doing inquiry so they may have
different observations and interpretations of the same phenomena. Students’ own background
knowledge and creativity is part of the reason there are different observations and
interpretations made about the behavior of the two organisms.

Scientific knowledge should be based on empirical data. This is why it is important for students
to collect their data and to have descriptions of what they are looking for.
Homework Day 1:
Instruct students to review their observations of each of the populations being studied and to formulate
a hypothesis regarding what will happen when Paramecium and Didinium interact. Students should
prepare a written statement of their hypothesis. On Day 2, students will discuss their hypotheses within
their groups and select one for testing.
Interactions Between Microscopic Populations
Day 2 Bell Ringer
Interactions Between Microscopic Populations
Resume the lesson by asking students to review their hypotheses from their homework and work in
groups to design an experiment to test their ideas. This will be the Day 2 Bell Ringer.
At this point students will ask your approval for their experimental design. Keep in mind that the goal of
this lesson is to have students make observations and investigate what is happening when these two
organisms interact. There are likely many kinds of interactions and behaviors students will observe. The
hypotheses thus may vary. The teacher should guide students so that their experimental design matches
their hypothesis, rather than guiding all students toward a predator/prey hypothesis. The teacher can
make a transparency of the attached Laboratory Report Guide to assist students in formulating their
experimental designs.
Each group will present their design, results and conclusions to the class. The teacher can determine a
method by which students will present their findings. Suggestions for presenting include using
transparencies, white boards or poster paper. Students will then prepare wet mounts of the cultures
and carry out their experiments, clean up and then prepare their reports.
Select one person from each group to present. The teacher has the option of scoring the presentation.
Lead a class discussion about the observations, hypotheses, and conclusions each group formed.
Include aspects of Nature of Science and Scientific Inquiry.
Debrief with the class additional aspects of the Nature of Science and Scientific Inquiry they might have
experienced (by the end of Day 2), such as:

Inquiry procedures are guided by the question asked. Different groups may have had different
procedures because they started with different questions.

Research conclusions must be consistent with the data collected. Their conclusions should match
the data they collected, even if their hypothesis was not supported. Concluding that an initial
hypothesis was incorrect is a valid scientific finding.
Interactions Between Microscopic Populations
Extensions
There are several extensions to this lesson, including: modify the pH, the temperature (colder or hotter),
introduce another organism such as the euglena or some pond water with a variety of organisms, or
have some pond organism identification books on-hand so students can identify some of the new
organisms they see. Probes used for measuring temperature and pH could be used during the
extensions. Students could use these ideas as the basis to develop science fair projects in which they
work independently to explore a problem in greater depth.
Modifications/Adaptations
Since students ideally would be discussing their ideas in groups or as a class with the teacher’s guidance,
the verbal nature of this lesson is well suited for students with special needs. Pairing challenged
students with regular education students is also an appropriate accommodation if students will be
working in pairs or in groups. Challenged students should be allowed to answer orally or to make
drawings of their ideas.
Evaluation
Student laboratory notebooks, with their observations, drawings, hypotheses, experimental design,
analysis and conclusions are evidence of student understanding. Additionally, student presentations and
contributions to the class discussion are also indications of student learning.
Teacher Learning Platform
During professional development, teachers will experience and practice debriefing the Nature of Science
component of this activity as well as other similar discussions about Scientific Inquiry and the Nature of
Science.
Attachments
Bell Ringers
Laboratory Report Guide Transparency
Student Lesson
Student Observation/ Data Tables
Resources
About the Didinium
http://www.microscope-microscope.org/applications/pondcritters/protozoans/ciliphora/didinium.htm
About the Paramecium
http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopyuk.org.uk/mag/articles/param1.html
About Darwin
Glencoe Science Biology, The Dynamics of Life, Chapter 15
Interactions Between Microscopic Populations
Bell Ringer: Day 1
Didinium and Paramecium
Are these
organisms
Eukaryotes or Prokaryotes?
How do you know?
Interactions Between Microscopic Populations
Bell Ringer Day 2: Interactions
Your individual
hypothesis was based on
yesterday’s separate
observations of Didinium
and Parmecium:
 Using ideas from last night’s homework,
develop a group hypothesis about the
behavior of these populations when they
are brought together
 Design an experiment to test your
group’s selected hypothesis

Get teacher’s approval
Interactions Between Microscopic Populations
Laboratory Report Guide
Main Question:
 How do two organisms, the Paramecium and the Didinium, interact?
Hypothesis:
 Provide a testable explanation for the question being asked
(Based on yesterday’s observations, you were asked to develop a
hypothesis as last night’s homework)
Experimental Design:
 Provide step by step descriptions of what you will do. Number the steps.
(Students will work in groups to design an experimental plan to test their
hypothesis - Day 2 Bell Ringer)
Materials List:
 List the materials and supplies that you will need to carry out your design.
Observations:
 Develop a data recording chart or table or use the handout provided
 Record your observations using qualitative and/or quantitative
measurements
 Include diagrams where possible
Analysis/Conclusions:
 Write conclusions and prepare to present your results to the class
(Answer the questions in Step 11.)
Interactions Between Microscopic Populations
Interactions Between Microscopic Populations: Student Lesson
Main Question:
How do two organisms, the Paramecium and the Didinium, interact?
Day 1: Part 1
Observing the organisms separately
1. Make a wet-mount slide of Didinium (using a measured amount from the culture, a
microscope slide, and a cover slip).
2. First find the Didinium on your slide. In your lab notebooks make a drawing so you can later
tell the difference between the Didinium and the Paramecium.
3. Record your observations (use your laboratory notebook or the attached sheet): draw
pictures of and/or describe in words what the Didinium are doing, describe how they move, and
what happens when they bump into each other.
4. Make a wet-mount slide of Paramecium (using a measured amount from the culture, a
microscope slide, and a cover slip).
5. Next find the Paramecium in on your slide. In your lab notebooks make a drawing so you can
later tell the difference between the Paramecium and the Didinium.
6. Record your observations: draw pictures of and/or describe in words what the Paramecia
are doing, describe how they move, and what happens when they bump into each other.
7. Clean up. Make wise choices as to how the organisms will be reused or disposed of at the
end of your experiment. Consult with your teacher. Always wash your hands with soap or
detergent after handling these organisms.
8. HOMEWORK: Hypothesis
From what you’ve observed in Part 1, describe what you think will happen when the
Paramecium and the Didinium interact. Record this as your hypothesis. Though all students are
investigating the same main question, the hypotheses you develop, as well as your
experimental design may differ from group to group. Tomorrow, you will discuss your
hypothesis with your group and decide on one hypothesis. Together you will design an
experiment to test your ideas.
Interactions Between Microscopic Populations
DAY 2: Part 2
Observing the Interactions
9. This step is done as a bell ringer with your group. Record in your laboratory notebooks, or
using the handout provided by your teacher how you will test your hypothesis. Design an
experimental plan that includes the following:
a) description of what you will do, step by step
b) list of materials that you will need
c) description of what you will measure, in other words, the kind of data you will collect
o Will you look for behaviors? What behaviors will you look for? How will you
record the behaviors you see?
o Will you count the number of organisms? What power of magnification will you
use? Will you count an organism if part of it is in the field of view?
o How long will you observe the populations?
o Where will you record your data?
o Has your teacher approved your design? Have teacher sign your procedure.
10. Carry out your experiment being careful to record your data so you can refer to it in your
analysis and conclusions.
11. Clean up as you did yesterday.
12. For your analysis and conclusions, answer the following questions in your laboratory
notebook:
a) In Part 1, what differences did you observe between the two populations of organisms?
b) In Part 2, what happened during your experiment? How did the organisms interact?
c) Within a biological community, different populations interact in various ways. Refer
back to your textbook and identify the kind of interactions you observed. What kind of
interactions did the Paramecium and Didinium exhibit?
d) Was you hypothesis supported by your data? Why or why not?
e) Many times an experiment answers one question but leads to many more. List two or
three questions you now have about the Didnium and Paramecium.
f) Some microscopes are equipped with an electric light. If a student was using one of
these microscopes, the longer the Didinium and Paramecium were under the
microscope, the hotter they would get (because of the heat coming from the
microscope light). Predict two different ways the increase in temperature might affect
the microorganisms’ behavior. (How would you test this prediction?)
g) Earlier, when we studied Darwin’s Theory of Evolution and the process of Natural
Selection, we saw that organisms with favorable variations are more successful. From
your observations, what structures and/or behaviors of the Didinium would provide an
adaptive advantage in their interactions with Paramecium?
Interactions Between Microscopic Populations
Interactions Between Microscopic Populations- Day 1
Student Handout
Didinium Drawing
Paramecium Drawing
What are they doing?
What are they doing?
Describe how they move.
Describe how they move.
Describe what happens when they bump into each
other.
Describe what happens when they bump into each
other.
Interactions Between Microscopic Populations
Interactions Between Microscopic Populations - Day 2
Student Handout
Hypothesis:
Experimental Design (See Step 9a of the Student Lesson)
Materials List
Observations: (See Step 9c of the Student Lesson for suggestions)
Analysis /Conclusions: (Answer Questions in Step 12 of the Student Lesson)
Interactions Between Microscopic Populations