Describing Variability of Organisms – Grade Eight
Ohio Standards
Connection:
Life Sciences
Benchmark B
Describe the characteristics
of an organism in terms of
a combination of inherited
traits and recognize
reproduction as a
characteristic of living
organisms essential to the
continuation of the species.
Indicator 3
Explain how variations in
structure, behavior or
physiology allow some
organisms to enhance their
reproductive success and
survival in a particular
environment.
Scientific Inquiry
Benchmark B
Analyze and interpret data
from scientific
investigations using
appropriate mathematical
skills in order to draw valid
conclusions.
Indicator 3
Read, construct and
interpret data in various
forms produced by self and
others in both written and
oral form (e.g., tables,
charts, maps, graphs,
diagrams and symbols).
Lesson Summary:
This lesson uses life-science content to help students
understand the difference between observations and
predictions. After practicing observations and predictions
in the pre-assessment, students will explore variability in a
real sample of organisms. Using measurement tools, student
groups will construct histograms demonstrating variability
in small samples of organisms. Students then will compare
their histograms and observe how consolidating their data
into one large data set affects the frequency distribution.
Students then will predict how the frequency distribution
might change given different sets of environmental
pressures.
Estimated Duration: Three hours
Commentary:
This lesson helps students understand the nature of
observation, data collection and prediction using real
organisms. Collecting real data helps students take
ownership of their own learning. Classroom discussion and
comparison of results among students promotes independent
thinking and helps students construct appropriate
understandings of concepts.
Pre-Assessment:
Distribute copies of Attachment A, Pre-Assessment and
Attachment B, Pre-Assessment Plates.
Scoring Guidelines:
See Attachment C, Pre-Assessment Answers for guidelines to
assessing student work.
Post-Assessment:
Distribute copies of Attachment D, Post-Assessment. Each
student will also require two sheets of graph paper.
1
Describing Variability of Organisms – Grade Eight
Ohio Standards
Connection:
Scientific Ways of
Knowing
Benchmark A
Use skills of scientific
inquiry processes (e.g.
hypothesis, record keeping,
description and
explanation).
Indicator 1
Identify the difference
between description (e.g.,
observation and summary)
and explanation (e.g.,
inference, prediction,
significance and
importance).
Scoring Guidelines:
Use Attachment E, Post-Assessment Answers, to score
student work.
Instructional Procedures:
Engage
1. Discuss definitions from the Pre-Assessment, noting
the relationship between description and explanation.
2. Discuss the variability of structures of organisms in
the Pre-Assessment.
3. Discuss how looking at structures can tell you a lot
about how the organisms live and the kinds of
environmental requirements they have.
4. Note to students that their Pre-Assessment compared
differences between two different species of animals,
but that a lot of variability can also be seen between
individuals within a species, too.
5.
Have students use the Think, Pair and Share strategy to produce lists of characteristics
that are different among students in the classroom. Have students first brainstorm lists of
characteristics, then consolidate their lists with a partner; and then share out with the rest
of the class. As students share their lists of characteristics with the class, list them on the
board.
6. Pose the following questions to the students:
 Why do people, and other species, have a lot of variability?
 Why don’t all organisms in a species look the same?
 Is variability beneficial to a species?
Write the last question on the board. This will be a guiding question for this lesson.
Explore
7. Collect enough specimens of one plant or animal species so that each student in the
classroom has several organisms to observe and describe. Ideally, you will have at least
100 organisms.
Instructional Tip:
Choose an organism that has a high degree of measurable variability. Use easily obtainable
plant products such as peanuts, Brazil nuts, apples, dried beans, bean pods or apples. An
easily obtainable and highly variable animal would be the invasive multicolored Asian lady
beetle, Harmonia axyridis. The beetles are found in many sizes, exoskeleton colors and
numbers of spots. See the Web site for the Ohio State University Extension for more
information about this species and how to collect it.
2
Describing Variability of Organisms – Grade Eight
Instructional Tip:
If collecting fruits or vegetables, some may come from the same plant. In this case, at least
some of the variability that your students see is from the environment and not from genetic
variability. If at all possible, do not collect samples (e.g., leaves) from the same parent
organism, because the purpose of this lesson is to explore heritable variability in a population
of organisms.
8. Divide students into teams of four and distribute a container of similarly sized samples to
each team.
9. Have each student pick one individual organism and record as much information about it
as possible. Tell students that they should be able to pick their organisms back out of a
mixture of organisms. Provide tools such as rulers, calipers and balances to help students
identify the masses, dimensions and colors of their organisms.
10. Have students return their organisms to the containers and mix them up. Ask students if
they can identify their organisms.
11. Impress on students the importance of detailed records and measurements.
12. Ask students to name the characteristics that they recorded for their organisms. List these
on the board as they are named.
13. Choose one trait, either a measure of mass or of length, for students to record for their
population of organisms. Have the groups measure their traits and record all of their
measurements on a piece of paper.
Instructional Tip:
Instruct students on measuring accurately to a specified level of precision. You will want all
students to observe and record comparable measurements that will fit on the same graph.
14. Hand out an overhead to that has a copy of a grid appropriate for graphing each group.
Alternatively, you could distribute dry-erase graphing boards. Give overhead or dry-erase
pens to each group.
15. Show an example of the histogram (bar graph) they will create on an overhead projector,
and demonstrate how they should space their units on the histogram. The x-axis will
represent a range of sizes and the y-axis will represent the number of organisms at each
size.
16. Ask students to graph their populations. Circulate around the room to make sure they do
this correctly. While students finish their histograms, draw large graph axes on the board.
You will use this to consolidate the information from students' histograms.
17. Ask a representative from a group to come to the board and draw his/her group's
histogram on your axes. Tell the student to put his/her histogram on the overhead
projector and shine it on the wall. Repeat with every group. Assuming that the total
sample has a high degree of variability, you should see an approximately normal bellshaped distribution with clumping in the middle.
18. Compare the shape of the combined class histogram with the ones that students placed on
the overhead. Show the students how each histogram was not a perfect representation of
the total population, and that a large number of organisms was needed to get a good
3
Describing Variability of Organisms – Grade Eight
picture of the variability present. Explain that as sample sizes increase, one obtains a
more accurate representation of the population.
Explain
19. Stimulate open-class discussion using the following questions.
a. With the histogram on the board, pose the questions:
 What would happen to this population of organisms if some of them did not
survive?
 What might the graph look like in the future?
Help bring this question alive by delivering a story about the organism that your class
measured and the environment in which it lives. For example, if your graph is based
on lady beetle length, tell students to imagine that a deadly virus is introduced that
favors small lady beetles as hosts. Cover up the portion of the histogram that pertains
to smaller beetles and ask the students what they think would happen to the
population. As another example, if students measured the mass of apples, explain to
the students that a native deer population only eats middle-sized apples, so only
middle-sized apples benefit from dispersal of their seeds. Cover up the extremely
small and extremely large measures on the histogram and ask students what they
predict would happen to the population over time.
b. Refer to the guiding question posed and written on the board at the beginning of the
lesson, "Is variability beneficial to a species?" You may want to pose the question
instead as, "What if the organisms that you measured only came in one size, and a
predator ate only that one size of organism?" Students should begin to understand that
variability helps organisms survive in different environments, as in the lady beetle
example above.
c. Have the students use Think-Pair-Share strategy to discuss other changes in the
environment that could affect the histogram of measurements.
20. On the board or on an overhead, write two columns, one with the heading "observation"
and the other with the heading "prediction." Have students volunteer observations and
predictions that they considered during this lesson.
21. Proceed to the Post-Assessment.
Differentiated Instructional Support:
Instruction is differentiated according to learner needs, to help all learners either meet the
intent of the specified indicator(s) or, if the indicator is already met, to advance beyond the
specified indicator(s).
 Have students working toward the indicators arrange their organisms on the table so that
they make physical models of a bar chart.
 Have students working beyond the indicators calculate summary statistics of histograms
so they can compare them mathematically.
4
Describing Variability of Organisms – Grade Eight
Extension:
 Have students design experiments or tests for the predictions that they made in this
lesson.
 Have students identify highly variable organisms that interest them, and design
investigations of their variability and potential advantages of these traits. This could
provide science-fair/ science-day topics for student investigation.
Homework Options and Home Connections:
Have students compare and contrast physical and behavioral traits of dog breeds in their
community, and consider how these traits are considered advantageous by breeders.
Interdisciplinary Connections:
Mathematics
 Measurement
Benchmark E: Estimate and compute various attributes, including length, angle
measure, area, surface area and volume, to a specified level of precision.
Indicator 3: Use appropriate levels of precision when calculating with measurements.
 Data Analysis and Probability
Benchmark A: Create, interpret and use graphical displays and statistical measures to
describe data; e.g., box-and-whisker plots, histograms, scatterplots, measures of center
and variability.
Indicator 1: Use, create and interpret scatterplots and other types of graphs as
appropriate.
Benchmark E: Evaluate the validity of claims and predictions that are based on data
by examining the appropriateness of the data collection and analysis.
Indicator 8: Describe how the relative size of a sample compared to the target population
affects the validity of predictions.
Materials and Resources:
The inclusion of a specific resource in any lesson formulated by the Ohio Department of
Education should not be interpreted as an endorsement of that particular resource, or any of
its contents, by the Ohio Department of Education. The Ohio Department of Education does
not endorse any particular resource. The Web addresses listed are for a given site’s main
page, therefore, it may be necessary to search within that site to find the specific information
required for a given lesson. Please note that information published on the Internet changes
over time, therefore the links provided may no longer contain the specific information related
to a given lesson. Teachers are advised to preview all sites before using them with students.
For the teacher: Sample of at least 100 organisms, overhead with copy of grid, overhead
markers.
For the students: sample of at least 100 organisms, overhead with copy of grid, overhead
markers, measurement tools (e.g., ruler, balance, caliper).
5
Describing Variability of Organisms – Grade Eight
Vocabulary:
 characteristic
 description
 explanation
 histogram
 observation
 prediction
 sample
 sample size
 traits
 variability
Technology Connections:
 Download images of organisms from the National Oceanic and Atmospheric
Administration Photo Library, at http://www.photolib.noaa.gov.
 Find information about agriculturally important organisms and their life histories,
including the Asian lady beetle, from the Ohio State University Extension at
http://www.ag.ohio-state.edu.
Research Connections:
Marzano, Robert J., et al. Classroom Instruction That Works: Research-Based Strategies for
Increasing Student Achievement. Alexandria. Association for Supervision and Curriculum
Development, 2001.
Nonlinguistic representations help students think about and recall knowledge. This
includes the following:
 Creating graphic representations (organizers);
 Making physical models;
 Generating mental pictures;
 Drawing pictures and pictographs;
 Engaging in kinesthetic activity.
Generating and testing hypotheses engages students in one of the most powerful and
analytic of cognitive operations. It deepens students’ knowledge and understanding. Any
of the following structured tasks can guide students through this process:
 Systems analysis;
 Problem solving;
 Historical investigation;
 Invention;
 Experimental inquiry;
 Decision making.
6
Describing Variability of Organisms – Grade Eight
General Tips:
 At least 100 organisms should be obtained for this exercise, to ensure that students will
observe the effects of sample size on population frequency distributions. Use plants or
animals that are easily obtainable at the grocery store or in your local environment.
 This lesson assumes that students have learned how to make precise and accurate
measurements. This skill was covered in the Mathematics Measurement Standard,
Benchmark D, in the five through seven grade band.
Attachments:
Attachment A, Pre-Assessment
Attachment B, Pre-Assessment Plates
Attachment C, Pre-Assessment Answers
Attachment D, Post-Assessment
Attachment E, Post-Assessment Answers
7
Describing Variability of Organisms – Grade Eight
Attachment A
Pre-Assessment
Name:_____________________________________
Directions: Answer the following questions.
1.
Define the word observation-
2.
Define the word prediction-
3.
Look at plate one and plate two. Make a list of the structures or body parts that each
animal has.
4.
Describe how these animals are the same and how they are different.
5.
Write as many predictions as you can think of about what these organisms do and how
their lives differ from each other. For example, do you think that they eat the same
thing?
8
Describing Variability of Organisms – Grade Eight
Attachment B
Pre-Assessment Plates
Plate is from the National Oceanic and Atmospheric Administration Photo Library, available
at www.photolib.noaa.gov.
9
Describing Variability of Organisms – Grade Eight
Plate is from the National Oceanic and Atmospheric Administration Photo Library, available
at www.photolib.noaa.gov.
10
Describing Variability of Organisms – Grade Eight
Attachment C
Pre-Assessment Answers
Name:_____________________________________
Directions: Answer the following questions.
1.
Define the word observation- Carefully measuring and recording something that will be
important for arriving at a judgment. Using the five senses.
2.
Define the word prediction- To tell about something that may be unknown, based on
observations that have been made.
3.
Look at plate one and plate two. Make a list of the structures or body parts that each
animal has.
Students should list basic body parts such as head, tail, body and fins. They also may list
structures such as mouth, eye, gill and scales.
4.
Describe how these animals are the same and how they are different.
Students should be able to list several differences between these organisms such as
placement and size of fins, relative size of eye, external gill openings, mouth shape, nose
shape, body armor, tail shape, direction of body flattening, etc.
5.
Write as many predictions as you can think of about what these organisms do and how
their lives differ from each other. For example, do you think that they eat the same
thing?
Students should base predictions on the observations they have made.
For example, the relatively larger eye of the seahorse implies that it relies more heavily
on vision. The nose of the sawfish suggests that it uses it as a weapon or foraging device,
and the lack of one on the seahorse implies it does not engage in the same activity. Many
other predictions can be made based on the observations.
11
Describing Variability of Organisms – Grade Eight
Attachment D
Post-Assessment
Name: ____________________________________
1.
Define the word observation-
2.
Define the word prediction-
3.
Write the title "Pennsylvania Black Bear Mass" on the top of one piece of graph paper
and write the title "Florida Black Bear Mass" on the top of another piece of graph paper.
Make histograms of the two sets of observations shown below on the two sheets of graph
paper. Remember to label your axes "mass (kg)" and "number of bears."
Pennsylvania Black Bear Mass
66-75
76-85 86-95
Mass (kg)
Number of
4
10
20
bears
Florida Black Bear Mass
35-45
46-55
Mass (kg)
Number of
2
12
bear
4.
96-105
106-115
116-125
126-135
136-145
44
66
34
16
6
56-65
66-75
76-85
86-95
96-105
106-115
30
56
46
28
18
8
Use your Pennsylvania Black Bear Mass histogram to answer the following questions.
a. What is the smallest mass for a bear in the Pennsylvania population? ______________
b. What is the largest mass for a bear in the Pennsylvania population? _______________
c. What is the most common mass for a bear in the Pennsylvania population? _________
5.
Use your Florida Black Bear Mass histogram to answer the following questions.
a. What is the smallest mass for a bear in the Florida population? _______________
b. What is the largest mass for a bear in the Florida population? ________________
12
Describing Variability of Organisms – Grade Eight
c. What is the most common mass for a bear in the Florida population? _____________
6.
Compare the Pennsylvania and Florida Black Bear histograms to answer the following
questions.
a.
How are the Pennsylvania and Florida bear populations different?
b.
If you want to see a large black bear, which state should you visit?
c.
If a population of bears is captured in Florida and transplanted to Pennsylvania,
which of the Florida bears do you think might have trouble surviving in
Pennsylvania? On what observations do you base this prediction?
13
Describing Variability of Organisms – Grade Eight
Attachment E
Post-Assessment Answers
1.
Define the word observation- Carefully measuring and recording something that will be
important for arriving at a judgment.
2.
Define the word prediction- To tell about something that may be unknown based on
observations that have been made.
3.
Write the title "Pennsylvania Black Bear Mass" on the top of one piece of graph paper
and write the title "Florida Black Bear Mass" on the top of another piece of graph paper.
Make histograms of the two sets of observations shown below on the two sheets of graph
paper. Remember to label your axes "mass (kg)" and "number of bears."
14
Describing Variability of Organisms – Grade Eight
Attachment E (continued)
Post-Assessment Answers
4.
Use your Pennsylvania Black Bear Mass histogram to answer the following questions.
a. What is the smallest mass for a bear in the Pennsylvania population? ___66 kg_____
b. What is the largest mass for a bear in the Pennsylvania population? ____145 kg____
c. What is the most common mass for a bear in the Pennsylvania population? 106-115 kg
5.
Use your Florida Black Bear Mass histogram to answer the following questions.
a. What is the smallest mass for a bear in the Florida population? ____35 kg_____
b. What is the largest mass for a bear in the Florida population? _____115 kg____
c. What is the most common mass for a bear in the Florida population? 66-75 kg
6.
Compare the Pennsylvania and Florida Black Bear histograms to answer the following
questions.
All student answers should be based on data that they observed in the data tables. Any
answers that are derived from unsubstantiated conjecture are incorrect.
a.
How are the Pennsylvania and Florida bear populations different?
Any or all of the following responses are correct.
15
Describing Variability of Organisms – Grade Eight
Attachment E (continued)
Post-Assessment Answers




The distributions of masses are shaped different, but both are bell-shaped
curves.
Some Pennsylvania bears are larger than the largest Florida bears.
The smallest Pennsylvania bears are not as small as the smallest Florida bears.
The most common-size of Pennsylvania black bear is larger than the most
common-size of Florida black bear.
b.
If you want to see a large black bear, which state should you visit?
You should go to Pennsylvania, because there are some bears there that are larger
than any that occur in Florida, plus the most common-sized black bear in
Pennsylvania is larger than the most common-sized black bear in Florida.
c.
If a population of bears is captured in Florida and transplanted to Pennsylvania,
which of the Florida bears do you think might have trouble surviving in
Pennsylvania? On what observations do you base this prediction?
The bears that range from 35 to 65 kg in mass do not appear to live in the
Pennsylvania population. This suggests that smaller bodied bears do not survive
well in this environment.
You may choose to describe this phenomenon known as Bergman's Rule, where animals
within the same species tend to have smaller adult sizes in lower latitudes and larger adult
body sizes in higher latitudes. This has been noted in such widely varying species as black
bear, white-tail deer and bald eagle.
16