Biology Station 7(B)
Natural Selection
Correlations to Texas Essential Knowledge and Skills:
Biology
(7) Science concepts. The student knows the theory of
biological evolution. The student is expected to:
(B) illustrate the results of natural selection in speciation,
diversity, adaptation, behavior, and extinction.
(2) Scientific processes. The student uses scientific methods
during field and laboratory investigations. The student is
expected to:
(C) organize, analyze, evaluate, make inferences, and
predict trends from data, and
(D) communicate valid conclusions.
Purpose: The
purpose of this
station is to reinforce
students’
understanding of the
results of change in
species.
Note: Text with a line
through it indicates this
part of the TEKS is not
being addressed in this
activity. Some TEKS
statements printed here
end with a ; or and and
nothing thereafter—this
indicates that further
TEKS statements follow
but are not included
here.
Teacher Notes About the TEKS
In the third grade, students were first introduced to differential survival of organisms due to
inherited traits. The concept was reinforced in grades four through six. The terms natural
selection, diversity, and speciation may be new to students in Biology, but the concept of
adaptation is not.
Background Information for the Teacher
The struggle for limited resources results in the increased potential for survival of individuals
that possess adaptations better suited for their environment(s). This is the concept behind
natural selection. That is, organisms that survive will presumably reproduce and contribute
their DNA to the gene pool. If a particular genetic variation continues to provide a survival
advantage, the frequency of the genes that produce that variation will increase. This slow change
to the gene pool can lead to speciation, the development of a new species from an existing one
through natural selection. Conversely, genetic variations that reduce the survival potential of
individuals can lead to extinction of a species.
Materials
Colored counters (chips) (20 blue and 20 red)
Paper bag
Student pages, including glossary (included in the blackline masters for this station)
Station information sheet (included in the blackline masters for this station)
Charles A. Dana Center at The University of Texas at Austin
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Essential Science Concepts for Exit-Level TAKS
Biology Station 7(B)
Natural Selection
Surviving species graphs (included in the blackline masters for this station)
Question card (see Advance Preparation)
Advance Preparation
1. For each student, make a copy of the student pages (including glossary) and station
information sheet. Make a copy of the station information sheet and a color copy of the
surviving species graphs for the station table.
2. Make a question card using question 4 from the Released TAKS Exit Level Retest for
Science, July 2006. This released test can be found at www.tea.state.tx.us/
student.assessment/resources/release/taks.
Station Setup
1. Place the paper bag and the blue and red chips on the station table.
2. Tape a copy of the station information sheet to the table. Students will use this to confirm
the station is set up correctly.
Procedures
1. When students arrive at the station, they should check the station setup against the station
information sheet at the table. If anything is missing or out of place, the students should
notify the teacher.
2. Students should read the procedures and answer the questions.
Guide to Student Responses
Focus Question: Explain how changes in an environment may change a population of
organisms.
Organisms possessing genetic variations that make it possible for them to do well in a
particular environment will likely reproduce and contribute DNA to the gene pool. If
conditions in the environment change, individuals with the genetic variations that are most
adaptable to the changing conditions will survive and contribute to the gene pool.
Questions: Part I
1. In Graph 1 below, the temperature is constant and is neither extremely cold nor extremely
hot. What does the data in Graph 1 indicate about whether a population will change or
evolve in this temperature-constant environment?
The population does not change or evolve.
2. Examine Graph 2 below, in which temperature increases over time. Predict how a change in
the environment may affect the number of individuals with the BB genotype.
Charles A. Dana Center at The University of Texas at Austin
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Essential Science Concepts for Exit-Level TAKS
Biology Station 7(B)
Natural Selection
If this trend continues, the number of individuals with the BB genotype will continue to
decrease.
Questions: Part II
1. Based on information from the graph, how many individuals with the genotype BB survived?
How many with the genotype BR survived? How many with the genotype RR survived?
1 BB individual, 4 BR individuals, 5 RR individuals
2. Using the information from the graph, select two appropriately colored counters for each of
the fourth-generation individuals represented. (For example, for each BR individual, place
one red and one blue chip into the bag.) Place the chips into the paper bag. Now reach into
the bag and, without looking, remove two chips at the same time. Record the colors of the
chips. Continue to remove two chips at a time, without placing them back into the bag,
until all the chips are gone. Record how many of each combination (BB, BR, RR) you select.
Answers vary, but note that students will count more individuals with RR genotype than
any other genotype.
3. From this information, which population would most likely survive over time in this hot
environment?
Individuals with genotype RR
4. Which population is least likely to survive if the environment becomes warmer?
Population with genotype BB
5. If this environment remains hot, what gene combinations would you expect to find in future
generations?
Individuals with genotypes RR and BR
Charles A. Dana Center at The University of Texas at Austin
3
Essential Science Concepts for Exit-Level TAKS
Biology Station 7(B)
Natural Selection
Blackline Masters
for
Biology Station 7(B)
Natural Selection
Contents:
Surviving species graphs (1 copy for station table)
Station information sheet (1 copy for station table and 1 for each student)
Student pages (1 copy for each student)
Glossary (1 copy for each student)
Charles A. Dana Center at The University of Texas at Austin
4
Essential Science Concepts for Exit-Level TAKS
Biology Station 7(B)
Natural Selection
Surviving Species Graphs
Charles A. Dana Center at The University of Texas at Austin
5
Essential Science Concepts for Exit-Level TAKS
Biology Station 7(B)
Natural Selection
Station Information Sheet
Biology Station 7(B)
Natural Selection
Charles A. Dana Center at The University of Texas at Austin
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Biology Station 7(B)
Natural Selection
Student Pages
Before You Begin
Check to see that all the items are present and organized according to the station
information sheet. If you notice a problem, notify the teacher immediately.
Materials
Colored chips (20 red and 20 blue)
Paper bag
Glossary
Focus Question: Explain how changes in an environment may change a population
of organisms.
Procedures
1.
Discuss the focus question with your teammate(s) and record your answer.
2.
The red and blue chips can be used to represent the different variations in
organisms that enable them to adapt and live in different environments.
•
Blue chips (B) represent the gene that inhibits an individual’s ability to
survive in hot temperatures.
•
Red chips (R) represent a gene that makes it possible for an individual to
survive in hot temperatures.
Charles A. Dana Center at The University of Texas at Austin
Student Page 1
Essential Science Concepts for Exit-Level TAKS
3.
Biology Station 7(B)
Natural Selection
Use the information in the table below to answer the questions that follow.
Gene Combinations and Heat Tolerance Table
Gene Combinations
Heat Tolerance
BB (two blue chips)
organism does not survive in a hot
environment
RR (two red chips)
organism can survive in a hot
environment*
BR (one red and one blue chip)
organism can survive in a moderately
warm environment**
*Hot environment = 33o–45o C
**Moderately warm environment = 22o–27o C
Questions: Part I
1.
In Graph 1 below, the temperature is constant and is neither extremely cold nor
extremely hot. What does the data in Graph 1 indicate about whether a
population will change or evolve in this temperature-constant environment?
Graph 1: Temperature Remains Moderate
Charles A. Dana Center at The University of Texas at Austin
Student Page 2
Essential Science Concepts for Exit-Level TAKS
2.
Biology Station 7(B)
Natural Selection
Examine Graph 2 below, in which temperature increases over time. Predict how
a change in the environment may affect the number of individuals with the BB
genotype.
Graph 2: Temperature Increases Over Time
Questions: Part II
Use the results for the fourth generation (shaded) in Graph 3 below to answer the
following questions.
Graph 3: Fourth Generation Population in Increasing Temperatures
Charles A. Dana Center at The University of Texas at Austin
Student Page 3
Essential Science Concepts for Exit-Level TAKS
Biology Station 7(B)
Natural Selection
1.
Based on information from the graph, how many individuals with the genotype
BB survived? How many with the genotype BR survived? How many with the
genotype RR survived?
2.
Using the information from the graph, select two appropriately colored counters
for each of the fourth-generation individuals represented. (For example, for
each BR individual, place one red and one blue chip into the bag.) Place the
chips into the paper bag. Now reach into the bag and, without looking, remove
two chips at the same time. Record the colors of the chips. Continue to remove
two chips at a time, without placing them back into the bag, until all the chips
are gone. Record how many of each combination (BB, BR, RR) you select.
BB =
BR =
RR =
3.
From this information, which population would most likely survive over time in
this hot environment?
4.
Which population is least likely to survive if the environment becomes warmer?
5.
If this environment remains hot, what gene combinations would you expect to
find in future generations?
NOTE: Because other students are going to do the activity after you, be sure to put
all the materials at the station back as you found them. Sometimes there will be
materials that need to be renewed or replaced. If you need assistance or have any
questions, ask your teacher.
Charles A. Dana Center at The University of Texas at Austin
Student Page 4
Essential Science Concepts for Exit-Level TAKS
Biology Station 7(B)
Natural Selection
Question Card
1.
Obtain the question card from your instructor.
2.
Read the question and discuss the answer with your teammate(s).
3.
Record the team’s consensus in your study folder and justify your answer.
4.
Record the team’s answer on the instructor’s diagnostic wall chart.
I Need to Remember
Complete this part AFTER the class discussion of the station.
I need to remember . . .
Charles A. Dana Center at The University of Texas at Austin
Student Page 5
Essential Science Concepts for Exit-Level TAKS
Biology Station 7(B)
Natural Selection
Glossary for Biology Station 7(B)
Extinction
Extinction is the cessation of existence of a species or group of organisms.
Gene pool
A gene pool is the total genetic material in a population at any one time.
Natural selection
Natural selection occurs when organisms with the most successful adaptations to
their environment survive and reproduce.
Population
A population is a group of organisms of one species that live in the same place at
the same time.
Speciation
Speciation is the evolutionary development of a new species from an existing one
through natural selection.
Charles A. Dana Center at The University of Texas at Austin
Student Page 6