Thermal Gradient Lab
By: Justin Schreer
Biology
A. Standards Addressed
B-6.1, B-6.2, B-1.1-9
Performance Objectives
Following completion of this lesson, students will be able to:
 Exemplify biological interactions
 Summarize how limiting factors affect population size
 Classify each type of limiting factor
 Compare density-dependent limiting factors to density-independent factors
and biotic limiting factors to abiotic limiting factors
 Infer the result of a change in a limiting factor on the size of a population
 Use appropriate laboratory apparatuses, technology, and techniques safely
and accurately when conducting a scientific investigation
 Use scientific instruments to record measurement data in appropriate
metric units that reflect the precision and accuracy of each particular
instrument
 Design a scientific investigation with appropriate methods of control to
test a hypothesis (including independent and dependent variables), and
evaluate the designs of sample investigations.
 Organize and interpret the data from a controlled scientific investigation
by using mathematics, graphs, models, and/or technology
 Evaluate the results of a controlled scientific investigation in terms of
whether they refute or verify the hypothesis
 Evaluate a technological design or product on the basis of designated
criteria (including cost, time, and materials)
 Compare the processes of scientific investigation and technological design
 Use appropriate safety procedures when conducting investigations
C. Lesson Plan
1. Concept Exploration (~5 min)
Begin by showing the students a bucket filled with grass shrimp. If the
shrimp have been in the bucket for a long time several shrimp will jump and
stick themselves to the side of the bucket. Ask students why the shrimp are
apparently acting ‘suicidal’ and write these hypotheses on the board. Place an
oxygen probe into the water and show that the oxygen level is very low. Ask
students why the oxygen level is so low and explain that all the shrimp in the
bucket are consuming all the oxygen and shrimp are trying to escape a low
oxygen environment. Next look at the students hypotheses and propose ways
to test each one. If temperature was not offered, propose it and discuss ways
to determine if temperature was causing shrimp to leave the bucket.
2. Concept Introduction (~20 min)
Discuss competition as it relates to the grass shrimp competing for space and
oxygen in a small environment. Identify the shrimp in the bucket as a
population because it is a group of organisms belonging to the same species
that live in a particular area. Show that population density measures the
number of individuals living in a defined space (shrimp in the bucket). Define
density-independent and density-dependent factors and how each relates to
grass shrimp. Allow students to identify several examples of each in regards
to the shrimp. Use this to lead into the lab activity.
3. Concept Application
Students will perform a lab, information is listed below. This lab requires one
hour. Grass shrimp should be collected from floating docks the night before
the lab and can be easily obtained using a dip net.
D. Review/Evaluation
Students will answer questions throughout the concept exploration and
introduction. This lab can be written up as a formal lab report, using percent of
shrimp in each compartment for analysis. This can be turned in and graded or a
participation grade can be given.
Thermal Selection Lab
Materials:
100-200 grass shrimp
1 small dip net
1 large Styrofoam cooler
1-2 hotplates
Silicon caulking
Duct tape
4-8 thermometers
1, 10 foot aluminum gutter
1 bag of ice
Procedure
Set-up:
Begin by cutting the aluminum gutter into a 6 foot section. Using the scrap
gutter, take a flattened piece to wall off each end. Duct tape should be hold the walls
in place and gaps filled with silicon caulking. (Test afterward to seal any leaks!).
Divide the gutter ‘trough’ into four equal sections and mark as cold, cool, warm, and
hot. This is the thermal gradient. Take the Styrofoam cooler and cut a square in the
size so that the trough will fit inside the square. The bottom cut of the square should
be the same height as the top of the hotplate to make sure the water level remains
equal on both sides of the trough during the experiment.
For the lab:
Place the trough on the hotplate and into the square cut out Styrofoam cooler. Fill
the cooler with ice. Turn the hotplate to a medium setting and place books in the
middle to keep the trough from bowing. Add enough water to make the depth about
8-10cm. Add around 50-100 shrimp to the trough equally and place 1-2
thermometers in the middle of each section of the trough to record water temperature.
Enough ice and heat should be applied to each side to create a thermal gradient of
cold, cool, warm, and hot water. Leave the shrimp undisturbed for at least 45
minutes. Count the number of shrimp before and after the wait. Calculate the
percentage of shrimp in each section. This almost always results in shrimp
congregating in colder to cooler waters of around 18-21 degrees and an almost
complete avoidance of water 30 degrees C or hotter.