Volume 6, Spring 2008 - Saddleback College

Fall 2007 Biology 3A Abstracts
species of insects remain relatively unknown. The
amount of oxygen input or carbon dioxide output in a
resting state may differ substantially than a flying form
of locomotion, contributed by factors such as dietary
energy content or temperature, even among species of
similar body masses. However, there is a direct
relationship between metabolic rate and body mass:
metabolic rate per gram of body mass decreases with
mass by a power less than 1.0 (Mueller & Diamond,
2001), therefore the total metabolic rate of an animal
increases proportionally with mass.
Gromphadorhina portentosa is a species of
large hissing cockroaches originating from
Madagascar. No published previous experiments have
been conducted on metabolic rates of this species.
Gathering information about furtive, hissing roaches
could offer insight for the comparison of energy costs
of a more diverse range of insects.
Materials and Methods
Procedure A. Cockroach metabolism at ambient,
elevated, and cold temperatures
Eight Madagascan hissing cockroaches were
individually placed on an analytical balance; weights
recorded (g) and labeled 1-8 for identification. Each
roach was placed in a plastic container and sealed by a
stopper that encircled a Pasco Temperature Sensor
attached to a Pasco Xplorer GLX device used to
measure carbon dioxide (CO 2 ) production in parts per
million (ppm) with readings every second (sec) for 15
minutes. Food consumption was restricted from the
roaches for at least one hour prior to testing to
eliminate increased metabolic rate from postabsorption.
MRs of the roaches were to be observed at
three variables: room temperature (23.0C), cold
(10.0C), and an elevated temperature (39.0C). They
were labeled according to weight and left to acclimate
to their ambient temperature and surroundings for 10
minutes. Roaches were handled carefully to keep them
in a calm state; sudden movements may lead to an error
in analyzing the results. The concentration of CO 2 in
the closed system of the container was recorded onto
the Xplorer GLX every second for 15 minutes.
Between each test, the roaches were released to their
normal surroundings to stabilize metabolic rates so
there would not be extreme changes in CO 2 production.
This same procedure was repeated with the
warm temperature, except the system was left in a
heating chamber adjusted to 39.0C. A light was
installed to replicate the room temperature environment
and to encourage the roaches to stay in an aroused, but
resting, state. The procedure was again repeated for
cold temperature. A thermoregulated refrigerator set at
10.0C was used with a light set inside to maintain
constant environmental factors.
Once complete, the data was transferred from
the Xplorer to a flash drive device and the table of
information (ppm/sec) was transferred as a .glx file to
be analyzed using Pasco’s Data Studio, and exported as
a text file (.txt) that could be read using Microsoft
Excel.
Procedure B. Calculating the rate of oxygen
consumption (STP)
To determine the metabolic rate of G.
portentosa, the data from all the roaches were graphed
as a scatter plot and a linear trendline was added. The
slope of this line was the rate of CO 2 production
(ppm/sec) and had to be set as a ratio to the amount of
moles (mol) of air in the container. This was calculated
by obtaining the volume of the container the, minus the
volume of the CO 2 sensor probe and the individual
roaches. Volumes were measured by filling the
container to the brim with water and pouring all the
liquid into a graduated cylinder, the final volume was
the volume of the container. The volume of the
cockroaches (V total ) was determined by submerging
them into a 250mL graduated cylinder of a known
initial volume (V i ) of liquid and subtracting that from
the final volume (V f ):
V total = V f – V i
The CO 2 sensor probe was found in a similar fashion
but with an 800mL beaker.
The volume of air in the container was
converted to standard temperature and pressure (STP)
using Boyle’s Gas Law:
P 1 V 1 = P 2 V 2
T 1 T 2
P 1 = atmospheric pressure (atm)
V 1 = volume of air in container (L)
T 1 = temperature variables (C)
P 2 = 1.00 atm
V 2 = volume of air in container at STP
T 2 = 273.15K
Atmospheric pressure (P 1 ) was found using a
barometer in an adjacent room. The temperature, T 1 ,
was the environment in which the roaches were set in.
The adjusted volume was then converted to moles of
air in the container by the Ideal Gas Law:
PV = nRT n = RT
PV
P = pressure (atm)
V = volume (L)
n = moles of air in container
R = gas constant (0.08206 Latm/molK)
T = temperature (K)
Using the graph of the CO 2 concentrations
versus time, a linear fit trendline was added in addition
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Saddleback Journal of Biology
Spring 2008