Metabolic Rate and Gas Production

All living organisms must utilize energy to maintain themselves and to carry out life activities. The rate of energy utilization is known as the metabolic rate. Eukaryotic organisms used chemical energy to drive energy requiring life processes. We will measure metabolic rate in both an anaerobic and aerobic organism by measuring the amount of C02 gas produced by these organisms. We will use the Vernier CO2 gas sensor inserted into an environmental chamber in which the organism is fermenting or respiring.

The oxidation of glucose to form carbon dioxide and water liberate energy through the process of photosynthesis. In photosynthesis, green plants convert sugars into chemical energy with the help of the sun. The sugars provide stable form in which energy can be stored and transported. However, these energy is converted into another chemical form known as adenosine triphosphate (ATP). When ATP is split, energy is release for cellular work and the resulting molecule is known as adenosine diphosphate (ADP). ADP is reconverted to ATP with energy derived from sugars or other nutrients.

The flow of energy from solar radiation captured by plants (via photosynthesis) to its use by both plants and animals. This energy drives many fundamental life processes such as movement, growth, and reproduction. The release of energy from food molecules occurs by two biochemical pathways. The first is called fermentation. Fermentation usually occurs in the absence of oxygen and referred to being anaerobic. The other biochemical mechanism of energy release is called cellular respiration.

Respiration ( Plants and animals)

O2 + sugar ---------------------------> CO2 + H2O + ATP ( chemical potential energy)

Photosynthesis ( plants and plant like protists)

CO2 + H2O + light energy -------------------------> O2 + sugar

Fermentation

C6H12O6 + 2Pi + 2 ADP ------> 2 CH3CH2OH + 2 CO2 + 2ATP + heat
Glucose Ethanol

The equation shows that for every molecule of glucose consumed: two moles each of ethanol, carbon dioxide, and ATP are produced as well as heat. You will begin by measuring the rate of CO2 productoin by yeast undergoing alcoholic fermentation. This rate will be related to the rate of ATP production which is a reflection of metabolic rate of yeasts.

The experiment will address the following questions:
Fermentation

Question 1: How will increasing the number of yeast cells influence the metabolic rate of the yeast suspensions?

Question 2: How will substituting galactose for glucose influence the metabolic rate of the yeast suspensions ?

Preparation of Yeast Samples:

1. Set up the three fermentation samples in test tubes according to the values specified in the following table:

Tube Label Suspending solution: Weight Yeast (grams)
Volume, % age, and type
1 glu- 0.3 6 ml - 20%- glucose 0.3
2 glu - 0.6 6ml - 20% -glucose 0.6
3 gal - 0.6 6ml - 20%-galactose 0.6

Measure gas production by your samples. Measurement can proceed when the sugar/yeast mixture begins to bubble and the parafilm bulges upward.

1. Turn on Lab Quest recorder by pressing the silver button on the upper left hand side of the unit.
2. Pour the entire yeast mixture from the test tube into petri dish and place the dish inside the large environmental chamber. Attach the cover which should have one opening. Insert CO2 sensor intot he second opening.

Question 3

Explain why measurements of an organism's rate of gas consumption or production can be used to estimate that organism's rate of ATP production.

Question 4

What is the comparison of the two quantities of yeast exposed to the same concentration of glucose (tube 1 and tube 2)?

Question 5

Explain the results for the comparison of the trials run with 0.6 grams yeast and either 20% glucose and 20% galactose.

Cellular Respiration by Corn Seedlings

Cellular respiration is the main process of ATP productoin used by plants, animals, and many microorganisms. The use of oxygen in the conversion of sugars to CO2 and water releases much more energy stored in sugar than fermentation does. It is about 16 times as much ATP is generated from fermentation of the same sugar. The overall reaction is shown below
C6H12O6 + 6 O2 + 32 ADP + 36Pi -------> 6CO2 + 6 H20 + 32 ATP + heat
The measurement of the rate of CO2 production by aerobic organism provides a useful measure of its rate of energy production. We will use a Vernier CO2 gas sensor inserted into a closed system containing corn seedlings undergoing cellular respiration.
The data will be used to address the question

Question 6:
In terms of the mass specific rates you calculated (g ATP/ gram of tissue x hour), did the yeast suspensions or corn seedlings have a higher metabolic rate?

Preparatoin of corn seedlings:
1. Obtain and weigh a 250 ml Nalgen bottle and record its weight. Tilt the bottle on its side and add about 25 corn seedlings with radicles, ranging from 1.0 to 3.0 cm in length.
2. Once the seeds are in the bottle, weigh the bottle with seeds. The weight of seeds can then be calculated and recorded on worksheet.
Measurement of CO2 production

1. Insert CO2 sensor into the neck of Nalgene bottle.
2. Measure the CO2.