Cellular Respiration

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Lab 8 Cellular Respiration and Fermentation

Objectives:
1. Observe the effects of cellular respiration on temperature in a closed system. 2. Investigate carbon dioxide production in both germinating pea seeds and crickets. 3. Perform an investigative study of the rate of cellular respiration in both pea seeds and crickets at various temperatures. 4. Compare the alcoholic fermentation of glucose, sucrose, and starch by yeast.

Introduction

All organisms must have a continual supply of external energy in order to maintain bodily functions and to combat entropy. Ultimately this source of energy is the sun. As you learned in the previous lab, plants can convert the sun’s energy into usable forms of chemical energy (E.g., glucose). In order for the energy to be made useful the chemical bonds that hold the atoms of these molecules together must be broken. The released energy is captured by high-energy phosphate bonds and combined with adenosine diphosphate (ADP) to form adenosine triphosphate (ATP), which is the energy currency of the body.

There are two processes that release this energy from the photosynthetic materials to form the energy molecule ATP. Those processes are cellular respiration and fermentation. Cellular respiration is an aerobic (requires oxygen) process, while fermentation is an anaerobic (occurs without oxygen) process. These enzyme-controlled reactions that occur during these processes are both oxidative (loss of electrons) and reductive (gain of electrons). Because the reactions are enzyme controlled they require less activation energy and therefore occur at nonlethal temperatures, continually releasing small amounts of energy that can be used to from ATP.

When compared to fermentation, the formation of ATP via cellular respiration is a relatively efficient process, as there are 36-38 ATP molecules formed per glucose molecule. Fermentation on the other hand only generates a net of 2 ATP molecules. This may bring up the question of why the body would even bother with fermentation and not just stick with the high-energy process of cellular respiration. Recall that ATP is the body’s energy currency and energy is needed for the body to continue all of its metabolic processes. Now recall that cellular respiration requires oxygen. During times when the body is in oxygen debt (I.e., there is little oxygen available for metabolic processes) the cell still needs energy and therefore it uses it’s next best option for energy production and proceeds with fermentation. There are two forms of fermentation, lactic acid and alcoholic fermentation. In today’s lab we will investigate alcoholic fermentation by yeast.

The equations for cellular respiration, lactic acid fermentation, and alcoholic fermentation are listed below:

Cellular Respiration

Glucose + Oxygen Carbon Dioxide + Water

C6H12 O6 +6O2 6CO2 + 6H2O

Alcoholic Fermentation

Glucose Carbon Dioxide + Ethyl Alcohol

C6H12O6 2CO2 + 2C2H5OH

Lactic Acid Fermentation

Glucose Lactic Acid

C6H12O6 2C3H6O3

Exercise I
Cellular Respiration and Heat Production

Body heat in birds and mammals is generated through the metabolic process of cellular respiration. Your task in this exercise is to investigate the null hypothesis that simple organisms do not produce heat as a by-product of cellular respiration. In order to test this null hypothesis there have been 3 250-mL flasks setup. Each flask has a two-hole rubber stopper with one of the holes closed off with cotton and the other hole housing a thermometer. One of the flasks has 6 live crickets, one has 6 germinating pea seeds, and the other is empty. You need to read the temperature of the thermometers in each of the flasks and decide whether the null hypothesis is supported...
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