Assignment 5: Respiration and Fermentation
Due September 20
Work sheet for assignment 5
Work sheet as a pdf file (in case you cannot open a doc file)
Before you attempt this exercise you should have a thorough understanding of the material in the first subtopic of Eukaryotes: Animal Cells II and the subtopic on Fungal Cells
In this exercise, we will examine some of the ways in which metabolism is studied in laboratories. We will look at the rate of aerobic respiration under different environmental conditions and also examine alcoholic fermentation. The set of reactions that comprise aerobic respiration is one of the most common energy conversion pathways found in organisms. It is the major process used by our own cells to generate ATP, the energy-currency molecule of the cell. Note that a cell can only use chemical energy in certain forms (ATP being the most common), much as we use a credit card or 20 dollar bill today. For example, there are gas stations that will refuse to make change for that $100 bill you are carrying. So either you will be refused gas outright or you will lose much of the potential energy of that bill, if it is accepted for the $50 worth of gas your car can hold. In some sense, the currency was deemed unsuitable by the gas attendant (no change available). Your cells are just as demanding of the proper chemical form of energy. They will be unable to carry on certain reactions vital to their own maintenance, if energy is not available in the proper chemical form. We will also look at alcoholic fermentation because it represents, or is at least very similar to, the oldest pathways known to generate ATP. It probably represents a pathway that is older than life itself; reactions used by proto-cells that were capable of generating energy and maintaining their structure to some extent, but were not yet capable of reproduction. Cell reproduction is a process crucial to life that we will explore later in the course.
You should have already studied the information on respiration in "Mitochondria and Peroxisomes" (first subtopic in Animal Cells II). To be sure that you understand the process of cellular respiration, view the following relationships diagram. If you do not understand the diagram, review the relevant material in Animal Cells II. You may also use this animation from Indiana U. to review the concepts of cellular respiration.
Relationships diagram: Fill in the boxes in this chart by choosing the correct term from each pull-down menu. When you think you have the correct answers for all of the blanks, click the "submit" button to check. If some answers are wrong, keep trying until you get it right. When all answers are correct, capture an image of the chart and submit it to question 1 in WebAssign. (There is no partial credit for this question, so be sure that all boxes are filled in correctly.)
ACTIVITY 1. RESPIRATION RATE IN AN ENDOTHERM
Multi-cellular animals rely on aerobic respiration to supply most of their energy needs. Thus, the rate of oxygen consumed by an animal can be used as a relative indication of overall metabolic activity. We will combine our study of aerobic respiration with an examination of the effects of temperature on an organism's metabolism metabolic rate.
In this graph, oxygen consumption is used as an indicator of how much energy is required for a particular activity.
An increase in temperature (within lethal limit) accelerates most biological processes.
Why?--think back to the enzyme laboratory. In most animals, a rise of 10 degrees in body temperature causes a 2- to 3-fold increase in the rate of oxygen consumption. However, this is not always the case; especially for birds and small mammals, the most commonly used experimental subjects for such studies. Thus we will have to consider the different ways that animals have evolved to cope with the temperature variations they encounter in their environments, before we can start our explorations.
How is respiration related to an animal's body temperature?
The crucial factor is that not all of the energy released during cellular respiration is converted into chemical energy. While much of the potential energy of food is converted into ATP, some is also released as heat. Most members of the animal kingdom allow this heat to escape into the environment, but two groups (mammals and birds) limit its escape by insulation (fat, fur and feathers). This allows mammals and birds to use trapped heat to control their body temperature so that it fluctuates by only a few degrees. Maintenance of a constant body temperature provides a more uniform internal environment for enzymatic reactions and thus increases metabolic efficiency.
Benefits come with costs.
For example, to maintain their relatively high internal temperatures, mammals must consume more food than an animal of the same size that cannot maintain a constant body temperature (such as a reptile). Additionally, maintaining a constant body temperature usually proves costly in terms of energy, especially at temperature extremes. Many mammals shiver at low temperatures. This increases metabolic rate for the sole purpose of producing heat to warm the body, so energy is expended even though the animal is not active. At high temperatures, the same mammals tend to sweat and/or pant. Panting has some serious disadvantages because it requires muscular work, which increases heat production and adds to the heat load. Additionally, it can result in blood alkalosis due to an excessive loss of carbon dioxide from the blood. Remember that it is important to understand both the costs and benefits of physiological adaptations in order to fully understand an organism's biology.
We tend to divide animals into two groups: endotherms and ectotherms.
The first group contains species which use metabolic heat to maintain a relatively constant body temperature. The second group contains the majority of animal species in which body temperature fluctuates relative to environmental temperature. Note, however, that ectotherms do have some control over their body temperature through other mechanisms, mainly behavioral. For example, a reptile can bask in the sun to raise body temperature or retreat into the shade to lower it. Modern reptiles and amphibians are ectotherms; in fact the terms endotherm and ectotherm were originally coined to distinguish the "warm-blooded" mammals and birds from "cold-blooded" reptiles and amphibians. Note though, that a reptile warmed by the sun may actually have a higher body temperature than a mammal. Today you will be measuring oxygen consumption during respiration of a mammal, but if you were ever to use an ectotherm for such a study, you would find a different scale of oxygen consumption and would need to observe the behavior of the animal to explain your results.
||This graph illustrates the effect of environmental temperature on the body temperature of an endotherm vs. an ectotherm.
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