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How does the energy usage per cell compare for different organisms?

  1. Jul 13, 2012 #1
    Recently I saw an article about sled dogs burning 10,000 calories in a day. Even when adjusted for mass, this is significantly more energy than a human athlete might use.

    This got me thinking: how much energy do bacteria use in a day? Trees? Fungi? Other animals?

    I can think of lots of variables that will affect energy usage, but I still see no reason why the data couldn't be gathered/compared.

    So far the only data I've seen is comparing sled dogs to humans, so please post anything you've seen along these lines.
  2. jcsd
  3. Jul 13, 2012 #2
    I suspect your source is incorrect. Mass has to be corrected for by Kleiber's Law, not a linear relationship.
    I don’t know what that “corrected for mass” means in this case. Maybe they mean that some dogs do better than what would be expected from Kleiber’s Law. However, I am not sure.
    I suspect what you mean is that dogs do better than humans under the hypothesis that metabolism is linear to mass. However, this hypothesis is wrong. Metabolism generally follows Kleiber's Law. Metabolism is proportional to the 3/4 power of mass.
    Metabolism generally scales with mass by Kleiber’s Law. Perhaps you could provide a reference, or tell us what the mass correction you are referring to means.
    Kleiber’s Law is an empirical relationship. It describes how metabolism scales with mass in all organisms, including animals and plants. Of course there are deviations from it. However, the law works very well considering all the different organisms it covers.
    A rigorous proof of Kleiber’s Law requires mathematics. However, the empirical demonstrations have been around a long time.
    Here is a link which merely states the scaling law relating metabolism with mass as an empirical finding.
    http://sciwrite.org/wp/wp-content/uploads/2011/05/PhsicsTodayArticle.pdf [Broken]
    “Life’s Universal Scaling Laws
    Figure 1: The basal metabolic rate of mammals and birds was first plotted by Max Kleiber in 1932. In this reconstruction, the slope of the best straight line fit is 0.74,… “
    See the plot, Figure 1, in the following link. It shows how the metabolism of different animals, including humans and dogs, scale with weight.

    Sorry I have no link for the following reference. However, I have the book in my hand.
    A physical explanation for the Kleiber’s Law is provided by Richard Dawkins in the following reference:
    “The Ancestors Tale” by Richard Dawkins (Mariner Books, 2005) pp 510-514.
    The chapter with the qualitative explanation for the scaling law is “The Cauliflower’s Tale”, which was written with Yan Wong. Kleiber's Law also applies to plants.
    The physical explanation of Kleiber’s Law has to do with the supply problem that organisms have. Large organisms have a supply porblem. The blood systems in animals and the vascular tubing in vascular plants have to transport stuff to and from tissues. Small organisms don't face the same problem to the same extent. Somehow, this leads to Kleiber's Law.
    The actual mathematical proof is not in the above reference, but a popularized distillation of the physical rule. The mathematical analysis was by biologists James Brown and Brian Enquist. I took this reference from Richard Dawkins
    G. B. West, J. H. Brown, B. J. Enquist, “The origin of the universal scaling laws in biology. In Scaling in Biology. (Oxford University Press, 2000).

    Also read:
    "Newton Rules Biology" by C. J. Pennycuick (Oxford University Press, 1992).
    It is a general treatment of scaling laws in biology.
    Last edited by a moderator: May 6, 2017
  4. Jul 14, 2012 #3
    Eukaryote cells for specific tissues don't vary is size. Therefore, the mass of an adult animal is linearly proportional to the number of cells it has.
    The metabolic rate of an adult animal varies with body types according to Klieber's rule. By metabolic rate, I mean the total rate of energy generation by the organism.
    Warm blooded animals seem to be the organisms of most interest in your question. The warm blooded animals are an example of organisms that satisfy Klieber's Law. The metabolic rate of an adult, warm blooded animal increases with the 3/4 power of the mass of the animal. Klieber's law isn't strictly true for juveniles, but it is valid for warm blooded animals.
    Therefore, the metabolism of a single cell decreases with the weight of the adult animal. The bigger the animal, the smaller the rate of energy generation by a single cell. The speed of metabolism is usually thought of in terms of single cells. Hence, the cells of heavy adult warm-blooded animals have a slower metabolism then lighter adult warm-blooded animals.
    Dogs and humans are warm blooded animals. Assuming that the adult human is heavier than the adult dog, the human will have a slower metabolism by Klieber's Law. Supposedly, this includes the case of a sled dog. Sled dogs are big, but their average mass is a little less than an adult human. I wonder about those breeds of dogs whose adult size exceeds the weight of an adult human.
    There are many caveats to Klieber's Law. Klieber's Law has it physical justification in the circulatory system of the animal. Therefore, it can't be extrapolated all the way back to organisms that don't have a circulatory system. For consistency, separate curves have to be drawn for warm-blooded and cold-blooded animals. I don't think Klieber's Law applies precisely to juvenile animals.
    Klieber's Law doesn't apply to individuals within a species. It really applies to average mass and average metabolic rate with a species with an interbreeding population. However, dogs and humans are separate species of warm blooded animal. Therefore, Klieber's Law should work fine in explaining how dogs and humans differ.
    Kliebers Law can be applied to vascular plants. Vascular plants have a circulatory system. However, it probably can't be applied to nonvascular plants. I don't think it applies to fungi or bacteria. It probably can't be valid for animals without a circulation system, like cnidaria or sponges. However, one never knows!
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