» How does metabolic rate scale with size?
Interest in the relationship between body mass and metabolic rate can be . LMM and PIC provide two alternatives for estimating this standard. An external file that holds a picture, illustration, etc. Scaling of metabolic ( respiration) rate in relation to wet body mass in (a,c) mammals and (b,d) birds. A famous illustration representing this relationship is shown in Figure 1. Similar to the Figure 2: Histograms of resting metabolic rates normalized to wet weight.Metabolic Rate - What Is Metabolic Rate - Basal Metabolic Rate - How Many Calories Burned In A Day
Further evidence for breaking of Kleiber scaling was provided recently for protists and prokaryotes J. The metabolic rate of an organism is condition dependent, and thus should be strictly defined if one wants to make an honest comparison across organisms.
The most extreme example we are aware of is that bees in flight increase their oxygen consumption and thus their energy consumption by about fold in comparison to resting conditions BNID Similarly, humans taking part in the strenuous Tour de France consume close to 10, kcal a day, about five times the normal resting value.
It is most common to refer to the resting metabolic rate, which operationally means the animal is not especially active but well fed.
As the alert reader can imagine, it is not easy to ensure rest for all animals, think of an orca killer whale as one example.
Metabolic Rate and Kleiber's Law
The values themselves are often calculated from the energy consumption rate that is roughly equal to the energy production rate, or in other cases from the oxygen consumption. A famous illustration representing this relationship is shown in Figure 1. The difference between Over the years, several models have been put forward to rationalize why the scaling is different from that expected based on surface area.
Most prominent are models that discuss the rate of energy supply in hierarchical networks, such as blood vessels in our body, which supply the oxygen required for energy production in respiration.
To give a sense of what this scaling would predict, in moving from a human of kg consuming W, i.
But as can be appreciated in Figure 1, the curve that refers to unicellular organisms is displaced in comparison to the curves depicting mammals by about that amount.
It works for plants as well. But the law's universality is baffling: Why should so many species, with their variety of body plans, follow the same rules?
An explanation for this kind of relationship was proposed further back in Suppose the organism has a size of L, then the surface area A L2, while the volume V L3 assuming that it is in the shape of a sphere. The theory considers the fact that the tissues of large organisms have a supply problem.
That is what blood systems in animals and vascular plants are all about: Small organisms don't face the problem to the same extent.
A very small organism has such a large surface area compared to its volume that it can get all the oxygen it needs through its body wall. Even if it is multicellular, none of its cells are very far from the outside body wall.
Metabolic rate (article) | Khan Academy
But a large organism has a transport problem because most of its cells are far away from the supplies they need. Insects literally pipe air into their tissues in a branching network of tubes called tracheae. Mammals have richly branched air tubes, but they are confined to special organs, the lungs.