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There is a symphony occurring in your body right now that allows you to survive. Multiple bodily functions are occurring synchronously at a microscopic and chemical level. Respiration, eating, sweating, hormonal signals, enzyme activity, and blood circulation are all different sections of an orchestra that is you.
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Jetzt kostenlos anmeldenThere is a symphony occurring in your body right now that allows you to survive. Multiple bodily functions are occurring synchronously at a microscopic and chemical level. Respiration, eating, sweating, hormonal signals, enzyme activity, and blood circulation are all different sections of an orchestra that is you.
In biology, we do not refer to the basic bioenergetic process as a symphony or an orchestra, but rather as a metabolism, or metabolic rate!
Metabolism is a catch-all term that refers to the totality of the biochemical reactions that provide energy and molecules to an organism. These reactions also require a sustained energy input by acquiring and synthesizing energy.
Some examples of metabolic functions are respiration, photosynthesis, thermoregulation, cell growth, nutrient transport, nerve function, muscle function or defense mechanisms.
A particularly important component of metabolism is thermoregulation, or how an organism keeps its body temperature constant.
Animals are further divided into two categories, depending on their ability to thermoregulate independently or not: endotherms and ectotherms.
Endotherm: An organism that uses its internal metabolism to thermoregulate.
Ectotherm: An organism that uses the external environment to thermoregulate.
Since the metabolic needs of organisms are constantly fluctuating throughout the day and seasons, measuring metabolism can feel clumsy and inadequate. It is even more difficult to compare the metabolism of two different organisms.
For example, the metabolism of a beaver building a den is different from a beaver resting, which is much different than the metabolism of a deciduous tree in the winter.
Instead, it is more adequate to speak of the amount of energy expenditure occurring over a period of time to perform metabolic tasks, or metabolic rate. The definition of metabolic rate is shown below.
Metabolic Rate is a measure of the amount of energy expenditure by an organism over a period of time to sustain its own life. It is often represented in kilocalories per day (kcal/day) or kilojoules per day (kJ/day).
An elevated metabolic rate is characterized by high activity and increased energy expenditure. The more active an organism is, the quicker its respiration, the quicker its heart pumps, the faster its muscles twitch.
Picture a cheetah chasing down a gazelle. That is a highly metabolic activity!
Metabolic rate doesn't only vary depending on the daily activity. Metabolic rates vary across species.
Occasionally, an organism needs to rest. I am sure you do too! Yet, even at rest, your body must perform basic metabolic tasks to keep you alive. In biology, this is called the basal metabolic rate, or BMR. The definition of BMR is as follows:
Basal metabolic rate (BMR) is the minimum energy expenditure by an endothermic animal at rest. This includes basic functions such as breathing, blood circulation, thermoregulation, and neural activity.
In ectotherms and plants, this is called the standard metabolic rate, or SMR. A key reason for basal metabolic rate (BMR) or standard metabolic rate (SMR) is to allow the scientist to compare metabolic rates across species.
Organisms can have shifting metabolic rates depending on the activities performed that day, but metabolic rates can also shift through the year. Endotherms can enter a state of torpor.
Torpor is a diminished metabolic state characterized by low-energy expenditure. It is adopted by endotherms during environmental stresses, such as extreme cold or heat, lack of nutrients or lack of water.
In the winter, endotherms enter hibernation, a prolonged state of torpor to escape the cold rigors of winter. Alternatively, some endotherms may enter estivation, which is a prolonged state of torpor to persist through torrid or arid summers.
Adjacent to torpor and hibernation, dormancy is a state of low-energy expenditure and low metabolic rate in plants during winter.
As an alternative to the basal metabolic rate, a second way to quantify metabolic rate is used.
Resting metabolic rate (RMR) is the minimum energy expenditure required by an endothermic animal when fully at rest
At rest is different in RMR compared to Basal Metabolic Rate (BMR). In RMR, a fully resting organism is also considered to be sleeping and fasting.
In 1932, Max Kleiber observed and researched the relationship between metabolic rate and weight (Fig. 1).
Logically speaking, this makes sense. If an organism has more moving parts than another, then its body must perform more metabolic maintenance and energy expenditure because it has more parts!
If you compare yourself to a snake, you have arms, whereas snakes do not. Your body must constantly pump blood to your appendages to keep them healthy and growing. Snakes, on the other hand, are not encumbered by the extra weight and metabolic rates associated with limbs.
Max Kleiber was able to quantify an equation correlating metabolic rate and weight, known as Kleiber’s Law, by plotting the two variables on a graph.
Figure 1 - An original graph from Max Kleiber's research showing a linear graphical relationship between body weight and heat production (i.e., metabolic rate).
Kleiber discovered that metabolic rate is proportional to weight by a power of ¾.
Kleiber’s law is a mathematical relationship that shows an organism’s metabolic rate is proportional to its weight, by a power of ¾. In equation form, R ∝ M¾, where R = Metabolic Rate and M = Mass (or weight).
In ecology, metabolic rates are used to compare food chains and food webs.
Observing metabolic rates can help quantify the dynamics between populations in an ecosystem. More precisely, the energy expenditures are fluxes and the organisms themselves are energy reservoirs.
An energy value can thus be assigned to populations, communities, or ecosystems. To do so, ecologists use an energy pyramid (Fig. 2).
Looking closer at the pyramid, we can also observe that with every increase in trophic level, there is a reduction in the size of the energy reservoir. Generally, as energy expenditure moves energy up the food chain, energy is lost by a ratio of 10 to 1. Also note, the weight of the organisms at the top of the pyramids tends to be higher than the weight of the organisms below it.
As humans, knowing our basal metabolic rates is important to ensure we have a diet that is balanced with our energy expenditure.If we can quantify our metabolic rate, and the amount of energy in our food, then we can ensure our energy inputs match our energy outputs.
To count the number of joules or calories our bodies need to function (i.e., BMR), we use the variables of weight, height, age, and sex. The basal metabolic rate (BMR), the energy expenditure of an organism at rest, is used to quantify metabolic rate because metabolism is the most consistent at rest.
There are two different variations of the general formula for metabolic rate: the revised Harris-Benedict BMR formula and the Mifflin-St-Jeor BMR formula.
Revised Harris-Benedict BMR Formula:
BMRMale = 13.4·Weight (kg) + 4.8·Height (cm) - 5.68·Age (yrs) + 88 kcal/day
BMRFemale = 9.25·Weight (kg) + 3.1·Height (cm) - 4.33·Age (yrs) + 447.6 kcal/day
The original version of the Harris-Benedict Formula is:
BMRMale = 6.23·Weight (kg) + 12.7·Height (cm) - 6.8·Age (yrs) + 66 kcal/day
BMRFemale = 4.35·Weight (kg) + 4.7·Height (cm) - 4.7·Age (yrs) + 655 kcal/day
Mifflin-St-Jeor BMR Formula:
BMR = 10·Weight (kg) + 6.25·Height (cm) - 5· Age (yrs) + Sex-Based Constant
Where,
The Sex-Based Constant is 5 kcal/day for males and -161 kcal/day for females.
Alternatively, there is a formula to calculate basal metabolic rate (BMR) which factors in body fat percentage. If you compare two individuals with the same weight, height, and age, the previous two BMR equations will yield the same results.
Yet if one individual is a football player and the other is a banker, we can correctly conjure their BMR should really be different. Here is an alternative way to calculate basal metabolic rate (BMR), called the Katch-McArdle BMR formula. It uses body fat percentage and weight as the variables. Notice that sex is not a variable.
Katch-McArdle BMR Formula:
BMR = 370 + 21.6·Weight (kg) · (1 - Body Fat %)
The range of basal metabolic rate (BMR) values for adult human males is 1600 to 2000 kcal/day, and for human females is 1400 to 1800 kcal/day. Equipped with this knowledge, try calculating your own basal metabolic rate! What value did you get?
Knowing your basal metabolic rate (BMR), you can now look at a food calorie chart or the food nutrition table printed on the packaging of the food you purchase.
Try it at home for a week or so, and see how the number of calories you ingest compares to your basal metabolic rate (BMR). Is it higher or lower? Keep in mind that we are estimating your basal metabolic rate, which doesn't factor in any additional exercise or activities you may be performing!
To better understand the range of values obtained from the basal metabolic rate (BMR) equations, here are a few exercises. You will use the Revised Harris-Benedict BMR formula and the Mifflin-St-Jeor BMR formula, and compare BMR from different individuals.
Answers
Metabolism is a catch-all term that refers to the totality of the biochemical reactions that provide energy and molecules to sustain an organism.
Metabolic rate is a measure of the amount of energy exerted by an organism over a period of time to sustain its own life.
Basal metabolic rate, or BMR, which is the minimum energy expended by an endothermic animal at rest. In ectotherms and plants, this is called the standard metabolic rate, or SMR.
Kleiber’s law states an organism’s metabolic rate is proportional to its mass, by a power of ¾, or R ∝ M¾.
In ecology, metabolic rates can be used to quantify the interactions between species populations.
Your metabolic rate is a measure of the amount of energy exerted by you over a period of time to sustain your life. It is often represented in kilocalories per day (kcal/day) or kilojoules per day (kJ/day).
Basal metabolic rate, or BMR, is the minimum energy expended by an endothermic animal at rest.
While some factors determining your metabolic rate cannot be changed, such as your height and age, one can increase their metabolic rate by exercising well, eating a protein rich and low-carb diet, and good sleeping habits.
While some factors determining your metabolic rate cannot be changed, such as your height and age, one can increase their metabolic rate by exercising well, eating a protein rich and low-carb diet, and good sleeping habits.
The most frequently use formula to calculate BMR is the Revised Harris-Benedict Formula:
BMRMale = 13.4·Weight (kg) + 4.8·Height (cm) - 5.68·Age (yrs) + 88
BMRFemale = 9.25·Weight (kg) + 3.1·Height (cm) - 4.33·Age (yrs) + 447.6
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SIGNUP SIGNUPFlashcards in Metabolic Rate15
Start learningTrue or False? Metabolism and metabolic rate are interchangeable terms.
False
Which of the following is not a metabolic process?
None of the choices
What is an autotroph?
An autotroph is an organism that gets its own food from the inorganic environment.
What is a heterotroph?
An organism that consumes other living organism to obtain energy.
What is an endotherm?
An organism that uses its internal metabolism to thermoregulate.
What is an ectotherm?
An organism that uses the external environment to thermoregulate.
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