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+ BIOL 370 > Lecture 10.1: Metabolic Scaling > Flashcards

Lecture 10.1: Metabolic Scaling Flashcards

1
Q

What is isometric scaling?

A

relationship among geometrically similar objects

  • variables change in direct proportion with size
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2
Q

What is allometric scaling?

A

relationship is often curvilinear

  • variables do not change in direct proportion with size
  • Y = aM^b
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3
Q

equation: Y = aM^b

log equation: log Y = b log M + log a

A
  • body mass (M): mass of the organism
  • intercept (a): proportionality constant – aids in comparing between datasets and asking questions related to levels
  • slope (b): mass exponent (or scaling exponent/coefficient) – provides information on how a variable of interest changes with body mass
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4
Q

What is isometry?

A

slope (b) = 1

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5
Q

What is hyperallometry?

A

slope (b) > 1

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6
Q

What is hypoallometry?

A

slope (b) < 1

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7
Q

Should allometric scaling of metabolic rate be viewed as a fundamental law in biology?

A

NO

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8
Q

What is metabolic rate?

A

amount of energy expended per unit time

  • sum of all energy transformation processes
  • rate of ATP turnover
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9
Q

What are the 3 types of metabolic rate?

A
  • standard or basal metabolic rate
  • maximal metabolic rate
  • hypometabolic rates (metabolically suppressed)
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10
Q

What are the 3 measurements of metabolic rate?

A
  • O2 consumption rate (VO2 or MO2)
  • CO2 production rate (VCO2 or MCO2)
  • heat dissipation
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11
Q

What contributes to an organism’s whole animal basal metabolic rate (BMR)?

A
  • not all organs contribute equally to whole body basal metabolic rate (BMR) – how much an organ makes up part of your body does not correlate with how much it contributes to BMR
  • subcellular processes contribute differently to whole animal metabolic rate – protein turnover and ion regulation contribute the greatest to dictating whole animal metabolic rate
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12
Q

How is metabolic rate scaled?

A

allometric relationship (can determine from the slope, which is not 1)

  • as body size increases, whole body metabolic rate increases – increases in heat production in various organisms
  • same allometric relationship between body size and whole body metabolic rate exists in unicellular organisms < ectotherms < homeotherms (but slopes differ)
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13
Q

Basal metabolic rate (BMR) scales with body mass with what scaling exponent (b)?

A

vast majority of studies indicate somewhere around 0.67 and/or 0.75

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14
Q

Do 1/3 laws or 1/4 laws govern scaling of metabolic rate?

A

–

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15
Q

What is the 1/3 law?

A

b = 0.67 or ⅔

  • based on 3 dimensions – ie. surface area to volume ratio
  • if size is growing by 1, metabolic rate is growing ⅔ – growth is proportional to the mass exponent
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16
Q

What is the 1/4 law?

A

b = 0.75 or ¾

  • includes additional component(s) beyond the 3D size/volume relationship
17
Q

What are the 2 broad categories of theories explaining the relationship between metabolic rate and body mass, and what are the 4 theories?

A

categories:

  • due to physical properties of being 3D organism
  • intrinsic properties of the cell/organism

theories:

  • surface area/volume
  • system composition
  • resource demand
  • resource transport
18
Q

Theories Explaining the Relationship Between Metabolic Rate and Body Mass

  1. Surface Area/Volume
A
  • oldest theory – “Rubner’s Law”
  • basal metabolic rate (BMR) is proportional to mass^2/3
  • based on simple geometric and physical principles
  • rate of metabolic heat production is matched to the rate of heat dissipation across the body surface
19
Q

Theories Explaining the Relationship Between Metabolic Rate and Body Mass

  1. Surface Area/Volume

Do smaller or larger animals lose more heat?

A

smaller animals lose more heat per volume due to their large SA:V ratio

  • very small organisms (ie. amoeba) have larger SA:V ratio compared to larger animals – absorb gasses and nutrients across their integument, which limits their maximal size
  • larger animals are more energy-efficient than smaller ones on a per-unit-mass basis – this is why there is an allometric relationship
20
Q

Theories Explaining the Relationship Between Metabolic Rate and Body Mass

  1. System Composition
A
  • proportion of metabolically active and inert tissues differ with body size – LARGER animals have GREATER proportion of metabolically inert tissue (ie. bone)
  • skeletal mass scales with body mass with b = ~1, which does NOT explain allometric relationship between metabolic rate and body mass
  • this theory is largely ignored
21
Q

Theories Explaining the Relationship Between Metabolic Rate and Body Mass

  1. Resource Demand
A

intrinsic properties of the cell define the metabolic rate scaling relationship

  • different properties → different resource demands → different scaling relationship as body size increases
  • 1 g of cells from a small animal has a higher intrinsic metabolic rate than 1 g of cells from a large animal
  • metabolic rate: scaling coefficient = 0.75
  • mass-specific metabolic rate: scaling coefficient = -0.25
  • larger animals have smaller mass-specific metabolic rate
22
Q

Theories Explaining the Relationship Between Metabolic Rate and Body Mass

Conclusion

A
  • big theories that explain metabolic rate scaling relationships (increase in metabolic rate with increase in body size) is resource demand and intrinsic properties of the cell
  • degree of membrane unsaturation decreases with increasing body mass in mammals and birds
23
Q

How does membrane unsaturation change with body mass in mammals and birds?

A

degree of membrane unsaturation DECREASES with INCREASING body mass in mammals and birds

  • smaller animals have greater % of unsaturation
  • larger animals have greater % saturation level in membrane
  • suggests that the membrane can function as a metabolic pacemaker
24
Q

What are control coefficients (Q)?

A

quantifies the contribution of each step in a pathway to regulating overall flux through that pathway

  • to determine Q for one site in a metabolic pathways, double the quantity of the enzyme at the site and determine the effect on overall pathway flux (rate)
  • Q of an entire pathway must add up to 1

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