Basic Principles of Animal Form and Function

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in body cells

Carbon

skeletons

Cellular

respiration

ATP

Heat

Energy lost

in feces

Energy lost in

nitrogenous

waste

Heat

Biosynthesis

Heat

Heat

Cellular

work

Slide 56

Quantifying Energy Use

Metabolic rate is the amount of energy an animal uses in a unit of time.

One way to measure it is to determine the amount of oxygen consumed or carbon dioxide produced.

Slide 57

Minimum Metabolic Rate and Thermoregulation

Basal metabolic rate (BMR) is the metabolic rate of an endotherm at rest at a “comfortable” temperature.

Standard metabolic rate (SMR) is the metabolic rate of an ectotherm at rest at a specific temperature.

Both rates assume a nongrowing, fasting, and nonstressed animal.

Ectotherms have much lower metabolic rates than endotherms of a comparable size.

Slide 58

Influences on Metabolic Rate

Metabolic rates are affected by many factors besides whether an animal is an endotherm or ectotherm.

Two of these factors are size and activity.

Metabolic rate is inversely related to body size among similar animals.

The higher metabolic rate of smaller animals leads to a higher oxygen delivery rate, breathing rate, heart rate, and greater (relative) blood volume, compared with a larger animal.

Slide 59

Relationship of Metabolic Rate to Body Size

Elephant

Horse

Human

Sheep

Dog

Cat

Rat

Ground squirrel

Mouse

Harvest mouse

Shrew

Body mass (kg) (log scale)

BMR (L O2/hr) (Iog scale)

10–3

10–2

10–2

10–1

10–1

10

10

1

1

102

102

103

103

(a) Relationship of BMR to body size

Shrew

Mouse

Harvest mouse

Sheep

Rat

Cat

Dog

Human

Horse

Elephant

BMR (L O2/hr) (per kg)

Ground squirrel

Body mass (kg) (log scale)

10–3

10–2

10–1

1

10

102

103

0

1

2

3

4

5

6

8

7

(b) Relationship of BMR per kilogram of body mass to body size

Slide 60

Activity greatly affects metabolic rate for endotherms and ectotherms.

In general, the maximum metabolic rate an animal can sustain is inversely related to the duration of the activity.

Different species use energy and materials in food in different ways, depending on their environment.

Use of energy is partitioned to BMR (or SMR), activity, thermoregulation, growth, and reproduction.

Activity, Metabolic Rate, and Energy Budgets