Chp 6Energy Metabolism

• Energy metabolism:

- Catabolism: processes breaking down organic molecules to release energy

- Anabolism: processes using energy to construct molecules

Why animals need energy?

Fundamentals of Animal Energetics• Energy is needed for work• Animals can use chemical,

electrical and mechanical energies (high grade energy) for work but not thermal energy (low grade energy).

• Efficiency of energy transformation = output/input of high-grade

• Efficiency: Always less than 1.

• Ex: glucose 70%ATP + 30% heat

Energy use• Energy (food) is used

for:– Maintenance – Growth (biosynthesis)– Work

• However, each conversion is inefficient– heat formation– Usable energy: from

feces(?!), body matter

Metabolic rate: Meaning and Measurement

• Energy for work + heat comes from energy consumed

• Rate of energy consumption = metabolic rate

• Energy is measured in calories or joules• Calorie: amount of heat needed to raise the temperature of 1 gm of

water by 1oC.

• Metabolic rate = consumption of energy: calories/unit of time or watts

• Significance of metabolic rates:– 1 - determines the amount of food an animal will need– 2 - the total rate of heat production is proportional to the total activity of

all its physiological mechanisms– 3 - an animal’s metabolic rate represents the use of food resources of

this animal’s ecosystem

Metabolic rate measurement

• Direct measurement • Indirect measurement– By respirometry

(box 6.4)

– By measuring the chemical-energy content of the organic matter that enters and leaves the animal’s body

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Metabolic rate• Read p 149

• Under aerobic metabolism, carbohydrates, proteins and lipids are burnt and produce CO2

• The rate of O2 consumption and CO2 formation vary with the 3 gps of nutrients (table 6.1)

• Respiratory quotient (lungs) R = moles CO2 produced /moles O2 consumed

• For convenience, O2 consumption is used to estimate the metabolic rate

Allows to estimate the kind of food that has been burnedBecause this is cumbersome to calculate, the number 20.2J/ml O2 is

used to calculate the MR from O2 consumption

Factors that affect metabolic rates

• 2 main factors:– physical activity– external temperature

• Other factors:– Age– Food ingestion– Gender– Time of the day– Body size– Reproductive condition– Hormonal state– Psychological stress

• For aquatic animal, the salinity of ambient water

• The food effect: specific dynamic action (SDA) = calorigenic effect of ingested food, especially proteins

• The SDA is about 25%-30% of the energy value of the meal.

• Basal metabolic rate = BMR = metabolism rate at rest, at thermoneutral zone, in homeotherms

• Thermoneutral zone = temperature at which the BMR is minimal

• Standard Metabolic Rate = MR of a poikilotherm while it is 1) fasting, 2) resting

Metabolic rate, size and activity• The maximal MR (Mmax)

during strong aerobic exercise tends to be 10 x the BMR

• The number of mitochondria per cells is higher in smaller species

• Smaller species have also a more extensive respiratory tubes and circulatory vessels

Heart size and Heart ?

• Heart size is proportional to body size

• However, smaller bodies have a higher MR

• How to provide the body with enough O2 to sustain a more intense MR?

Relationship between size and metabolic rate

• The total BMR increases with size, however, it does not proportionally increase with weight

• Weight-specific metabolic rate: relationship constant through homeo and poikilotherms (allometric relationship)

• M = aWb

• b = 0.65-0.75• a varies with groups

•

Heart size and Heart ?

• Heart size is proportional to body size

• However, smaller bodies have a higher MR

• How to provide the body with enough O2 to sustain a more intense MR?

Heart size and Heart ?• Heart size is proportional to

body size• However, smaller bodies

have a higher MR

• How to provide the body with enough O2 to sustain a more intense MR?

• By having an increased Heart Rate and an increased Respiratory Rate

• Ecological consequences:– Smaller species need more

food per unit of body weight

– Smaller species draw more resources from the ecosystem

– Smaller species accumulate more toxins than larger one.

Energetics of food and growth• Proteins and carbohydrates = 4

kCal/gm, lipids – 9 kCal/gm• Energy absorption efficiency =

absorbed/ingested energy• Growth growth efficiency=

chemical-bondd energy of tissue added by growth (net)/ingested energy

• Net growth efficiency = chemical-bond energy of tissue added by growth (net)/absorbed energy

• Growth efficiency declines with age

Practical consequences• Farming and aquaculture:

animals are slaughtered when they have reached their peak growth.

• Afterward, there is a decrease in the investment

• All life processes cost energy • Mental effort costs some,

however, brain maintenance is overall costly