Chp 6 Energy Metabolism

1. 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?

2. 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 Fundamentals of Animal Energetics

3. Energy use • Energy (food) is used for: • Maintenance • Growth (biosynthesis) • Work • However, each conversion is inefficient •  heat formation • Usable energy: from feces(?!), body matter

4. 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

5. 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 Metabolic rate measurement ___

6. 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 burned Because this is cumbersome to calculate, the number 20.2J/ml O2 is used to calculate the MR from O2 consumption

7. 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. Factors that affect metabolic rates

8. 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

9. 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 Metabolic rate, size and activity

10. 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 ?

11. 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 Relationship between size and metabolic rate

12. 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 ?

13. 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. Heart size and Heart ?

14. 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 Energetics of food and growth

15. 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 Practical consequences