Phys Eco Exm 2 Section 1: Energy Metabolism & Measuring Energy Expenditure

What does metabolism include

The physical role of nutrients and intermediary metabolism.

What is energy metabolism

The overall use of chemical energy, including oxidation of food to produce ATP.

What units are used to measure energy

Calories/kcal, joules, and watts.

What is the difference between potential and kinetic energy

Potential energy is stored chemical energy. Kinetic energy is energy associated with motion or heat.

What happens to food energy during digestion and absorption

Energy is transferred into ATP and transformed into heat because the process is inefficient.

What are the major uses of energy in animals

Maintenance, biosynthesis, and physical work.

Why do maintenance, biosynthesis, and physical work produce heat

These processes are inefficient, so some energy is transformed into heat.

How does high metabolism contribute to endothermy

Heat produced by high metabolism maintains high body temperatures in birds and mammals.

How can diet trials measure energy expenditure

Provide diets with different energy levels, monitor body mass gain/loss, and determine intake required for 0% mass change.

How do digestibility studies measure energy expenditure

Measure the energy value of all food consumed and all material excreted.

What assumption is required for energy-focused digestibility studies

No change in body mass or body composition.

What is direct calorimetry

Measuring total heat production to determine energy expenditure.

What is the advantage and disadvantage of direct calorimetry

Most accurate in principle but difficult in practice.

What is indirect calorimetry

Using gas exchange to approximate heat production.

Why can O₂ consumption estimate heat production

Heat produced per volume of O₂ consumed is nearly constant regardless of substrate.

What differs among carbohydrates, lipids, and proteins during oxidation?

The amount of CO₂ produced.

What is respiratory quotient (RQ)?

Volume of CO₂ produced divided by volume of O₂ consumed.

What does RQ indicate?

Which metabolic substrate an animal is oxidizing.

What is the RQ of carbohydrates?

1.0.

What is the RQ of lipids?

0.71.

What is the RQ of proteins?

0.83.

What is doubly labeled water used for?

Measuring energy expenditure in the field.

How does doubly labeled water work?

The animal receives stable isotopes ²H and ¹⁸O. Hydrogen is lost as water, while oxygen is lost as water and CO₂.

How is energy expenditure calculated using doubly labeled water?

The difference in isotope loss estimates CO₂ production, and energy expenditure is calculated using RQ.