L6Energy

The Burden of Food

Overview

• Chapter 7 of Animal Physiology discusses the energy concepts related to physiological processes in animals.

What Is Energy?

• Energy is defined as the capacity to do work or supply heat.

• It exists as:

  • Stored Potential Energy

  • Active Motion (Kinetic Energy)

Potential Energy

• Definition: Stored energy.

• An object's ability to store energy is determined by its position.

  • Key Aspects: Electrons in the outermost shells have the greatest potential energy.

  • Electron Shells: 1st, 2nd, 3rd levels of electron shells indicate energy level.

Kinetic Energy

• Definition: The energy of movement, also known as thermal energy.

• Measured as temperature:

  • Low temperature implies slow-moving molecules (perceived as "cold").

  • High temperature implies rapid-moving molecules (perceived as "hot").

Heat and the First Law of Thermodynamics

• Heat: The thermal energy transferred between objects at different temperatures (Molecular kinetic energy).

• First Law of Thermodynamics:

  • Energy is conserved; it cannot be created or destroyed.

  • Energy can be transferred or transformed.

The Second Law of Thermodynamics

• Second Law: Entropy always increases.

  • Chemical reactions produce products with less ordered and usable energy.

• Entropy (S): Amount of disorder among molecules.

• Processes tend to lower potential energy and increase disorder.

The Second Law of Thermodynamics in Action

• Demonstrated via isolated systems, such as a water-filled copper pipe.

  • Initial and later states show the energy of random versus directional motion.

Physiological Work Dominated by Chemical Energy

• Physiological work is primarily derived from chemical energy.

• Mechanical or electrical work can also be performed but heat cannot be utilized effectively without a temperature differential.

Animals Degrade Energy

• High-grade energy is transformed into low-grade energy in animals, which is used for physiological work.

• Energy flow from chemical energy to heat is irretrievable.

Efficiency of Energy Transformation

• Energy output is always less than one.

  • Examples: Glucose converts to ATP (70%) + heat (30%).

  • ATP used in muscle contraction (25-30% usage, with rest as heat).

Uses of Energy by an Animal

• Absorbed Chemical Energy: Used for growth, biosynthesis, and maintenance.

• Leaves the system as heat, chemical energy, or external work.

Energy Flow Diagram (Figure 7.2)

• Absorbed chemical energy leads to:

  • Growth (accumulated in body tissues)

  • Internal maintenance (degradation)

  • Generation of external work (mechanical energy).

Animal Heat Production

• Energy is consumed through heat and external work conversions.

• Rate of metabolic activity influences the heat production of animals.

Metabolic Rate

• Defines how much energy is consumed over time.

• Uses include:

  1. Estimating food requirements of animals.

  2. Measuring overall physiological activities.

  3. Understanding resource utilization in ecosystems.

Measuring Metabolic Rates

Lavoisier's Calorimeter

• A direct calorimeter measures animal heat production, enclosing animals in ice-filled jackets to measure melting ice as heat output.

Modern Calorimetry

• Complex and costly, with advancements leading to indirect calorimetry methods.

Indirect Calorimetry Theory

• Combustion of glucose yields large amounts of energy:

  • C6H12O6 + 6O2 → 6CO2 + 6H2O + 2,820 kJ/mol.

Ratios: Heat Production to O2 and CO2 Consumption

• Monitoring the ratios during the aerobic metabolism of carbohydrates, lipids, and proteins.

Respiratory Quotients (RQ Values)

• Measure of moles of CO2 produced versus O2 consumed during aerobic processes.

Factors Affecting Metabolic Rates

• Large Effects: Physical activity, environmental temperature.

• Smaller Effects: Meal ingestion, body size, age, gender, O2 levels, hormonal status.

Specific Dynamic Action (SDA)

Overview

• Concept showing the metabolic response to food consumption.

• Energy expenditure spikes post-meal consumption.

Importance of Standardization

Basal Metabolic Rate (BMR)

• Definition: BMR is the rate of energy expenditure per unit time by warm-blooded animals at rest in a thermally neutral environment, not undergoing any physical activity, and after a period of fasting (typically overnight).

• Measurement Conditions: To obtain an accurate measurement of BMR for mammals and birds, it is essential to conduct tests in thermoneutral zones where temperature does not influence metabolic rate. This ensures the energy expenditure reflects the basal needs without the added variable of thermoregulation.

• Importance: BMR is critical for understanding the energy needs of an organism, determining food intake, and assessing overall health.

Standard Metabolic Rate (SMR)

• Definition: SMR refers to the standard metabolic rate of ectothermic animals, such as amphibians, fish, and mollusks, under specific resting conditions.

• Measurement Requirements: Like BMR, SMR is measured while the animal is fasting and resting, but it applies to organisms that depend on external temperatures for regulating their body heat. Measurements are often taken at a defined temperature where the animal's metabolism is stable and unaffected by thermal stress.

Effect of Body Size on Food Requirements

• Overview: This concept explains how an animal's size influences its metabolic needs and food consumption. Typically, larger animals require more energy than smaller ones, but the relationship is not linear.

• Details: The body mass/metabolism relationship illustrates that as body size increases, the BMR increases, but not in direct proportion, leading to an exemption of the assumption that larger animals would simply eat more based on body mass alone.

• Figures for Different Species: Graphical representations in studies show quantitative comparisons of weekly food intake across various species, highlighting significant variances that reflect adaptability to ecological niches and physiological capabilities.

Whole-Body BMR vs. Body Weight

• Examination of Metabolic Rates: Studies focusing on placental mammals assess how BMR relates to body weight, showing integrative physiological processes at play.

• Significant Findings: Generally, larger mammals exhibit a lower metabolism per unit of body weight compared to smaller mammals. This phenomenon emphasizes the physiological adaptations that animals have developed in relation to their size, becoming more efficient in maintaining energy balance as body mass increases.

• Integration with Ecological Practices: Understanding these correlations is valuable in ecological research, resource management, and conservation strategies as it highlights how energy use can impact survival and adaptability in various environments.