Metabolic Rates and Gas Exchange

Metabolic Rates Within Species

  • The study of metabolic rates focuses on how organisms convert biochemical energy into biological work.

Total Metabolic Rates Across Species

  • Comparative metabolism suggests that metabolic rates vary widely across species.

Skeletal Mass

  • Definition of Allometry: The study of the size and shape relationships across different functionalities of organisms.

    • If b > 1, the relationship exhibits positive allometry, where larger animals possess a relatively larger proportion of skeletal mass compared to their overall body mass.

    • Analyzing skeletal mass through allometric relationships facilitates predictions of traits for species yet to be measured.

    • A graph presented demonstrates a comparative study of skeletal mass against body mass (in kg).

Heart Rate and Heart Mass

  • Allometric scaling also applies to heart rate and heart mass, influencing metabolic capabilities across various species.

Scope of Allometry in Biology

  • Theories of allometry explain vast biological patterns, indicating that numerous biological functions do not increase proportionally with body mass. These include:

    • Lifespan

    • Resting heart rate

    • Wingbeat frequency

    • Organ mass (grams), etc.

    • The variation in these functions signifies that evolutionary changes in size are complex and cannot be simplified into a linear relationship.

Respiratory System Overview

  • Definition of External Respiration: The process by which organisms facilitate gas exchange, crucial for maintaining life through cellular respiration.

    • Example: Bluefin Tuna

    • Characteristics: Two separate species, size up to 21ft, weighing around 1600 lbs.

    • Conservation status: Only 2.6% remaining from initial population due to extensive fishing; a 64% decline since the 1970s.

    • Size changes: Average size has decreased from 1200 lbs in the 1970s to about 600 lbs by 2015.

Gas Exchange and Circulation

  • Overall Equation for Cell Respiration:

    • C_6H_{12}O_6 + 6O_2
      ightarrow 6CO_2 + 6H_2O + ext{~2860 kJ}

    • Mechanisms:

    1. Ventilation: Movement of water or air across specialized gas exchange organs.

    2. Gas Exchange: The diffusion process through respiratory surfaces, allowing oxygen to enter the blood and carbon dioxide to exit.

    3. Circulation: The transport of gases via blood to and from body tissues.

    4. Cellular Respiration: The metabolic process utilizing O2 to produce CO2 and energy at the cellular level.

Dalton's Law

  • Statement: The total pressure of a gas mixture equals the sum of partial pressures of individual gases.

  • Ideal Gas Law Equation: PV = nRT

    • Where

    • P = Pressure

    • n = Number of moles

    • V = Volume

    • R = Universal gas constant

    • T = Absolute temperature

Changes in Pressure

  • Examined how decreasing the volume of gas affects its partial pressure:

    • Pressure increases when volume decreases due to the relationship P = rac{nRT}{V}.

    • Conversely, raising the volume reduces pressure, showing an inverse relationship.

Atmospheric Pressure Measurement

  • Methodology: Atmospheric pressure is measured using a barometer, compiling the heights of mercury in a glass column.

    • Standard pressure: 1 atmosphere (atm) is equivalent to 760 mm Hg at sea level.

    • Calculations of Partial Pressures in the atmosphere:

    • For Nitrogen (78%): 0.78 imes 760 = 593 ext{ mm Hg}

    • For Oxygen (21%): 0.21 imes 760 ext{ (Find average)} = 160 ext{ mm Hg}

    • Adjustments for Carbon Dioxide (0.04%): 0.0004 imes 760 = 0.3 ext{ mm Hg}

Effects of Altitude

  • As altitude increases, the absolute pressure decreases, influencing the availability of oxygen.

    • Key Point: While the percentage of oxygen remains constant at about 21%, the total atmospheric pressure diminishes, further reducing individual oxygen availability at high elevations.

Solubility of Gases in Water

  • Oxygen solubility in water is exceptionally low, about 0.003 mL per 100 mL of water.

  • Factors Influencing Solubility:

    • Temperature: Higher temperatures reduce gas solubility.

    • Presence of Solutes: More solutes lead to decreased air solubility in the solution.

    • Differences Between Fresh and Salt Water: Freshwater typically holds higher oxygen concentrations than seawater due to solute concentration effectiveness.

Fick's Law of Diffusion

  • This principle states:

    • Rate of diffusion = k imes A imes rac{(P_2 - P_1)}{D}

    • Where:

      • k = diffusion constant dependent on gas solubility,

      • A = surface area available for diffusion,

      • P_2 and P_1 indicate partial pressure at two points,

      • D = distance or thickness of membranes.

    • Understanding Fick's Law aids in making conclusions on how gases move from high to low partial pressures through various media (both water and air).

Specialized Respiratory Systems

  • Adaptations in respiratory systems enhance diffusion capabilities by maximizing surface areas while minimizing membrane thickness.

    • Example: In human lungs, the respiratory surface spans approximately 140 m² and maintains a thickness of just 0.2 microns.

Implications Based on Fick's Law in Biology

  • When considering the surface area and barrier thickness based on Fick's Law, varying organ morphologies and evolutionary adaptations emphasize the necessity for large surface areas in efficient gas exchange.

  • This adaptive significance is particularly apparent in aquatic species needing to overcome the drastically lower oxygen solubility in water compared to air.