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Unit 2: Animals

Energy and Temperature

  • Date: Feb. 20, 2026
  • Instructor: Dr. Ana Longo
  • Course: BSC2011-Spring 2026

Today's Outline

  • Chapter 28: Transformation of Energy and Matter
    • 28.2 An Animal's Energy Needs Can Be Quantified
    • 28.3 Responses to Temperature Help Clarify Homeostasis

Learning Objectives

  • Explain the fundamental reasons that animals need energy.
  • Explain what an animal's metabolic rate is and how it can be measured.
  • Specify the advantages and disadvantages of both regulation and conformity.
  • Define homeostasis and give an example of it.
  • Describe how a negative-feedback control system works.

Animals as Heterotrophs

  • Animals are classified as heterotrophs:
    • Definition: Require preformed organic molecules as sources of energy and chemical building blocks.
    • Obtain energy by breaking the chemical bonds of organic compounds obtained from other organisms.
    • Build their tissues from the matter present in preexisting organic compounds obtained from other organisms.
    • Need chemical building blocks for growth and to replace cells throughout life.

Nutritional Requirements

  • Animals eat to obtain:
    • Energy
    • Chemical building blocks
  • Essential nutrients include:
    • Nutrients: Amino acids, fatty acids, minerals, carbohydrates, proteins.
    • Examples of essential nutrients:
    • Linoleic acid and alpha-linoleic acid - must be included in the diet (omega-3 and omega-6 fatty acids).
    • Vitamin A (retinol) - essential for vision and other functions.
      • Chemical Structure of Vitamin A:
      • C20H30OC_{20}H_{30}O

Visual Acuity Studies in Various Species

  • Research highlighted that:
    • Estimated visual acuity of about 600 species.
    • Humans can see the world 100 times more detail than mice and fruit flies.
    • Source: Eleanor Caves, Smithsonian Magazine, 2018.

Metabolic Rate

  • Definition: The amount of chemical bond energy consumed and converted to heat per day.
  • Three types of food molecules contribute to metabolic rate:
    • Lipids (fats and oils)
    • Carbohydrates
    • Proteins
  • Example of metabolic reaction:
    • Organic compound + O_2
      ightarrow CO_2 + H_2O + ext{heat}

Measurement of Metabolic Rate

  • Measured by determining:
    • The rate of O2O_2 consumption, as it has a one-to-one relationship with the heat generated during aerobic metabolism.

Cost of Exercise

  • The rate of O2O_2 consumption varies among species during exercise:
    • (A) Humans, (B) Fishes, (C) Birds
    • As physical activity increases, so does metabolic rate.

Basal Metabolic Rate (BMR)

  • Definition: BMR is measured when an animal is in a comfortable thermal environment and has not eaten recently.
  • BMR is expressed as extmlextO2/[gimeshr]ext{ml } ext{O}_2/[g imes hr].
  • BMR per gram body weight decreases with animal size showing that small mammals require more food per gram of body weight than large mammals.

Regulation vs. Conformity

  • Regulation: An internal environment that remains constant even as external factors change.
  • Conformity: The internal environment varies so that it matches the external environment.

Homeostasis

  • Definition: The stability of the internal environment and mechanisms that maintain it.
  • Homeostasis is parallel to regulation, possessing similar advantages and disadvantages. It is also energetically expensive.
  • Example: Thermoregulation - maintains body temperature within a narrow range (typically 0°C to 40°C).

Responses to Temperature Changes

Homeothermy (Endotherms)
  • Metabolic rate is affected by external temperatures. If it falls below the thermoneutral zone (TNZ):
    • Metabolic rate increases to maintain warmth.
  • Conversely, if it rises above TNZ:
    • Metabolic rate also rises to lose heat.
Poikilothermy (Ectotherms)
  • Poikilothermic animals' metabolic rate rises with external temperature:
    • Internal temperatures rise, accelerating biochemical processes.
  • Some species can tolerate extreme temperatures, for example:
    • Desert lizards can survive at 40°C to 50°C.
    • Antarctic fishes can thrive at temperatures as low as -2°C.
Behavioral Regulation
  • Poikilotherms manage body temperature through behavior, such as:
    • Basking in the sun for warmth.

Mechanisms of Thermoregulation in Homeotherms

  • In cold environments, homeothermic animals can:
    • Shiver (skeletal muscle contraction generates heat).
    • Engage in non-shivering thermogenesis where brown adipose tissue generates heat.
  • Insulation through fur and feathers helps retain heat.
  • Specialized blood flow patterns can also conserve heat.
  • In hot environments, cooling mechanisms include:
    • Evaporative cooling (sweating or panting).

Thermoregulation Control System

  1. Controlled Variable: Body temperature
  2. Sensors: Temperature sensors in the body provide feedback on current temperature.
  3. Effectors: Tissues that generate heat through shivering or non-shivering methods.
  4. Control Mechanism: Compares current body temperature to a set point (e.g., 37°C) and activates effectors if necessary.

Positive Feedback

  • Definition: Deviation from a set point amplifies the response, destabilizing the system.
  • Not typical in homeostasis but can be beneficial when controlled.

Next Class Preview

  • Topics to be covered include:
    • 29.1 Animals Prosper in Diverse Thermal Environments
    • 29.2 Animals Live in the Ocean, Fresh Water, and Intermediate Salinities
    • 29.3 The Phenotypes of Individual Animals Can Change in Response to Environmental Change
    • 29.4 Animals Have Biological Clocks Tuned to Cycles in Their Environment