Chapter 39 - Animal Form & Function

Anatomy vs Physiology

• Anatomy: structure of biological components (cells, tissues, organs)

• Physiology: how those structures function

• Structure determines function

  • Natural selection favors forms that improve efficiency of biological processes

Structure → Function (Examples)

Form-function relationships are shaped by natural selection acting on efficiency

• Membrane proteins form hydrophilic channels through lipid bilayers, allowing selective ion/molecule transport

• Secretory cells contain abundant rough ER and Golgi apparatus for protein synthesis and export

• Phagocytic cells contain many lysosomes to digest pathogens efficiently

• Neurons have long axons for long-distance signal transmission and branched dendrites for receiving inputs

Adaptation

• A heritable trait that increases fitness in a specific environment

• Arises through natural selection acting on genetic variation within populations

• Individuals with advantageous traits have greater fitness → leave more offspring → increase allele frequency over generations

• Example: finch beak shapes adapted to specific food sources

Fitness and Natural Selection

• Fitness = ability of an individual to produce viable offspring

• Natural selection requires heritable variation, differential survival, and differential reproduction

• Traits that increase fitness become more common over generations

• Selection acts on phenotypes but changes allele frequencies in populations

• Leads to evolutionary adaptation over time

Fitness Trade Offs

A compromise where improving one trait reduces performance in another due to limited resources

• Organisms must allocate finite energy among competing processes (growth, reproduction, immunity)

• Prevents simultaneous optimization of all traits

• Reflects evolutionary constraints and resource allocation strategies

• Ex: include reproduction vs immune function

Cricket Experiment (Trade Off Example)

• Manipulated reproductive effort and immune function in male crickets

• Increased reproductive investment led to reduced immune function (lower bacterial lysis)

• Increased immune stimulation reduced reproductive output (smaller spermatophores)

• Demonstrates energy allocation trade-off between reproduction and immunity

• Conclusion: investing in one physiological system reduces resources available for others

Genetic Diversity vs. Phenotypic Plasticity

• Genetic diversity = variation in DNA among individuals → heritable differences across generations

• Phenotypic plasticity = ability of a single genotype to produce different phenotypes in response to environment

• Genetic differences persist regardless of environment; plasticity changes with environment

• Plasticity occurs within an individual’s lifetime, while genetic variation occurs across generations

Adaptation vs. Acclimatization

• Adaptation = genetic change in a population over generations due to natural selection

  • Involves allele frequency changes

  • Occurs over evolutionary timesacles

• Acclimatization = reversible physiological change in response to environmental change

  • Does not alter DNA

  • Occurs over short timescales

  • Ex: increased RBC production at high altitude

Levels of Organization in Animals

• Cells: basic functional units of life

• Tissues: groups of cells that perform a common function

• Organs: consist of two or more tissue types working together

• Organ systems: groups of organs that coordinate to perform major functions

Epithelial Tissue: Structure & Function

• Forms protective layers covering surfaces and lining cavities

• Simple epithelium allows diffusion/absorption; stratified epithelium provides protection

• Cells are tightly packed

• Has polarity: apical surface faces environment, basolateral surface attaches to basal lamina

• Tight junctions and desmosomes maintain structural integrity

Connective Tissue: Structure and Types

• Consists of cells embedded in an extracellular matrix

• Matrix contains fibers: collagen (strength), elastin (elasticity), reticular (supportive mesh)

• Loose connective tissue acts as packing material

• Dense connective tissue connects structures (tendons, ligaments)

• Supporting tissue (bone, cartilage) provides structure; fluid tissue (blood) transports materials

Muscle Tissue: Types and Functions

• Skeletal muscle attaches to bones and produces voluntary movement

• Cardiac muscle forms heart walls and contracts rhythmically to pump blood

• Smooth muscle lines organs and controls involuntary movements (e.g., digestion, blood flow)

• Cells differ in structure (striated vs non-striated) and control (voluntary vs involuntary)

• All types contract in response to electrical signals

Nervous Tissue: Structure and Function

• Composed of neurons and supporting cells; enables communication throughout the body

  • Neurons: transmit electrical signals via changes in membrane permeability to ions

  • Dendrites receive signals

  • Axons transmit signals to other cells

  • Supporting cells regulate ion balance and provide nutrients

Surface Area to Volume Ratio

• Surface area determines rate of exchange (oxygen, nutrients, waste)

• Volume determines metabolic demand and production of heat/waste

• As size increases, volume increases faster than surface area → decreasing SA:V ratio

• This limits diffusion efficiency in larger organisms

SA:V and Metabolic Rate

• Metabolic rate is the total energy consumption of an organism

• Mass-specific metabolic rate (per gram) decreases as body size increases

• Small animals have high SA:V, lose heat quickly, and require higher metabolic rates

• Large animals retain heat better and have lower mass-specific metabolic rates

• Scaling reflects constraints imposed by surface area for exchange

Diffusion Constraints in Large Organisms

• Diffusion distance increases as body size increases

• Longer distances slow transport of oxygen, nutrients, and wastes

• Cells must remain small or develop transport systems

• Multicellular organisms evolve circulatory systems to overcome diffusion limits

Adaptations to Increase Surface Area

• Flattening (e.g., gill lamellae)

• Folding (e.g., intestinal villi)

• Branching (e.g., capillary networks)

• These adaptations maximize exchange rates for gases and nutrients

• Essential for maintaining metabolic demands in larger organisms

Homeostasis Importance

• The maintenance of stable internal conditions within tolerable limits

• Conditions fluctuate around a set point

  • Dynamic equilibrium, not constant

• Critical for enzyme function, membrane stability, and cellular processes

• Variables: temperature, pH, ion concentration

• Maintained through regulatory feedback systems

Negative Feedback Mechanism

• Negative feedback restores conditions toward a set point by reversing deviations to maintain homeostasis

• Involves sensor, integrator, and effector components

• Sensor detects change; integrator compares to set point; effector produces response

• Example: body temperature regulation via sweating or shivering (most common mechanism to maintain homeostasis)

Positive Feedback Mechanism

• Positive feedback amplifies disturbances and drives the system farther from the set point

  • Disturbance is still triggered, sensed, and integrated

  • But it uses amplifiers instead of effectors

• Less common in the body

• Perpetuates change

• Examples: blood clotting, childbirth, milk production

Regulators vs Conformers

• Regulators maintain stable internal conditions despite environmental changes

• Conformers allow internal conditions to vary with environment

• Most animals fall along a spectrum between these extremes

• Regulation requires energy; conformation conserves energy

• Example: mammals (regulators) vs many aquatic animals (conformers)

Endothermy vs Ectothermy

• Endotherms generate heat internally through metabolism

  • High metabolic rates and require more food

• Ectotherms rely on external heat sources

  • Lower metabolic rates and depend on environmental conditions

Homeothermy vs Poikilothermy

• Homeotherms maintain relatively constant body temperature

  • Most endotherms are homeotherms

• Poikilotherms allow body temperature to vary with environment

  • Many ectotherms are poikilotherms

• Describes temperature stability, not heat source

Heat Exchange: Conduction

• Direct transfer of heat between objects in physical contact

• Rate of exchange depends on temperature gradient, surface area, and conductivity

  • Impacts heat gain/loss depending on the gradient

• Example: turtle absorbing heat from warm rock (an ectotherm)

Heat Exchange: Convection

• Heat transfer via movement of fluids (air or water)

• Special case of conduction involving moving medium

• Increased fluid movement increases heat transfer rate

• Example: wind increasing heat loss from skin

Heat Exchange: Radiation

• Heat transfer via electromagnetic waves without direct contact (doesn’t require a medium)

• All objects emit thermal radiation based on temperature

• Example: body losing heat to environment or gaining heat from sun

• Important for long-distance heat exchange

Heat Exchange: Evaporation

• Heat loss via phase (liquid → gas)

• Requires energy input, removing heat from body

  • Example: sweating or panting

  • Effective cooling mechanism in hot environments

• Can be dangerous in cold conditions due to excessive heat loss

Countercurrent Heat Exchange

• Involves adjacent blood vessels with opposite flow directions

• Maintains temperature gradient along entire length of exchange system

  • Maximizes heat transfer from warm to cold fluid

  • Minimizes heat loss to environment

• Important adaptation in aquatic animals

Body Size and Heat Retention

• Larger animals have lower SA:V → retain heat more effectively

  • Require less energy per unit mass to maintain temperature

• Smaller animals have larger SA:V → lose heat rapidly

  • Require higher metabolic rates to compensate for heat loss

• Influences behavior, habitat, and physiology

Thermoregulation Strategies

• Endotherms = use metabolic heat production and insulation

• Ectotherms = rely on their environment

  • Certain behavioral strategies (basking, shade seeking)

• Both types can use behavioral thermoregulation

• Strategies depend on environment and energy availability

Torpor and Hibernation

• Torpor = reduced metabolic rate and body temperature

  • Estivation = torpor during hot/dry conditions

• Hibernation = prolonged torpor during cold periods

• Reduces energy expenditure during unfavorable conditions

• Represents temporary shift toward poikilothermy

Application: Tortoise SA:V Example

• Larger tortoises = low surface area to volume ratios

  • Lower ratio → slower heat exchange with environment

• Large tortoises have lower mass-specific metabolic rates

  • B/c larger animals = more feed efficient

  • Don’t need to metabolize as much to maintain their body heat

  • Heat takes longer to leave their body due to size

• Small tortoises require more energy per unit mass

  • Smaller animal = higher mass-specific metabolic rate

• Demonstrates structure/size relevance to physiology

Application: Trade Off Interpretation

• If a trait improves one function but reduces another, a trade-off is present

• Example: increased reproduction reduces immune function

• Look for inverse relationships between traits

• Energy allocation limits the performance of multiple systems