Chapter 11-13 Overview Diversity of Eukaryotic Life

Bilateral symmetry evolutionary advantage

Allows directional movement and cephalization (head-first interaction with environment)

Why cephalization improves survival

Sensory organs encounter environment first, improving feeding and predator avoidance

Functional consequence of being acoelomate

Lack of internal cavity limits organ complexity and size

Why flatworms rely on diffusion

No circulatory/respiratory systems + small, flattened body

Selective advantage of dorsoventral flattening

Maximizes surface area to volume ratio for gas exchange

Why larger organisms cannot rely on diffusion alone

Diffusion distance becomes too great for efficient transport

Difference between protostome and deuterostome development

Mouth forms first vs. second from blastopore

Relationship between mesoderm and coelom formation

Coelom develops within mesoderm layer

Why flatworms are triploblastic

They develop ectoderm, mesoderm, and endoderm

Functional limitation of incomplete digestive system

Single opening must serve as both mouth and anus

Advantage of branched digestive tract in flatworms

Increases surface area for nutrient distribution without circulatory system

Why tapeworms lack a digestive system

They absorb pre-digested nutrients from host intestine

Adaptive advantage of microtriches

Increases absorptive surface area in parasitic environment

Selective pressure leading to loss of sensory structures in parasites

Stable host environment reduces need for sensing external stimuli

Trade-off of parasitic lifestyle (trematodes/cestodes)

Loss of locomotion and sensory complexity but gain reliable nutrient source

Function of scolex in tapeworms

Anchors worm to host intestinal wall

Why proglottids are advantageous

Allow continuous production and release of reproductive units

Difference between immature, mature, and gravid proglottids

No sex organs → both organs → egg-filled only

Why hermaphroditism is beneficial in flatworms

Increases reproductive success when mates are scarce

Biological significance of “penis fencing”

Determines parental role in hermaphrodites

Function of protonephridia

Osmoregulation and nitrogen waste removal

Mechanism of flame cells

Cilia create current to filter interstitial fluid

Why osmoregulation is critical in freshwater flatworms

Prevents excess water accumulation

Why flatworms lack a circulatory system

Diffusion is sufficient due to small size and flat shape

How nervous system reflects cephalization in flatworms

Anterior ganglia act as primitive brain

Why ladder-like nervous system is efficient

Provides basic coordination without high energy cost

Relationship between locomotion and hydrostatic skeleton

Muscles act against fluid-filled body for movement

Role of circular vs longitudinal muscles

Elongation vs shortening of body segments

Why ciliated epidermis aids locomotion

Allows gliding over mucus layer

Difference between free-living and parasitic flatworms

Free-living have sensory/locomotion structures; parasites have attachment/absorption adaptations

Why trematodes have suckers

To attach securely inside host

Why parasites often have reduced digestive systems

Nutrients already processed by host

Ecological impact of flatworms

Include both free-living predators and harmful parasites

Why flatworms are considered simple bilaterians

Lack specialized systems but show key bilaterian traits

Evolutionary significance of triploblasty

Allows development of more complex tissues and organs

Why lophotrochozoans do not molt

They grow without shedding exoskeleton

Key feature distinguishing lophotrochozoans

Trochophore larvae or lophophore feeding structure

Larval stage significance

Dispersal and different ecological niche than adults

Why parasitic flatworms produce many eggs

Increases likelihood of successful transmission

Energy trade-off in parasites

Less energy spent on movement, more on reproduction

Why flatworms are good models for regeneration studies

Ability to regrow entire body from fragments

Mesenchyme function in acoelomates

Fills space and provides structural support

Why flatworms are limited in size

Diffusion constraints and lack of circulatory system

Ecdysozoa defining trait

Growth by molting (ecdysis) of a cuticle

Why molting is necessary

Exoskeleton/cuticle restricts continuous growth

Major ecdysozoan phyla

Nematoda and Arthropoda

Key difference: nematodes vs arthropods body cavity

Pseudocoelom vs true coelom (hemocoel)

Nematode body plan

Cylindrical, unsegmented, pseudocoelomate

Function of pseudocoelom in nematodes

Hydrostatic skeleton and internal transport

Why nematodes lack circulatory system

Diffusion sufficient due to body size/structure

Unique nematode trait (eutely)

Fixed number of cells in adult

Why eutely is useful in research

Allows precise study of cell lineage (e.g., C. elegans)

Functional consequence of only longitudinal muscles

Thrashing/whip-like movement

Why nematodes cannot move smoothly

No circular muscles for coordinated movement

Osmoregulation in nematodes

Renette cells and excretory pore

Nitrogen waste removal in nematodes

Diffusion across body wall

Why nematodes lack cilia/flagella

Unique adaptation (even sperm lack motility structures)

Reproductive strategy of nematodes

Mostly dioecious with sexual dimorphism

Selective advantage of sexual dimorphism

Increases reproductive efficiency

Parasitic nematode advantage

Access to stable nutrient-rich environment

Trade-off of parasitism in nematodes

Dependence on host + reduced independence

Example: Trichinella spiralis transmission

Undercooked meat (larvae in muscle)

Example: Wuchereria bancrofti transmission

Mosquito vector → lymphatic blockage

Ecological impact of nematodes

Major parasites of humans, animals, and plants

Arthropod defining features

Exoskeleton, jointed appendages, segmented body

Exoskeleton composition

Chitin + proteins (sometimes CaCO₃)

Major constraint of exoskeleton

Limits growth and flexibility

Solution to rigidity of exoskeleton

Jointed appendages

Tagmosis definition

Specialization of body segments into functional regions

Advantage of tagmosis

Increased specialization and efficiency

Typical insect tagmata

Head, thorax, abdomen

Why arthropods are evolutionarily successful

Appendage specialization + exoskeleton + tagmosis

Function of hemocoel

Body cavity filled with hemolymph (open circulation)

Difference: open vs closed circulatory system

Hemolymph bathes organs vs blood in vessels

Hemocyanin function

Oxygen transport pigment in hemolymph

Why diffusion alone is insufficient in arthropods

Larger body size and complexity

Arthropod respiratory adaptations

Gills, book lungs, tracheal systems

Function of tracheal system

Direct oxygen delivery to tissues

Function of book lungs

Increase surface area for gas exchange

Why exoskeleton limits gas exchange

Impermeable barrier to diffusion

Excretory system in insects

Malpighian tubules (water conservation)

Excretory system in crustaceans

Green (antennal) glands

Why specialized excretion is needed in arthropods

Cuticle prevents waste diffusion

Sensory adaptation in arthropods

Setae (mechanoreceptors and chemoreceptors)

Why sensory structures are necessary

Exoskeleton reduces surface sensitivity

Function of jointed appendages

Enable diverse movement (walking, swimming, feeding)

Why arthropods have high diversity

“Variations on a theme” of appendages

Examples of appendage specialization

Butterfly proboscis, mosquito piercing mouthparts

Why specialization increases fitness

Allows exploitation of different ecological niches

Arthropod molting process

New soft cuticle forms → expand body → shed old cuticle

Hormonal control of molting

Ecdysone regulates ecdysis

Risk during molting

Increased vulnerability before cuticle hardens

Ecological role of arthropods

Pollination, decomposition, food webs

Example of coevolution

Fig and fig-wasp relationship

Mutualism definition (arthropods)

Both species benefit (e.g., pollination)

Parasitoid strategy

Larvae feed on host and eventually kill it

Difference: parasite vs parasitoid

Parasite usually does not kill host; parasitoid does

Defense mechanisms in arthropods

Mimicry, eyespots, startle displays