Chapter 27: Introduction to Animal Diversity Flashcards
What key features define animals as a kingdom?
Eukaryotic, multicellular heterotrophs (ingest food).
No cell walls; cells supported by structural proteins like collagen.
Motility at some life stage (e.g., larvae or adults).
Nervous and muscle tissues (except sponges).
Sexual reproduction (dominant diploid stage); some asexual.
Hox genes regulate body plan development.
Describe the evolutionary origins of animals. What evidence supports this?
Hypothesized origin: Evolved from a colonial, flagellated protist ancestor (similar to choanoflagellates).
Evidence:
Genetic similarities between choanoflagellates and sponges.
Fossil records (e.g., Dickinsonia, 570 MYA Ediacaran biota).
Cambrian Explosion (~541 MYA): Rapid diversification of animal phyla.
How are animals classified based on body symmetry? Provide examples.
Asymmetrical: No symmetry (e.g., sponges).
Radial symmetry: Body parts arranged around a central axis (e.g., jellyfish, sea anemones).
Bilateral symmetry: Distinct left/right halves (e.g., insects, mammals).
Associated with cephalization (sensory organs concentrated at the head).
What are the three germ layers in animal embryos, and what do they form?
Ectoderm: Outer layer → skin, nervous system.
Mesoderm: Middle layer → muscles, bones, circulatory system.
Endoderm: Inner layer → digestive tract, liver, lungs.
Diploblasts (e.g., cnidarians) have only ectoderm and endoderm.
Triploblasts (most animals) have all three layers.
Compare protostomes and deuterostomes in development.
Trait Protostomes Deuterostomes
Cleavage Spiral and determinate Radial and indeterminate
Fate of Blastopore Becomes the mouth Becomes the anus
Coelom Formation Schizocoelous (mesoderm splits) Enterocoelous (mesoderm buds from gut)
Examples Arthropods, mollusks, annelids Echinoderms, chordates
What are the major animal phyla, and how do they differ in complexity?
Porifera (sponges): No tissues/organs; filter feeders.
Cnidaria (jellyfish): Radial symmetry, stinging cells (cnidocytes).
Platyhelminthes (flatworms): Bilateral, acoelomate.
Annelida (earthworms): Segmented body, coelomate.
Arthropoda (insects): Exoskeleton, jointed appendages.
Mollusca (snails): Soft-bodied, many with shells.
Chordata (vertebrates): Notochord, dorsal nerve cord.
Explain the significance of Hox genes in animal diversity.
Hox genes are regulatory genes that control body plan development (e.g., segment identity in arthropods, limb formation in vertebrates).
Duplication and diversification of Hox genes allowed for evolutionary innovations (e.g., wings, complex organs).
Example: A single Hox gene mutation can transform antennae into legs in fruit flies.
What is the Cambrian Explosion, and why is it important?
Cambrian Explosion: Rapid diversification of animal phyla ~541–485 MYA.
Causes:
Evolution of predation (arms race).
Oxygenation of oceans.
Hox gene complexity.
Significance: Established most major animal body plans seen today.
How do animals contribute to ecosystem services?
Pollination: Bees, bats, birds.
Decomposition: Earthworms, beetles.
Nutrient cycling: Coral reefs, soil fauna.
Food webs: Herbivores, predators, prey.
Human benefits: Food (livestock), medicine (e.g., horseshoe crab blood for bacterial detection).
What are the evolutionary adaptations enabling animal colonization of land?
Lungs (or lung derivatives) for air breathing.
Limbs for terrestrial locomotion (tetrapods).
Amniotic egg (reptiles, birds) or placenta (mammals) for embryo protection.
Water-conserving organs (e.g., kidneys).
Example: Transition from lobe-finned fish to early tetrapods (e.g., Tiktaalik).
Compare acoelomate, pseudocoelomate, and coelomate body plans.
Acoelomate: No body cavity (e.g., flatworms). Organs packed in mesoderm.
Pseudocoelomate: Fluid-filled cavity between mesoderm and endoderm (e.g., roundworms).
Coelomate: True coelom (fluid-filled cavity within mesoderm) for organ cushioning/movement (e.g., annelids, humans).
What role does segmentation play in animal evolution?
Segmentation (metamerism): Repeated body units (e.g., earthworm segments, insect body regions).
Advantages:
Specialization of segments (e.g., limbs, organs).
Redundancy (damage to one segment isn’t fatal).
Evolutionary flexibility (e.g., arthropod appendages).
How do parasitic animals adapt to their lifestyle? Provide examples.
Adaptations:
Reduced sensory/ locomotory organs (e.g., tapeworms).
Attachment structures (hooks/suckers in tapeworms).
High reproductive output (e.g., Schistosoma eggs).
Examples:
Ectoparasites: Ticks, fleas.
Endoparasites: Tapeworms, Plasmodium (malaria parasite).
Why are invertebrates critical to biodiversity?
97% of animal species are invertebrates.
Roles:
Pollinators (bees).
Decomposers (beetles).
Keystone species (coral reefs).
Food sources (krill in marine ecosystems).
