exam 4

Animal Origins Overview

• Characteristics Distinguishing Animals:

  • Multicellular organisms that develop from a single cell.

  • Heterotrophic, meaning they consume other living or dead organisms.

  • Possess internal digestion processes.

  • Most animals are mobile, facilitated by specialized muscle tissues.

  • Have nervous systems for coordination and response to stimuli.

Multicellularity

• Cellular Differentiation:

  • Animals have differentiated cells with specialized functions.

  • This leads to an increase in complexity, unlike single-celled organisms.

  • Humans and plants are examples of multicellular organisms.

Feeding Mechanism

• Heterotrophic Nature:

  • Animals consume other organisms (living or dead) for energy.

  • Fungi also heterotrophs but digest food externally (absorptive heterotrophy).

• Internal Digestion:

  • Animals utilize an internal gut, which connects with the outside environment for digestion.

Mobility

• Animal Movement:

  • Most animals can move, a trait supported by specialized muscle and nervous tissues.

  • Sponges are exceptions; they are largely sessile and exhibit minimal movement.

Phylogenetic Relationships

• Evolutionary History:

  • Kingdom Animalia is considered monophyletic, originating from a common ancestor.

  • First animals are believed to have emerged approximately 800 million years ago.

  • Evidence of Monophyly:

    • Cellular morphology (collagen, proteoglycans, desmosomes).

    • The presence of Hox genes responsible for body patterns and axis formation.

Development Patterns

• Embryonic Development:

  • Cleavage patterns (early cell divisions) can vary among animal groups.

  • Types of Cleavage:

    • Radial Cleavage: Even divisions; ancestral to most animals excluding sponges.

    • Spiral Cleavage: More complex, seen in mollusks.

• Germ Layers:

  • Diploblastic Animals: Have two layers (ectoderm, endoderm).

  • Triploblastic Animals: Possess three layers (ectoderm, endoderm, mesoderm).

Animal Body Plans

• Defining Features:

  • General structure, arrangement of organ systems, and integrated functioning.

• Key Features:

  • Symmetry (bilateral, radial, asymmetric).

  • Body cavity structure (acoelomates, pseudocoelomates, coelomates).

  • Segmentation in body (facilitates specialization).

Symmetry in Animals

• Types of Symmetry:

  • Animals symmetrical can be divided into similar halves.

  • Asymmetrical Animals: Lack symmetry (e.g., placozoans, sponges).

  • Radial Symmetry: Body parts arranged around a central axis (e.g., cnidarians).

Gastrulation Process

• Blastula Formation:

  • The blastula invaginates to form the gut (gastrula) with germ layers:

    • Endoderm (gut)

    • Ectoderm (skin, nerves)

  • Diploblastic: Species with ectoderm and endoderm.

  • Triploblastic: Species with an additional mesoderm layer that forms coelom.

Coelom and Body Cavities

• Body Cavity Classification:

  • Acoelomates: No body cavity (e.g., flatworms).

  • Pseudocoelomates: False body cavity between germ layers (e.g., roundworms).

  • Coelomates: True body cavity lined with mesoderm (e.g., segmented worms).

• Hydrostatic Skeleton: Body cavities can assist in movement.

Neurological Coordination

• Nervous Systems:

  • Central nervous systems coordinate muscle action and sensory information processing.

  • Animals detect various stimuli such as light, sound, and chemical signals.

Feeding Strategies in Animals

• Five Principles:

  • Filter feeders.

  • Herbivores.

  • Predators.

  • Parasites.

  • Detritivores.

• Specific feeding methods:

  • Filter Feeding: Used by animals like flamingoes and blue whales.

  • Herbivory: Involves eating plant material, often with adaptations for digestion.

  • Predation: Involves capturing other animals, aided by specialized structures.

  • Parasitism: Living within or on a host to obtain nutrients.

  • Detritivory: Feeding on decomposed organic matter.

Life Cycle Variability Among Animals

• Developmental Patterns:

  • Direct Development: Young similar to adults (e.g., humans).

  • Metamorphosis: Immature larval stage differs from adult (e.g., butterflies, frogs).

• Dispersal:

  • Many animals disperse to find new habitats or mates, involving larvae as temporary members of the plankton community before settling.

Overview of Major Animal Groups

• Sponges: Simple organisms with specialized cells, no distinct tissues.

• Ctenophores and Placozoans: Exhibit basic structures with minimal complexity.

• Cnidarians: Possess tissues and specialized cells for predation, exhibit diverse body forms (polyp, medusa).

• Bilaterians: Characterized by three germ layers and bilateral symmetry.