Lecture 2 - Architectural Pattern of an Animal

• A group of animal species that share the same level of organizational complexity is known as a grade.
• Hierarchical Organization – 5 Levels

  • Protoplasmic grade of organization
  • Metazoans
  • Cell-tissue Grade
  • Tissue-organ Grade
  • Organ-system grade
• Protoplasmic grade of organization – protists are the simplest eukaryotes, but they still carry out life functions and show division of labor among the various cell structures.
• Metazoans are multicellular animals that have cells specialized for particular functions. This is the Cellular grade of organization.
• Cell-tissue Grade – Usually, specialized cells are grouped together and perform their

  common function as a coordinated unit, a tissue.

  • Jellyfish
• Tissue-organ Grade – Tissues are then assembled into organs like the heart (primarily muscle tissue, but connective, nervous, and epithelial also present).

  • Flatworms
• Organ-system grade – In the highest level of organization, organs work together as organ systems like the circulatory system.
• Symmetry

  • Spherical Symmetry
  • Radial Symmetry
  • Biradial Symmetry
  • Bilateral Symmetry
• Spherical symmetry occurs when any plane

  passing through the center divides the body into mirror image halves.

  • Mostly found among the protists.
• Radial symmetry applies when more than

  two planes passing through the longitudinal

  axis can divide the organism into mirror image halves.

  • Jellyfish
• Biradial symmetry – two planes will divide the

  organism.

  • Comb jellies
• The Cnidarians (jellyfish, corals & sea anemones) and Ctenophores (comb jellies), the radial or biradial animals, comprise the Radiata.

  • No front/back
  • Weak swimmers
  • Can interact with environment in all directions.
• Bilateral symmetry is found in organisms

  where one plane can pass through the

  organism dividing it into right and left halves.

  • Better for directional movement.
  • Monophyletic group called Bilateria.
• Bilateral symmetry is associated with cephalization, differentiation of a head.
• Regions of a Bilaterally Symmetrical Animal

  • Anterior-posterior (transverse plane)
  • Dorsal-ventral (frontal plane)
  • Left-right (sagittal plane)
  • Proximal-distal
  • Medial-lateral
• Body Cavities

  • The gut forms from the archenteron during gastrulation.
  • The blastocoel persists in some, but usually fills with mesoderm.
  • Pseudocoel and coelom are fluid filled body cavities that cushion organs and provide support.
• Three body plans possible:

  • Acoelomate (no body cavity)
  • Pseudocoelomate (body cavity between endoderm & mesoderm)
  • Coelomate (body cavity surrounded by mesoderm)
• Coeloms surrounded by mesoderm can arise in two ways:

  1. Schizocoely – mesodermal cells fill the blastocoel, forming a solid band of tissue around the gut, then a space opens inside the mesodermal band.
  2. Enterocoely – portions of the gut lining form pockets that pinch off and form a ring of mesoderm.
• Gastrulation allows animals to proceed to

  tissue level organization.

  • Diploblastic – 2 germ layers

  Cnidarians,

  Ctenophores

  • Triploblastic – 3 germ layers
• Segmentation is a serial repetition of similar body segments along the body.

  • Each segment is a metamere or somite.
• A tissue is a group of similar cells specialized for performing a common function.
• Tissues are classified into four main categories:

  • Epithelial
  • Connective
  • Muscle
  • Nervous
• Epithelial tissue covers the outside of the body and lines organs and cavities within the body.
• Connective tissue functions mainly to bind and support other tissues.
• Muscle tissue is composed of long cells called muscle fibers capable of contracting in response to nerve signals.

  • Smooth
  • Skeletal
  • Cardiac
• Nervous tissue senses stimuli and transmits signals throughout the animal.
• A neuron (nerve cell) receive signals at the dendrites and send them out via the axons.