Architectural Pattern of an Animal

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Architectural Pattern of an Animal

• Chapter 9

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The Appearance of Major Body Plans

• The Cambrian explosion marks the earliest fossil
  appearance of all major groups of living animals
  plus some groups that are only known from
  fossils.
• All major body plans appeared at this time.
• Result of extensive selection.
• Are limiting determinant of future adaptational
  variants.

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Body Plans

• One way in which zoologists categorize the
  diversity of animals is according to general
  features of morphology and development.
• A group of animal species that share the same
  level of organizational complexity is known as a
  grade.

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Hierarchical Organization 5 Levels

• 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.
• Shown by the simplest metazoans Volvox, sponges.

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Hierarchical Organization 5 Levels

• 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

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Hierarchical Organization 5 Levels

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

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Animal Body Plans

• Body plans are constrained by ancestry, major
  features may become modified, but are rarely
  lost.
• Animal body plans differ in their grade of
  organization, body symmetry, number of germ
  layers, and type of body cavity.

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Symmetry

• Spherical symmetry occurs when any plane passing
  through the center divides the body into mirror
  image halves.
• Mostly found among the protists.

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Symmetry

• 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

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Radiata

• 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.

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Symmetry

• 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.

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Cephalization

• Bilateral symmetry is associated with
  cephalization, differentiation of a head.
• Nervous tissue, sense organs, and often the mouth
  are located in the head.
• Advantages for organisms moving head first
  directional movement.
• Elongation along anteroposterior axis.

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Regions of a Bilaterally Symmetrical Animal

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

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Body Cavities

• Examples of body cavities include the gut,
  blastocoel, and a pseudocoel or coelom.
• 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.

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Body Cavities

• In protostomes, mesoderm forms as endodermal
  cells from near the blastopore migrate into the
  blastocoel.
• Three body plans possible
• Acoelomate (no body cavity)
• Pseudocoelomate (body cavity between endoderm
  mesoderm)
• Coelomate (body cavity surrounded by mesoderm)

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Body Cavities

• Coeloms surrounded by mesoderm can arise in two
  ways
• Schizocoely mesodermal cells fill the
  blastocoel, forming a solid band of tissue around
  the gut, then a space opens inside the mesodermal
  band.
• Enterocoely portions of the gut lining form
  pockets that pinch off and form a ring of
  mesoderm.

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Developmental Patterns

• Sponges develop only to blastula stage, then
  reorganize to form adult.
• Gastrulation allows animals to proceed to tissue
  level organization.
• Diploblastic 2 germ layers
• Cnidarians, Ctenophores
• Triploblastic 3 germ layers

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Other Key Features of Body Plans

• In some organisms, the gut does not form a
  complete tube.
• Waste must come back out the mouth.
• Food must be digested waste expelled before
  eating again.
• A complete gut forms a tube within a tube body
  plan.

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Other Key Features of Body Plans

• Segmentation is a serial repetition of similar
  body segments along the body.
• Each segment is a metamere or somite.
• May include external internal components.
• Obscured in many animals, like humans.
• Permits greater body mobility and complexity of
  structure function.

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Components of Metazoan Bodies

• Extracellular Components - noncellular
  components of metazoan animals
• Body fluids
• Extracellular structural elements

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Tissue Structure and Function

• Cellular Components - Tissues

• A tissue is a group of similar cells specialized
  for performing a common function.
• Different types of tissues have different
  structures that are suited to their functions.
• Tissues are classified into four main categories
• Epithelial
• Connective
• Muscle
• Nervous

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Epithelial Tissue

• Epithelial tissue covers the outside of the body
  and lines organs and cavities within the body.
• Squamous, cuboidal, columnar.
• Simple vs. stratified.

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Connective Tissue

• Connective tissue functions mainly to bind and
  support other tissues.
• Contains sparsely packed cells scattered
  throughout an extracellular matrix.

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Muscle Tissue

• Muscle tissue is composed of long cells called
  muscle fibers capable of contracting in response
  to nerve signals.
• Smooth
• Skeletal
• Cardiac

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Nervous Tissue

• 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.

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Complexity and Body Size

• Increased complexity allows for an increase in
  body size.
• Larger size decreases the surface area to volume
  ratio.
• Necessitates complex systems for respiration,
  nutrition, and excretion diffusion not
  adequate.
• Buffers environmental fluctuation.
• Escape predators.

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Complexity and Body Size

• Cost of maintaining body temperature is less per
  gram of body weight than in small animals.
• Energy costs of moving a gram of body weight over
  a given distance less for larger animals.