21.1 The Advent of Tissues
• Body plan – overall structure of an animal; the way
its parts fit together
• All animals are heterotrophic, multicellular, and do
not have cell walls.
• The best part about being multicellular is that cells
can become specialized and there is a division of labor.
• Tissues are the first great innovation in the animal
body plan. Tissues are groups of similar cells that are organized
into a functional unit.
• Most animals have some type of symmetry.
- Radial symmetry: wheel-like;
can slice it like a pie and each piece is similar; ex. sea anemone, starfish
- Bilateral symmetry: left and
right half is similar; ex. humans
21.2 Origin of Body Cavities
• Flatworms are bilaterally symmetrical, cephalized,
and have organs.
• Cephalization – a definite head end develops
• An acoelomate is an animal without a body cavity. Ex.
flatworm
• A pseudocoelomate is an animal with a body cavity that
develops in between the mesoderm and endoderm. Ex. roundworm
• Coelomates are animals with a body cavity inside the
mesoderm. Ex. mollusk
21.3 Four Innovations in Body Plans
• SEGMENTATION:
- Annelids were
the first animals with segmented bodies.
- Arthropods and
chordates are also segmented.
• LIMB & SKELETONS:
- Arthropods developed jointed limbs
- Arthropods have an external skeleton (exoskeleton)
to support their bodies.
• CHANGE IN EMBRYONIC DEVELOPMENT
- Protostomes are
animals that develop according to signaling by molecules in different parts
of the egg.
- Deuterostomes
are animals that develop according to genes inside the cells.
• CHORDATES:
- All chordates
have 3 characteristics (at some point in their lives): a notochord, a dorsal
nerve chord, and pharyngeal slits.
- Most chordates
are vertebrates that have a sturdy endoskeleton |