1. CHAPTER 9 PATTERNS OF ORGANIZATION

2. How are body plans organized?
SYMMETRY: the arrangement of parts around a center point or line.

3. Asymmetry: the arrangement of parts without a center point or line
Asymmetry: the arrangement of parts without a center point or line. EX: Sponge
Radial: any plane passing through the central axis divides the animal into mirror images.

4. Biradial: the paired arrangement of some structures in radial animals.

5. Pentaradial: the arrangement of structures in fives around a radial animal.

6. Bilateral: the arrangement of parts such that a single plane passing between the upper and lower surfaces divides the animal into mirror images.

7. Advantages:
1. Cephalization: the concentration of nervous and sensory structures to form a head at the anterior end.

8. Proximity of the brain or ganglia to the sense organs speeds reception and processing of sensory
information.
The degree of cephalization tends to increase with the complexity of other organs and organ systems

9. Grade of Tissue
Tissue grade: bodies are composed of cells organized into tissues but are lacking organs and organ systems. e.g. Porifera
Diploblastic: animals with two distinct tissue layers derived from ectoderm and endoderm. e.g. Cnidaria

10. Triploblastic: animals with three distinct tissue layers derived from ectoderm, endoderm and mesoderm.

11. BODY CAVITY:
Acoelomate: no body cavity, the central space is filled with loosely packed cells (mesenchyme). e.g. Platyhelminthes

12. Psuedocoelomate: the central body cavity lies between the endoderm and mesoderm, no special mesodermal peritoneum lining e.g Nematoda

13. Coelomate: the central body cavity develops within the mesoderm tissue, specialized mesodermal peritoneum completely lines the central cavity e.g. annelids, chordates

14. Advantages for having a central body Cavity
1. allows for the expansion and movement of internal organs
2. allows for specialization of the digestive tract
3. facilitates the exchange of gases, nutrients and waste.
4. provides storage of gametes
5. can serve as a hydrostatic skeleton
6. facilitates increased body size