BIO202H5 Chapter Notes - Chapter 2: Bilateria, Mesoglea, Water Vascular System
Document Summary
Chapter two notes body plans, skeletons, and development. The transition from unicellular protists to multicellular animals occurred more than 600 million years ago. Animal multicellularity probably originated from a colony of heterotrophic protists in which daughter cells remained together as a cluster rather than dispersing as independent, single-celled organisms. Some modern protists live in colonies, and a few species have transient phases in which some cells differentiate into gamete-like cells. Cancerous tumours illustrate the consequences when one cell line ceases to cooperate: here, a renegade cell breaks from normal controls, proliferates by mitosis, and can threaten the. 2. 2a. 2 increase in size survival of the animal. The limits imposed on size are a direct consequence of the non-linear relationship between surface area and volume for any three-dimensional object: when the surface area doubles, the volume increases by the power of three.
