Bsci207 Midterm Study Guide
2010 Study Guide for BSCI207 Midterm 2
Ch. 32: Metazoans
Key Concepts:
● Understand the set of characteristics that distinguish the metazoan clade
● Understand processes governing early development of metazoans (cleavage, gastrulation, etc)
● Be familiar with the phylogenetic tree that organizes relationships between metazoans using their synapomorphies (pg. 697 in book)
● Know the hypotheses that potentially explain metazoan origins
● Know the hypotheses regarding the origins of bilaterians
Study Questions:
1. What is the significance of bilateral symmetry?
Bilateral symmetry triggered cephalization: the evolution of a head region where structures for feeding and sensing are concentrated. Locating and capturing food is particularly efficient when movement is directed by a dinstinctive head region. Also, with extensive musculature, a bilaterally symmetric body plan enables rapid, directed movement and hunting.
2. What are some benefits of segmental symmetry?
Different parts can evolve separately to become specialized for different tasks. In worms, partitions define individual coelomic chambers, which are filled with fluid to provide a hydrostatic skeleton. Increases feature w/out inventing new one
3. Why do so many fossils start to appear after the Cambrian explosion? The presence of a few habitats in which burial occurred rapidly and decomposition occurred slowly enabled 5 times as many species to be represented.
4. What are the two hypotheses concerning the origin of bilaterians and what are their differences? 1-Bilateria and Placozoa share a more recent common ancestor than either does to Cnidaria
2- Bilateria and Ctenophora share a more recent common ancestor than either does to Cnidaria.
5. If the stereotypical aliens from the movies (with large heads) were actually the future descendants of Homo sapiens, what form of heterochrony must have taken place?
Peramorphorsis . –descendant adult w/ exaggerated features of ancestral adult
Ch. 32: Metazoans
Key Concepts:
● Understand the set of characteristics that distinguish the metazoan clade
● Understand processes governing early development of metazoans (cleavage, gastrulation, etc)
● Be familiar with the phylogenetic tree that organizes relationships between metazoans using their synapomorphies (pg. 697 in book)
● Know the hypotheses that potentially explain metazoan origins
● Know the hypotheses regarding the origins of bilaterians
Study Questions:
1. What is the significance of bilateral symmetry?
Bilateral symmetry triggered cephalization: the evolution of a head region where structures for feeding and sensing are concentrated. Locating and capturing food is particularly efficient when movement is directed by a dinstinctive head region. Also, with extensive musculature, a bilaterally symmetric body plan enables rapid, directed movement and hunting.
2. What are some benefits of segmental symmetry?
Different parts can evolve separately to become specialized for different tasks. In worms, partitions define individual coelomic chambers, which are filled with fluid to provide a hydrostatic skeleton. Increases feature w/out inventing new one
3. Why do so many fossils start to appear after the Cambrian explosion? The presence of a few habitats in which burial occurred rapidly and decomposition occurred slowly enabled 5 times as many species to be represented.
4. What are the two hypotheses concerning the origin of bilaterians and what are their differences? 1-Bilateria and Placozoa share a more recent common ancestor than either does to Cnidaria
2- Bilateria and Ctenophora share a more recent common ancestor than either does to Cnidaria.
5. If the stereotypical aliens from the movies (with large heads) were actually the future descendants of Homo sapiens, what form of heterochrony must have taken place?
Peramorphorsis . –descendant adult w/ exaggerated features of ancestral adult