<p>Here’s some FRQs with answers. </p>
<ol>
<li>Describe the differences between the terms in each of the following pairs:</li>
</ol>
<p>a. Acoelomate - Coelomate
b. Radial Symmetry - Bilateral Symmetry</p>
<ol>
<li>Explain how each of the features listed in question 1 can be used to construct an evolutionary history of these common animal phyla:
Porifera
Cnidaria
Platyhelminthes
Nematoda
Annelida
Mollusca
Arthropoda
Echinodermata
Chordata</li>
</ol>
<p>Answers:</p>
<p>1a. A coelom is a fluid-filled body cavity and arises from within mesoderm tissue early in embryonic development. It is a significant advance in the course of animal evolution because it provides space for elaborate body systems like a transport system. More advanced phyla, such as echinodermata and chordata have a coelom. An animal that does name have a coelom (acoelomate) lacks internal cavities and complex organs. Primitive acoelomate phyla are Cnidaria, Porifera and Platyhelminthes. Some animals have a pseduocoelom, an internal cavity that is only partly lined with mesoderm tissue. This fluid-filled pseudocoelom functions as a hydrostatic skeleton, providing support and making movement easier. An animal phylum with a pseduocoelom is the Nematoda. </p>
<p>1b. If symmetry is radial, several planes can pass through the long axis and divide the animal into similar parts. An example of an animal with radial symmetry is the hydra. If only one plane can bisect the animal into left and right halves, the symmetry is bilateral. Primitive organisms show radial symmetry, advanced organisms show bilateral symmetry. Chordates all have bilateral symmetry. The embryo of the echinoderm demonstrates bilateral symmetry but reverts to the primitive radial symmetry as an adult. </p>
<ol>
<li>There is a great diversity among all the animals, and they can be grouped and distinguished by several characteristics. These characteristics include the number of cell layers, whether they have a true coelom, symmetry at early cleavage, body plan and whether they are protostomes or deuterostomes. The phyla listed above begin with the most primitive and oldest on top and end with the most advanced and most recently evolved at the bottom.
The most primitive animals, the Porifera, or sponges, and Cnidaria are diploblastic; they lack a mesoderm. Instead, they have a mesoglea, a noncellular, gluey later between the ectoderm and endoderm that helps keep them together. All of the other phyla are triploblastic with three germ layers. The ectoderm will become the skin and nervous system. The endoderm will become the internal organs. The mesoderm will become the blood, bones and muscle. The most primitive phylum, Porifera, has no symmetry. The slightly more advanced Cnidaria have radial symmetry. All triploblastic animals have bilateral symmetry. Animals with no true coelom, for example, Porifera, Cnidaria and Platyhelminthes, are primitive. The Nematoda lack a true coelom, but they have a pseducoelom. All the others have a true coelom. The two most advanced phyla are the Echinodermata and Chordata, tehy are both deuterostomes. All the remaining phyla are more primitive and are protostomes.</li>
</ol>
<p>I notice 2 didn’t define protostomes vs. deuterostomes, which seems like it would be important to know. Protostomes and deuterostomes are subdivisions of coelomates. In protostomes, the blastopore becomes the mouth. In deuterotsomes, the blastopore becomes the anus. Protostome animals include annelids, mollusks and arthropods. Deuterostomes include echinoderms and chordates. </p>
<p>Sorry if there are any typos. It’s early.</p>
oh well, 15 days till the exam!!!</p>
Thought I’d move it up to page 1 from page 6. :D</p>