Diversity and Organisms Term Paper

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Diversity and Organisms

Phylogeny is the patterns of lineage branching, produced by the true evolutionary history of the organisms being considered (UCMP Web site). Speciation is the changes in related organisms to the point where they are different enough to be considered separate species. This occurs when populations of one species are separated and adapt to their new physiological, geographic, or behavioral environment (Evolution Library Web site).

Plants have a reproductive cycle, which has an "alternation" between a haploid (n=one copy of each chromosome) gametophyte generation and a diploid (2n=two copies of each chromosome) sporophyte generation. The haploid gametophyte produces haploid gametes, which fuse to form a diploid zygote. The zygote grows by mitosis into the diploid multicellular sporophyte, in which meiosis occurs in special regions creating haploid spores. The spores disperse, germinate into haploid gametophytes starting the cycle anew (Kennesaw Web site).

As plants have evolved, the sporophyte has become dominant, and this is advantageous to evolution as crossing over of chromosomes results in genetic variability in offspring, which is often crucial to the survival of the species (Dreamscape Web site).

4. The common ancestor to all plants is a multicellular terrestrial green algae that lived almost 430 million years ago. The three characteristics common to gymnosperms and angiosperms are: cell walls with cellulose; development of a plate during cell division; and, during reproduction, the sporophyte phase is dominant (The World of Biology Web site).

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5. The two main characteristics are that they are vascular and seed bearing.

6. In plant evolution one of the major steps was the transition from an aquatic to terrestrial environment. The earliest were seedless vascular plants. Then developed the various angiosperms and gymnosperms, which had vascular system, roots, leaves, and stems, as well as seeds. The earliest land plants needed water for reproduction as the sperm had to swim to fertilize the egg. Successful land plants developed spores and seeds that protected the sperm and egg from drying out. The advanced plants had a seed within a seed coat, which contained food for the developing embryo. By using in reproduction "alternating generations," plants have ensured genetic recombination. (The World of Biology Web site).

7. During evolution, animals separated into two lineages: protostomes and deuterostomes. The basic differences are: the protostomes have spiral, determinate cleavage while the deuterostomes have radial, indeterminate cleavage. The blastopore forms the mouth in protostomes while it forms the anus in deuterostomes. The protostomes have a schizocoelous coelom formation while the deuterostomes have enterocoelous coelom. Protostomes are animals that have a dorsal (back) heart and….....

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