Question

1. summarize the endosymbiotic theory. 12. explain how taxonomy and phylogeny are similar yet unique fields of study. 13. explain what phylogenetic trees show and what evidence is used to construct them.

Explanation:

Question 11: Summarize the endosymbiotic theory.

The endosymbiotic theory proposes that eukaryotic cells evolved from a symbiotic relationship between different prokaryotic organisms. Specifically, it suggests that mitochondria and chloroplasts (in photosynthetic eukaryotes) were once free - living prokaryotes (likely alpha - proteobacteria for mitochondria and cyanobacteria for chloroplasts) that were engulfed by a larger prokaryotic cell. Over time, this symbiotic relationship became obligate, with the engulfed organisms losing some of their independent functions and becoming organelles within the host cell. Key evidence includes the fact that mitochondria and chloroplasts have their own circular DNA (similar to prokaryotic DNA), their own ribosomes (similar in size to prokaryotic ribosomes), and they reproduce independently within the cell by a process similar to binary fission. Also, the inner membranes of these organelles have a structure and function similar to those of prokaryotic cell membranes.

• Similarities: Both taxonomy and phylogeny are concerned with the study of the relationships between organisms. They aim to organize and understand the diversity of life on Earth. Both use characteristics of organisms (such as morphological, genetic, or physiological traits) to group and compare organisms.
• Differences:
• Taxonomy is the science of naming, defining, and classifying organisms into groups (taxa) such as species, genera, families, etc. It focuses on the identification and classification of organisms based on shared characteristics, with a strong emphasis on the rules of nomenclature (e.g., binomial nomenclature for species).
• Phylogeny, on the other hand, is the study of the evolutionary history and relationships among organisms or groups of organisms. It focuses on reconstructing the evolutionary tree (phylogenetic tree) that shows the evolutionary descent and relationships, often using methods like analyzing DNA sequences, morphological evolution over time, or fossil records to determine the evolutionary relatedness and the order of divergence of different lineages.

• What phylogenetic trees show: Phylogenetic trees are graphical representations that show the evolutionary relationships among different organisms or groups of organisms. They depict the pattern of descent, showing which groups are more closely related (share a more recent common ancestor) and which are more distantly related. The branches of the tree represent lineages, and the nodes (branch points) represent common ancestors from which different lineages diverged. They can also show the relative timing of evolutionary events (in some cases, with calibrated trees) and the evolution of different traits along the lineages.
• Evidence used to construct them:
• Morphological evidence: Comparing the physical structures of organisms. For example, the presence of homologous structures (structures with a common evolutionary origin, even if they have different functions, like the forelimbs of mammals) can indicate a close evolutionary relationship.
• Molecular evidence: Analyzing DNA, RNA, or protein sequences. By comparing the sequences of genes or proteins between different organisms, we can determine the degree of similarity, which reflects the degree of evolutionary relatedness (more similar sequences suggest a more recent common ancestor).
• Fossil evidence: Fossils provide a record of past organisms. By studying the age (through radiometric dating) and morphological characteristics of fossils, we can place extinct organisms in the phylogenetic tree and understand the evolutionary transitions over time.
• Behavioral evidence (in some cases): For example, in some animal groups, similar behavioral patterns (like mating rituals or social behaviors) that are likely to have an evolutionary basis can be used to infer relationships, although this is less common than the other types of evidence.

Answer:

The endosymbiotic theory states that eukaryotic cells arose from symbiotic associations of prokaryotes. Mitochondria (from engulfed aerobic prokaryotes) and chloroplasts (from engulfed photosynthetic prokaryotes, like cyanobacteria) were once free - living. These organelles now have their own circular DNA, prokaryote - like ribosomes, reproduce via binary fission, and have inner membranes similar to prokaryotic membranes, supporting their origin from engulfed prokaryotes that became dependent on the host cell.

Question 12: Explain how taxonomy and phylogeny are similar yet unique fields of study.