Answers must be in essay form. Outline form is not acceptable. Labeled diagrams may be used to supplement discussion, but in no case will a diagram alone suffice. It is important that you read each question completely before you begin.
Scenario: During an investigation of a freshwater lake, an AP Biology student discovers a previously unknown microscopic organism. Further study shows that the unicellular organism is eukaryotic.
Identify FOUR organelles that should be present in the eukaryotic organism and describe the function of each organelle.
Prokaryotic cells lack membrane-bound organelles found in eukaryotes. However, prokaryotes must perform many of the same functions as eukaryotes. For THREE of the organelles identified in part (a), explain how prokaryotic cells carry out the associated functions.
According to the endosymbiotic theory, some organelles are believed to have evolved through a symbiotic relationship between eukaryotic and prokaryotic cells. Describe THREE observations that support the endosymbiotic theory.
| Eukaryotic Organelle | Function | How Prokaryotes Achieve This |
|---|---|---|
| Nucleus | Houses and protects DNA, regulates gene expression | Prokaryotes have a nucleoid region where DNA is concentrated, but not enclosed by a membrane. Gene regulation occurs in the cytoplasm. |
| Mitochondria | ATP production through cellular respiration | Prokaryotes perform cellular respiration using enzymes embedded in their plasma membrane or in the cytoplasm for fermentation. |
| Rough ER | Protein synthesis and processing | Prokaryotes synthesize proteins using free ribosomes in the cytoplasm. Post-translational modifications are simpler and occur in the cytoplasm. |
1. Similarities in DNA: Mitochondria and chloroplasts have their own DNA, which is circular (like bacterial DNA) and not linear like nuclear DNA. They also have their own ribosomes that resemble bacterial ribosomes.
2. Membrane Structure: These organelles have double membranes, which could be explained by an ancestral prokaryote being engulfed and then surrounded by the host cell's membrane. The inner membrane would be from the prokaryote, the outer from the host.
3. Reproduction Method: Mitochondria and chloroplasts reproduce independently of the cell via a process similar to binary fission, which is how bacteria reproduce. They are not synthesized by the cell de novo.
Additional observation: Some mitochondria and chloroplasts are similar in size to prokaryotic cells, and certain antibiotics that inhibit bacterial protein synthesis also affect these organelles.
• Use clear, concise language and complete sentences
• Connect each organelle's structure to its function
• For part (b), explicitly state which organelle you're discussing
• For part (c), explain how each observation supports the theory