Chlamydomonas is a unicellular green alga. How does it differ from a photosynthetic bacterium, which is also single-celled? How does it differ from a protozoan, such as an amoeba? How does it differ from larger green algae, such as sea lettuce (Ulva)?

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1. Identify the key characteristics of Chlamydomonas, a unicellular green alga, including its eukaryotic cell structure, chloroplasts for photosynthesis, and flagella for movement.
2. Compare the cellular structure of Chlamydomonas with a photosynthetic bacterium, noting that bacteria are prokaryotic (lacking a defined nucleus and organelles) and use different pigments and mechanisms for photosynthesis.
3. Contrast Chlamydomonas with a protozoan like an amoeba by focusing on their modes of nutrition and locomotion. Chlamydomonas is primarily photosynthetic, while amoebas are heterotrophic and ingest food through phagocytosis.
4. Discuss the differences in size and complexity between Chlamydomonas and larger green algae such as Ulva. Highlight that Ulva is multicellular, has differentiated tissues, and a more complex structure compared to the unicellular Chlamydomonas.
5. Summarize the evolutionary significance of these differences, emphasizing how variations in cellular structure, nutrition, and complexity reflect adaptations to different environmental niches.

Key Concepts

Cellular Structure

Chlamydomonas is a eukaryotic organism, meaning it has a complex cellular structure with a defined nucleus and membrane-bound organelles. In contrast, photosynthetic bacteria, like cyanobacteria, are prokaryotic, lacking a nucleus and organelles. This fundamental difference in cellular organization affects their metabolic processes and ecological roles.

Photosynthesis Mechanisms

Chlamydomonas performs photosynthesis using chloroplasts, which contain chlorophyll and other pigments to capture light energy. Photosynthetic bacteria, however, utilize different pigments and may perform photosynthesis through simpler mechanisms, such as anoxygenic photosynthesis, which does not produce oxygen. Understanding these differences is crucial for comparing their ecological functions.

Organism Complexity

Chlamydomonas is a unicellular alga, while protozoans like amoebas are also unicellular but belong to a different kingdom (Protista) and exhibit more complex behaviors, such as phagocytosis. Larger green algae, such as sea lettuce (Ulva), are multicellular and exhibit tissue differentiation, which allows for more complex structures and functions. This complexity influences their ecological interactions and life cycles.