Diatom morphology: Which statement best describes diatoms, focusing on their unique cell covering and overall structural organization used for identification in phycology and paleoecology?

Introduction / Context:
Diatoms are a cornerstone group in aquatic ecosystems and an important tool in environmental reconstruction. Their highly ornamented silica walls are diagnostic and preserve well in sediments, enabling long-term records of ecological change.

Given Data / Assumptions:

• The question seeks the best descriptive feature of diatoms.
• Options include various wall compositions and cellular features.
• We assume standard introductory phycology terminology.

Concept / Approach:
Diatoms possess a frustule made of hydrated silica (opal), composed of two overlapping halves called the epitheca and hypotheca, like a petri dish. The frustule features fine pores and species-specific ornamentation. In contrast, cellulose-based walls are more typical of many plants and some other algae, not diatoms. Most diatoms lack flagella, except some male gametes in centric forms. Their pigments include chlorophyll a and c plus fucoxanthin, not chlorophyll b as a dominant accessory.

Step-by-Step Solution:
Identify the hallmark frustule: silica-based wall with two valves.Exclude cellulose-coated descriptions, which are inaccurate for diatoms.Exclude flagellated and eyespot descriptions, which fit other algae such as euglenoids or green flagellates.Exclude chlorophyll a and b description; diatoms primarily use chlorophyll a and c with fucoxanthin.

Verification / Alternative check:
Scanning electron microscopy reveals detailed silica patterns; geochemical analyses confirm silicon dioxide composition of frustules.

Why Other Options Are Wrong:

• Cellulose coated with silicon: wall is silicon-based, not cellulose with a coating.
• Flagella and eyespot: not characteristic for diatoms overall.
• Chlorophyll a and b: pigment profile does not match diatoms.

Common Pitfalls:
Confusing diatom pigments with those of green algae and assuming all microalgae have similar cell walls.

Final Answer:
Cells have intricate shells of silicon dioxide with two halves