Description
Diatoms are unicellular, photosynthetic algae with unique silica cell walls and are major components of aquatic phytoplankton, contributing significantly to global oxygen production.
Structure and Classification
Diatoms possess a rigid, glass-like cell wall called a frustule made of silicon dioxide, which has intricate and distinct geometrical patterns.
They are generally classified into two main groups:
Centric diatoms: Radially symmetrical and typically found in marine environments.
Pennate diatoms: Bilaterally symmetrical, usually found in freshwater habitats, and capable of slow gliding movement by secreting mucilage.
Cellular size ranges from about 5 μm to 0.5 mm, making them among the larger unicellular microorganisms.
Habitat and Ecological Role
Diatoms are distributed globally in marine and freshwater environments, often forming large blooms in cold or nutrient-rich waters.
They serve as primary producers, forming the base of aquatic food chains and providing sustenance for zooplankton and fish larvae.
Diatoms account for 20–25% of global oxygen production through photosynthesis, thus playing a major role in atmospheric and aquatic oxygen dynamics.
Reproduction and Life Cycle
Diatoms primarily reproduce asexually by binary fission, which leads to a gradual decrease in cell size due to the unique bipartite frustule structure.
To restore their maximum size, diatoms undergo sexual reproduction and produce auxospores—a specialized structure that enlarges before forming a new frustule.
Some diatoms form resting spores or auxospores to withstand unfavorable environmental conditions and resume growth when conditions improve.
Unique Features
Their pigment composition (chlorophyll a & c, carotenoids like fucoxanthin) gives diatoms a characteristic golden-brown color.
Food reserves are primarily stored as chrysolaminarin and oil, instead of starch.
Diatoms lack flagella except in the male gametes of centric types.
Diatoms are crucial in environmental monitoring, paleontology, and biotechnology due to their abundance, ecological roles, and uniquely patterned silica shells.