What is the difference between a bacterium and an algae?
Question
The other day, I came across a chart comparing microbes, and it got me thinking about the actual difference between bacteria and algae. I’d seen both mentioned in environmental studies and wondered how they really stack up at the cellular level. This explanation helped me finally make sense of how distinct these two groups truly are.
Answer ( 1 )
Cell type
Bacteria are prokaryotes: no membrane‑bound nucleus, 70S ribosomes, circular DNA. Algae are eukaryotes (except cyanobacteria which are called blue‑green algae historically), with true nucleus, 80S ribosomes and organelles like chloroplasts.
Metabolism
Many bacteria are heterotrophs, some are photo‑ or chemo‑autotrophs. All true algae perform oxygenic photosynthesis using chlorophyll a plus accessory pigments.
Cell wall
Typical bacterial walls contain peptidoglycan. Algal walls are built of cellulose, pectin or silica, never peptidoglycan.
Size and shape
Bacteria are usually 0.5–5 µm and come in rods, cocci, spirals. Algae are larger, from 10 µm unicells to giant kelp meters long.
Reproduction
Bacteria divide by binary fission. Algae use mitosis, meiosis and complex alternation of generations, plus sexual gametes.
Ecological role
Algae are primary producers, forming the base of aquatic food webs. Bacteria recycle nutrients, fix nitrogen, decompose matter and some cause disease.
Bottom line
So, a bacterium is a simple prokaryote, an alga is a photosynthetic eukaryote; their cell structure, genetics and ecological roles differ a lot.