Eukaryotes and prokaryotes
Eukaryotic microalgae (such as Chlorella, Scenedesmus or Haematococcus) have a defined nucleus and membrane-bound organelles, including the chloroplast. Cyanobacteria (such as Spirulina or Anabaena) are prokaryotes: they lack a nucleus and membranous organelles, and carry out photosynthesis on internal membranes (thylakoids).
The chloroplast
In eukaryotic microalgae, the chloroplast is the organelle where photosynthesis takes place. It contains the pigments (chlorophylls and carotenoids) and the thylakoids, the membranes where the light reactions occur. Its shape varies by species: in Chlorella it is a single cup-shaped chloroplast.
Cell wall and membrane
Most microalgae have a cell wall that provides shape and protection; its composition varies (cellulose, polysaccharides, silica in diatoms). Some, such as Dunaliella, lack a rigid wall, which gives them osmotic flexibility. Beneath the wall is the plasma membrane, which regulates exchange with the medium.
Other organelles and structures
Besides the nucleus and chloroplast, eukaryotic microalgae have mitochondria, vacuoles and, in many cases, motility structures such as flagella (for example, the two flagella of Chlamydomonas) and a light-sensitive eyespot. Some accumulate starch or lipid reserves in granules.
FAQ
Eukaryotic microalgae do (a nucleus and chloroplast). Cyanobacteria, however, are prokaryotes and have no nucleus or membrane-bound organelles.
In the chloroplast of eukaryotic microalgae, and on the internal membranes (thylakoids) in cyanobacteria.
Sources
- Richmond, A. & Hu, Q. (eds.) (2013). Handbook of Microalgal Culture: Applied Phycology and Biotechnology. Wiley-Blackwell.
- Chisti, Y. (2007). Biodiesel from microalgae. Biotechnology Advances, 25(3), 294–306.
- Spolaore, P. et al. (2006). Commercial applications of microalgae. Journal of Bioscience and Bioengineering, 101(2), 87–96.
- Mata, T.M. et al. (2010). Microalgae for biodiesel production and other applications: A review. Renewable and Sustainable Energy Reviews, 14(1), 217–232.
Scientific outreach based on specialised literature. Scientific review: pending.
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