Though the prokaryotic Cyanobacteria (commonly referred to as Blue-green Algae) were traditionally included as "Algae" in older textbooks, many modern sources regard this as outdated and restrict the term Algae to eukaryotic organisms. All true algae therefore have a nucleus enclosed within a membrane and chloroplasts bound in one or more membranes. Algae constitute a paraphyletic and polyphyletic group, as they do not include all the descendants of the last universal ancestor nor do they all descend from a common algal ancestor, although their chloroplasts seem to have a single origin.
Algae lack the various structures that characterize land plants, such as phyllids and rhizoids in nonvascular plants, or leaves, roots, and other organs that are found in tracheophytes. Many are photoautotrophic, although some groups contain members that are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some unicellular species rely entirely on external energy sources and have limited or no photosynthetic apparatus.
Nearly all algae have photosynthetic machinery ultimately derived from the Cyanobacteria, and so produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago.
biofuel feedstock, present one of the most exciting possibilities as a future solution to our energy problems, especially that of transportation fuel. In the last few years, activity in this field has been accelerating fast.
- The yields of oil and fuels from algae are much higher (10-100 times) than competing energy crops
- Algae can grow practically anywhere, thus ensuring that there is no competition with food crops.
- Algae are excellent bio remediation agents - they have the potential to absorb massive amounts of CO2 and can play an important role in sewage and wastewater treatment.
- Algae are the only feedstock that have the potential to completely replace world's consumption of transportation fuels.
- Algae are already being used in a wide variety of industries and applications, and many newer applications are being discovered. Such a wide range of end-uses enable companies to produce both fuels and non-fuel products from the same algae feedstock
- Bio diesel