Algae are unicellular ,colonial and multicellular organisms.They are found in ponds,lakes,sea etc.They have chlorophyll so they can prepare their own food.Chlamydomonas ,volvox and spirogyra are the examples of algae.
Algae are a diverse group of aquatic organisms that have the ability to conduct photosynthesis. Certain algae are familiar to most people; for instance, seaweeds (such as kelp or phytoplankton), pond scum or the algal blooms in lakes. However, there exists a vast and varied world of algae that are not only helpful to us, but are critical to our existence.
Definition
The term "algae" covers many different organisms capable of producing oxygen through photosynthesis (the process of harvesting light energy from the sun to generate carbohydrates). These organisms are not necessarily closely related. However, certain features unite them, while distinguishing them from the other major group of photosynthetic organisms: the land plants.
Primarily, algae are not highly differentiated in the way that plants are, according to the authors of "Algae: Anatomy, Biochemistry, and Biotechnology, 2nd Ed." (CRC Press, 2014). That is to say, they lack true roots, stems and leaves, and a vascular system to circulate water and nutrients throughout their bodies. Second, many algae are unicellular, according to a 2014 articlepublished in the journal Current Biology. They also occur in a variety of forms and sizes. They can exist as single, microscopic cells; they can be macroscopic and multicellular; live in colonies; or take on a leafy appearance as in the case of seaweeds such as giant kelp. Picoplankton are between 0.2 to 2 micrometers in diameter, while the fronds of giant kelp are as large as 60 meters in length. Lastly, algae are found in a range of aquatic habitats, both freshwater and saltwater.
By virtue of these characteristics, the general term "algae" includes prokaryotic organisms — cyanobacteria, also known as blue-green algae — as well as eukaryotic organisms (all other algal species). "Since "algae" do not form a natural group that has descended from a common ancestor, including cyanobacteria into the informal group "algae" is common," said Linda Graham, a professor of botany at the University of Wisconsin-Madison. "The term 'eukaryotic algae' excludes cyanobacteria." It is also interesting to note that chloroplasts, which are the site of photosynthesis in land plants, are adapted forms of cyanobacteria. These early cyanobacteria were engulfed by primitive plants cells sometime in the late Proterozoic, or in the early Cambrian period, according to the University of California Museum of Paleontology.
(Prokaryotes include bacteria and archaea. They are simpler organisms without an organized cell structure and their DNA floats freely as a tangled mass within the cytoplasm. On the other hand, eukaryotes are all other living organisms: protists, plants, fungi What Are Protists?and animals. Their cells are more organized. They have structures called organelles to execute a range of cellular functions and their DNA is housed in a central compartment called the nucleus.)