Algae belong to the Protista kingdom, that is, the one that groups together organisms that cannot be considered animals, plants, fungi or bacteria. And, although they are popularly known as the "plants of the sea", algae cannot be identified with vegetables, since they do not have all their characteristics and functions.
They have a simple structure called thallus instead of root, stem and leaves or vascular tissue, since when living in water they do not need those organs to absorb it. They are organisms made up of eukaryotic cells (with nuclei) and are divided into unicellular cells - they usually form part of the filoplacton - and multicellular cells, although they do not group together forming tissues, but all cells perform all the functions. Another fundamental characteristic of algae is that they are autotrophs: they generate organic matter from inorganic matter using the energy of light (photosynthesis). Their reproduction can be asexual by spores or sexual, through gametes. They grow at the bottom of the sea or glued to rocks and are found in seas, rivers and lakes. Its morphology is very varied (filamentary, laminar, calcareous, etc.), and may be microscopic or reach more than 50 meters in length. There are more than 30,000 known species of algae.
The color of the pigmentation that they use to carry out photosynthesis varies depending on the depth in which they live and allows establishing three large groups of algae. Greens (chlorophytes) fully take on the color of chlorophyll and thrive in salty and sweet waters at shallow depths. Brown algae (pheophytes) have a slightly more sensitive pigment to light that allows them to live in deeper waters. And finally, red algae (rhodophytes) use a pigment of that color capable of capturing very dim light at a great distance from the surface.