by Mark Edwards
lgae can be such lively little critters that some scientists consider them animals. Many can swim, such as dinoflagellates that have little whip-like structures called flagella which pull or push them through the water. Some algae squish part of their body forwards and crawl along solid surfaces.
Others among the infinite variations of species are made of fine filaments with cells joined from end to end. Some clump together to form colonies while others float independently. Seaweeds may grow in nearly any shape, such as cones, tubes, filaments, circles or may imitate the shape of land plants. Seaweeds developed in parallel evolution with land plants.
Major steps in cell complexity occurred with the evolutionary progression from a virus to bacterium and then from the prokaryotic cells of bacteria to the eukaryotic cells of algae.
Cell walls enable algae protection from the surrounding environment, typically water and pressure, called osmotic pressure. Cell walls regulate osmotic pressure produced by water trying to flow in or out of the cell through its semi-permeable membranes due to a differential in the solution concentrations. Algae typically possess cell walls constructed of cellulose, glycoproteins and polysaccharides. Some species have a cell wall composed of silicic, (silicon) or alginic acid.
Red algae, for example, are a large group of about 10,000 species of marine algae, including seaweed. These include coralline algae, which live symbiotically with corals, secrete calcium carbonate and play a major role in building coral reefs. Red algae such as dulse (Palmaria palmata) and laver (nori/gim) are a traditional part of European and Asian cuisine and are used to make other products such as agar, carrageenans and many food ingredients.
The broad algae classification includes:
| Bacillariophyta – diatoms Charophyta – stoneworts Chlorophyta – green algae Chrysophyta – golden algae | Cyanobacteria – blue-green Dinophyta – dinoflagellates Phaeophyta – brown algae Rhodophyta – red algae |
Green algae evolved with chloroplasts, which enables photosynthesis and enhances available O2 in the atmosphere. Prochlorococcus, a blue-green alga, is among the smallest organisms on earth at 0.6 microns, (millionths of a meter), but is one of the most abundant organisms on the planet. A single drop of water may contain more than 100,000 of these single-celled organisms. Trillions of these minute cells make up invisible forests and provide about half the photosynthesis in the oceans.
Even though all algae species combined represent only 0.5% of total global biomass by weight, algae produce about 70% of the net global production of oxygen on Earth – more than all the forests and fields combined. Algae use nitrogen to manufacture amino acids, nucleic acids, chlorophyll and other nitrogen compounds. Cyanobacteria are able to fix nitrogen absorbed from the air, as well as from water, in a process known as diazotrophy. Since the atmosphere is nearly 80% nitrogen, nitrogen fixing is a strong competitive advantage for growth because water-based nitrogen is often limited.
Nitrogen fixing also means that algae biomass has significant value as a low energy input, high nitrogen fertilizer. Algae fixes nitrogen naturally without added energy. About 90% of the cost of commercial synthetic fertilizers comes from the energy used to extract nitrogen from the air.
Algae, often called microscopic phytoplankton, grow in most bodies of water, moist places, on and in trees and even in rocks. This little plant provides the foundation for the marine food chain, feeding both microbial and animal plankton; zooplankton. Subtract algae and phytoplankton from the water column and fish, shellfish, reptiles and many other aquatic creatures could not survive.
