Algae is a term used to describe a large and diverse group of eukaryotes, photosynthetic organisms. Algae can be unicellular, live in colonies or even be multicellular. The wide variety of algae makes them difficult to classify. Algae span terrestrial and marine environments, growing almost anywhere there is water and sunlight. Algae, like plants, are photosynthetic organisms. One group of algae, the green algae, is even classified with plants because of how similar the organisms are.
Algae, as a group, produce the vast majority of the oxygen of the Earth. They exist in almost every part of the ocean that receives sunlight, in enormous quantities. Many other species survive by filtering algae from the water, and many more depend on the oxygen they produce. Algae require a variety of nutrients in addition to sunlight. When conditions are perfect and nutrients are not limited, algae can experience exponential growth. This can lead to proliferation from algaewhere massive amounts of algae bloom at the same time.
The algae quickly become too thick, killing many of the algae in the middle of the bloom. Bacteria and other organisms move in to feed on the dead algae, depleting the oxygen in the water. This creates an oxygen “dead zone” in the ocean, which can be deadly for many species. In addition, toxins produced by some algae can be harmful or deadly to wildlife and humans.
Shape and structure of algae
Typical” algae (if any) consist of an cell eukaryoticsimilar to that of a plantwith a core attached to a membrane, chloroplasts y mitochondria. Chloroplasts photosynthesise sugars, which are degraded by mitochondria. While many algal species are found as free-living unicellular organisms, others take the form of colonies or multicellular organisms. Below is an example of a Euglenaa seaweed unicellular free-living algae. This alga has a film thick, spiralling around the cell for protection. Other algae may have cell walls or other protective coverings.
Other algae live in more complex arrangements. The algal colony below is dependent on each other, but still functions as individuals for the most part. As you can see, the algae on the outer edge of the colony are specialised for defence and have large spines. This helps the whole colony to survive, without each algae having to produce spikes.
The largest algae, however, exist as multicellular organisms. These algae, such as the kelps seen below, can grow hundreds of feet tall, exploiting the entire column of light in the ocean. Unlike most terrestrial plants, these plants are not vascular and have no special way of transporting water. Therefore, they must remain in the marine environment. They have a number of adaptations that help them cope with the harsh conditions of the ocean, such as floating organs that carry them towards the light and specialised anchors that help them to root themselves to the ocean floor.
However, there is also a class of organisms known as cyanobacteria (blue-green algae), which photosynthesise, but are only prokaryotes. Although they contain all the biochemical pathways necessary to carry out the photosynthesisthey do not have membrane-bound organelles or nuclei. They are therefore bacteria. Scientists believe that these smaller and simpler algae represent the chloroplastbefore the process of endosymbiosis. In other words, scientists believe that cyanobacteria and chloroplasts are related, and that chloroplasts and mitochondria are simply smaller organisms that have co-evolved with their larger cohosts.
Where are they found?
Everywhere. Algae are found practically everywhere on the planet. The marine environment is saturated with them. The freshwater environment is also full of algae, as seen in any green pond or lake in summer. You may be surprised, but there are even algae that have colonised the terrestrial environment. Certain species of algae are found exclusively on snow-covered mountains, thousands of feet above sea level. Here, there is enough sunlight, water and nutrients for the algae to thrive.
While most algae are found within the part of the water column that contains sunlight, scientists have also found organisms genetically similar to algae that do not photosynthesise. Thus, while photosynthesis was probably the shared characteristic of evolving algae, advanced derived forms have sometimes lost the need for it. These organisms can thrive where there is no sunlight, increasing the variety of algae as a group.
Algae and humans
Algae impact and affect humans on several levels. First, algae represent the most potent source of oxygen in the atmosphere. If algae were to die suddenly, the world would quickly suffocate from lack of oxygen. While this is unlikely, humans must be aware of their impacts on algae. Algae, like the grass and plants of the terrestrial world, are the base of the food chain. Without algae, the rest of the food chain would collapse. Even humans eat algae, in almost all cultures and regions near the ocean.
And it should be noted how easily humans can disrupt the life cycle of algae. For example, agricultural runoff has been shown to be a major cause of algal blooms near populated areas. This unintentional release of nutrients into the ocean causes algae to grow rapidly, leading to the oxygen-starved conditions described above. Worse, some algae release toxins that are harmful to humans. Think staying out of the water will keep you safe? Think again. The wind can blow toxins into the air and affect any organism that is too close to the sea.