Plants are not the only organisms capable of carrying out photosynthesis. In this lesson we will look at algae and how an algal species can be differentiated from other organisms and microbes.
Green Polar Bears
I love going to the zoo. I like to see the exotic animals from all over the world all lined up, one after another.
My favorite has always been the bear exhibits. Those huge predators in all different colors are the peak of North American predators. I like to start with the black bears. It is possible, however unlikely, that I could wake up in the morning, look out my window, and see a black bear strolling through my backyard. I love that connection.Next are the brown bears.
They are so huge and powerfully built. The last enclosure houses the polar bears – beautiful white beasts, perfectly evolved to the frozen Arctic landscape. But wait.
That polar bear isn’t white. It’s green! Is this some sort of Irish leprechaun polar bear?Would you believe that the green color is due to microscopic organisms living inside the individual hairs of the bear? Evolution produced a fur coat made of hollow hair shafts to help insulate the polar bear against the cold, harsh environment it lives in. Here in the more temperate United States, those hollow, transparent hairs have become an ecosystem of their own.Algae have taken advantage of the clear, protected, and sunbathed coat of the zoo polar bears growing inside each hair shaft. The algae don’t hurt the bear. They just make it appear more festive every St. Patrick’s Day!
But what exactly are algae? Algae is the name given to a large and diverse group of oxygenic, phototrophic, eukaryotic microorganisms.
Algae are eukaryotic, which means they have a nucleus. This differentiates them from bacteria and photosynthetic Cyanobacteria. They are oxygenic phototrophs, meaning they use light as their energy source for growth and produce oxygen as a byproduct, like plants.
But what distinguishes algae from plants is that algae do not have any tissue differentiation. Plants can differentiate their tissues into roots, trunks, and leaves, all very different tissue types. In contrast, algae are composed of cells that are generally all the same.
Despite the differences between plants and algae, many algal species are closely related to plants. But the algae are very diverse. Some algae, like Euglena, are closer evolutionarily to single-celled protozoa than to plants. The main unifying characteristic that determines if a species is considered an algae is that all algae contain or have a very recent ancestor that contained chlorophyll a.Chlorophyll a is a green pigment used by algae for photosynthesis. Chlorophyll a is what gives the algae and the polar bear fur the green color. But not all algae appear green.
There are some algae with other pigments, in addition to chlorophyll a, that makes them appear red or brown in color.As usual, in biology there are several exceptions to the algae rules. Remember those Euglena that are more related to protozoa than plants? Some Euglena species will spontaneously lose their chloroplasts and continue living as free-swimming algae that feed by absorbing nutrients from the environment.Another genus, Prototheca, has also lost its chloroplasts and become a parasite. Prototheca has been found on the skin and in joints of dogs and, more rarely, in humans, causing inflammation.
But these are exceptions, as the vast majority of algae are obligate phototrophs.
The diversity also extends to other aspects of algal life. Many algae live and grow as single, microscopic cells.
Others form long chains of cells called filaments. Still other algae, like some seaweeds, can form large aggregates of cells up to 50 meters long.Algae can be found in nearly any environment that is moist and receives enough sunlight for growth. Wet soils and both fresh and salt water are usually teeming with algae.
They are one of the major members of the oceanic phytoplankton community. Phytoplankton are the large populations of free-floating microbes found throughout the oceans. It is estimated that these planktonic algae and Cyanobacteria are responsible for 80% of the total photosynthesis on Earth.In addition to natural water sources, algae are a common inhabitant of pools, water storage tanks, and fish tanks. It is common to see fish scavenging and eating the algae that grows on the glass of aquariums, an ecofriendly way of dealing with this problem.
There are a couple more common and well-known groups of algae.The first group is the diatoms, which have a cell wall composed of silica. Silica is the major component of sand and is used to make glass and fiberoptic cables, so it makes a very strong cell wall. The diatoms make silica cell walls that are very intricate, geometric, and diverse. When the diatom dies, the hollow silica cell walls sink to the bottom of the ocean where they can resist decay for millions of years. As a result, there are beautifully preserved fossil diatoms that are around 200 million years old.Another large group are the dinoflagellates, made up of many diverse organisms, including phototrophic algae.
This diverse group includes some species that live in symbiosis with corals in reefs. The coral provides the dinoflagellates with shelter, while the algae shares nutrients with the coral. During photosynthesis, the algae captures carbon dioxide from the water and transforms it into organic carbon that can be used by the algae but also shared with the coral. The health of the reef depends on the survival of both organisms.
Other dinoflagellates can also exist as free-swimming cells. Have you ever heard of an algal bloom? An algal bloom is a massive population explosion of free-floating, phototrophic organisms, often composed of dinoflagellates, that usually occurs from an influx of nutrients, specifically nitrogen and phosphorus. Some species of algae release toxic compounds into the water.
During a bloom, the levels can become so high that fish die in large numbers. Humans that consume the water can become very sick as well.
Let’s review the world of algae.
Algae are a group of oxygenic, phototrophic, eukaryotic microorganisms. Algae have a nucleus, exist as microscopic cells, and generate oxygen through photosynthesis. The majority of algae use chlorophyll a as the dominant photosynthetic pigment.Algae can live in nearly any environment as long as there is moisture and adequate sunlight for growth.
This can include natural and artificial water sources and moist soils. Algae can grow as single cells, long filaments, or huge aggregates, but there is no tissue differentiation in algal colonies.Diatoms are a group of algae that make complex geometric cell walls out of silica. This silica is highly resistant to decay, resulting in very impressive fossil beds over 200 million years old.
Dinoflagellates are an important member of the marine ecosystem. Some species exist in symbiosis with corals, maintaining the health of the coral reef system. Other species are responsible for massive algal blooms. The population explosion during a bloom can release toxins into waterways that can kill fish and sicken anyone who drinks from the contaminated water.
After seeing this video, students should be able to:
- Define algae
- Explain how plants and algae differ
- Understand what is necessary for algae to grow
- Recall some types of algae, such as diatoms and dinoflagellates
- Explain how algae can be toxic