Stramenopiles: Diatoms, Golden Algae & Brown Algae

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  • 0:00 Stramenopiles
  • 0:45 Diatoms
  • 1:52 Brown Algae
  • 2:45 Golden Algae
  • 3:36 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

In this lesson, explore the group of organisms called the stramenopiles, and check out some of the algae in this group. Then, test your understanding with a brief quiz.


We are not alone. On Earth, I mean. There are quite a few other living things on this planet. Some are big, some aren't. Some we take for granted, others we don't even realize are there at all. That can be the case with stramenopiles, a large group of organisms composed of cells with a distinct form of chlorophyll. There are roughly 100,000 species of different stramenopiles, most of which are various types of algae. You may not always know that they're there, but the stramenopiles are a big part of many ecosystems. After all, we're not alone.


Let's get to know some of our stramenopiles. How about we start with the diatoms, unicellular algae that can be found in both salt and fresh water. Despite being single-cell organisms, diatoms are a major part of food chains and are part of the collective groups of marine organisms we call plankton. In fact, diatoms are the most common of the phytoplankton, which are organisms within a plankton community that create their own food from light using photosynthesis. So, diatoms themselves are very small. But, get enough of them together and they can create ribbons or blooms large enough to see. The other thing that makes diatoms unique is that each individual cell is covered with a hard cell wall made of silica, called a frustule. Diatoms die, their hard frustules sink to the bottom of the ocean or lake, and build up layers of silica-rich sediment. This sediment is used commercially for filters, insulation, and as an abrasive.

Brown Algae

Now, not all of the stramenopile algae are unicellular like diatoms. In fact, some can get quite a bit bigger. The brown algae are large, multicellular marine algae. If you've ever been to places like California and seen the giant seaweed forests, you've seen brown algae. The largest of the brown algae, a cold-water marine group of kelp called Macrocystis, can grow up to 200 feet long. So, when we talk about forests of brown algae, we really mean vast underwater forests. These large groups of brown algae are extremely important for marine ecosystems. Animals live in them, use them to hide from predators, and even eat them. There are even some species of kelp that we eat as humans.

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