Diatoms: Definition, Characteristics & Types

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Pseudopods: Definition & Function

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:01 Definition of Algae Groups
  • 0:25 Diatomaceous Earth
  • 0:58 What Are Diatoms?
  • 1:49 Groups of Diatoms
  • 2:25 Forms of Diatoms
  • 3:45 General Ecology
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Adrienne Brundage
Diatoms are a large group of single-celled algae that are encased in a silica cell wall. They are a very diverse group and are known for their interesting physical structure.

Definition of Algae Groups

Algae are photosynthetic organisms, or living things that create energy from sunlight. This is a very diverse group, and includes single-celled organisms, all the way up to huge multi-celled masses. One major group of the algae are the diatoms. Diatoms are characterized by being unicellular with a silica-based cell wall called a frustule.

Diatomaceous Earth

Read any article about how to clean your home naturally, and you're sure to run across something called diatomaceous earth. This is a miracle substance, it seems! It can be used to clean, disinfect, get rid of pests, and even used by companies to filter everything from pool water to beer. What a diverse substance! But what is it? Where does it come from? Well, diatomaceous earth is a powdery substance made from the fossilized remains of a single-celled algae known as a diatom.

What Are Diatoms?

Diatoms are biological producers, meaning they produce energy in the form of sugar from sunlight. This gets energy into our world so the rest of us can eat it. Thanks, diatoms!

Diatoms exist as single cells, although some of them flock together in colonies that create some really pretty forms. You can find diatoms in colonies that are shaped like filaments or ribbons, in zigzag shapes, in fan shapes, or even in the shape of stars. Each individual cell is covered in a hardened frustule made from silica. This frustule gives each cell a particular shape:

Aren't these beautiful? And these are just a few of the thousands of different forms that diatoms can take. Nature is amazing! Diatoms first showed up in the fossil record right around the Jurassic period, so dinosaurs and diatoms hung out together long before we were around to study them.


A Widespread Group

There are over 100,000 species of diatoms that we know about on earth, and these species can be found wherever there is water, from oceans, to lakes, to even damp soils and puddles in your backyard.

Most diatoms are microscopic, so we can't see them with the naked eye. There are a few species that reach up to two millimeters long, though, but these are rare. For the most part, you don't know that diatoms are there, although they are extremely important in the world. A recent study estimated that 45% of the primary production in the oceans was accomplished by diatoms. What a busy organism!

Beautiful Forms

The diatom is most known for its silica shell, or frustule. The frustule is broken up into two halves, which overlap each other, kind of like the two halves of a petri dish. This shell formation allows the diatom to divide easily into daughter cells. Each daughter cell keeps one-half of the frustule, and then adds on more silica to form a full cell wall. After death, the frustule persists in the environment, which is where we get diatomaceous earth.

The physical form of the diatom is how scientists classify these organisms. Most scientists break up diatoms into two major groups: Centrales, the centric diatoms, and Pennales, the pennate diatoms.

The centric diatoms are radially symmetrical, with parts radiating out from a central point. The pennate diatoms exhibit bilateral symmetry, meaning the left and right halves are mirror images of each other. As we study diatoms in more depth and learn more about their evolution and DNA, we will be revising this basic understanding of their classification. It is even possible that we haven't discovered all of the species out there, and there may be one or two examples that don't fall into these categories. Isn't biology a wonderfully exciting science?

General Ecology

Diatoms live in water, or in very moist environments. They are also subject to changing weather patterns, just like all living things on earth. In general, diatoms exhibit a boom and bust life cycle. When conditions are favorable, the diatoms reproduce very, very quickly, often out-competing most other life forms in the environment. This is the boom (also known as a bloom of diatoms) portion of their cycle. This part of the cycle tends to happen when nutrients and sunlight are in great abundance, such as during the spring and early summer months.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account