Looking At Diatoms Under The Microscope: Characteristics And Classification

What Are Diatoms?

Looking At Diatoms Under The Microscope: Characteristics And Classification

Diatoms are a type of single-celled algae. They are photosynthetic which means that they are related to the process of photosynthesis, where sunlight is used by the plants or algae to transform – or synthesize – certain nutrients from both water and carbon dioxide.

Diatoms have a cell wall that is made of silicon dioxide. It is transparent. The cell wall is always hydrated with some water – albeit a very small amount which means that diatoms are water basic organisms known as aquatic organisms. 

Diatoms are a common type of algae that differ from bacteria because, like plant and animal cells, they contain a nucleus. 

Where Will You Find Diatoms?

Diatoms are found in areas that have some water in or around them. For instance, they will often be found in a pond, puddle, swimming pool or lake.

They are also sometimes found in rivers and on or around stones that are damp. They are found in both fresh water and salty waters and can also be found in moist soils.

What Do Diatoms Look Like?

Diatoms can be identified as being slimy with a thin film. Under a microscope, diatoms are greatly loved by enthusiasts. They have a wide range of appearances under the microscope and all are very beautiful!

These diatoms come in a range of shapes such as circles, squares, ribbons, stars and zigzags. Because of their beautiful shapes under the microscope, they are known as ‘jewels of the sea’.

Classifying Diatoms 

When studying algae like diatoms, the process is very complicated as there are so many different species out there. There is believed to be between 12,000 and 200,000 species of diatoms.

They are considered to be one of the most diverse groups on the planet and they are believed to have been around for a very very long time! 

Let’s take a quick look at the history of diatoms before we dive into them under the microscope!

So, they’re believed to date back to the triassic period and the best fossils are from the early Jurassic period. It is thought that the diatoms are up to 250 million years old!


Because diatoms are considered to be algae, they are actually defined as protists rather than being specifically defined as plants, animals or fungus.

They are classed as Division Chrysophyta in the Class Bacillariophyceae which is classified this way because of their cell wall that contains hydrated silica. 

Some characteristics of this class are the fact that they secrete silica, they store oils instead of starch and they have endoplasmic cysts. 

Within this class, the diatoms are then further divided into two main orders. These are the Centrales and the Pennales. 


Centrales are characterized in this way as they are cylindrical, have an annulus and have a valve striae which is arranged in relation to a point.


Pennales are characterized in this way as they are symmetrical, shaped like a pen and they have a valve triage which is arranged in relation to a point.

Lifecycle Of A Diatom

Diatoms are interesting to study and their reproduction cycle is very interesting. Usually, diatoms divide and reproduce when a single cell divides into two new cells, known as vegetative division.

During this cycle, the new cell is formed within the old cell, and it is smaller than the ‘parent’ cell. During the process of reproduction, the younger cell takes a valve of the parent frustule and builds its own hypotheca.

This can happen many times a day, but it doesn’t always. The amount of times this happens per day will depend on the amount of dissolved silica that is available to it. 

Because the new cells form inside the parent cell and the parent cell remains the same size, the new cells will become smaller in size each time they divide.

This is why the diatoms are such interesting shapes when you view them through a microscope! Every cell will vary in shape and size.

As you were probably thinking, there is a point where this process must end and the frustule must restore its original size.

This is when a cell known as an auxospore is produced and it contains a different cell wall to the ones that were previously created. The process then can begin again.

The way that the diatoms are made up influences the way the organism reproduces. They are able to reproduce in two different ways – asexual reproduction and sexual reproduction.

This depends on what the cell needs at the time of reproduction.It is known as asexual reproduction when the cell divides in two.

When the cell has divided enough times, as explored above, the diatom completes a different type of reproduction which is known as sexual reproduction.

During this, the male and female sex cells fuse to form a fertilized cell which grows into a new diatom. This is known as meiosis. The lifecycle of a diatom is difficult to get your head around but it is also very fascinating!

Under The Microscope

Viewing diatoms under the microscope is a great experience. The diatoms are made up of such complicated patterns and they are a joy to look at.

These species are so complex and intricate that they are often used in the testing of a microscope lens as they provide the ultimate test for detail!

Preparing the diatom is quite an easy process once you know how to do it properly. Read on for some detailed instructions on the preparation of wet mounts for viewing diatoms:

  1. Apply the sample to a microscope slide using some water. 
  2. Place the slide onto the microscope and get viewing! 

If you want to get the best possible view of the diatom, you can apply hydrogen peroxide to the sample. This will remove some of the organic matter, meaning that you will have a clearer view of what you are looking at. If you want to do this, follow these instructions:

  1. Add some hydrochloric acid to the sample in order to remove the calcium carbonate that may be on the sample. 
  2. Rinse the sample with water to remove this hydrochloric acid. 
  3. Dry the sample out.
  4. Place it on the microscopic slide and get viewing!

Diatoms have been studied for many years, and have been observed using a microscope since the 18th century. They are very easy to find, and therefore very easy to study. 

Usually, when you are observing diatoms, you will use a 100x-400x magnification on your microscope. If you are lucky, you may even see other organisms on your slides that feed off the diatoms.

What You Will See

Diatoms are beautiful when you study them through a microscope. They are known as the jewels of the sea because they have very intricate structures and patterns.

They are also symmetrical, like many other jewels. Not only are they beautiful to look at, they are also very important ecologically as they are a very key source of food for so many other marine organisms and microorganisms.

What Is The Structure Of Diatoms?

What Is The Structure Of Diatoms?

Diatoms are made up of a cytoplasm which is covered by the hard cell wall known as the frustule. Diatoms can range from 2 to 200 micrometers and they come in various shapes and sizes. 

Diatoms consist of two valves connected by a band structure.These valves are known as the epitheca and the hypotheca. 

Most diatoms do not move very far of their own accord, and they simply float through the water if they are to move. However, there are some scientists who have found that diatoms can glide through the surface of the water on their own.

The reason they think this is because they often are followed by a trail of mucus. There is little evidence for how the diatoms glide but it is believed to have something to do with the mucus that it secretes in the process.

The structure of these diatoms does vary greatly because of the sheer amount of different types there are in existence. How many exactly is not even known!

What Do Diatoms Eat?

In order to produce energy and keep themselves going, diatoms complete photosynthesis. This means that diatoms need carbon dioxide, water and sunlight to survive.

The speed at which they can reproduce is, therefore, related to the availability of these things. The energy that they use comes from sunlight which is converted into the energy that diatoms need to reproduce. 

Because diatoms are so commonplace and they are found in so many different places, diatoms are responsible for 25% of the oxygen on the earth – the gas released during the process of photosynthesis.

While the way that they produce their energy is similar to plants, diatoms are different in many ways. They are very unique due to their silica cell wall (referred to as a frustule).

Most of the energy that they produce goes towards building the silica polymers inside the cell which make up the frustule. In contrast, plants use the process of photosynthesis to create their own food and nutrients. 

What Eats Diatoms?

Diatoms provide food for many different microorganisms in the water. There are certain other things that also eat diatoms, including some types of snail.

Are Diatoms Harmful?

Diatoms are all over everything in nature, so they can’t be too harmful to humans! However, there are some diatoms that are considered to be harmful.

This is because certain diatoms contain an acid called domoic acid which can be poisonous to humans. This acid is also harmful to some marine animals such as fish, birds and mammals.

There have been known cases of humans becoming poisoned because of the domoic acid present in certain diatoms.

As well as these cases, some diatoms have been known to cause irritation to the eyes and skins of humans. While this does affect us as humans, it is not a risk to our lives.

Uses Of Diatoms

Diatoms have many uses for us in everyday life. These include: 

  • Soundproofing 
  • Stone polishing 
  • Use as an insulator
  • Toothpaste 
  • Skin medications
  • Medicines

Facts About Diatoms

Diatoms are the key producers in the ocean. They also produce silica in high quantities which means that their cell wall is very hard.

The cell wall of diatoms remain after they die, so they sink to the bottom of the body of water. Here, large rocks are formed that are made up of the dead diatoms. 

Final Thoughts

After reading this article you should know everything there is to know about the diatom! Grab your microscope and start observing this fantastic single-celled algae.

It really is worth a look because it forms such fantastic patterns. There’s a reason it is known as the jewels of the sea, and you really shouldn’t miss out!

Jennifer Dawkins

Leave a Comment

Your email address will not be published. Required fields are marked *