Diatom Characteristics and Their Role in Aquatic Ecosystems
An Introduction to Diatom
The members of the division bacillariophyte are known as diatoms. Diatoms mean to cut into two. The name of these organisms is based on the cell wall of the diatoms that is divided into two parts. Diatoms belong to the kingdom Protista.
The Salient Features of the Protista Kingdom:
The living organisms included in this kingdom are as follows: dinoflagellates, diatoms, euglenoids, slime molds, and protozoans.
All the organisms included in this kingdom are unicellular and eukaryotic in nature.
The mode of nutrition in protists is of different types:
Holophytic or Photosynthesis
These organisms can synthesize their own food. The synthesis of food can be done by the method of photosynthesis.
Holozoic Mode of Nutrition
These organisms possess a similar mode of nutrition as that of animals. In these organisms, the food is first ingested and then digested.
Absorptive
Some protists obtain their food from dead organic matter substances. These types of protists secrete some extracellular enzymes. These enzymes convert complex or compound substances into simple substances. These produced simple substances are easily absorbed by the body surface of the protists.
Mixotrophic Mode of Nutrition
Some protists have different types of modes of nutrition.
Mode of Reproduction
Protists reproduces both by sexual and asexual means of reproduction. Types of reproduction in protists are discussed below:
Asexual Reproduction
This is the most common method of reproduction in the members of the protist kingdom. Asexual reproduction takes place in favorable conditions. It is of the following types:
Binary Fission:
In this type of reproduction two types of reproduction two daughter cells are formed by the division of one mother cell. After this step, each daughter cell formed in binary fission grows in size to form a normal organism.
Spore Formation:
Some of the protists possess a special structure that is known as sporangia. Production of Spores takes place in this sporangia. The bursting of sporangia takes place after some time and all the spores become free (released into the environment). These spores form a new cell after germination.
Sexual Reproduction
In the sexual reproduction process two gametes (haploid in nature) fuse to form a zygote (diploid in nature). This fusion is known as syngamy. This fusion can be divided into three types.
Isogamy:
The isogamy mode of fusion is the easiest way of sexual reproduction. In isogamy, the fusing gametes are morphologically similar but physiologically they may be similar or dissimilar.
Anisogamy:
The fusing gametes are morphologically dissimilar but physiologically they may be similar or dissimilar.
Oogamy:
This type of fusion is developed from anisogamy. In this type of fusion, the male gamete is small and motile while the female gamete is large and non-motile. This female gamete is known as an egg. In it, the formation of male and female gametes takes place in sex organs.
Diatom is composed of two words Di and atoms that indicate two halves. The body of the diatom is divided into two halves. The scientific name of the diatom is Chrysophyta. The word Chrysophyta means golden color. Therefore, diatoms are golden in color. Diatoms are also known as golden algae. The cell structure of diatoms is unicellular. These organisms are eukaryotic in nature. They have the holophytic mode of nutrition because they possess chloroplast.
Division of Diatoms- Chrysophyta or Bacillariophyta.
Class- Bacillariophyceae
Diatoms Under Microscope
Diatoms under a microscope can be easily visible. These organisms are not easily visible by the naked eye, thus need to view the diatoms under the microscope. Diatoms under the microscope make very interesting specimens. They have complex patterns on their surface with very fine punctures. Fine pores in the frustules of some of the animals are used to measure the resolving power of a microscope lens.
General Characteristics of Diatoms
Habitat:
Diatom is generally found in both freshwater and marine water.
The Shell of Diatom:
Diatoms have silica in their shell wall. Their cell wall is called a shell or frustule. Diatoma has overlapping shell walls. The color of the shell of the diatoms is generally transparent. The cell wall of these organisms is generally composed of cellulose. In this cellulosic cell wall, the silica particles are embedded in many places. Due to this reason, the cell wall appears to be made up of silica.
Nucleus of the Diatom:
Diploid nucleus is present in the diatom.
Pigments Present in the Diatoms:
The cell wall of diatoms consists of chloroplasts. In the chloroplast of the diatoms, the pigments are present. These pigments are chlorophyll a, chlorophyll c, and xanthophyll. This xanthophyll is also known as fucoxanthin. Due to these pigments diatoms appear golden in color.
Movement of the Diatoms:
Diatoms are immotile, because of the absence of flagella in them. They generally float on the surface of the water with the help of low molecular weight stored fats. The movement of some diatoms is done with the help of the slimy secretion. This slimy secretion is an oily material excreted by the diatoms. This provides the lubrication for the movement of the diatoms.
Mode of Nutrition in Diatoms:
The diatoms are autotrophic in nature. The form of stored food in the diatoms are leucosin (chrysolaminarin) and fats (oils).
The Shape of Diatoms:
The diatoms found in nature are of two types. One is round in shape and the other is elongated. On the basis of shape, diatoms can be classified into two types. These types are discussed below:
Types of Diatoms
Pennate Diatoms.
Centric Diatoms
Let us discuss these two forms one by one.
Pennate Diatoms:
These types of diatoms are elongated in shape. These diatoms can be divided bilaterally. Therefore, they have bilateral symmetry. Pennate diatoms are motile in nature. They move by gliding movement.
Centric Diatoms:
These types of diatoms are round-circular in shape. They possess radial symmetry. These forms of diatoms are non-motile in nature.
Reproduction in Diatoms
The diatoms reproduce both by sexual and asexual means. Diatoms mainly reproduce by the asexual mode of reproduction, by binary fission. Sexual reproduction is very rare in them. Sexually they reproduce by the gametic meiosis. The zygote formed during sexual reproduction is called auxospore. Auxospore is a asexual structure. When the diatoms reproduce by asexual means, their size decrease because of silica. To overcome this problem, they reproduce by the sexual mode of reproduction.
Use of Diatoms
Soundproofing
Filtration of oils and syrups
Stone polishing
As a heat insulator in steam boilers. They are used as thermostats because the kieselguhr is a bad conductor of electricity.
Diatoms are used as toothpaste.
Some diatoms are used in making skin medicines.
Diatoms are used in the manufacturing of certain medicines.
Diatoms are used as an insecticide, as they dry them by absorbing oil.
Did You Know That?
The cell wall of the diatoms has silica in very large quantities. Due to this reason, their cell wall is hard. The cell wall does not get destroyed after their death so, at the bottom of the sea, very huge rocks of dead diatoms are formed which are known as diatomite or diatomaceous earth or kieselguhr.
Diatoms are the chief producers in the ocean.
Diatoms are known as golden algae or jewels of the sea.
How to Master the Concept of Diatom Quickly?
There are various methods that help grasp all concepts of Diatoms, their Features, Characteristics, Types, Reproduction and Uses as well. Students can retain the basic concepts of diatoms for a long time with the help of these simple hacks we're going to suggest here. Whether for learning the concepts of diatom for competitive exams, for surprise tests or for exams, students only need to follow some guidelines to make it a quick affair.
Students often use simple methods like teaching the same concepts that they want to learn, to others; taking regular intervals in between continuous study sessions or even by making important notes of the same concepts themselves to learn the concept faster, easier and to retain the same concept for a long time.
There are multiple assignments students need to complete which makes it difficult to master all the topics they complete in a particular time. So these easy tips will definitely lower their burden and help them learn faster.
Note Down All the Queries - Don't forget to write down all the doubts and queries in any particular concept while studying diatom as it helps in solving the same queries and doubts later. Students can also ask their teachers and mentors to clear the noted queries which strengthen the basic concepts of each and every subject.
Highlight the Key Information - While studying the concepts Diatoms, its Features, Characteristics, Types, Reproduction and Uses always highlight the key information with the help of a highlighter or any other tool to make it more clear and visible. Highlighting the key information always attracts students attention so they never miss out on the key concepts.
Learning the Same Information in Different Ways - It is important to learn the concepts of diatoms in different ways, students can break down the concepts and revise them regularly or alternatively in their own ways to make them simple and understandable.
Cover Multiple Subjects Every Day - Students need to cover multiple concepts of diatoms everyday like its Features, Characteristics, Types, Reproduction and Uses as getting stuck on one particular concept can waste their time and in the end, they can't cover all the concepts in a fixed period of time.
Revise the Concepts at Regular Intervals - Revising the concepts of diatoms at regular intervals is not only necessary to catch it faster but also helps students remember it for the longest possible period. There are several studies that reveal that revising concepts at regular intervals provides a better understanding of the same.
Simplify Difficult Terms in their Own Way - To break down all concepts of diatoms into smaller parts not only simplifies the difficult concepts but also improves the reasoning skills of students as well. A short table, chart or process explaining key concepts is a better way to break down difficult terms.
Practice the Process not the Result - While learning the important concepts of diatoms it is necessary to focus on the process and not the outcome as students can easily forget the concepts if they focus only on the outcome. In order to hold the concepts and memorize them for long, it is important to stick with the process.
Keep Practicing and Testing Yourself - Students need to practise all concepts of diatoms and keep giving tests in a smaller span of time to know where they stand. It could be one unit test or the whole concept test depending on students' learning capability. But it is important to test yourself and keep improving and learning from mistakes.
FAQs on Diatoms: Definition, Features & Importance
1. What are diatoms as per the Biology syllabus for 2025-26?
Diatoms are microscopic, single-celled algae belonging to the Kingdom Protista, specifically under the group Chrysophytes. They are found in almost all aquatic environments, including oceans, freshwater, and even damp soils. Diatoms are renowned for being major photosynthetic organisms, contributing significantly to the primary productivity of marine ecosystems.
2. What are the main characteristics and features of diatoms?
Diatoms exhibit several unique features that distinguish them:
Cell Wall: They possess a unique cell wall called a frustule, which is made of silica. This wall consists of two overlapping shells that fit together perfectly, much like a soap box.
Indestructibility: The silica in their cell walls makes them extremely durable and resistant to decay.
Photosynthetic Pigments: Their golden-brown colour comes from a mix of pigments, including chlorophyll a, chlorophyll c, and fucoxanthin.
Food Storage: They store food reserves as chrysolaminarin (leucosin) and oils, not as starch.
Symmetry: They are generally classified into two groups based on symmetry: pennate (bilaterally symmetrical) and centric (radially symmetrical).
3. Why are diatoms called the 'chief producers' in the oceans?
Diatoms are called the 'chief producers' in oceans because of their immense photosynthetic capacity. They are responsible for performing a large percentage of all photosynthesis in marine environments, estimated to produce about 20% to 25% of the world's oxygen. By converting sunlight into chemical energy, they form the crucial base of most aquatic food webs, providing essential nutrition for zooplankton, which in turn are consumed by larger organisms like fish and whales.
4. What is diatomaceous earth and what are its main commercial uses?
Diatomaceous earth (or kieselguhr) is a naturally occurring, soft, siliceous sedimentary rock. It is formed from the fossilised remains of diatoms that have accumulated over millions of years. Because the silica frustules are hard, porous, and chemically inert, diatomaceous earth has several important uses:
Filtration: Used to filter syrups, oils, and water in swimming pools.
Abrasives: Used as a mild abrasive in products like toothpaste and metal polishes.
Insulation: Used as an insulator in steam boilers and for soundproofing due to its porous nature.
Pest Control: Used as a natural insecticide that abrades the waxy layer of insects, causing them to dehydrate.
5. How do diatoms reproduce?
Diatoms primarily reproduce asexually through binary fission. During this process, the two halves of the frustule separate, and each half becomes the larger shell (epitheca) for a new daughter cell, which then synthesizes its own smaller inner shell (hypotheca). They can also reproduce sexually, a process that is typically triggered when the cells reach a critically small size, to restore the population's original cell dimensions.
6. Why is sexual reproduction necessary for diatoms to maintain their population size?
Sexual reproduction is crucial for diatoms because their primary mode of reproduction, asexual binary fission, leads to a progressive reduction in the average cell size of the population. With each division, the new cell formed from the smaller half (hypotheca) is smaller than its parent. Over successive generations, this would lead to a population of unviably small cells. Sexual reproduction counteracts this by producing a special zygote called an auxospore. This auxospore can grow to the original, maximum size before forming a new frustule, thereby restoring the size and vigour of the diatom population.
7. What are the main types or classifications of diatoms?
Traditionally, diatoms are classified into two main orders based on the symmetry of their frustule:
Centric Diatoms (Order Centrales): These diatoms exhibit radial symmetry. Their frustules are typically circular, triangular, or cylindrical when viewed from the top. They are generally non-motile and are common in marine plankton.
Pennate Diatoms (Order Pennales): These diatoms have bilateral symmetry. Their frustules are elongated, boat-shaped, or needle-like. Many pennate diatoms possess a slit called a raphe, which allows for gliding movement.
8. What makes the cell wall of a diatom so unique and indestructible?
The uniqueness and indestructibility of a diatom's cell wall, or frustule, stems from its composition and structure. It is composed of hydrated silicon dioxide, essentially a form of glass. This makes it incredibly strong and resistant to chemical and physical degradation. The intricate structure of two overlapping halves (the epitheca and hypotheca) that fit together like a box provides further structural integrity, protecting the cell within. This durability is why frustules can persist for millions of years in sediments, forming diatomaceous earth.
9. If most diatoms lack flagella, how do they move or stay afloat?
Most diatoms, especially centric ones, stay afloat in the water column by storing low-density oils as a food reserve, which increases their buoyancy. They are largely passive and are carried by water currents. However, some pennate diatoms are capable of movement. They achieve a gliding motion by secreting a slimy substance (mucilage) through a specialized slit in their frustule called a raphe. This secretion propels them along surfaces.
10. Can you provide some common examples of diatoms?
Certainly. Diatoms are incredibly diverse, with thousands of species. Some common examples include:
Navicula: A common boat-shaped pennate diatom found in freshwater.
Cyclotella: A drum-shaped centric diatom often found in the plankton of lakes and oceans.
Pinnularia: A large pennate diatom with a distinct, elongated shape, commonly studied in biology labs.
Thalassiosira: A genus of centric diatoms that are a vital component of marine phytoplankton.
