🔍 Size and Scale
Most diatoms are between 2-200 micrometers in size. To put this in perspective, about 50 average-sized diatoms could fit across the width of a human hair! Despite their tiny size, there are over 100,000 different species of diatoms.
Plant and Protoctist Kingdoms » Diatom Characteristics
What you'll learn this session
Study time: 30 minutes
- Understand what diatoms are and their unique characteristics
- Explore the structure and composition of diatom cell walls
- Learn about different types of diatom shapes and symmetry
- Discover how diatoms reproduce and their life cycles
- Examine the ecological importance of diatoms in marine environments
- Investigate practical applications of diatoms in industry and science
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Unlock This CourseIntroduction to Diatoms
Diatoms are some of the most beautiful and important microscopic organisms in our oceans. These single-celled protoctists are like tiny glass houses floating in water, each one uniquely designed and perfectly adapted to marine life. They're so small you need a microscope to see them, yet they produce about 20% of all the oxygen we breathe!
What makes diatoms special is their incredible glass-like cell walls called frustules. Think of them as living jewellery boxes - each species has its own intricate pattern and design that's remained unchanged for millions of years.
Key Definitions:
- Diatom: A single-celled protoctist with a glass-like cell wall made of silica.
- Frustule: The two-part silica cell wall of a diatom, like a petri dish with a lid.
- Silica: A compound made of silicon and oxygen that forms glass-like structures.
- Protoctist: A kingdom of organisms that includes single-celled and simple multicellular life forms.
Structure and Cell Wall Composition
The most remarkable feature of diatoms is their frustule - a cell wall made entirely of silica (the same material used to make glass). This frustule consists of two halves that fit together like a box and its lid, called the epitheca (larger half) and hypotheca (smaller half).
The Silica Cell Wall
Diatoms extract dissolved silica from seawater and use it to build their cell walls. This process is called biomineralisation. The silica forms intricate patterns with tiny holes called areolae, which allow nutrients and waste products to pass through whilst maintaining the cell's structure.
⚖ Epitheca
The larger, upper half of the frustule that acts like a lid. It overlaps the hypotheca slightly, creating a secure seal.
⚗ Hypotheca
The smaller, lower half that fits inside the epitheca like the bottom of a box.
🔴 Areolae
Tiny pores in the silica wall that allow materials to pass in and out of the cell whilst maintaining strength.
Amazing Fact
Diatom frustules are so precisely made that they're used to test the quality of microscope lenses! The intricate patterns can only be seen clearly with high-quality optics.
Types and Symmetry
Diatoms come in two main groups based on their symmetry and understanding these groups helps us identify different species and understand their lifestyles.
Centric Diatoms
These diatoms have radial symmetry - they look the same when rotated around their centre, like a wheel or flower. Most centric diatoms are circular, triangular, or have multiple sides. They're typically planktonic, meaning they float freely in the water column.
⛺ Characteristics of Centric Diatoms
Circular or radially symmetrical shapes, often with spines or projections to help them float. They reproduce mainly through sexual reproduction and are usually found in open ocean waters.
Pennate Diatoms
These have bilateral symmetry - they have a distinct left and right side, like a boat or feather. Many pennate diatoms are elongated and have a central line called a raphe that helps them move.
⬇ Characteristics of Pennate Diatoms
Boat-shaped or elongated with bilateral symmetry. Many can move using their raphe and are often found attached to surfaces or sediments in coastal waters.
Reproduction and Life Cycles
Diatoms have a fascinating reproduction system that's quite different from other organisms. They can reproduce both sexually and asexually and their life cycle involves some interesting size changes.
Asexual Reproduction
Most of the time, diatoms reproduce by simply dividing in half. However, there's a catch - each new cell inherits one half of the parent's frustule and must build a new half to complete its cell wall. This means one daughter cell is always slightly smaller than the parent.
The Size Problem
Because one daughter cell gets smaller with each division, diatom populations would eventually become too small to survive. This is where sexual reproduction comes to the rescue!
🔥 Cell Division
Parent cell splits, each daughter gets one frustule half and builds a new smaller half.
🔨 Size Reduction
After many divisions, cells become critically smaller.
🔧 Sexual Reproduction
Small cells undergo sexual reproduction to restore original size.
Sexual Reproduction
When diatoms become too small, they undergo sexual reproduction. Two small cells come together, shed their frustules and fuse to form a large cell called an auxospore. This auxospore then builds a new, full-sized frustule, restoring the population to its original size.
Case Study Focus: Thalassiosira - A Marine Centric Diatom
Thalassiosira species are common marine centric diatoms found in oceans worldwide. They form long chains connected by silica threads, creating beautiful microscopic necklaces. During spring blooms, these diatoms can be so numerous that they colour the water brown and can be seen from space satellites!
Ecological Importance
Diatoms are absolutely crucial to life on Earth. They're primary producers, meaning they use sunlight to make food through photosynthesis, forming the base of most marine food webs.
Oxygen Production
Diatoms produce approximately 20% of all oxygen on Earth - that's more than all the rainforests combined! Every fifth breath you take contains oxygen made by these tiny organisms.
Carbon Cycling
Diatoms absorb carbon dioxide from the atmosphere during photosynthesis. When they die, many sink to the ocean floor, effectively removing carbon from the atmosphere and helping to regulate Earth's climate.
🌎 Global Impact
Diatoms process about 6.7 billion tonnes of silica annually and are responsible for nearly 40% of marine primary productivity. Their seasonal blooms support entire ocean ecosystems.
Practical Applications
Humans have found many clever uses for diatoms and their unique properties. Their applications range from everyday products to cutting-edge technology.
Diatomaceous Earth
Fossilised diatom frustules form deposits called diatomaceous earth or diatomite. This material has many uses because of its unique properties - it's lightweight, has tiny pores and is chemically inert.
🍺 Filtration
Used in water filters and swimming pool filters due to the tiny pores in frustules.
🚩 Insecticide
Natural pest control - the sharp edges damage insect exoskeletons.
🔧 Abrasives
Gentle abrasive in toothpaste and metal polishes due to hardness of silica.
Modern Applications
Scientists are studying diatom frustules to develop new materials and technologies. The intricate patterns and strength of these natural structures inspire designs for everything from optical devices to building materials.
Environmental Indicators
Different diatom species prefer different water conditions, making them excellent indicators of water quality and environmental change. Scientists can examine diatom communities to assess pollution levels, pH changes and climate variations over time.
Adaptations for Marine Life
Diatoms have evolved remarkable adaptations that make them perfectly suited to life in marine environments.
Buoyancy Adaptations
Since silica is denser than water, diatoms need special adaptations to stay afloat in the sunlit surface waters where they can photosynthesise.
▲ Structural Adaptations
Many planktonic diatoms have spines, horns, or chain-forming abilities that increase surface area and reduce sinking rates. Some store oil droplets to increase buoyancy.
Nutrient Acquisition
Diatoms need silica, nitrogen and phosphorus to grow. They've evolved efficient mechanisms to absorb these nutrients from seawater, even when concentrations are very low.
Conclusion
Diatoms are truly remarkable organisms that demonstrate how something incredibly small can have an enormous impact on our planet. From producing the oxygen we breathe to supporting marine food webs and inspiring human technology, these microscopic protoctists are essential to life on Earth. Understanding their characteristics helps us appreciate the complexity and beauty of marine ecosystems and the interconnectedness of all life.