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Unlock This CourseAll life on Earth can be organised into three major groups called domains. This system was developed by scientist Carl Woese in the 1970s when he discovered that not all single-celled organisms are the same. The three domains are Bacteria, Archaea and Eukarya. Understanding these domains is crucial for marine scientists because the ocean contains representatives from all three, each playing vital roles in marine ecosystems.
Key Definitions:
Marine environments contain the most diverse collection of life on Earth. From the sunlit surface waters to the deepest ocean trenches, representatives from all three domains have adapted to survive. Understanding these domains helps scientists classify new species, study evolution and understand how marine ecosystems function.
Bacteria are single-celled prokaryotic organisms found everywhere in the ocean. They're incredibly important for marine ecosystems because they form the base of many food webs and recycle nutrients. Marine bacteria are diverse and include both helpful and harmful species.
Bacterial cells are relatively simple but highly efficient. They lack a nucleus, so their genetic material floats freely in the cell. Most bacteria have a cell wall made of peptidoglycan, which gives them structure and protection. Many marine bacteria can move using whip-like structures called flagella.
No nucleus, genetic material in cytoplasm, cell wall present, often have flagella for movement.
Binary fission - splits into two identical cells. Very rapid, can double every 20 minutes in ideal conditions.
Cyanobacteria (blue-green algae), Vibrio bacteria, nitrogen-fixing bacteria in sediments.
Cyanobacteria are among the most important bacteria in the ocean. They perform photosynthesis like plants, producing oxygen and forming the base of many marine food chains. Some species, like Trichodesmium, can fix nitrogen from seawater, making this essential nutrient available to other marine life. However, when conditions are right, cyanobacteria can form harmful blooms that create dead zones in the ocean.
Archaea look similar to bacteria under a microscope, but they're actually more closely related to us! These remarkable organisms are often found in extreme marine environments where other life cannot survive. They're the ultimate survivors of the ocean world.
Like bacteria, archaea are single-celled prokaryotes without a nucleus. However, their cell walls are made of different materials and their genetic machinery works more like ours. Many archaea are extremophiles, thriving in conditions that would kill most other organisms.
Can live in boiling water, highly acidic or salty conditions and areas with no oxygen.
Binary fission like bacteria, but genetic processes more similar to eukaryotes.
Methanogens in deep-sea sediments, halophiles in salt ponds, thermophiles near hydrothermal vents.
Deep-sea hydrothermal vents spew water heated to over 400°C, creating one of Earth's most extreme environments. Here, archaea called hyperthermophiles thrive in temperatures that would instantly kill most life. These organisms use chemicals from the vents for energy instead of sunlight, forming the foundation of unique ecosystems that exist in complete darkness thousands of metres below the ocean surface.
Eukarya includes all organisms with cells that have a nucleus - from tiny marine algae to massive whales. This domain contains the most familiar marine life, including fish, seaweeds, dolphins and countless microscopic organisms that drift in the plankton.
Eukaryotic cells are more complex than prokaryotic cells. They have a membrane-bound nucleus containing their genetic material, plus other specialised structures called organelles. This complexity allows for more sophisticated functions and larger, more complex organisms.
Membrane-bound nucleus, organelles like mitochondria and chloroplasts, can be single or multicellular.
Mitosis for growth, meiosis for sexual reproduction, many different reproductive strategies.
Fish, marine mammals, seaweeds, phytoplankton, sea anemones, corals.
Each domain has evolved different strategies for reproduction, reflecting their cellular complexity and environmental challenges. Understanding these differences helps marine scientists study how organisms survive and thrive in ocean environments.
Both bacteria and archaea primarily reproduce through binary fission - a simple process where the cell copies its genetic material and splits into two identical cells. This allows rapid population growth when conditions are favourable. Some can also exchange genetic material through processes like conjugation.
Eukaryotes have much more diverse reproductive strategies. Single-celled eukaryotes may reproduce asexually through mitosis or sexually through meiosis. Multicellular organisms like fish and marine mammals have complex reproductive systems involving specialised organs and behaviours.
The three domains represent different branches on the tree of life. Scientists believe that bacteria evolved first, followed by archaea and finally eukaryotes. Interestingly, eukaryotic cells likely formed when an ancient archaeal cell engulfed bacterial cells, which became organelles like mitochondria and chloroplasts.
Many marine eukaryotes provide perfect examples of endosymbiosis - organisms living inside other organisms for mutual benefit. Coral polyps contain zooxanthellae (algae) that photosynthesise and provide food, while the coral provides protection. Similarly, many marine protists contain bacterial or archaeal symbionts that help them survive in specific ocean conditions. This cooperation between different domains of life is essential for marine ecosystem functioning.
Understanding the three domains helps marine scientists organise and study ocean life. When researchers discover new species in the deep sea or identify microorganisms in water samples, they use domain characteristics to begin classification. This system provides a framework for understanding biodiversity and evolutionary relationships in marine environments.
Today's marine scientists use DNA analysis to classify organisms accurately. By comparing genetic sequences, they can determine which domain an organism belongs to and understand its evolutionary relationships. This is especially important for studying marine microorganisms that are difficult to identify using traditional methods.
Domain classification helps scientists study marine biodiversity, track the spread of marine diseases, understand ecosystem functions and discover new organisms with potential biotechnology applications. Many marine bacteria and archaea produce unique compounds that could lead to new medicines or industrial processes.