Rucete ✏ Campbell Biology In a Nutshell
Unit 5 THE EVOLUTIONARY HISTORY OF BIOLOGICAL DIVERSITY — Concept 27.5 Prokaryotes Play Crucial Roles in the Biosphere
Although prokaryotes are microscopic, their collective biological impact is massive. They are essential to ecosystem function, especially in recycling nutrients and sustaining life on Earth through diverse ecological roles.
Chemical Recycling
- Prokaryotes play key roles in biogeochemical cycles, especially the cycling of carbon, nitrogen, and other elements.
- Decomposers (many chemoheterotrophic bacteria and archaea):
- Break down dead organisms and waste products.
- Release nutrients like carbon and nitrogen back into the environment.
- Autotrophic prokaryotes (e.g., cyanobacteria):
- Fix CO₂ into organic compounds, supporting food chains.
- Release oxygen (O₂), contributing to atmospheric levels.
- Nitrogen-fixing prokaryotes convert N₂ gas into usable forms (e.g., ammonia), supporting plant growth.
- Prokaryotes can both increase and decrease nutrient availability:
- Some release nutrients from minerals (e.g., potassium).
- Others immobilize nutrients for their own use.
Example: Soil Nutrient Availability
- Burkholderia glathei, a soil bacterium, was shown to enhance potassium uptake in pine seedlings.
- Different bacterial strains released more K⁺ from soil minerals, demonstrating how bacteria influence plant nutrition.
Ecological Interactions
Prokaryotes engage in various symbiotic relationships with other organisms:
- Mutualism: Both species benefit.
- Example: Bioluminescent bacteria in flashlight fish help attract prey and mates while receiving nutrients.
- Commensalism: One species benefits, the other is unaffected.
- Example: Skin-dwelling bacteria benefit from oils and shelter without affecting humans.
- Parasitism: The prokaryote harms the host.
- Disease-causing prokaryotes are called pathogens.
- Many parasites do not immediately kill their hosts, allowing prolonged exploitation.
Ecosystem Dependence on Prokaryotes
- In ecosystems like hydrothermal vents, entire communities rely on chemoautotrophic prokaryotes that use hydrogen sulfide to produce organic matter.
- When the vent stops releasing chemicals, the bacteria die—and the whole community collapses.
- This shows how prokaryotes form the base of many food webs, even in environments with no sunlight.
In a Nutshell
Prokaryotes are indispensable for ecosystem function. They recycle nutrients, support food webs through autotrophic processes, and participate in essential symbiotic relationships. From soil to sea vents, their metabolic activities sustain life on Earth—and their disappearance would threaten all ecosystems.