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Explain how some algal species are able to survive during periods of nutrient starvation and extreme temperatures. (Site 1)
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Algae survive nutrient starvation and extreme temperatures using a combination of physiological, biochemical and life‑history strategies. Key mechanisms are:
- Formation of resistant dormant stages
- Many algae form thick‑walled resting cells (resting cysts, spores, akinetes, zygotes) that reduce metabolic activity and tolerate dessication, cold or heat. Examples: dinoflagellate resting cysts, cyanobacterial akinetes, diatom resting spores.
- Dormant cells persist in sediments or attached surfaces and germinate when conditions improve.
- Storage and remobilization of reserves
- Accumulate carbon and energy reserves (starch, triacylglycerol/lipids, polyhydroxyalkanoates, polyphosphate) during good conditions and mobilize them during starvation.
- Autophagy and controlled breakdown of cellular components recycle nutrients internally.
- Altered metabolism and nutrient scavenging
- Strong downregulation of growth and photosynthesis to lower energy demand.
- Upregulation of high‑affinity nutrient transporters and enzymes (e.g., alkaline phosphatase for scavenging organic P) to capture trace nutrients.
- Some cyanobacteria fix atmospheric N2 in specialized cells (heterocysts) when combined nitrogen is scarce.
- Cellular protection against temperature stress
- Heat‑shock and cold‑shock proteins (molecular chaperones) stabilize and refold proteins.
- Antioxidant systems (superoxide dismutase, catalase, peroxidases) and photoprotective mechanisms (non‑photochemical quenching, carotenoids, mycosporine‑like amino acids) reduce oxidative damage from stress.
- Production of compatible solutes/cryoprotectants (glycerol, trehalose, glycine betaine) that protect proteins and membranes from freezing/desiccation.
- Membrane and biochemical adjustments
- Alter membrane lipid composition (increase unsaturated fatty acids in cold to maintain fluidity; adjust saturation for heat tolerance) to preserve membrane function.
- Adjust enzyme isoforms and metabolic pathways to operate efficiently at new temperatures.
- Behavioral and ecological strategies
- Vertical migration in the water column to reach more favorable temperatures or nutrient layers.
- Forming colonies or extracellular polymeric substances (EPS/biofilms) that buffer cells from rapid environmental changes and retain moisture/nutrients.
- Switching to mixotrophy/heterotrophy in some groups to use dissolved organic carbon when photosynthesis or inorganic nutrients are limiting.
Together these strategies let algal cells endure prolonged stress with minimal energy use, repair damage, and rapidly resume growth when nutrients and favorable temperatures return.
- Formation of resistant dormant stages
- Many algae form thick‑walled resting cells (resting cysts, spores, akinetes, zygotes) that reduce metabolic activity and tolerate dessication, cold or heat. Examples: dinoflagellate resting cysts, cyanobacterial akinetes, diatom resting spores.
- Dormant cells persist in sediments or attached surfaces and germinate when conditions improve.
- Storage and remobilization of reserves
- Accumulate carbon and energy reserves (starch, triacylglycerol/lipids, polyhydroxyalkanoates, polyphosphate) during good conditions and mobilize them during starvation.
- Autophagy and controlled breakdown of cellular components recycle nutrients internally.
- Altered metabolism and nutrient scavenging
- Strong downregulation of growth and photosynthesis to lower energy demand.
- Upregulation of high‑affinity nutrient transporters and enzymes (e.g., alkaline phosphatase for scavenging organic P) to capture trace nutrients.
- Some cyanobacteria fix atmospheric N2 in specialized cells (heterocysts) when combined nitrogen is scarce.
- Cellular protection against temperature stress
- Heat‑shock and cold‑shock proteins (molecular chaperones) stabilize and refold proteins.
- Antioxidant systems (superoxide dismutase, catalase, peroxidases) and photoprotective mechanisms (non‑photochemical quenching, carotenoids, mycosporine‑like amino acids) reduce oxidative damage from stress.
- Production of compatible solutes/cryoprotectants (glycerol, trehalose, glycine betaine) that protect proteins and membranes from freezing/desiccation.
- Membrane and biochemical adjustments
- Alter membrane lipid composition (increase unsaturated fatty acids in cold to maintain fluidity; adjust saturation for heat tolerance) to preserve membrane function.
- Adjust enzyme isoforms and metabolic pathways to operate efficiently at new temperatures.
- Behavioral and ecological strategies
- Vertical migration in the water column to reach more favorable temperatures or nutrient layers.
- Forming colonies or extracellular polymeric substances (EPS/biofilms) that buffer cells from rapid environmental changes and retain moisture/nutrients.
- Switching to mixotrophy/heterotrophy in some groups to use dissolved organic carbon when photosynthesis or inorganic nutrients are limiting.
Together these strategies let algal cells endure prolonged stress with minimal energy use, repair damage, and rapidly resume growth when nutrients and favorable temperatures return.
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