Overview
This lecture continues the discussion on abiotic factors in ecosystems, focusing on wind, pH, and salinity, and introduces the nitrogen cycle and its fixation processes.
Wind as an Abiotic Factor
- Wind is air in motion and a major abiotic (nonliving) factor affecting organism distribution.
- Strong wind increases transpiration (water loss) in plants, risking permanent wilting.
- Wind raises evaporation rates from living surfaces.
- Wind aids in pollination, especially for wind-pollinated plants.
- Wind helps disperse fruits and seeds, reducing overcrowding.
- Wind creates waves in aquatic habitats, promoting water aeration.
- Wind influences predation and animal migration by aiding scent location.
- Wind speed is measured with an anemometer; wind direction with a wind vane or windsock.
pH as an Abiotic Factor
- pH measures hydrogen ion concentration, indicating acidity or alkalinity.
- pH affects organism distribution in soil and freshwater habitats.
- Some plants thrive in acidic, others in alkaline, and some in neutral soils.
- pH is measured using a pH scale or universal indicator.
Salinity as an Abiotic Factor
- Salinity is the salt concentration in water bodies (not soils).
- Aquatic environments: freshwater (low/no salt), marine (high/stable salt), estuarine (variable salt).
- Salinity affects the osmotic pressure of living cells, influencing organism survival.
- Each aquatic organism is adapted to its habitat’s salinity.
- Salinity is measured by titration.
Nitrogen Cycle and Fixation
- The nitrogen cycle is the movement of nitrogen and compounds through the atmosphere, soil, plants, and animals.
- Nitrogen is required for protein synthesis in plants, which animals obtain by eating plants/other animals.
- Plants absorb nitrogen as nitrates, not as nitrogen gas.
- Nitrogen fixation is the process of making nitrogen available to plants, either non-biologically or biologically.
Non-Biological Nitrogen Fixation
- During thunderstorms, atmospheric nitrogen combines with oxygen to form nitrogen oxides, which dissolve in rainwater to form acids.
- These acids enter the soil, react with chemicals, and form nitrates absorbed by plants.
Biological Nitrogen Fixation
- Living organisms, mainly bacteria and some algae, convert nitrogen to nitrates.
- Symbiotic bacteria (like Rhizobium) in legume root nodules fix nitrogen for plants.
- Free-living bacteria (e.g., Clostridium) and algae (e.g., Nostoc, Anabaena, Cyanobacteria) also fix nitrogen in the soil.
- Decomposition by bacteria recycles nitrogen from dead plants/animals.
Key Terms & Definitions
- Abiotic factor — a nonliving environmental component affecting living organisms.
- Transpiration — loss of water vapor from plant surfaces.
- pH — measure of acidity or alkalinity.
- Salinity — salt concentration in water.
- Nitrogen fixation — process of converting nitrogen gas into nitrates usable by plants.
- Symbiotic bacteria — bacteria living in partnership with plant roots, fixing nitrogen.
- Free-living bacteria — bacteria that fix nitrogen independently.
Action Items / Next Steps
- Assignment: Explain how water/rainfall, wave action, soil composition, soil texture, and topography affect the distribution of living organisms, using biological terms in five well-explained paragraphs.
- Prepare to discuss how biological organisms fix nitrogen in the soil and draw a nitrogen cycle flow chart in the next lesson.