CHAPTER 3 NOTES
CYCLES IN NATURE
THE WATER (H2O) CYCLE:
· Begins with plants absorbing water through roots.
· Animals obtain water by drinking it or consuming plants.
· Water returns to the ecosystem through transpiration, respiration, perspiration, excretion or decomposition.
· Water then returns to the soil, lakes or oceans through condensation, precipitation and runoff.
THE CARBON (C) CYCLE: Standard B1. 42
· Begins as CO2 in the atmosphere
· CO2 is breathed in by plants (autotrophs) and used to make sugar during photosynthesis.
· Animals (primary consumers) obtain the carbon by consuming the plants.
· Secondary consumers obtain the carbon by consuming the primary consumers.
· Carbon returns to the ecosystem through respiration or decomposition.
· Carbon is stored in fossil fuels and is released when the fossil fuels are burned (human activity).
NOTE: Fossil fuels formed when the decomposers could not keep up with the rate that animals and plants were dying. Layers of energy-rich organic material (contains carbon) turned into coal and oil over time.
THE NITROGEN (N2) CYCLE:
· Begins as N2 in the atmosphere and it falls to the earth dissolved in the rain.
· Plants absorb nitrogen along with water.
· Nitrogen fixing bacteria in the roots of legumes (plants) convert N2 into nitrates (NO3).
· Lightning coverts the N2 in the atmosphere into nitrates (NO3).
· People (human activity) add nitrates to the soil with fertilizer.
· Plants absorb nitrates along with water and change them into proteins.
· Animals consume the plants and change the plant proteins into animal proteins.
· Nitrogen is returned to the ecosystem through excretion (NH4) or decomposition.
· Bacteria in the soil will convert the nitrates into nitrogen gas in a process called denitrification.
THE PHOSPHORUS (P) CYCLE:
· Begins stored in rocks and sediments which humans mine to make fertilizer.
· Humans add phosphorus to the soil using the fertilizer OR phosphorus is added through erosion.
· Plants absorb phosphorus through their roots along with water to make organic compounds like DNA.
· Animals consume the plants to make more organic compounds.
· Phosphorus is returned to the ecosystem through decomposition.
Why are there cycles in nature? Because biological systems do not use up matter, they transform it so it flows from one biological thing to another.