Nutrient Cycles

• Elements are taken up by producers (plants) / stored as organic matter
• Passed on across trophic level / consumer digest and absorb food / stored as organic matter
• Decomposers decay detritus and excretory products / return inorganic ions to environment / taken up by producers
• Warm temp / higher enzyme activity / faster decomposition

Table 9-14-1: Use of nutrients in plants and animals

Carbon Cycle

• Producers, consumers, decomposers
  • Add CO2 to the air by respiration
  • Carbon is stored in tissues as organic matter (carbohydrates, lipids, proteins)
  • Carbon is passed along food web by feeding
• Plants remove CO2 from air by photosynthesis
• Animals excrete carbon as waste products
• Decomposers decay detritus and excretory products / add carbon to soil
  • Detrivores digest detritus to small pieces / large surface area
  • Saprophytes digest smaller detritus by
    • Extracellular digestion by secreting enzymes
    • Absorb resulting nutrients across plasma membrane
    • Releases inorganic matter (CO2, H2O, mineral ions) into soil
• Fossil fuels
  • Combustion releases CO2 into air
  • Fossilisation of carbon atoms in organic compounds in dead remains (plants, animals) and excretory products (animals)
• Respiring organisms must not die to release stored carbon / differs from other cycles

Respiration, Photosynthesis and CO2

• Photosynthesis takes up more CO2 than is released by respiration
• CO2 concentration
  • Higher at night than at daylight; light-dependent reaction cannot take place
  • Peaks at winter time due to high oil consumption; low rate of photosynthesis due to cooler temp, shorter day length, loss of leaves
• Variation in a graph due to wind mixing CO2 with the surrounding air
  • Graph should show conc over whole area rather over a specific area
• Rate of photosynthesis and respiration are balanced in a rain forest
  • Forests grow for a long time and have stored lots of carbon in their tissues, other plants have stored carbon as cellulose and lignin

Nitrogen Cycle

• *processes involved in restoring nitrate conc in soil after cultivation is abandoned

1) Assimilation (→Building up organic molecules)

• Plants take up NITRATE NO3/AMMONIA NH3 from the soil by active transport
  • Used to synthesis amino acids / synthesise proteins / new cells and tissues
• Primary consumers feed on plants
  • Proteins are digested into amino acids and absorbed
  • Amino acids synthesise new proteins
• Nitrogen is passed along the trophic level through the food web

2) Ammonification*

• Detritus/leaves from plants/excretion from animals/dead animals
• Broken down by saprotrophs/decomposition
• Releases ammonia/ammonium ions (from decay)
• Ammonia dissolves in H2O → NH3 + aq → NH4+

3) Nitrification*

• Ammonium NH4+ / nitrite NO2-
• Nitrite / nitrate
• By aerobic nitrifying bacteria

4) Denitrification

• Removal of nitrogen from NO2- and NO3- to make N2(g)
• By anaerobic denitrifying bacteria (NO3- as a RS)

5) Nitrogen Fixation*

• N2(g) is converted to nitrates by lightning N2(g) + O2 → NO3-
  • NITROGEN GAS IS CONVERTED TO NH3/NH4+
• By Haber process: N2(g) + H2 → ammonia NH3
  • //used to make fertilisers / added to soil / leakage of ions into river
• By Nitrogen-fixing bacteria by anaerobic nitrogenase
• Live free in soil/nodules on the roots of legumes (peas, beans)
• NH4+ is assimilated by legumes into amino acids
  • //Mutualistic relationship → bacteria get their carbon-containing compounds from the plant while the plant gets nitrates