15 Nutrient Cycles

Nitrogen containing biological molecules (organic - in biotic phase)

nucleic acids DNA and RNA

proteins and their monomers - amino acids

ATP /ADP

Nitrogen fixation

• carried out by nitrogen fixing bacteria.

• They reduce the nitrogen gas (N2) into ammonia/ammonium ions (NH3/NH4+)

• Can be free living in the soil or within root nodules of legumes

• (Ammonia can dissolve in the soil to form ammonium ions)

Nitrifcation

• Carried out by nitrifying bacteria.

1. The oxidation of ammonium ions (NH4+) to nitrite ions (NO2- )

2. The oxidation of nitrites (NO2- ) to nitrates (NO3 - ) by nitrifying bacteria.

· Plants take up the nitrates through their roots by active transport (organic, biotic)

Decomposition and ammonification

• The saprobiotic microorganisms secrete enzymes on to the nitrogen-containing compounds (e.g. DNA, proteins, urea)

• This is extracellular digestion

• The products are absorbed by the saprobionts but ammonium ions are released into the environment

Denitrification

• the loss of nitrates from the soil under anaerobic conditions (often in water-logged soil).

• Nitrates (NO3-) are converted to nitrogen gas (N2 )

Describe the nitrogen cycle (inc the biotic/abiotic phases) - could be asked a q that starts at any point in it

Phosphorous Cycle

• Saprobionts decompose using extracellular digestion.

• Phosphate ions (PO43- ) are released into soils, lakes, rivers and oceans.

• Some ions are absorbed by plants and algae and are used to form molecules, such as phospholipids, ATP and nucleic acids.

• The phosphate ions are then passed to the animals.

• Some of the dissolved phosphates in oceans can, by sedimentation, form rocks.

• The phosphates in sedimentary rocks are only returned to the cycle if erosion occurs.

What biological molecules is phosphorus found in?

Phospholipids, ATP, DNA, RNA, nucleic acids

Describe the phosphorus cycle visually

Fertilisers

• Contain nitrates and phosphates which are often limiting factors in plant and algal growth

  • Proteins - use nitrates

  • Nucleic acids - use nitrates + phosphates

  • Phospholipids - use phosphates

  • ATP - uses phosphates and nitrates

Natural fertilisers

Consist of organic plant or animal matter, containing complex organic compounds, e.g. urea, which releases mineral ions as it decays

• Cheap, long-lasting release, however may be too slow, unknown concentrations + may be difficult to spread

Artificial fertilisers

· Manufactured and contain concentrated mineral ions (especially NPK compounds) in an inorganic, soluble and ready-to-use form.

• Rapid release, smaller amounts as concentrated, however expensive to buy/make

Mycorrhizae

• fungi that grow in association with plant roots and improve the plant's uptake of water and inorganic ions.

• It is a mutualistic relationship between two species in which they both benefit nutritionally

• They grow in and around the roots producing a large system of threads of hyphae

• This provides the fungus with carbohydrates from the plant.

• Large surface area of the thread like hyphae leads to increased water uptake

Eutrophication

• An ‘algal bloom’ occurs

• A dense layer of algae forms on the surface of the water, absorbing light and preventing it from penetrating to lower depths

• plants below the surface cannot photosynthesise and therefore die

• Increased competition between algae results in death of algae too.

• When the algae and plants die, they are decomposed by bacteria and other saprobiotic organisms, whose populations suddenly increase.

• The increase in aerobic respiration by bacteria uses up oxygen.

• The dissolved oxygen in the water becomes depleted, causing many species of invertebrates and fish to die