Nutrient cycles & global warming

  • Created by: Ikra Amin
  • Created on: 15-10-14 20:11

Nutrient cycles

Elements that are important to organisms are constantly being recycled between biotic and abiotic phases.

Unlike energy, nutrients cycle between the biotic and abiotic components of ecosystems within which they exist as organic and inorganic compounds.

ORANGIC compounds:

  • found inside organisms (living or dead) 
  • large, complex molecules that all contain the element Carbon.

INORGANIC compounds:

  • Simple, small molecules
  • tend to be found in the abiotic phase
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The Carbon Cycle - PLANTS

  • Carbon enters the cycle in INORGANIC FORM as atmospheric CARBON DIOXIDE. 
  • Primary producers extract CO2 molecules from the air or water and utilise these to form COMPLEX ORGANIC COMPOUNDS through the process of PHOTOSYNTHESIS. 
  • The carbon is FIXED into a more useful form.

Complex organic molecule made in photosynthesis:

  • Glucose
  • Lipids
  • Starch
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The Carbon Cycle - ANIMALS

  • Carbon-containing organic compounds pass along food chains when the producers are eaten, digested and absorbed by animals.
  • Some of the carbon-containing organic compounds, e.g. GLUCOSE, provide an energy source for primary consumers (herbivores_ who release carbon as CO2 produced in respiration.
  • Some of the carbon-containing organic compounds are on to higher order consumers (carnivores) along food chains and they in turn release CO2 back into the atmosphere/water during RESPIRATION.
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Role of microorganisms in carbon cycle

DECOMPOSERS recycle the carbon-containing organic compounds in dead producers and consumers, and in waste products.

These decomposers include SAPROBIOTIC bacteria and fungi (saprobionts), which feed by SECRETING EXTRACELLUR ENZYMES onto the detritus (partially decomposed organic matter) to DIGEST the complex carbon-containing organic compounds (e.g. starch) into smaller, soluble molecules.

Some of these products of digestion (e.g. glucose) are absorbed and utilised by these microorganisms. Some of the carbon is released as CO2 produced in RESPIRATION.





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The Carbon Cycle

The 2 biochemical processes that maintained the levels of atmospheric CO2 are photosynthesis and respiration. 

How humans influence the Carbon cycle

Humans BURN FOSSIL FUELS (coal, oil, natural gas). Leads to production and released of vast quantities of CO2 into atmosphere. Atmospheric levels of CO2 are steadily rising. This leads to ENHANCED greenhouse effect and therefore global warming.

Cutting down of tropical rain forests to make room for crops and homes due to an expanding human population. Large scale DEFORESTATION affects the carbon cycle as burning of trees releases CO2 into the atmosphere. Less trees = less photosynthesis = less CO2 absorbed from the atmosphere.

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Greenhouse effect & Climate change

Energy radiated by the Sun is largely in the form of visible light.Some of this energy is absorbed by the Earth which warms up and itself radiated energy, as IR, back into space.Some of the energy radiated from the Earth's surface is absorbed by gases in the atmosphere (GREENHOUSE GASES), so warming it up. Greenhouse gases create the GREENHOUSE EFFECT which is necessary to keep the Earth warm.

The GREENHOUSE EFFECT is natural, in which some of the outgoing, long-wave radiation from the earth is reflected back to the surface by clouds, gases, dust and water vapour thereby warming the earth to a temperature that supports life.

Human activity has led to a release of a variety of gaseous pollutants (incl. CO2) into the atmosphere, culminating in an ENHANCED greenhouse effect:

  • Greenhouse gases absorb Infrared heat radiated from the Earth.
  • This prevents heat from escaping into space and reflects it back to the Earth's surface.
  • When more than the usual amount of long-wave radiation is reflected back to the Earth's surface, global temperatures rise.
  • This results in GLOBAL WARMING - this has occured when the MEAN GLOBAL TEMP INCREASED by around 0.6
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Greenhouse gases

METHANE, CH4. Produced in:

  • Anaerobic decay of organic matter by bacteria in waterlogged conditions (bogs/rice fields)
  • Cows. Fermentation by bacteria in the guts of animals
  • Decay of domestic waste in landfill sites

Since industrial revolution, atmospheric methane levels have risen by 150% and is a worse greenhouse gas than CO2 in terms of absorbing IR. However, it doesn't stay in the atmosphere for very long as it reacts with Oxygen in the air and produces CO2 + H2O.

CO2 has more effect because more molecules being produced.

Methane emissions could be reduced by:

  • Recyling
  • Fewer cattle
  • Use as biofuel
  • Improve efficiency + productivity of livestock production (e.g. by altering diets)
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Greenhouse gases


  • Produced by burning fossil fuels. Levels of CO2 in atmosphere have risen by over 30% since industrial revolution. 
  • Produced by respiration but used in photosynthesis. 

Climate change and crop plants 

  • Soil and atmospheric temperatures are very important to the growth of crops. 
  • Small changes in temp can affect growth because temp directly affects the ENZYMES that control the rate at which biochemical reactions occur 

Each crop species have 3 key temps:

  • Minimum temp at which biochemical reactions can occur
  • Maximum temp at which biochemical reactions can occur
  • Optimum temp at which biochemical reactions can occur
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Photosynthesis and limiting factors

  • Photosynthesis is affected by a number of environment variables. TEMP, LIGHT INTENSITY, CO2 CONC, WATER AVAILABILITY. 
  • In COOLER climates photosynthesis is TEMPERATURE LIMITED, and so any increase in atmospheric temp will lead to higher rates of photosynthesis.
  • As photosynthesis is controlled by enzymes, temps above the optimum temp of these enzymes will reduce rate of photosynthesis.

Increases in the temp result in higher rates of photosynthesis when no other factors are limiting. Above an optimum temp, where the rate of photosynthesis is at a maximum, the rate declines. 

Increasing temp:

  • Increased kinetic energy=more collisions=increased number of enzyme substrate complexes formed=increased product

IF THE CO2 CONCENTRATION RISES, THE RATE OF PHOTOSYNTHESIS MAY INCREASE, because CO2 is a limiting factor for photosynthesis. However, rising CO2 would not indefinetly increase rates of photosynthesis as other factors such as temp or light intensity would become limiting.

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Climate change

Climate change+Soil salinity: SALT CONC.COULD RISE IN SOIL IF TEMPS RISE. This is occurs because global warming increases evaporation. This may reduce plant growth as the water potential of the soil falls, so less water is taken up by osmosis through the roots.

Climate change and insect pests

  • Insects core body temp varies much more and closely parallels that of its environment (it's ECTOTHERMIC). A rise in environmental temps, therefore, results in an increase in an insect's core body temp. This, in turn, affects features such as the insect's activitiy, growth+reproduction.
  • Found that INCREASE in mean environmental temp will affect insect pests in several ways: 

- Complete their life cycles in a shorter time (there may be more generations in a year)

- Higher number of pests will survive over winter. They'll emerge and infect crops earlier

- Many tropical and sub-tropical pests will spread into areas where, at present, the climate is cooler

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Climate change+distribution of animals&plants

Animals affected by temp changes as this often acts as an environmental cue for development or for for particular behaviours:

  • Salmonid fish - stop growing in later summer when river water temps have risen. If river warms up earlier due to climate change they might stop growing early resulting in underweight fish with reduced survival chances. 
  • In some reptile incubation temp of eggs determines the sex of the young. If climate change increases temps then extreme sex rations (mostly females) could occur. This would threaten the future of such species.

Seasonal changes include variations in the duration of sunlight, precipitation, temp & other life controlling factors.

The timing of such events as:

  • plant budding + floral blooms in the spring, summer+autumn
  • spring+autumn migration patterns of some bird+mammal species
  • den making+emergence dates of hibernating animals
  • appearance of fireflies,mosquitoes+other insects
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The Nitrogen Cycle

Nitrogen is vital for all living organisms (need for proteins+DNA), it's an essential component of nucleic acids (DNA+RNA) - in the bases. ADP,ATP,amino acids,proteins+enzymes are other organic compounds which always contain nitrogen also. 

Nitrogen makes up nearly 80% of the earth's atmosphere, it's a scarce resource for living organisms. Nitrogen shortage can lead to lack of growth + even death. The difficulty arises from the fact that nitrogen gas is INERT (unreactive) and therefore useless to most living organisms when it's in the gaseous state. Lack of nitrogen would lead to stunted growth as the organisms unable to make proteins which are needed for growth. 

Nitrogen cycle:

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The Nitrogen Cycle

Nitrogen is vital for all living organisms (need for proteins+DNA), it's an essential component of nucleic acids (DNA+RNA) - in the bases. ADP,ATP,amino acids,proteins+enzymes are other organic compounds which always contain nitrogen also. 

Nitrogen makes up nearly 80% of the earth's atmosphere, it's a scarce resource for living organisms. Nitrogen shortage can lead to lack of growth + even death. The difficulty arises from the fact that nitrogen gas is INERT (unreactive) and therefore useless to most living organisms when it's in the gaseous state. Lack of nitrogen would lead to stunted growth as the organisms unable to make proteins which are needed for growth. 

Nitrogen cycle:

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The Nitrogen Cycle

4 Main stages of Nitrogen cycle:

  • Nitrogen fixation; Ammonificiation and decay; Nitrification; Denitrification

1) NITROGEN FIXATION - Nitrogen gas is converted into a nitrogen-containing compound that is more useful to organisms. 

  • Carried out by NITROGEN FIXING BACTERIA. Convert nitrogen into AMMONIA using a REDUCTION reactiom catalysed by the enzyme NITROGENASE.
  • Some of these bacteria live in special swellings on the roots (root nodules) of plants called legumes.
  • The bacterium recieves water + sugars from the plant and in return supplies the plant with AMMONIA. The ammonium ions can be used to make PROTEINS and other nitrogen containing organic compounds which are required by the plant, such as NUCLEIC ACIDS. This mutually beneficial relationship between bacteria+plant = symbiosis. (Both organisms benefit) 
  • Types of legums: clover, peas, beans

There's also FREE LIVING NITROGEN FIXING BACTERIA in the soil. The ammonia that they produce dissolves in water in the soil to form ammonium ions

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Ammonification and decay/decomposition

  • Nitrogen is passed through food chains in the form of organic compounds.
  • When organisms die, excrete urea or egest faeces, decomposers such as BACTERIA + FUNGI convert the organic nitrogen locked up in these organic compounds into AMMONIA. 
  • This is converted into AMMONIUM COMPOUNDS in the soil, so returning the nitrogen to the ABIOTIC PHASE. These organisms are SAPROBIOTIC MICROORGANISMS/SAPROBIONTS. 

Saprobiotic microorganisms are fungi/bacteria that perform extracellular digestion. They cause decay by secreting enzymes on to the detritus so the dead/waste material is digested externally. They absorb some of the products of digestion and use them, but some (e.g. ammonia) are released into the environment. 

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Types of nitrogen


  • Nitrogen gas
  • Ammonium ions
  • Nitrites
  • Ammonia
  • Nitrates


  • Protein
  • DNA 
  • RNA
  • ATP
  • Amino acids
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  • Carried out by NITRIFYING BACTERIA
  • These bacteria transform ammonium ions into nitrates.
  • This releases energy which they use for synthesis or organic molecules such as carbohydrates. For this reason, these bacteria are described as AUTOTROPHS.

Green plants are also called autotrophs. The difference between these 2 autotrophs is:

  • Green plants use light energy to synthesis organic matter (PHOTOautotrophs)
  • Some bacteria oxidise chemical compounds (e.g. nitrites) to release energy they need to synthesise organic matter (CHEMOautotrophs)

2 stages of nitrification carried out by 2 different nitrifying bacteria:


Ammonia (NH3) ----> Nitrites (NO2-) ---> Nitrates (NO3-) 

Plants take up nitrogen from soil in the form of NITRATES through their roots by active transport. this is how most of the nitrogen returns to the biotic phase.

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  • Oxygen is used by the bacteria in the form of nitrates.
  • This is loss of nitrates from the soil under ANAEROBIC conditions (often in water-logged soil). 
  • It's due to reduction reactions carried out by DENITRIFYING BACTERIA. Aerating the soil will reduce this process. 

Nitrogen flow through food webs

  • The inorganic nitrogen is taken up by plants from the soil, largely in the form of nitrates which is then used to synthesise nitrogen containing organic molecules such as proteins or DNA. 
  • These move into other organisms when they eat the plants, and digest and absorb the organic compounds.

Types of organisms will consume the nitrogen in:

  • Living plant material: herbivores+omnivores
  • Dead plant+animal material: saprobionts/decomposers
  • Living animals: carnivores (secondary/primary etc. consumers)+omnivores
  • Dead animals: saprobionts/decomposers
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Role of microorganisms in nitrogen cycle

Nitrogen fixing bacteria:

  • Reduce nitrogen gas in the atmosphere to ammonia which dissolves in water to form ammonium ions

Saprobiotic bacteria:

  • Decompose dead/wasre material and convert nitrogen containing organic matter into ammonia. 
  • Carry out extracellular digestion by releasing enzymes

Nitrifying bacteria: 

  • Oxidise ammonia to nitrites to nitrates 
  • Important process as plants take up nitrogen from soil in form of nitrates

Denitrifying bacteria:

  • Convert nitrate ions in the soil to nitrogen gas in the atmosphere 
  • These bacteria operate in anaerobic conditions
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Crop rotation

This is where farmers grow different crops in a field at different times.

Legumes (e.g. clover) are often incorporated into the rotation. They will be grown for part of the year, then ploughed into the soil and left to decay. 

This can improve crop yield as nitrogen fixing bacteria in the clover convert nitrogen gas to ammonia. The clover uses nitrogen to make proteins etc. when left to decya, saprobiotic bacterial will convert the proteins to ammonia, and nitrifying bacteria will convert this to nitrates.

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