Biology unit 4 module 4.2 revision

checklist and bullet points of knowledge required. 

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  • Created on: 01-01-13 20:56
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Module 4.2
Chemical elements are recycled in ecosystems. Microorganisms play a key role in achieving this.
Know the importance of respiration and photosynthesis and human activity in giving rise to short
term fluctuations and long term global carbon dioxide concentration.
Understand how carbon dioxide and methane cause more heat to be retained.
Appreciate the role of microorganisms as decomposers and in the guts of animals in giving rise
to carbon dioxide and methane.
Appreciate the role of coccolithophores in the oceans for converting carbon dioxide into calcium
carbonate in their shells and reducing its amount in the atmosphere.
Analyse and interpret data which show the effect of global warming on yield of crop plants, life
cycles/number of insects, distribution/numbers of wild animals and plants.
Know the nitrogen cycle involves the conversion from organic nitrogen compounds to inorganic
compounds which can then re-enter living organisms and be made into organic nitrogen
compounds once again.
Appreciate there are several steps and that without microorganisms they would not occur
resulting in depletion of this element and collapse of the ecosystem.
Know the processes of saprobiotic nutrition, ammonification, nitrification, nitrogen fixation and
denitrification in relation to the nitrogen cycle.
Know the forms of nitrogen as proteins, ammonium compounds, nitrites and nitrates
Understand the environmental issues from the use of fertilisers (leaching and eutrophication)
Analyse and interpret data which show eutrophication.
Key words
Saprobiotic microorganisms: also known as saprophyte, this is an organism that obtains its food from
the dead or decaying remains of other organisms.
Nitrogen fixation
Eutrophication: consequence of an increase in nutrients especially nitrates and phosphates, in
fresh-water lakes and rivers, that often leads to a decrease in biodiversity.

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Carbon cycle
The amount of carbon in the
atmosphere has increased due to:
The combustion of fossil
fuels, such a coal, oil and peat.
Deforestation, especially
of the rainforests, removed loads
of photosynthesising biomass
which can no longer remove
carbon dioxide from the
Saprophytic decomposers ­ secrete enzymes on to the dead organisms. These enzymes break down
complex molecules into smaller, soluble molecules that the saprophytic microorganisms absorb by
diffusion.…read more

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Greater rainfall and intense storms
The nitrogen cycle
Production of ammonia
from organic ammonium containing
o Urea
o Proteins
o Nucleic acid
o Vitamins
Saprobiotic organisms feed
on these materials releasing
ammonia, which then forms
ammonium ions in the soil.
Nitrogen returns to the
non-living component of the
Plants use light energy to produce organic compounds.
Bacteria however obtain energy from chemical reactions involving inorganic ions.
Conversion of ammonium ions to nitrate ions.
This is oxidation ­ so releases energy.…read more

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Mutualistic nitrogen-fixing bacteria ­ live in nodules on the roots of plants such as
peas and beans. They obtain carbohydrates from the plant and the plant acquires
amino acids from the bacteria.
When soil becomes waterlogged ­ and therefore short of oxygen.
Anaerobic denitrifying bacteria.
Convert soil nitrates into gaseous nitrogen.
Reduces availability of nutrients for plants.
Aerated soils prevent this.…read more

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Nitrates in drinking water is harmful to humans and environment ­ eutrophication.
o Caused by leaching of fertiliser into watercourses
1. Nitrate is a limiting factor for algal growth.
2. As nitrate concentration increases as a result of leaching, and algae grow
3. Algae grow at the surface of water ­ so it gets densely populated with algae ­
algal bloom.
4. This dense layer absorbs light and prevents it from penetrating to lower depths.
5.…read more


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