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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…

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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…

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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…

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o 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…

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o 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…


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