In nitrogen is too unreactive to be used by

the light independent reaction CO2 is also converted to O2 by
the plant. It is taken up by the leaf through the stomata and diffuses through
to the chloroplast, where it combines with RuBP to form an unstable six-carbon
molecule. This breaks down into two GP molecules which are converted to TP
using the NADPH and ATP from the light dependent reaction. The two TP molecules
combine to form a hexose sugar that can be used to form other compounds. After
disassociating with other compounds, O2 is released into the air.


respiration, more CO2 is released into the atmosphere and chemical
energy is produced from internal processes in a plant in several stages. During
glycolysis, two ATP molecules are used to phosphorylate glucose and break it
down into two 3-carbon molecules. These are then converted to pyruvate,
reducing two molecules of NAD and using the energy released to convert four
molecules of ADP to ATP. Pyruvate diffuses from the cytoplasm to the mitochondrial
matrix in the link reaction, where it gets converted into acetyl coenzyme A and
releases a CO2 molecule as well as reducing another NAD molecule. In
the Krebs cycle, acetyl coenzyme A is combined into a six-carbon compound.

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Carbon bonds are broken down step-by-step, releasing CO2 and energy
in the form of ATP and NADH with each broken bond.


is used in the formation of amino acids, which are used to construct proteins.

Although the air is around 80% nitrogen, in this form nitrogen is too unreactive
to be used by plants. Nitrates, however, can be used. This is achieved by the
nitrogen cycle, wherein gaseous nitrogen is converted to nitrates. Nitrogen
fixing bacteria in the soil and nodules of plant roots convert nitrogen in the
air to inorganic nitrogen compounds, as does lightning. The Haber process
converts gaseous nitrogen to ammonia, which are then converted to nitrates by
nitrifying bacteria found in the soil. These compounds are all taken up by the
plants, which use them to create proteins from amino acids. When these plants
are eaten by animals, their biomass is transferred to the animal. Waste
material is broken down by decomposers, returning nitrogen to the soil in the
form of ammonia where it is converted to nitrates by nitrifying bacteria again.

Decomposers also break down the bodies of dead animals, returning the nitrogen
in their biomass to the soil as ammonia as well.


is a process that kills all organisms living in a body of water. Excess
nutrients from fertilisers travel through underground water channels into
rivers or lakes, or are flushed into them by rainwater. These cause an algal
bloom, a large growth of plants that require these nutrients to grow. This
blocks out the sunlight and uses up the oxygen in the lake in a positive
feedback loop, killing plants that required sunlight. These plants are
decomposed, using up even more oxygen. The ecosystem ultimately dies when so
much oxygen is used up that none of the lifeforms can survive.