16 Ecology and Applied Environmental Science
It is often emitted by eutrophic water bodies, septic tanks and sewers
where the oxygen dissolved in the waste has been exhausted, initially by
the action of aerobic microorganisms. Later, anaerobic microorganisms
develop, some of which use the sulphate present in waste as a recipient of
hydrogen, resulting in the production of H 2 S.
Autotrophic organisms generally supply heterotrophic organisms with
nutrients consisting of various complex compounds, such as polysaccharides, proteins and fats. These substances cannot pass through the cell walls
and must first be broken down into simpler ones, such as carbohydrates,
amino acids and fatty acids. Most microorganisms break them down as necessary using special extracellular enzymes, whereas higher organisms use
their specialized peptic system. In any case the heterotrophic cell ultimately
synthesizes its complex components from the simpler foods that enter the
cell and from the products of their breakdown, which is carried out within
it. The reactions of synthesis are endothermic and the necessary energy is
provided by ATP. In the absence of sunlight and food, photosynthetic and
chemosynthetic cells may obtain the energy they need through oxidation of
their protoplasm. This phenomenon is known as endogenous respiration.
The reactions of synthesis are interconnected with the reactions of energy
and form a total of at least 1000 secondary chemical reactions, which are
necessary to support the life of the cell. Observation of the small, single-celled
organism Escherichia coli (coliform bacterium), for example, shows it to be
an astonishing chemical factory. Within that microscopic cell an average of
1400 molecules are produced every second. As a comparison, in humans’
initial efforts to produce a protein, successive chemical reactions lasting for
several months are necessary.
2.6 liMiting nutriEnt
An organism requires chemical elements in proportions that are in general
determined by the chemical composition of its cells, and thus it uses available nutrients in those proportions. Thus the conclusion can be drawn that
the quantity of living matter produced at a certain moment in time in given
environmental conditions will be limited by the chemical element that is
least available in those proportions, barring the influence of other negative
factors. This is a special formulation of von Liebig’s “law of the minimum”
(Chapter 4).
In general, the limiting factor is some environmental parameter. Often
it is one component of the nutrients, in which case it is called the limiting
nutrient. For instance, in terms of mass, on average C, N, P are present in
the protoplasm of algae in the proportion of C:N:P = 41:7:1. Assuming that
there is a surplus of other elements (oxygen, hydrogen, trace elements, etc.),
energy, and the other factors that play some part in production, the limiting
It is often emitted by eutrophic water bodies, septic tanks and sewers
where the oxygen dissolved in the waste has been exhausted, initially by
the action of aerobic microorganisms. Later, anaerobic microorganisms
develop, some of which use the sulphate present in waste as a recipient of
hydrogen, resulting in the production of H 2 S.
Autotrophic organisms generally supply heterotrophic organisms with
nutrients consisting of various complex compounds, such as polysaccharides, proteins and fats. These substances cannot pass through the cell walls
and must first be broken down into simpler ones, such as carbohydrates,
amino acids and fatty acids. Most microorganisms break them down as necessary using special extracellular enzymes, whereas higher organisms use
their specialized peptic system. In any case the heterotrophic cell ultimately
synthesizes its complex components from the simpler foods that enter the
cell and from the products of their breakdown, which is carried out within
it. The reactions of synthesis are endothermic and the necessary energy is
provided by ATP. In the absence of sunlight and food, photosynthetic and
chemosynthetic cells may obtain the energy they need through oxidation of
their protoplasm. This phenomenon is known as endogenous respiration.
The reactions of synthesis are interconnected with the reactions of energy
and form a total of at least 1000 secondary chemical reactions, which are
necessary to support the life of the cell. Observation of the small, single-celled
organism Escherichia coli (coliform bacterium), for example, shows it to be
an astonishing chemical factory. Within that microscopic cell an average of
1400 molecules are produced every second. As a comparison, in humans’
initial efforts to produce a protein, successive chemical reactions lasting for
several months are necessary.
2.6 liMiting nutriEnt
An organism requires chemical elements in proportions that are in general
determined by the chemical composition of its cells, and thus it uses available nutrients in those proportions. Thus the conclusion can be drawn that
the quantity of living matter produced at a certain moment in time in given
environmental conditions will be limited by the chemical element that is
least available in those proportions, barring the influence of other negative
factors. This is a special formulation of von Liebig’s “law of the minimum”
(Chapter 4).
In general, the limiting factor is some environmental parameter. Often
it is one component of the nutrients, in which case it is called the limiting
nutrient. For instance, in terms of mass, on average C, N, P are present in
the protoplasm of algae in the proportion of C:N:P = 41:7:1. Assuming that
there is a surplus of other elements (oxygen, hydrogen, trace elements, etc.),
energy, and the other factors that play some part in production, the limiting