369
Primary Production in the Oceans
The rest of the energy of the excited electrons is used in a series of enzymatic
reactions of riboflavin phosphate and nicotinamide adenine dinucleotide phosphate (NADP).
4NADP + 2H 2 O + 2ADP + 2P → 4NADPH + O 2 + 2ATP
(9.3)
The protons are from water, and the excited electrons are from the reduced form
of NADP. The hydroxide from the water yields molecular oxygen and donates
electrons to chlorophyll via the cytochrome I chain.
3. The CO 2 is assimilated in a cyclic series of reactions utilizing the reducing action
of NADPH (protonated form of NADP) and the phosphorylating power of ATP.
These reactions, which can take place in the dark, lead to the production of carbohydrates (CH 2 O).
CO 2 + 4NADPH + ATP → CH 2 O + H 2 O + 4NADP + ADP + P
(9.4)
Combining Equation 9.1 to Equation 9.3 gives
CO 2 + H 2 O → CH 2 O + O 2
(9.5)
Labeled 14 CO 2 finds its way very quickly into compounds other than carbohydrates.
Compounds such as fats and amino acids are synthesized from intermediates in the carbon cycle in addition to being produced from CH 2 O.
The photosynthetic quotient (PQ = molecules of O 2 liberated/ molecules of CO 2 assimilated)
differs from 1.0 because of the production of other classes of compounds. The PQ is 1.4 if only
lipids are formed; the PQ is 1.05 when amino acids are formed using NH 3 and 1.6 using NO 3
– .
Values of 1.20 to 1.39 are common for natural populations provided there are adequate nutrients. At low light intensities, heterotrophic utilization of compounds such as acetate may take
place. This may be advantageous because it requires less energy than to fix CO 2 .
The energy required for metabolic processes is obtained by the oxidation of the photosynthesized organic compounds. This process is known as respiration. The simple overall
reaction is
CH 2 O + O 2 → CO 2 + H 2 O
(9.6)
The respiration quotient (RQ; molecules of CO 2 liberated/ molecules of O 2 assimilated)
lies close to 1.0. Thus, fats and protein are not normally used. Respiration takes place in
the light and dark at approximately the same rate. The rate is about 5 to 10% of the maximum rate of photosynthesis of cells grown under optimal conditions. The respiration that
occurs in the light is assumed to be the same as in the dark.
9.1.1 Phytoplankton Production
Both the amount and the rate at which phytoplankton are produced are important to
consider with respect to the availability of organic carbon to the food chain. The standing crop is the amount of living phytoplankton at a given time in a given amount of seawater (mg C m –3 of seawater) or beneath a given surface of seawater (mg C m –2 ). The rate of
primary production (P) is defined as the weight of inorganic carbon fixed photosynthetically
Primary Production in the Oceans
The rest of the energy of the excited electrons is used in a series of enzymatic
reactions of riboflavin phosphate and nicotinamide adenine dinucleotide phosphate (NADP).
4NADP + 2H 2 O + 2ADP + 2P → 4NADPH + O 2 + 2ATP
(9.3)
The protons are from water, and the excited electrons are from the reduced form
of NADP. The hydroxide from the water yields molecular oxygen and donates
electrons to chlorophyll via the cytochrome I chain.
3. The CO 2 is assimilated in a cyclic series of reactions utilizing the reducing action
of NADPH (protonated form of NADP) and the phosphorylating power of ATP.
These reactions, which can take place in the dark, lead to the production of carbohydrates (CH 2 O).
CO 2 + 4NADPH + ATP → CH 2 O + H 2 O + 4NADP + ADP + P
(9.4)
Combining Equation 9.1 to Equation 9.3 gives
CO 2 + H 2 O → CH 2 O + O 2
(9.5)
Labeled 14 CO 2 finds its way very quickly into compounds other than carbohydrates.
Compounds such as fats and amino acids are synthesized from intermediates in the carbon cycle in addition to being produced from CH 2 O.
The photosynthetic quotient (PQ = molecules of O 2 liberated/ molecules of CO 2 assimilated)
differs from 1.0 because of the production of other classes of compounds. The PQ is 1.4 if only
lipids are formed; the PQ is 1.05 when amino acids are formed using NH 3 and 1.6 using NO 3
– .
Values of 1.20 to 1.39 are common for natural populations provided there are adequate nutrients. At low light intensities, heterotrophic utilization of compounds such as acetate may take
place. This may be advantageous because it requires less energy than to fix CO 2 .
The energy required for metabolic processes is obtained by the oxidation of the photosynthesized organic compounds. This process is known as respiration. The simple overall
reaction is
CH 2 O + O 2 → CO 2 + H 2 O
(9.6)
The respiration quotient (RQ; molecules of CO 2 liberated/ molecules of O 2 assimilated)
lies close to 1.0. Thus, fats and protein are not normally used. Respiration takes place in
the light and dark at approximately the same rate. The rate is about 5 to 10% of the maximum rate of photosynthesis of cells grown under optimal conditions. The respiration that
occurs in the light is assumed to be the same as in the dark.
9.1.1 Phytoplankton Production
Both the amount and the rate at which phytoplankton are produced are important to
consider with respect to the availability of organic carbon to the food chain. The standing crop is the amount of living phytoplankton at a given time in a given amount of seawater (mg C m –3 of seawater) or beneath a given surface of seawater (mg C m –2 ). The rate of
primary production (P) is defined as the weight of inorganic carbon fixed photosynthetically