OC211(OA211) Phytoplankton & Primary Production Dr Purdie SOC (566/18) LECTURE 3 Week 3 (i) Respiration& Chemosynthesis

RESPIRATION Dark Respiration is the opposite reaction to photosynthesis and occurs in all living aerobic organisms plants animals and bacteria. However: There is more than one type of respiration known: 1)Chlororespiration or Mehler reaction. 2)Photorespiration 3)Dark Respiration or Mitochondrial Respiration

CHLORORESPIRATION or MEHLER REACTION This is light dependant and not involving oxidation of carbon species. It is the reversal of the electron transport chain in chloroplasts.

RESPIRATION 1)Chlororespiration or Mehler reaction. 2)Photorespiration 3)Dark Respiration or Mitochondrial Respiration (1) (2) (3)

PHOTORESPIRATION This is light dependant production of CO 2 and consumption of oxygen resulting from biosynthesis and metabolism of glycolic acid. No ATP is produced unlike dark respiration. RuBisCO can bind CO 2 as well as O 2 i.e. carboxylase and oxygenase activity. As an oxygenase it catalyses the oxygenation of: RuBP (5C) to 2- phosphoglycollic acid (2C) and PGA (3C). The phosphoglycolic acid then hydrolysed to phosphate and glycollic acid

DARK OR MITOCHONDRIAL RESPIRATION Comprises the reactions of: Glycolysis Tricarboxylic acid (TCA) cycle Oxidative phosphorylation and Oxidative phosphate pentose pathway. Respiration is also a major source of carbon skeletons for biosynthesis. C 6 H 12 O 6 + 6O 2 + ADP +Pi  6CO 2 + 6H 2 O + ATP It is probable that “dark respiration” occurs in the light.

RESPIRATION Schematic representation of the processes contributing to net CO 2 assimilation and O 2 evolution in a microalgal cell Running counter to the photosynthestic reactions are the various processes of photorespiration, dark respiration and Mehler reaction.

PHOTORESPIRATION Both CO 2 and O 2 compete for RuBP at the same site on the enzyme so high conc. of CO 2 and low O 2 favour carboxylation and high conc. O 2 and low CO 2 favour oxygenation. Can be % of photosynthetic rate in higher plants is wasteful to plant. Not really known how important in marine algae. Difficult to measure. Fig 5.10 Falkowski & Raven;Aquatic Photosynthesis

CHEMOSYNTHESIS Some bacteria can satisfy their primary energy requiremenys by utilizing simple inorganic compounds or reduced elements that are high in energy. eg Ammonia - nitrifying bacteria- Nitrosomonus Nitrite - nitrifying bacteria - Nitrobacter Ferrous iron - iron bacteria Hydrogen gashydrogen bacteria Sulphursulphur bacteria These bacteria reduce or fix CO 2 and biosynthesise organic compounds using chemical energy from the oxidation reactions

CHEMOSYNTHESIS Dehydrogenase enzymes produce reducing compounds eg NADH (Nicatinamide Adenine Dinucleotide) egAH 2 + H 2 O  AO + 4[H + + e-] 4[H + + e-] + ADP + Pi + O2  2H 2 O + ATP 2[H + + e-] + NAD  NADH 2 ATP and NADH 2 then used for assimilation of CO 2 NADH 2 + 3ATP + CO2  (CH 2 O) + H 2 O + ADP + Pi + NAD

CHEMOSYNTHESIS The BlackSea Below m water contains sulphide and no oxygen. Photosynthesis limited to surface 50m Chemosynthesis maximum between 180 and 200m Bacteria obtain H 2 S diffusing from below and O 2 or nitrate diffusing from above Fig 50; Parsons, Takahashi and Hargrave; Biological Oceanographic Processes

CHEMOSYNTHESIS Hydrothermal Vents High Biomass is found associated with these systems in the deep sea but are along way from photoautotrophic production source. Vent fauna depend on H2S utilised by sulphur oxidising bacteria eg Thiomicrospira and Beggiatoa. Energy released by oxidation used to form organic matter. The reaction requires molecular oxygen provided by surrounding waters. CO 2 + H 2 S + O 2 + H 2 O  CH 2 O + H 2 SO 4 Mats of chemosynthetic bacteria are fed on by limpets, prawns etc and suspended bacteria by suspension feeders. Some vent fauna have chemosynthetic bacteria in their gills