Algal Photosynthesis


Algae are a very diverse group of predominantly aquatic photosynthetic organisms that account for almost 50% of the photosynthesis that takes place on Earth. Algae have a wide range of antenna pigments to harvest light energy for photosynthesis giving different types of algae their characteristic colour. Early work done with algae contributed much to what is presently known about the carbon dioxide fixation pathway and the light harvesting reactions. The processes of photosynthesis in algae and higher plants are very similar. From among the three types of carbon dioxide‐concentrating mechanisms known in photosynthetic organisms, two types are found in different types of algae. Algae are proposed to play a role in the global carbon cycle by helping remove excess carbon dioxide from the environment. Recently, algae are recognized as a promising biodiesel source due to its efficient absorption and conversion of solar energy into chemical energy.

Key Concepts:

  • Algal photosynthesis account for almost half of the photosynthetic carbon fixed every year.

  • Scientists have utilized different algal species including algal mutants to study different aspects of photosynthesis.

  • Algae's efficiency at pulling inorganic carbon out of the environment is dependent on growth condition which implies the presence of an inducible carbon dioxide‐concentrating mechanism in algal cells.

  • The proposed mechanism for carbon dioxide acquisition in algae includes active HCO3 accumulation, Rubisco packaging in specialized structures and the presence of a carbonic anhydrase near the location of Rubisco.

  • Carbonic anhydrase is an enzyme that interconverts carbon dioxide and hydrogencarbonate which supply Rubisco with carbon dioxide from the pool of HCO3.

  • The major antenna pigments in algae include chlorophylls, phycobiliproteins and carotenoids and the variation in the composition and relative abundance of these pigments give algae their distinctive colour.

  • Antenna complexes are proteins with many bound antenna pigments which are important in absorbing light energy.

  • Algal photosynthesis is thought to increase with increase in nutrient, that is, N, P and Fe availability.

  • If the algal photosynthesis would increase more carbon dioxide would be removed from the environment.

  • Algae grow faster and are very efficient in absorbing and converting solar energy into chemical energy which is mainly in the form of triacylglycerols.

Keywords: algae; photosynthesis; Calvin cycle; phytoplankton

Figure 1.

General scheme of algal photosynthesis showing the separation of the electron transport chain and the Calvin Cycle.

Figure 2.

General arrangement of antenna complexes in algae. In green algae as well as in higher plants (a) the antenna complex is in the membrane and associates with the photosystem in the membrane. In red algae and cyanobacteria (b) the antenna complex is a phycobilisome and is a soluble protein. The phycobilisome attaches to the photosystem where the photosystem extends from the membrane.

Figure 3.

SeaWiFS satellite image showing chlorophyll content in the ocean. This image was an average of images taken in June 1998. The bright green and yellow colours indicate high levels of chlorophyll. From Feldman . Image provided by the SeaWiFS Project, NASA, Goddard Space Flight Center and ORBIMAGE.



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Further Reading

Aizawa K and Miyachi S (1986) Carbonic anhydrase and CO2 concentrating mechanisms in microalgae and cyanobacteria. FEMS Microbiology Reviews 39: 215–233.

Falkowski PG and Raven JA (1997) Aquatic Photosynthesis. Oxford: Blackwell Scientific Press.

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Gantt E (1981) Phycobilisomes. Annual Review of Plant Physiology 32: 327–347.

Gest H (1988) Sun‐beams, cucumbers, and purple bacteria. Photosynthesis Research 19: 287–308.

Harwood JL and Guschina IA (2009) The versatility of algae and their lipid metabolism. Biochimie 91: 679–684.

van den Hoek C, Mann DG and Jahns HM (1995) Algae – An Introduction to Phycology. Cambridge: Cambridge University Press.

Moroney JV and Somanchi A (1999) How do algae concentrate CO2 to increase the efficiency of photosynthetic carbon fixation? Plant Physiology 119: 9–16.

Moroney JV and Ynalvez RA (2007) The proposed CO2 concentration in Chlamydomonas reinhardtii. Eukaryotic Cell 6: 1251–1259.

Raven J (1997) Inorganic carbon acquisition in marine autotrophs. Advances in Botanical Research 27: 85–209.

Salisbury FB and Ross CW (1992) Plant Physiology, 4th edn. Belmont, CA: Wadsworth Publishing.

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Moroney, James V, and Ynalvez, Ruby A(Sep 2009) Algal Photosynthesis. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000322.pub2]