Chlorophyll a

Chlorophyll a is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light.[3] It also reflects green-yellow light, and as such contributes to the observed green color of most plants. This photosynthetic pigment is essential for photosynthesis in eukaryotes, cyanobacteria and prochlorophytes because of its role as primary electron donor in the electron transport chain.[4] Chlorophyll a also transfers resonance energy in the antenna complex, ending in the reaction center where specific chlorophylls P680 and P700 are located.[5]

Chlorophyll a
Structure of chlorophyll a
IUPAC name
Chlorophyll a
Systematic IUPAC name
Magnesium [methyl (3S,4S,21R)-14-ethyl-4,8,13,18-tetramethyl-20-oxo-3-(3-oxo-3-{[(2E,7R,11R)-3,7,11,15-tetramethyl-2-hexadecen-1-yl]oxy}propyl)-9-vinyl-21-phorbinecarboxylatato(2−)-κ2N,N′]
Other names
3D model (JSmol)
ECHA InfoCard 100.006.852
EC Number
  • 207-536-6
E number E140 (colours)
RTECS number
  • FW6420000
Molar mass 893.509 g·mol−1
Appearance Green
Odor Odorless
Density 1.079 g/cm3[1]
Melting point ~ 152.3 °C (306.1 °F; 425.4 K)[2]
Solubility Very soluble in ethanol, ether
Soluble in ligroin,[2] acetone, benzene, chloroform[1]
Absorbance See text
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Distribution of chlorophyll a

Chlorophyll a is essential for most photosynthetic organisms to release chemical energy but is not the only pigment that can be used for photosynthesis. All oxygenic photosynthetic organisms use chlorophyll a, but differ in accessory pigments like chlorophyll b.[4] Chlorophyll z can also be found in very small quantities in the green sulfur bacteria, an anaerobic photoautotroph.[6] These organisms use bacteriochlorophyll and some chlorophyll a but do not produce oxygen.[6] Anoxygenic photosynthesis is the term applied to this process, unlike oxygenic photosynthesis where oxygen is produced during the light reactions of photosynthesis.

Molecular structure

The molecular structure of chlorophyll a consists of a chlorin ring, whose four nitrogen atoms surround a central magnesium atom, and has several other attached side chains and a hydrocarbon tail.

Structure of chlorophyll a molecule showing the long hydrocarbon tail

Chlorin ring

Chlorin, the central ring structure of the chlorophyll a

Chlorophyll a contains a magnesium ion encased in a large ring structure known as a chlorin. The chlorin ring is a heterocyclic compound derived from pyrrole. Four nitrogen atoms from the chlorin surround and bind the magnesium atom. The magnesium center uniquely defines the structure as a chlorophyll molecule.[7] The porphyrin ring of bacteriochlorophyll is saturated, and lacking alternation of double and single bonds causing variation in absorption of light.[8]

Side chains

C-3 position Chlorophyll a
The green boxed CH3 is the methyl group at the C-7 position chlorophyll a

Side chains are attached to the chlorin ring of the various chlorophyll molecules. Different side chains characterize each type of chlorophyll molecule, and alters the absorption spectrum of light.[9] [10] For instance, the only difference between chlorophyll a and chlorophyll b is that chlorophyll b has an aldehyde instead of a methyl group at the C-7 position.[10]

Hydrocarbon tail

Chlorophyll a has a long hydrophobic tail, which anchors the molecule to other hydrophobic proteins in the thylakoid membrane of the chloroplast.[4] Once detached from the porphyrin ring, this long hydrocarbon tail becomes the precursor of two biomarkers, pristane and phytane, which are important in the study of geochemistry and the determination of petroleum sources.


Chlorophyll a biosynthetic pathway utilizes a variety of enzymes.[11] Genes code for the enzymes on the Mg-tetrapyrroles of both bacteriochlorophyll a and chlorophyll a.[11] It begins with glutamic acid, which is transformed into a 5-aminolevulinic acid (ALA). Two molecules of ALA are then reduced to porphobilinogen (PBG), and four molecules of PBG are then coupled, forming protoporphyrin IX.[7] When forming protoporphyrin, Mg-chelatase acts as a catalyst for the insertion of Mg into the chlorophyll a structure.[11] The pathway then uses either a light-dependent process, driven by the enzyme protochlorophyllide oxidoreductase. Protochlorophyllide is a precursor to the production of a chlorophyll a molecule, or a light-independent process driven by other enzymes, to form a cyclic ring, and the reduction of another ring in the structure.[7] Attachment of the phytol tail completes the process of chlorophyll biosynthesis.[12]

Reactions of photosynthesis

Absorbance of light

Light spectrum

Chlorophyll ab spectra-en
Absorption spectrum of chlorophyll a and chlorophyll b. The use of both together enhances the size of the absorption of light for producing energy.

Chlorophyll a absorbs light within the violet, blue and red wavelengths while mainly reflecting green. This reflectance gives chlorophyll its green appearance. Accessory photosynthetic pigments broaden the spectrum of light absorbed, increasing the range of wavelengths that can be used in photosynthesis.[4] The addition of chlorophyll b next to chlorophyll a extends the absorption spectrum. In low light conditions, plants produce a greater ratio of chlorophyll b to chlorophyll a molecules, increasing photosynthetic yield.[9]

Light gathering

Chlorophyll a antenna complex
The antenna complex with energy transfer within the thylakoid membrane of a chloroplast. Chlorophyll a in the reaction center is the only pigment to pass boosted electrons to an acceptor (modified from 2).

Absorption of light by photosynthetic pigments converts photons into chemical energy. Light energy radiating onto the chloroplast strikes the pigments in the thylakoid membrane and excites their electrons. Since the chlorophyll a molecules only capture certain wavelengths, organisms may use accessory pigments to capture a wider range of light energy shown as the yellow circles.[5] It then transfers captured light from one pigment to the next as resonance energy, passing energy one pigment to the other until reaching the special chlorophyll a molecules in the reaction center.[9] These special chlorophyll a molecules are located in both photosystem II and photosystem I. They are known as P680 for Photosystem II and P700 for Photosystem I.[13] P680 and P700 are the primary electron donors to the electron transport chain. These two systems are different in their redox potentials for one-electron oxidation. The Em for P700 is approximately 500mV, while the Em for P680 is approximately 1,100-1,200 mV.[13]

Primary electron donation

Chlorophyll a is very important in the energy phase of photosynthesis. Two electrons need to be passed to an electron acceptor for the process of photosynthesis to proceed.[4] Within the reaction centers of both photosystems there are a pair of chlorophyll a molecules that pass electrons on to the transport chain through redox reactions.[13]

See also


  1. ^ a b c Anatolievich KR. "Chlorophyll a". Archived from the original on 2014-11-29. Retrieved 2014-08-23.
  2. ^ a b Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0.
  3. ^ "Photosynthesis". Archived from the original on 2009-11-28.
  4. ^ a b c d e Raven PH, Evert RF, Eichhorn SE (2005). "Photosynthesis, Light, and Life". Biology of Plants (7th ed.). W. H. Freeman. pp. 119–127. ISBN 0-7167-9811-5.
  5. ^ a b Papageorgiou G, Govindjee (2004). "Chlorophyll a Fluorescence, A Signature of Photosynthesis". 19. Springer: 14, 48, 86. Cite journal requires |journal= (help)
  6. ^ a b Eisen JA, Nelson KE, Paulsen IT, Heidelberg JF, Wu M, Dodson RJ, et al. (July 2002). "The complete genome sequence of Chlorobium tepidum TLS, a photosynthetic, anaerobic, green-sulfur bacterium". Proceedings of the National Academy of Sciences of the United States of America. 99 (14): 9509–14. Bibcode:2002PNAS...99.9509E. doi:10.1073/pnas.132181499. PMC 123171. PMID 12093901.
  7. ^ a b c Zeiger E, Taiz L (2006). "Ch. 7: Topic 7.11: Chlorophyll Biosynthesis". Plant physiology (4th ed.). Sunderland, MA: Sinauer Associates. ISBN 0-87893-856-7.
  8. ^ Campbell MK, Farrell SO (20 November 2007). Biochemistry (6th ed.). Cengage Learning. p. 647. ISBN 978-0-495-39041-1.
  9. ^ a b c Lange L, Nobel P, Osmond C, Ziegler H (1981). Physiological Plant Ecology I – Responses to the Physical Environment. 12A. Springer-Verlag. pp. 67, 259.
  10. ^ a b Niedzwiedzki DM, Blankenship RE (December 2010). "Singlet and triplet excited state properties of natural chlorophylls and bacteriochlorophylls". Photosynthesis Research. 106 (3): 227–38. doi:10.1007/s11120-010-9598-9. PMID 21086044.
  11. ^ a b c Suzuki JY, Bollivar DW, Bauer CE (1997). "Genetic analysis of chlorophyll biosynthesis". Annual Review of Genetics. 31 (1): 61–89. doi:10.1146/annurev.genet.31.1.61. PMID 9442890.
  12. ^ Zeiger & Taiz 2006, Figure 7.11.A: The biosynthetic pathway of chlorophyll
  13. ^ a b c Ishikita H, Saenger W, Biesiadka J, Loll B, Knapp EW (June 2006). "How photosynthetic reaction centers control oxidation power in chlorophyll pairs P680, P700, and P870". Proceedings of the National Academy of Sciences of the United States of America. 103 (26): 9855–60. Bibcode:2006PNAS..103.9855I. doi:10.1073/pnas.0601446103. PMC 1502543. PMID 16788069.

External links

7-Hydroxymethyl chlorophyll a reductase

7-Hydroxymethyl chlorophyll a reductase (EC, HCAR) is an enzyme with systematic name 71-hydroxychlorophyll a:ferredoxin oxidoreductase. This enzyme catalyses the following chemical reaction

71-hydroxychlorophyll a + 2 reduced ferredoxin + 2 H+ chlorophyll a + 2 oxidized ferredoxin + H2O

7-Hydroxymethyl chlorophyll is a reductase that contains FAD and an iron-sulfur center.

Accessory pigment

Accessory pigments are light-absorbing compounds, found in photosynthetic organisms, that work in conjunction with chlorophyll a. They include other forms of this pigment, such as chlorophyll b in green algal and higher plant antennae, while other algae may contain chlorophyll c or d. In addition, there are many non-chlorophyll accessory pigments, such as carotenoids or phycobiliproteins, which also absorb light and transfer that light energy to photosystem chlorophyll. Some of these accessory pigments, in particular the carotenoids, also serve to absorb and dissipate excess light energy, or work as antioxidants. The large, physically associated group of chlorophylls and other accessory pigments is sometimes referred to as a pigment bed.The different chlorophyll and non-chlorophyll pigments associated with the photosystems all have different absorption spectra, either because the spectra of the different chlorophyll pigments are modified by their local protein environment or because the accessory pigments have intrinsic structural differences. The result is that, in vivo, a composite absorption spectrum of all these pigments is broadened and flattened such that a wider range of visible and infrared radiation is absorbed by plants and algae. Most photosynthetic organisms do not absorb green light well, thus most remaining light under leaf canopies in forests or under water with abundant plankton is green, a spectral effect called the "green window". Organisms such as some cyanobacteria and red algae contain accessory phycobiliproteins that absorb green light reaching these habitats.In aquatic ecosystems, it is likely that the absorption spectrum of water, along with gilvin and tripton (dissolved and particulate organic matter, respectively), determines phototrophic niche differentiation. The six shoulders in the light absorption of water between wavelengths 400 and 1100 nm correspond to troughs in the collective absorption of at least twenty diverse species of phototrophic bacteria. Another effect is due to the overall trend for water to absorb low frequencies, while gilvin and tripton absorb higher ones. This is why open ocean appears blue and supports yellow species such as Prochlorococcus, which contains divinyl-chlorophyll a and b. Synechococcus, colored red with phycoerythrin, is adapted to coastal bodies, while phycocyanin allows Cyanobacteria to thrive in darker inland waters.


The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. For example, the chlorophycean CW clade, and chlorophycean DO clade, are defined by the arrangement of their flagella. Members of the CW clade have flagella that are displaced in a "clockwise" (CW, 1–7 o'clock) direction e.g. Chlamydomonadales. Members of the DO clade have flagella that are "directly opposed" (DO, 12–6 o'clock) e.g. Sphaeropleales. They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some algae may store food in the form of oil droplets. Green algae usually have a rigid cell wall made up of an inner layer of cellulose and outer layer of pectose.


Chlorophyll (also chlorophyl) is any of several related green pigments found in the mesosomes of cyanobacteria, as well as in the chloroplasts of algae and plants. Its name is derived from the Greek words χλωρός, khloros ("pale green") and φύλλον, phyllon ("leaf"). Chlorophyll is essential in photosynthesis, allowing plants to absorb energy from light.

Chlorophylls absorb light most strongly in the blue portion of the electromagnetic spectrum as well as the red portion. Conversely, it is a poor absorber of green and near-green portions of the spectrum, which it reflects, producing the green color of chlorophyll-containing tissues. Two types of chlorophyll exist in the photosystems of green plants: chlorophyll a and b.

Chlorophyll b

Chlorophyll b is a form of chlorophyll. Chlorophyll b helps in photosynthesis by absorbing light energy. It is more soluble than chlorophyll a in polar solvents because of its carbonyl group. Its color is green, and it primarily absorbs blue light.In land plants, the light-harvesting antennae around photosystem II contain the majority of chlorophyll b. Hence, in shade-adapted chloroplasts, which have an increased ratio of photosystem II to photosystem I, there is a higher ratio of chlorophyll b to chlorophyll a. This is adaptive, as increasing chlorophyll b increases the range of wavelengths absorbed by the shade chloroplasts.


Chlorophyta or Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it refers to a highly paraphyletic group of all the green algae within the green plants (Viridiplantae) and thus includes about 7,000 species of mostly aquatic photosynthetic eukaryotic organisms. In newer classifications, it refers to the sister of the streptophytes/charophytes. The clade Streptophyta consists of the Charophyta in which the Embryophyta emerged. In this sense the Chlorophyta includes only about 4,300 species. About 90% of all known species live in freshwater.

Like the land plants (bryophytes and tracheophytes), green algae contain chlorophyll a and chlorophyll b and store food as starch in their plastids.

With the exception of Palmophyllophyceae, Trebouxiophyceae, Ulvophyceae and Chlorophyceae, which show various degrees of multicellularity, all the Chlorophyta lineages are unicellular. Some members of the group form symbiotic relationships with protozoa, sponges, and cnidarians. Others form symbiotic relationships with fungi to form lichens, but the majority of species are free-living. Some conduct sexual reproduction, which is oogamous or isogamous. All members of the clade have motile flagellated swimming cells. While most species live in freshwater habitats and a large number in marine habitats, other species are adapted to a wide range of land environments. For example, Chlamydomonas nivalis, which causes Watermelon snow, lives on summer alpine snowfields. Others, such as Trentepohlia species, live attached to rocks or woody parts of trees. Monostroma kuroshiense, an edible green alga cultivated worldwide and most expensive among green algae, belongs to this group.


Chromerida is a phylum of unicellular alveolates, which includes photosynthetic species Chromera velia and Vitrella brassicaformis. General features of the phylum include spherical cells each with a thick cell wall, chloroplast present with chlorophyll a only (no chlorophyll b or c), and an internal developing flagellum at some lifestages.

They often live in close association with corals, and studies suggest their closest relatives is the parastic group Apicomplexa, which evolved from photosynthetic ancestors, making Chromerida the last remaining photosynthetic members of an otherwise parasitic branch within Alveolata.Carter Lab at University of Sydney has undertaken new experiments to isolate novel Chromerids, using the same methods that were used to isolate Chromera velia and Vitrella brassicaformis. These methods were agreed at the First Chromera Conference and Workshop held at the Heron Island Research Station, Queensland, Australia from November 21–25, 2011.


Eustigmatophytes are a small group (12 genera; ~41 species) of eukaryotic algae that includes marine, freshwater and soil-living species.All eustigmatophytes are unicellular, with coccoid cells and polysaccharide cell walls. Eustigmatophytes contain one or more yellow-green chloroplasts, which contain chlorophyll a and the accessory pigments violaxanthin and β-carotene. Eustigmatophyte zoids (gametes) possess a single or pair of flagella, originating from the apex of the cell. Unlike other heterokontophytes, eustigmatophyte zoids do not have typical photoreceptive organelles (or eyespots); instead an orange-red eyespot outside a chloroplast is located at the anterior end of the zoid.

Ecologically, eustigmatophytes occur as photosynthetic autotrophs across a range of systems. Most eustigmatophyte genera live in freshwater or in soil, although Nannochloropsis contains marine species of picophytoplankton (2–4 μm).

The class was erected to include some algae previously classified in the Xanthophyceae.

Humboldt Current

The Humboldt Current, also called the Peru Current, is a cold, low-salinity ocean current that flows north along the western coast of South America. It is an eastern boundary current flowing in the direction of the equator, and extends 500–1,000 km (310–620 mi) offshore. The Humboldt Current is named after the Prussian naturalist Alexander von Humboldt. In 1846, von Humboldt reported measurements of the cold-water current in his book Cosmos.The current extends from southern Chile (~45th parallel south) to northern Peru (~4th parallel south) where cold, upwelled, waters intersect warm tropical waters to form the Equatorial Front. Sea surface temperatures off the coast of Peru, around 5th parallel south, reach temperatures as low as 16 °C (61 °F). This is highly uncharacteristic of tropical waters, as most other regions have temperatures measuring above 25 °C (77 °F). Upwelling brings nutrients to the surface, which support phytoplankton and ultimately increase biological productivity.The Humboldt Current is a highly productive ecosystem. It is the most productive eastern boundary current system. It accounts for roughly 18-20% of the total worldwide marine fish catch. The species are mostly pelagic: sardines, anchovies and jack mackerel. The system's high productivity supports other important fishery resources as well as marine mammals (eared seals and cetaceans) and seabirds. Periodically, the upwelling that drives the system's productivity is disrupted by the El Niño-Southern Oscillation (ENSO) event, often with large social and economical impacts.

The Humboldt has a considerable cooling influence on the climate of Chile, Peru and Ecuador. It is also largely responsible for the aridity of Atacama Desert in northern Chile and coastal areas of Peru and also of the aridity of southern Ecuador. Marine air is cooled by the current and thus is not conducive to generating precipitation (although clouds and fog are produced).

Light-harvesting complexes of green plants

The light-harvesting complex (or antenna complex) is an array of protein and chlorophyll molecules embedded in the thylakoid membrane of plants and cyanobacteria, which transfer light energy to one chlorophyll a molecule at the reaction center of a photosystem.

The antenna pigments are predominantly chlorophyll b, xanthophylls, and carotenes. Chlorophyll a is known as the core pigment. Their absorption spectra are non-overlapping and broaden the range of light that can be absorbed in photosynthesis. The carotenoids have another role as an antioxidant to prevent photo-oxidative damage of chlorophyll molecules. Each antenna complex has between 250 and 400 pigment molecules and the energy they absorb is shuttled by resonance energy transfer to a specialized chlorophyll-protein complex known as the reaction center of each photosystem. The reaction center initiates a complex series of chemical reactions that capture energy in the form of chemical bonds.

For photosystem II, when either of the two chlorophyll a molecules at the reaction center absorb energy, an electron is excited and transferred to an electron acceptor molecule, pheophytin, leaving the chlorophyll a in an oxidized state. The oxidised chlorophyll a replaces the electrons by photolysis that involves the oxidation of water molecules to oxygen, protons and electrons.

Under changing light conditions, the reversible phosphorylation of light harvesting chlorophyll a/b binding proteins (LHCII) represents a system for balancing the excitation energy between the two photosystems.The N-terminus of the chlorophyll a-b binding protein extends into the stroma where it is involved with adhesion of granal membranes and photo-regulated by reversible phosphorylation of its threonine residues. Both these processes are believed to mediate the distribution of excitation energy between photosystems I and II.

This family also includes the photosystem II protein PsbS, which plays a role in energy-dependent quenching that increases thermal dissipation of excess absorbed light energy in the photosystem.


Microalgae or microphytes are microscopic algae, typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist individually, or in chains or groups. Depending on the species, their sizes can range from a few micrometers (μm) to a few hundred micrometers. Unlike higher plants, microalgae do not have roots, stems, or leaves. They are specially adapted to an environment dominated by viscous forces. Microalgae, capable of performing photosynthesis, are important for life on earth; they produce approximately half of the atmospheric oxygen and use simultaneously the greenhouse gas carbon dioxide to grow photoautotrophically. Microalgae, together with bacteria, form the base of the food web and provide energy for all the trophic levels above them. Microalgae biomass is often measured with chlorophyll a concentrations and can provide a useful index of potential production. The standing stock of microphytes is closely related to that of its predators. Without grazing pressures the standing stock of microphytes dramatically decreases.The biodiversity of microalgae is enormous and they represent an almost untapped resource. It has been estimated that about 200,000-800,000 species in many different genera exist of which about 50,000 species are described. Over 15,000 novel compounds originating from algal biomass have been chemically determined. Most of these microalgae species produce unique products like carotenoids, antioxidants, fatty acids, enzymes, polymers, peptides, toxins and sterols.

Oreti River

The Oreti River is one of the main rivers of Southland, New Zealand, and is 170 kilometres (110 mi) long. The river has been identified as an Important Bird Area by BirdLife International because, for much of its length, it supports breeding colonies of black-billed gulls.The New Zealand Ministry for Culture and Heritage gives a translation of "place of the snare" for Ōreti.The Oreti has its headwaters close to the Mavora Lakes between Lake Te Anau and Lake Wakatipu, and flows south across the Southland Plains to its outflow into Foveaux Strait at the southeastern end of Oreti Beach. En route, it runs through the towns of Lumsden and Winton, before passing through the city of Invercargill, close to the river's estuary.

For the final part of the river's length, around the city of Invercargill and the river's estuary just south of the city, it is known as the New River, a name occasionally encountered to refer to the whole river. It shares this estuary with several smaller rivers, most notably the Waihopai River.

The New River Estuary, which meets the end of the Oreti River before it reaches the sea, is in decline. Recent science reports show that regions of the upper estuary are under stress and showing eutrophication. There is excessive macroalgal growth including sediment quality decline and high concentrations of chlorophyll-a in the water column. Chlorophyll-a was used as an indicator of eutrophic conditions in the water column, and is a colour pigment present in many types of algae that can give an indication of how much algae is present in the water column.The Invercargill Rowing Club relocated to the river in 1958.

Peridinin-chlorophyll-protein complex

The peridinin-chlorophyll-protein complex (PCP or PerCP) is a soluble molecular complex consisting of the peridinin-chlorophyll a-protein bound to peridinin, chlorophyll, and lipids. The peridinin molecules absorb light in the blue-green wavelengths (470 to 550 nm) and transfer energy to the chlorophyll molecules with extremely high efficiency. PCP complexes are found in many photosynthetic dinoflagellates, in which they may be the primary light-harvesting complexes.

Photosynthetic pigment

A photosynthetic pigment (accessory pigment; chloroplast pigment; antenna pigment) is a pigment that is present in chloroplasts or photosynthetic bacteria and captures the light energy necessary for photosynthesis.

Plants pigments (in order of increasing polarity):

Carotene: an orange pigment

Xanthophyll: a yellow pigment

Phaeophytin a: a gray-brown pigment

Phaeophytin b: a yellow-brown pigment

Chlorophyll a: a blue-green pigment

Chlorophyll b: a yellow-green pigmentChlorophyll a is the most common of the six, present in every plant that performs photosynthesis. The reason that there are so many pigments is that each absorbs light more efficiently in a different part of the electromagnetic spectrum. Chlorophyll a absorbs well at a wavelength of about 400–450 nm and at 650–700 nm; chlorophyll b at 450–500 nm and at 600–650 nm. Xanthophyll absorbs well at 400–530 nm. However, none of the pigments absorbs well in the green-yellow region, which is responsible for the abundant green we see in nature.


Phycobilins (from Greek: φύκος (phykos) meaning "alga", and from Latin: bilis meaning "bile") are light-capturing bilins found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads (though not in green algae and plants). Most of their molecules consist of a chromophore which makes them coloured. They are unique among the photosynthetic pigments in that they are bonded to certain water-soluble proteins, known as phycobiliproteins. Phycobiliproteins then pass the light energy to chlorophylls for photosynthesis.

The phycobilins are especially efficient at absorbing red, orange, yellow, and green light, wavelengths that are not well absorbed by chlorophyll a. Organisms growing in shallow waters tend to contain phycobilins that can capture yellow/red light, while those at greater depth often contain more of the phycobilins that can capture green light, which is relatively more abundant there.

The phycobilins fluoresce at a particular wavelength, and are, therefore, often used in research as chemical tags, e.g., by binding phycobiliproteins to antibodies in a technique known as immunofluorescence.


SeaWIFS (Sea-Viewing Wide Field-of-View Sensor) was a satellite-borne sensor designed to collect global ocean biological data. Active from September 1997 to December 2010, its primary mission was to quantify chlorophyll produced by marine phytoplankton (microscopic plants).

Vitrella brassicaformis

Vitrella brassicaformis, also known as a 'chromerid', is a species of alveolates isolated from the Great Barrier Reef. Its closest known relative is Chromera velia. Vitrella differs from Chromera in having a more complex lifecycle, for instance involving a range of sizes and morphologies. Also, while Vitrella is greenish coloured, Chromera is brown coloured. The differences are in the types of secondary pigments that characterize each genus. Both genera lack chlorophyll b or c; these absences link the two taxonomically, as algae bearing only chlorophyll a are quite few amid the biodiversity of life. Phylogenetically, both Vitrella and Chromera are relatives of the obligately parasitic phylum Apicomplexa, which includes Plasmodium, the agent of malaria. Both Vitrella brassicaformis and Chromera velia are photosynthetic.

Yellow-green algae

Yellow-green algae or the Xanthophyceae (xanthophytes) are an important group of heterokont algae. Most live in fresh water, but some are found in marine and soil habitats. They vary from single-celled flagellates to simple colonial and filamentous forms. Xanthophyte chloroplasts contain the photosynthetic pigments chlorophyll a, chlorophyll c, β-carotene, and the carotenoid diadinoxanthin. Unlike other heterokonts, their chloroplasts do not contain fucoxanthin, which accounts for their lighter colour. Their storage polysaccharide is chrysolaminarin. Xanthophyte cell walls are produced of cellulose and hemicellulose. They appear to be the closest relatives of the brown algae.


Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus Symbiodinium, but some are known from the genus Amphidinium, and other taxa, as yet unidentified, may have similar endosymbiont affinities. The true Zooxanthella K.brandt is a mutualist of the radiolarian Collozoum inerme (Joh.Müll., 1856) and systematically placed in Peridiniales. Another group of unicellular eukaryotes that partake in similar endosymbiotic relationships in both marine and freshwater habitats are green algae zoochlorellae.

Zooxanthellae are photosynthetic organisms, which contain chlorophyll a and chlorophyll c, as well as the dinoflagellate pigments peridinin and diadinoxanthin. These provide the yellowish and brownish colours typical of many of the host species. During the day, they provide their host with the organic carbon products of photosynthesis, sometimes providing up to 90% of their host's energy needs for metabolism, growth and reproduction. In return, they receive nutrients, carbon dioxide, and an elevated position with access to sunshine.

Types of tetrapyrroles


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