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6.2: Photosynthetic Pigments - Biology

6.2: Photosynthetic Pigments - Biology



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Extract and Separate the Pigments

  1. Lay a strip of filter paper on the bench.
  2. About 2 cm from the bottom of the strip, place a fresh spinach leaf and rub a coin across the leaf to transfer pigment to the strip.
  3. The instructor will be provided with a spoonful of Spirulina powder that has been soaked in 10ml acetone overnight.
    • On a separate strip, the instructor will apply the Spirulina extract approximately 2cm from the bottom of the strip.
  4. Suspend the strips by a dowel or paper clip in a tube with about 3ml chromatography solution (2 isooctane: 1 acetone: 1 diethyl ether).
  5. Develop the strips until the solvent reaches about 2 cm from the top.

Chromatography Analysis

  1. How many different pigments separate from the spinach extract? From the spirulina?
  2. Are all pigments represented between the two extracts?
  3. The mobile phase is non-polar. What are the properties of each pigment?
  4. Measure the Rf of each pigment.


Photosynthetic Pigments

Pigments are chemical compounds which reflect only certain wavelengths of visible light. This makes them appear "colorful". Flowers, corals, and even animal skin contain pigments which give them their colors. More important than their reflection of light is the ability of pigments to absorb certain wavelengths.

Because they interact with light to absorb only certain wavelengths, pigments are useful to plants and other autotrophs --organisms which make their own food using photosynthesis. In plants, algae, and cyanobacteria, pigments are the means by which the energy of sunlight is captured for photosynthesis. However, since each pigment reacts with only a narrow range of the spectrum, there is usually a need to produce several kinds of pigments, each of a different color, to capture more of the sun's energy.

There are three basic classes of pigments.

There are several kinds of chlorophyll, the most important being chlorophyll "a". This is the molecule which makes photosynthesis possible, by passing its energized electrons on to molecules which will manufacture sugars. All plants, algae, and cyanobacteria which photosynthesize contain chlorophyll "a". A second kind of chlorophyll is chlorophyll "b", which occurs only in "green algae" and in the plants. A third form of chlorophyll which is common is (not surprisingly) called chlorophyll "c", and is found only in the photosynthetic members of the Chromista as well as the dinoflagellates. The differences between the chlorophylls of these major groups was one of the first clues that they were not as closely related as previously thought.

The picture at the right shows the two classes of phycobilins which may be extracted from these "algae". The vial on the left contains the bluish pigment phycocyanin, which gives the Cyanobacteria their name. The vial on the right contains the reddish pigment phycoerythrin, which gives the red algae their common name.

Phycobilins are not only useful to the organisms which use them for soaking up light energy they have also found use as research tools. Both pycocyanin and phycoerythrin fluoresce at a particular wavelength. That is, when they are exposed to strong light, they absorb the light energy, and release it by emitting light of a very narrow range of wavelengths. The light produced by this fluorescence is so distinctive and reliable, that phycobilins may be used as chemical "tags". The pigments are chemically bonded to antibodies, which are then put into a solution of cells. When the solution is sprayed as a stream of fine droplets past a laser and computer sensor, a machine can identify whether the cells in the droplets have been "tagged" by the antibodies. This has found extensive use in cancer research, for "tagging" tumor cells.


6.2: Photosynthetic Pigments - Biology

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Abstract

The present study was designed to validate the applicability of photosynthetic performance using a PAM fluorometer and photosynthetic pigments in Euglena gracilis as endpoint parameters in toxicity assessment of liquid detergents using a dish washing liquid detergent during short- (0–72 h) and long-term (7 days) exposure. In short-term experiments, the detergent affected the photosynthetic efficiency with EC50 values (calculated for Fv/Fm) of 22.07%, 7.27%, 1.4% and 2.34%, after 0, 1, 24 and 72 h, respectively. The relative electron transport rate (rETR) and quantum yield measured with increasing irradiances were also inhibited by the detergent. The most severe effect of the detergent on the light-harvesting pigments (μg mL −1 ) was observed after 72 h where chlorophyll a and total carotenoids were decreased at concentrations above 0.1% and chlorophyll b was decreased at concentrations above 0.5%. In long-term experiments, the detergent reduced the photosynthetic efficiency of cultures giving an EC50 value of 0.867% for Fv/Fm. rETR and quantum yield with increasing irradiance were shown to be adversely affected at concentrations of 0.1% or above. A decrease in chlorophyll a and total carotenoids (μg mL −1 ) was observed at concentrations of 0.05% detergent or above. Chlorophyll b was shown to be comparatively less affected by detergent stress, and a significant decrease was observed at concentrations of 0.5% or above. However, there was no prominent decrease in per cell (Euglena) concentration of any pigment. It can be concluded that photosynthesis and light-harvesting pigments in E. gracilis were sensitive to detergent stress and can be used as sensitive parameters in toxicity assessment of detergents in aquatic environments.


Photosynthetic Performance and Pigment Composition of Leaves from two Tropical Species is Determined by Light Quality

Instituto de Investigação Cientìfica Tropical Centro de Estudos de Produção e Tecnologia Agrìcolas Tapada da Ajuda, Ap. 3014 1301-901 Lisbon Portugal [email protected] Search for more papers by this author

Estação Agronómica Nacional, Dept. Fisiologia Vegetal, Av. República, 2784-505 Oeiras, Portugal

Estação Agronómica Nacional, Dept. Fisiologia Vegetal, Av. República, 2784-505 Oeiras, Portugal

Estação Agronómica Nacional, Dept. Fisiologia Vegetal, Av. República, 2784-505 Oeiras, Portugal

Universidade Agostinho Neto, Fac. Ciências Agrárias, P.O. Box 815, Luanda, Angola

Instituto Investigação Cientìfica Tropical, Centro de Estudos de Produção e Tecnologia Agrìcolas, Tapada Ajuda, Ap. 3014, 1301-901 Lisbon, Portugal

Instituto de Investigação Cientìfica Tropical Centro de Estudos de Produção e Tecnologia Agrìcolas Tapada da Ajuda, Ap. 3014 1301-901 Lisbon Portugal [email protected] Search for more papers by this author

Estação Agronómica Nacional, Dept. Fisiologia Vegetal, Av. República, 2784-505 Oeiras, Portugal

Estação Agronómica Nacional, Dept. Fisiologia Vegetal, Av. República, 2784-505 Oeiras, Portugal

Estação Agronómica Nacional, Dept. Fisiologia Vegetal, Av. República, 2784-505 Oeiras, Portugal


Pigments and the Absorption of Light

This shows that carbon dioxide and water are turned into glucose and oxygen in a plant, using light as energy.

The carbon dioxide enters the plant by stomata (in the leaves) or lenticels (in the stem). The water enters through the roots and moves up through the plant in xylem vessels. Light is required as an energy source for the reaction and chlorophyll is necessary to absorb the light.

The glucose made may be used to make other substances or it may be used in respiration. The oxygen may diffuse out through the stomata or it may be used in respiration.

Light energy is necessary but it must be harvested and trapped by the photosynthetic pigments to be of any use.

Chlorophyll absorbs light from the visible part of the electromagnetic part of the spectrum, but there are several types of chlorophyll.

  • chlorophyll a
  • chlorophyll b
  • chlorophyll c
  • bacteriochlorophyll (found in photosynthetic bacteria!)

There are also other families of pigments, such as the carotenoids.

Not all wavelengths of light are equally absorbed and different chlorophylls absorb more strongly in different parts of the visible spectrum.

Absorption and Action Spectrums

The action spectrum shows the rate of photosynthesis at different wavelengths.

The absorption spectrum shows how strongly the pigments absorb at different wavelengths.

The absorption spectrum and action spectrum show that the wavelengths that are most strongly absorbed (red and blue) are the ones that cause photosynthesis to proceed at the fastest rate. Green is not strongly absorbed rather it is reflected, causing leaves to look green.

The shorter the wavelength, the more energy it contains. During photosynthesis the light energy is converted into chemical energy. The absorbed light excites electrons in the pigment molecules and the energy can be passed on to be used by the plant.

Photosystems

The pigments are arranged in funnel shaped photosystems that sit on the thylakoid membranes in the chloroplasts.

In each photosystem, several hundred pigment molecules, called accessory pigments, are clustered around a particular pigment molecule, known as the primary pigment.

The various accessory pigments absorb light of different wavelengths and pass the energy down the photosystem. Eventually the energy reaches the primary pigment that acts as a reaction centre.


Composition of Photosynthetic Pigments in a Red Alga Kappaphycus Alvarezi Cultivated in Different Depths ☆

The red alga Kappaphycus alvarezii (Doty) Doty ex P.C. Silva has been introduced and mono cultivated in Indonesia as a seaweed commodity. This species is specifically grown in shallow and clear seawater, although there are several reports concerning the cultivation in deep seawater. It is interesting to know compositional changes of chlorophylls and carotenoids when K. alvarezii is grown at different depths. In this investigation, therefore K. alvarezii green and brown variants were cultivated at about 0.2 m (normal grown condition), 1 m, and 2 m depths and successfully obtained different ratios of chlorophyll and carotenoid composition at different depths. Quantitative analyses of chlorophylls to carotenoids ratio were carried out using data of chromatogram peak area. This investigation subsequently evaluated the photo and thermo-stability of the pigment extracts to examine the effects of pigment composition on the degradation rate of the pigments. This investigation was aimed to provide information regarding compositional change of the pigments by acclimation in terms of cultivation depths and pigment stability in vitro at condition of natural pigment composition in this alga.


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Biology4alevel600

Photosynthetic pigments are pigments presented in chloroplasts or photosynthetic bacteria. They capture light energy necessary for photosynthesis and convert it to chemical energy .
  • A pigment is any substance that absorbs light.
  • The color of the pigment comes from the wavelengths of light that are reflected (not absorbed).
  • If pigments absorb all wavelengths they will appear black.
  • If pigments reflect most of the wavelengths they will appear white.
  • The light absorption pattern of a pigment is called the absorption spectrum.
  • dissipated as heat
  • re-emitted as a longer wavelength of light - fluorescence
  • captured in a chemical bond (carbon gain!)

2. Carotenoids: orange pigments that protect chlorophyll from damage by the formation of single oxygen atoms (free radicals). They can also absorb wavelengths of light that chlorophyll cannot absorb, and pass on some of the energy from the light to chlorophyll. They absorb strongly in the blue-violet range. Carotenoids are usually masked by the green chlorophylls.

There are 2 types of carotenoid:

  • Chlorophyll a is the most abundant pigment in most plants. Its absorption peaks are 430nm (blue) and 662nm (red). It emits an electron when it absorbs light.
  • Chlorophyll b is similar to chlorophyll a, but its absorption peaks are 453nm and 642nm. It has a similar role to chlorophyll a, but is not as abundant.
  • Carotenoids : carotene and Xanthophylls.

An absorption spectrum is a graph showing the percentage of light absorbed by pigments, for each wavelength of light.


Chlorophyll is not just one substance. There are several different chlorophylls, e.g. chlorophyll a and chlorophyll b.

  • Each is a molecule which has a hydrophilic head and hydrophobic tail.
  • The head always contains a magnesium ion and plays a key part in the absorbing or harvesting of light.
  • The hydrophobic tail anchors to the thylakoid membrane.

As well as the chlorophylls there are other accessory pigments, e.g. carotenoids which also absorb light energy. There are a range of photosynthetic pigments found in different species.

The graphs below show the specific wavelengths of light which are absorbed by a range of pigments. The data for the absorption spectrum was collected by measuring the absorbance of a range of different wavelengths of light by a solution of each pigment, chlorophyll a, chlorophyll b, and carotenoids, separately. Following this, plants were illuminated at each wavelength of light, in turn, to investigate the amount of photosynthesis achieved at each wavelength.