Chlorophyll a and accessory pigment relationship

Wavelengths of light and photosynthetic pigments (article) | Khan Academy

chlorophyll a and accessory pigment relationship

chlorophyll a is the main pigment, chlorophyll b and carotenoids are accessory pigments. accessory pigments help broaden the absorbtion. Chlorophyll is the pigment that allows plants—including algae—to convert sunlight into organic compounds in the process of photosynthesis. Chlorophylls are greenish pigments which contain a porphyrin ring. One very visible accessory pigment is fucoxanthin the brown pigment which colors kelps.

You can see these different colors when white light passes through a prism: Red light has the longest wavelength and the least energy, while violet light has the shortest wavelength and the most energy. Although light and other forms of electromagnetic radiation act as waves under many conditions, they can behave as particles under others. Each particle of electromagnetic radiation, called a photon, has certain amount of energy. Types of radiation with short wavelengths have high-energy photons, whereas types of radiation with long wavelengths have low-energy photons.

However, the various wavelengths in sunlight are not all used equally in photosynthesis. Instead, photosynthetic organisms contain light-absorbing molecules called pigments that absorb only specific wavelengths of visible light, while reflecting others. The set of wavelengths absorbed by a pigment is its absorption spectrum.

In the diagram below, you can see the absorption spectra of three key pigments in photosynthesis: The set of wavelengths that a pigment doesn't absorb are reflected, and the reflected light is what we see as color. For instance, plants appear green to us because they contain many chlorophyll a and b molecules, which reflect green light. Each photosynthetic pigment has a set of wavelength that it absorbs, called an absorption spectrum. Absorption spectra can be depicted by wavelength nm on the x-axis and the degree of light absorption on the y-axis.

The absorption spectrum of chlorophylls includes wavelengths of blue and orange-red light, as is indicated by their peaks around nm and around nm. As a note, chlorophyll a absorbs slightly different wavelengths than chlorophyll b. Both chlorophylls also absorb in the orange-red end of the spectrum with longer wavelengths and lower energy. The origins of photosynthetic organisms in the sea may account for this. Shorter wavelengths with more energy do not penetrate much below 5 meters deep in sea water.

The ability to absorb some energy from the longer hence more penetrating wavelengths might have been an advantage to early photosynthetic algae that were not able to be in the upper photic zone of the sea all the time. The molecular structure of chlorophylls. The action spectrum of photosynthesis is the relative effectiveness of different wavelengths of light at generating electrons. If a pigment absorbs light energy, one of three things will occur.

chlorophyll a and accessory pigment relationship

Energy is dissipated as heat. The energy may be emitted immediately as a longer wavelength, a phenomenon known as fluorescence. Energy may trigger a chemical reaction, as in photosynthesis. Chlorophyll only triggers a chemical reaction when it is associated with proteins embedded in a membrane as in a chloroplast or the membrane infoldings found in photosynthetic prokaryotes such as cyanobacteria and prochlorobacteria. Absorption spectrum of several plant pigments left and action spectrum of elodea righta common aquarium plant used in lab experiments about photosynthesis.

Images from Purves et al. The structure of the chloroplast and photosynthetic membranes Back to Top The thylakoid is the structural unit of photosynthesis. Only eukaryotes have chloroplasts with a surrounding membrane. Thylakoids are stacked like pancakes in stacks known collectively as grana. The areas between grana are referred to as stroma. While the mitochondrion has two membrane systems, the chloroplast has three, forming three compartments. Structure of a chloroplast.

Stages of Photosynthesis Back to Top Photosynthesis is a two stage process.

chlorophyll a and accessory pigment relationship

The first process is the Light Dependent Process Light Reactionsrequires the direct energy of light to make energy carrier molecules that are used in the second process. The Dark Reactions can usually occur in the dark, if the energy carriers from the light process are present. Recent evidence suggests that a major enzyme of the Dark Reaction is indirectly stimulated by light, thus the term Dark Reaction is somewhat of a misnomer.

The Light Reactions occur in the grana and the Dark Reactions take place in the stroma of the chloroplasts. Overview of the two steps in the photosynthesis process. Water is split in the process, releasing oxygen as a by-product of the reaction.

The incorporation of carbon dioxide into organic compounds is known as carbon fixation. The energy for this comes from the first phase of the photosynthetic process. Living systems cannot directly utilize light energy, but can, through a complicated series of reactions, convert it into C-C bond energy that can be released by glycolysis and other metabolic processes.

Photosystems are arrangements of chlorophyll and other pigments packed into thylakoids. Many Prokaryotes have only one photosystem, Photosystem II so numbered because, while it was most likely the first to evolve, it was the second one discovered. Photosystem I uses chlorophyll a, in the form referred to as P Photosystem II uses a form of chlorophyll a known as P Both "active" forms of chlorophyll a function in photosynthesis due to their association with proteins in the thylakoid membrane.

Action of a photosystem. This image is from the University of Minnesota page at http: Photophosphorylation is the process of converting energy from a light-excited electron into the pyrophosphate bond of an ADP molecule. This occurs when the electrons from water are excited by the light in the presence of P The energy transfer is similar to the chemiosmotic electron transport occurring in the mitochondria.

Light energy causes the removal of an electron from a molecule of P that is part of Photosystem II. These O-2 ions combine to form the diatomic O2 that is released. The electron is "boosted" to a higher energy state and attached to a primary electron acceptor, which begins a series of redox reactions, passing the electron through a series of electron carriers, eventually attaching it to a molecule in Photosystem I. Light acts on a molecule of P in Photosystem I, causing an electron to be "boosted" to a still higher potential.

The electron is attached to a different primary electron acceptor that is a different molecule from the one associated with Photosystem II.

What is the relationship between chlorophyll a, accessory pigment?

The electron from Photosystem II replaces the excited electron in the P molecule. This energy is used in Carbon Fixation. Cyclic Electron Flow occurs in some eukaryotes and primitive photosynthetic bacteria. Noncyclic photophosphorylation top and cyclic photophosphorylation bottom. These processes are better known as the light reactions. The above diagrams present the "old" view of photophosphorylation. This is the fundamental process by which chlorophyll "captures" the energy of sunlight.

There are several kinds of chlorophyll, the most important being chlorophyll "a".

Algae, Phytoplankton and Chlorophyll

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".

chlorophyll a and accessory pigment relationship

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.

Carotenoids are usually red, orange, or yellow pigments, and include the familiar compound carotene, which gives carrots their color. These compounds are composed of two small six-carbon rings connected by a "chain" of carbon atoms.

Algae, Phytoplankton and Chlorophyll - Environmental Measurement Systems

As a result, they do not dissolve in water, and must be attached to membranes within the cell. Carotenoids cannot transfer sunlight energy directly to the photosynthetic pathway, but must pass their absorbed energy to chlorophyll.

For this reason, they are called accessory pigments.