The purpose of photosynthesis is to convert theenergy in photons (the infinitesimally smallpackets of energy that make up light) into thechemical bonds of sugar molecules.
Plants(and animals that eat plants) can then store theenergy and get it back out when they need it bybreaking those chemical bonds. The tricky part ofphotosynthesis is that it takes a very preciseamount of energy to form a particular chemicalbond. Furthermore, the photons from differentcolors of light contain different amounts ofenergy.
You probably know the colors ofthe spectrum (Red, Orange, Yellow, Green, Blue,Indigo, Violet); well, those colors are inascending order of energy -- a photon of bluelight has more energy than a photon of red light(this is true because of Planck's Law, which aphysicist could explain better than I).
Aparticular pigment molecule (like chlorophyll) isspecialized for absorbing a particular color oflight and converting the light energy into theappropriate amount of chemical energy for making achemical bond (actually there are many othermolecules that help the pigment perform thisenergy conversion, but only the pigment itself canabsorb the light). Chlorophyll just absorbs blueand red light; it hardly absorbs any green lightat all, so the green gets reflected back to oureyes, which is why leaves appear green. Otherpigments that plants have in their leaves absorblight of different colors, so they reflect red,orange, yellow, or blue light and appear to bethose colors to our eyes. Because the white lightcoming from the sun is actually made up of photonsof all the different colors, it is veryadvantageous to the plant to have many pigmentsthat can absorb such a wide range of the availablecolors of light.
Different photosynthetic organisms use differentcombinations of pigments, which have differentcolors because they absorb and reflect differentfrequencies of light.
Plants and greenalgae (plants are really advanced green algae)contain chlorophyll a (which is teal-green),chlorophyll b (which is yellow-green), andbeta-carotene (which is yellow), thus giving thema green color. Brown algae and their unicellularrelatives (e.g. diatoms) have chlorophylla,chlorophyll c, and lipid pigments calledfucoxanthins,which together give them agolden-brown color. Red algae possess chlorophylla and lipid-based pigments called phycobilins,which give them the brilliant red(or deep blue)color. These different combinations of pigmentsare more or less efficient at collecting light atcertain frequencies and at certain levels of lightintensity (too much will damage the pigment).Thus, they parcel out the Sun's energy to make themost use of it and to not compete with otherphotosynthetic organisms.
Why is chlorophyll needed for 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.
Why Are Pigments Such As Chlorophyll Needed For Photosynthesis
These pigments do not carry out photosynthesis directly, but pass their energy to chlorophyll-a. For this reason they are known as accessory (helper) pigments.
Why is chlorophyll needed for photosynthesis?
Pigments are chemicals that absorb some wavelengths of light and reflect others. This makes them coloured. The most important of the photosynthetic pigments is which gives plants their green colour.
Pigments Involved in Photosynthesis
The light-independant reactions of photosynthesis occur in the stroma of the chloroplast and involve the conversion of carbon dioxide and other compounds into glucose. The light-independent reactions can be split into three stages, these are carbon fixation, the reduction reactions and finally the regeneration of ribulose bisphosphate. Collectively these stages are known as the Calvin Cycle.
LabBench Activity Plant Pigments and Photosynthesis
Chlorophylls are green pigments that absorb blue and red light. The most important is chlorophyll-a, which is found in all plants. Many many marine plants also contain other chlorophylls (b, c or d).