Although they may cover the same subject, the articles are written for a variety of audiences. Some are basic narratives aimed at the general public, others are comprehensive courses aimed at college students. All of these are quite good and several should be checked out for comparison.
M Farabee from Estrella Mountain Community College has written a highly recommended online biology course text that includes a detailed section on photosynthesis with emphasis on the physical aspects of the process. June B. There are many useful animations. There is much here to enjoy and it is fun to roam around through the site. A truly wonderful site! It covers the details of photosynthesis and how it relates to the rest of life.
There is much good information here, as well as good humor and illustrations. Specific Subject Sites There are many sites that specialize in a certain aspect of photosynthesis.
Here are some of the best arranged by topic. It is located at the California Institute of Technology and includes researchers from several major universities. Scott and Kelly Nyk. See Fig. Their site contains links to their research, grants and videos. As part of the mandate from the DoE, these sites post progress reports as well as other important information.
The goal is to produce hydrogen or other solar fuels from sunlight utilizing artificial photosynthesis. Washington University, St.
Artificial Photosynthesis is one of the areas of research for this new center. When you have a big organism and you become irritating to it, the immunological system just kicks in and kills the invading organism'. And he assured me that we have just become so irritating to the earth, she'll just kill us.
Which makes me happier. It says that there is something much bigger than us, which we forget about the earth. And she is much more powerful than us. She'll get rid of us if we don't take care of her. See also Fig. It is a very detailed article with many illustrations. This is followed by an excellent description of phosphorylation and the two photosystems.
The site is profusely illustrated. The Z-Scheme Fig. Z-Scheme of Electron Transport in Photosynthesis. The Khan Academy has a couple useful animated class lectures on the light reactions of use to middle- and high school students. Both are well done in the typical Salman Khan manner. From June B. Blankenship at Washington University St. It is a well-done text with basic diagrams.
We recommend it to all students. The interactive link maps on this site link to many very important equations. The Z-Scheme is the description of the electron transfer in oxygenic photosynthesis. However for a scheme, see Figure 3, shown above.
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. 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 right , a 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. The first process is the Light Dependent Process Light Reactions , requires 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. 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. 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. We now know where the process occurs in the chloroplast, and can link that to chemiosmotic synthesis of ATP. Chemiosmosis as it operates in photophosphorylation within a chloroplast. Halobacteria, which grow in extremely salty water, are facultative aerobes, they can grow when oxygen is absent.
Purple pigments, known as retinal a pigment also found in the human eye act similar to chlorophyll. The complex of retinal and membrane proteins is known as bacteriorhodopsin, which generates electrons which establish a proton gradient that powers an ADP-ATP pump, generating ATP from sunlight without chlorophyll.
This supports the theory that chemiosmotic processes are universal in their ability to generate ATP. Carbon dioxide enters single-celled and aquatic autotrophs through no specialized structures, diffusing into the cells. The Calvin Cycle occurs in the stroma of chloroplasts where would it occur in a prokaryote? Carbon dioxide is captured by the chemical ribulose biphosphate RuBP. RuBP is a 5-C chemical. Six molecules of carbon dioxide enter the Calvin Cycle, eventually producing one molecule of glucose.
The reactions in this process were worked out by Melvin Calvin shown below. Melvin Calvin took charge of this work at the end of the war in order to provide raw materials for John Lawrence's researches and for his own study of photosynthesis. Using carbon, available in plenty from Hanford reactors, and the new techniques of ion exchange, paper chromatography, and radioautography, Calvin and his many associates mapped the complete path of carbon in photosynthesis.
The accomplishment brought him the Nobel prize in chemistry in Eventually there are 12 molecules of glyceraldehyde phosphate also known as phosphoglyceraldehyde or PGAL , a 3-C , two of which are removed from the cycle to make a glucose. Remember the complexity of life, each reaction in this process, as in Kreb's Cycle, is catalyzed by a different reaction-specific enzyme. C-4 Pathway Back to Top Some plants have developed a preliminary step to the Calvin Cycle which is also referred to as a C-3 pathway , this preamble step is known as C The resulting sugars are now adjacent to the leaf veins and can readily be transported throughout the plant.
C-4 photosynthsis involves the separation of carbon fixation and carbohydrate systhesis in space and time. The capture of carbon dioxide by PEP is mediated by the enzyme PEP carboxylase, which has a stronger affinity for carbon dioxide than does RuBP carboxylase When carbon dioxide levels decline below the threshold for RuBP carboxylase, RuBP is catalyzed with oxygen instead of carbon dioxide.
The product of that reaction forms glycolic acid, a chemical that can be broken down by photorespiration, producing neither NADH nor ATP, in effect dismantling the Calvin Cycle. C-4 plants, which often grow close together, have had to adjust to decreased levels of carbon dioxide by artificially raising the carbon dioxide concentration in certain cells to prevent photorespiration.
C-4 plants evolved in the tropics and are adapted to higher temperatures than are the C-3 plants found at higher latitudes. Common C-4 plants include crabgrass, corn, and sugar cane. Note that OAA and Malic Acid also have functions in other processes, thus the chemicals would have been present in all plants, leading scientists to hypothesize that C-4 mechanisms evolved several times independently in response to a similar environmental condition, a type of evolution known as convergent evolution.
We can see anatomical differences between C3 and C4 leaves.Chlorophyll is a complex molecule. The most common and abundant pigment is chlorophyll a. Distinguish between organisms known as autotrophs and those known as heterotrophs as pertains to their modes of nutrition.
Water enters the root and is transported up to the leaves through specialized plant cells known as xylem pronounces zigh-lem. Visible light is one small part of the electromagnetic spectrum. The hydrogen ions are allowed to pass through the thylakoid membrane through an embedded protein complex called ATP synthase. As the electron passes along these proteins, energy from the electron fuels membrane pumps that actively move hydrogen ions against their concentration gradient from the stroma into the thylakoid space. The source of electrons for photosynthesis in green plants and cyanobacteria is water.
Images from Purves et al. The replacing of the electron enables chlorophyll to respond to another photon. A photon strikes photosystem II to initiate photosynthesis.
Both chlorophylls also absorb in the orange-red end of the spectrum with longer wavelengths and lower energy. The longer the wavelength or the more stretched out it appears , the less energy is carried. The sun emits an enormous amount of electromagnetic radiation solar energy.
In red algae, the action spectrum is blue-green light, which allows these algae to use the blue end of the spectrum to grow in the deeper waters that filter out the longer wavelengths red light used by above ground green plants.
The Cellular Foundation of Life 5. Most of the time, the photosynthetic process uses water and releases the oxygen that we absolutely must have to stay alive. This results in fish kills and changes in soil pH which can alter the natural vegetation and uses of the land.
Environmental educators use music to teach children about climate change. The transparent epidermis layer allows light to pass through to the palisade mesophyll cells where most of the photosynthesis takes place. Carbon dioxide enters single-celled and aquatic autotrophs through no specialized structures. Photosystem I absorbs a second photon, which results in the formation of an NADPH molecule, another energy carrier for the Calvin cycle reactions.