Oxygenic photosynthesis, provides energy to organism and allows for carbon fixation, all the while producing oxygen as a byproduct. In plants, algae and cyanobacteria, photosynthesis releases oxygen. This is called oxygenic photosynthesis. Although there are some differences between oxygenic photosynthesis in plants, algae, and cyanobacteria, the overall process is quite similar in these organisms.
Photosynthesis is not only needed by photosynthetic organism for energy but also for carbon fixation. However, when other reduced compounds serve as the electron donor, oxygen is not generated; these types of photosynthesis are called anoxygenic photosynthesis.
Figure 4. Eukaryotes and cyanobacteria carry out oxygenic photosynthesis, producing oxygen, whereas other bacteria carry out anoxygenic photosynthesis, which does not produce oxygen. Cyanobacteria and plant chloroplasts have both photosystems, whereas anoxygenic photosynthetic bacteria use only one of the photosystems.
Both photosystems are excited by light energy simultaneously. The flow of electrons in this way is called the Z-scheme. Only PSI is used during cyclic photophosphorylation; the high-energy electron of the PSI reaction center is passed to an ETS carrier and then ultimately returns to the oxidized PSI reaction center pigment, thereby reducing it. Figure 6. Click to see a larger image. The electron flow described here is referred to as the Z-scheme shown in yellow in [a].
After the energy from the sun is converted into chemical energy and temporarily stored in ATP and NADPH molecules having lifespans of millionths of a second , photoautotrophs have the fuel needed to build multicarbon carbohydrate molecules, which can survive for hundreds of millions of years, for long-term energy storage.
The carbon comes from CO 2 , the gas that is a waste product of cellular respiration. The Calvin-Benson cycle named for Melvin Calvin [—] and Andrew Benson [—] , the biochemical pathway used for fixation of CO 2 , is located within the cytoplasm of photosynthetic bacteria and in the stroma of eukaryotic chloroplasts. The light-independent reactions of the Calvin cycle can be organized into three basic stages: fixation, reduction, and regeneration see Metabolic Pathways for a detailed illustration of the Calvin cycle.
Additionally, other bacteria and archaea use alternative systems for CO 2 fixation. Although most bacteria using Calvin cycle alternatives are chemoautotrophic, certain green sulfur photoautotrophic bacteria have been also shown to use an alternative CO 2 fixation pathway.
In prokaryotes, in which direction are hydrogen ions pumped by the electron transport system of photosynthetic membranes? Skip to main content. Microbial Metabolism. Search for:. Photosynthesis Learning Objectives Describe the function and locations of photosynthetic pigments in eukaryotes and prokaryotes Describe the major products of the light-dependent and light-independent reactions Describe the reactions that produce glucose in a photosynthetic cell Compare and contrast cyclic and noncyclic photophosphorylation.
Think about It In a phototrophic eukaryote, where does photosynthesis take place? Think about It Why would a photosynthetic bacterium have different pigments?
Think about It Describe the three stages of the Calvin cycle. Key Concepts and Summary Heterotrophs depend on the carbohydrates produced by autotrophs, many of which are photosynthetic, converting solar energy into chemical energy. Different photosynthetic organisms use different mixtures of photosynthetic pigments , which increase the range of the wavelengths of light an organism can absorb. Photosystems PSI and PSII each contain a light-harvesting complex , composed of multiple proteins and associated pigments that absorb light energy.
Trebst and M. Avron, eds. Kuhlenmeier, C. Lau, R. Lemasson, C. Lewin, R. Starr, H. Stolp, H. Truper, A. Balows, H. Schlegel, eds. Lightbody, J. Linko, P. Botany 8 : — Mereschkowsky, C. Miller, L. Myers, J. Nakamura, H. Tokyo 10 : — Niklowitz, W. Norris, L. Botany 6: 64— Ogawa, T. Oren, A. Natl Acad.
USA 74 : — Padan, E. Pelroy, R. Petrack, B. Pringsheim, E. Rippka, R. Ris, H. Sachs, J. Engelmann, Leipzig. Sadewasser, D. Acta — Sagan, L. Schopf, J. Dobhansky, M. Hecht, and W. Steere, eds. Seewaldt, E. Shatkin, A. Sherman, L. Hollaender et al. Plenum Press, New York, pp. Shields, L. Stanier, R. Stevens, G. Stewart, A. Stizenberger, E. Mitteleuropas Systematisca geordnet mit Zugrund elegung lines neuen systems , Heinrich, Dresden, 41 pp.
Susor, W.
0コメント