Photosynthetic Units

Leaf tissues of aurea mutants of tobacco and Lespedeza have been shown to have higher photosynthetic capacity per molecule of chlorophyll, a higher saturation intensity, a simpler lamellar structure, and the same quantum yield as their dark green parents. Here we report on the values of photosynthetic units for both types of plants and some algae. The unit has been assumed to be about as uniform and steady in the plant world as the quantum efficiency. The number on which all theoretical discussions have been based so far is 2400 per O₂ evolved or CO₂ reduced. With dark green plants and algae our determinations of units by means of 40 µsec flashes superimposed on a steady rate of background photosynthesis at 900 ergs cm^-2 sec^-1 of red light yielded mostly numbers between 2000 and 2700. However, the photosynthetic unit turned out to be very variable, even in these objects. In aurea mutants the unit was distinctly smaller, averaging 600 chl/CO₂. By choosing the right combination of colors for flash and background light, units as low as 300 chl/CO₂ or 40 chl/e^- could be measured consistently. We found five well-defined groups of units composed of multiples of its smallest member. These new findings are discussed in terms of structural entities that double or divide under the influence of far-red light.     

Concentration Units

Most people are familiar with the concept that animals come in all shapes and sizes and that the body plan of some animals can completely transform during their lifetime. Well-known examples of such complex life cycles of terrestrial animals include butterflies and frogs. Many people are unaware, however, that complex life cycles are exceedingly prevalent in marine environments. Marine invertebrates, such as sea urchins, sea stars, and crabs, all have a microscopic pelagic larval stage that looks nothing at all like the familiar adult form. The authors have developed a lesson to teach students about complex life cycles using crab larvae and adult crabs. This lesson allows 3rd- to 6th-grade students to compare and contrast body plans while learning about adaptations the larvae and adults have made to their respective habitats. Throughout the lesson, students practice skills important for scientific inquiry: making observations, drawing what they see, asking and answering questions, and learning to use scientific tools such as microscopes.     

Units of enzyme activity

Units of enzymes activity, recommended by the Nomenclature Committee on enzymes of the International Union of Biochemistry are described the unit E (U), introduced in 1961 and its derivatives: specific activity, molecular (molar) activity, enzyme catalytic centre activity, enzyme solution concentration; the unit catal, introduced in 1972 and its derivatives. Information presented is essential to ensure correct expression of enzyme activity.     

Photosynthetic Units of Phototrophic Organisms

Photoautotrophic organisms play a key role in the biosphere of the Earth, converting solar energy of the 350-1000 nm range into biochemically available form. In contemporary aquatic and terrestrial ecosystems, the dominating groups are the oxygen evolving cyanobacteria, algae, and higher plants. Anoxygenic phototrophic microorganisms occupy mainly ecological niches with extreme environmental conditions. Despite diverse evolution of all these taxonomic groups, their photosynthetic apparatus has a similar molecular design and identical principles of operation. This review covers recent data about features of the structural and functional organization of pigment-protein complexes of the basic types of photosynthetic units in prokaryotes and eukaryotes. A correspondence between the optical properties of various photosynthetic units and the natural light conditions is discussed.