The cyclic pathway of ATP formation functions mainly …
A second photosynthetic adaptation exists in succulent plants adapted to very arid conditions. These plants open their stomata primarily at night and close them during the day (opposite of most plants). This conserves water during the day, but prevents CO2 from entering the leaves. When stomata are open at night, CO2 is taken up and incorporated into a variety of organic acids. This mode of carbon fixation is called crassulacen acid metabolism (CAM). The organic acids made at night are stored in vacuoles of mesophyll cells until morning, when the stomata close. During daytime, light reactions supply ATP and NADPH for the Calvin cycle. A this time, CO2 is released from the organic acids made the previous night and is incorporated into sugar in the chloroplasts.
The cyclic pathway of ATP formation functions mainly to
ð Produces ATP from this light driven electron current. Produces oxygen as a by-product. During cyclic electron flow, electrons ejected from P700 reach ferredoxin and flow back to P700. This process produces ATP and unlike noncyclic electron flow, the cyclic electron flow does not produce NADPH or O2.The Calvin cycle uses ATP and NADPH to convert CO2 to sugar:ATP and NADPH produced by the light reactions are used in the Calvin cycle to reduce carbon dioxide to sugar.ð The Calvin cycle turns three times to fix three molecules of CO2 into glyceraldehyde 3-phosphate (G3P). The cycle can be divided into three phases:Phase 1: Carbon Fixation. The Calvin cycle begins when each molecule of CO2 is attached to a five-carbon sugar, ribulose biphosphate (RuBP).
There are two important conditions for the various antenna pigments of photosynthesis to efficiently convey light energy to the photochemical reaction center. One is that the antenna pigment molecules need to be located close to each other to efficiently pass on the excitation energy. For this reason, they are incorporated into proteins and accumulated within the thylakoid membrane. The second is that since the shorter the wavelength, the higher the light energy, there needs to be a sophisticated mechanism to absorb short-wavelength light and transfer its energy to long-wavelength pigments. Pigments found in algae and cyanobacteria vary in color because the spectrum of sunlight differs in water depending on the conditions of absorption and scattering. As shown in Column Figure 16-3, the light energy absorbed by the respective pigments is efficiently transferred to chlorophyll a, and therefore, a wide range of visible light can be used in photosynthesis.
Cyclic Electron Flow occurs in some eukaryotes and primitive ..
( light regenerates the ATP and NADH)
The one molecule of G3P produced by the Calvin cycle becomes the starting point of a metabolic pathway that synthesizes organic compounds.
pathway and showed that the pathway operated in a cyclic ..
During noncyclic electron flow, the photosystems of the thylakoid membrane transform light energy to the chemical energy stored in NADPH and ATP. This process:
type of photosynthesis called C4 pathway.
For many plants, the initial carbon dioxide fixation product in the Calvin cycle is phosphoglycerate (with 3 carbon atoms), whereas in other plants, carbon dioxide is fixed as malic acid or aspartic acid (with 4 carbon atoms). Those in the former group, which includes rice, spinach, and trees, are called C3 plants, and those in the latter, which includes corn, are known as C4 plants.
In C4 plants, photosynthesis occurs in a roundabout way: carbon dioxide is fixed once by phosphoenolpyruvate carboxylase with a bicarbonate ion (HCO3: against which oxygen does not compete) as the substrate, but other enzymes release carbon dioxide in the cell again, and finally RuBisCO refixes the carbon dioxide for good. Although the C4 photosynthetic reaction uses extra energy (ATP), oxygenase activity of RuBisCO is not induced even when extracellular carbon dioxide concentration is low, thus allowing efficient photosynthesis. In this way, C4 plants have thrived over tens of millions of years, reducing the carbon dioxide concentration in the atmosphere from approx. 1% to the current 0.03%. In-depth research on the application of C4 photosynthesis has been actively carried out, with the aim of increasing the productivity of C3 plants such as rice.
complex to cyclic electron flow around photosystem I.
Photosynthesis is an
of an intact chloroplast, which integrates the two stages of photosynthesis.
In hot, arid climates plants have evolved the 475 million years they've been around to have alternative methods of carbon fixation.