The first stage is called the light-dependent process, or light reactions, because it requires sunlight. Image by Jen Valenzuela (CC-BY). Correct Wrong. Which compound is a metabolic intermediate of the light-independent reactions in photosynthesis? In the light-dependent reactions, energy from sunlight is absorbed by chlorophyll and that energy is converted into stored chemical energy. Visible light ranges from 380 nanometers at the violet end of the spectrum, to 750 nanometers at the red end of the spectrum. Humans can see only a fraction of this energy, which portion is therefore referred to as “visible light”. A photon strikes photosystem II to initiate photosynthesis. Photosynthesis is a two-stage process. The light reaction of photosynthesis initiates only when it is supplied with light energy. In the light-dependent reactions, energy absorbed by sunlight is stored by two types of energy-carrier molecules: ATP and NADPH. There are five major chlorophylls: a, b, c and d and a related molecule found in prokaryotes called bacteriochlorophyll. The most outdated name is dark reactions, because light is not directly required (Figure 1). The excited electron must then be replaced. The carotenoids found in fruit—such as the red of tomato (lycopene), the yellow of corn seeds (zeaxanthin), or the orange of an orange peel (β-carotene)—are used as advertisements to attract seed dispersers. Biology is brought to you with support from the Amgen Foundation. During this stage, light energy is converted into adenosine triphosphate (ATP) and NADPH. B. Pigments in the photocenter absorb light. Magnesium is associated with the center of the ring. The net result is a low pH in the thylakoid lumen, and a high pH in the stroma. At the other end of the spectrum toward red, the wavelengths are longer and have lower energy (figure \(\PageIndex{c}\)). The cytochrome b6f complex, an enzyme composed of two protein complexes, transfers the electrons from the carrier molecule plastoquinone (Pq) to the protein plastocyanin (Pc), ultimately facilitating the transfer of electrons from PSII to PSI. energy CO2 water ATP and NADPH . movement of materials through a membrane against a concentration gradient; requires energy from the cell. Light independent reactions of photosynthesis are anabolic reactions that lead to the formation of a sex-carbon compound, glucose in plants. Chlorophyll b differs from chlorophyll a in that it has a CHO group instead of a CH3 group associated with one part of the ring (indicated in the red box, are responsible for the green color of leaves). Figure 1. Light-Dependent Reactions. Pigments reflect or transmit the wavelengths they cannot absorb, making them appear in the corresponding color. The light-dependent reactions begin in photosystem II. Figure \(\PageIndex{e}\): (a) Chlorophyll a, (b) chlorophyll b, and (c) β-carotene are hydrophobic organic pigments found in the thylakoid membrane. Notice how each pigment has a distinct set of peaks and troughs, revealing a highly specific pattern of absorption. The actual step that converts light energy into chemical energy takes place in a multiprotein complex called a photosystem, two types of which are found embedded in the thylakoid membrane, photosystem II (PSII) and photosystem I (PSI) (figure \(\PageIndex{h}\)). God bless all people who dooo! The ATP represents stored chemical energy. Which is the best hypothesis for the scientific question "How does light intensity affect the rate of photosynthesis?". Chlorophyll a and chlorophyll b are found in plant chloroplasts and will be the focus of the following discussion. Violet has the shortest wavelength and therefore carries the most energy, whereas red has the longest wavelength and carries the least amount of energy. Those two chlorophylls can undergo oxidation upon excitation; they can actually give up an electron. What is required for both the light-dependent and light-independent reactions to proceed? Which of the following is not a step in the light dependent reactions? and electrons. With dozens of different forms, carotenoids are a much larger group of pigments. A. ATP supplies the energy to produce glucose and other carbohydrates. (credit: modification of work by NASA). Thus, PSII captures the energy to create proton gradients to make ATP, and PSI captures the energy to reduce NADP+ into NADPH. (credit: Jason Hollinger). Light energy excites electrons. 2. Energy travels through the electron transport chain, which pumps hydrogen ions into the thylakoid space. Figure \(\PageIndex{j}\): The electron transport chain, water photolysis, and photophosphorylation in the light-dependent reactions. Which compound is produced during regeneration? Water molecules are split. 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