Respuesta :
Answer and Explanation:
LIGHT DEPENDENT STAGE
This is the initial stage. Chlorophyll molecules absorb light energy which is used to split water molecules into oxygen and hydrogen atoms. The oxygen is released in the atmosphere or used by plants in respiration. ATP is also formed using solar energy absorbed by chlorophyll molecules.
LIGHT INDEPENDENT STAGE
The process involves carbon dioxide with hydrogen atoms which combine to form a simple sugar. This is called carbon dioxide fixation. The energy required for this reaction is produced by ATP from the light stage reaction.
Explanation:
Photosynthesis is a chemical pathway that’s integral to producing energy in plants and other primary producers. Energy in the form of molecules of glucose is produced from light, water and carbon dioxide while oxygen is released. This occurs in several complex steps, photosynthesis is a rate limited reaction, depends on several factors including carbon dioxide concentration, ambient temperature and light intensity; the energy is retrieved from photons, I.e. particles of light, and water is used as a reducing agent. This occurs in the thykaloids, where pigment molecules like chlorophyll reside.
The chloroplast is a membrane bound organelle found in plants. It contains several invaginations of a plasma membrane called the thylakoid membrane. This contains chlorophyll pigments, in stacks called granum, while the internal spaces of the organelle are called the lumen. Liquid surrounds the granum, forming the stroma.
A. During the Light- Dependent Reaction or Photolysis:
- Light is absorbed by pigments in phosystem II (PSII). This energy is transferred among pigments til it gets to the reaction center, and is transferred to P680; this promotes an electron to a higher energy level where it then goes to an acceptor molecule.
- Water supplies the chlorophyll in plant cell with replacement electrons for the ones removed from photosystem II. Additionally, water (H2O) split by light during photolysis into H+ and OH- acts as a source of oxygen along with functioning as a reducing agent.
- the electron moves down an electron transport chain (to PS I)where it experiences continuous energy loss. This energy fuels the pumping of H+ from the stroma to thykaloid, leading to the formation of a gradient. The H+ move along their gradient and cross through ATP synthase, into the the stroma.
- ATP synthase converts ADP and Pi to the energy storage molecule ATP.
- The electron gets to photosystem I where it goes to pigments at P700. It absorbs light energy, the electron is promoted to a higher energy level, and passed to an electron acceptor. This leaves a space for another electron which is then replaced by one from photosystem II.
- In the ETC, the molecule NADP is reduced to NADPH by providing H+ ions. NADP and NADPH are integral to the Calvin cycle where monosaccharides or sugars like glucose are produced after the modification of several molecules.
B. While, in the Light Independent Reaction called the Calvin Cycle:
- During the initial stage, three molecules of ribulose bisphosphate, RuBP are reduced and carbon is fixed from an inorganic CO2 to an organic form by the enzyme RuBisCO. With every molecule of CO2 fixed, 2 molecules of 3-phosphoglyceric acid are produced. 3-PGA is a 3 carbon molecule with a phosphate attached.
- Next, NADPH and ATP facilitate the addition of electrons to or reduction of 6 molecules of 3PGA to 6 molecules of G3P (glyeraldehyde 3-phosphate). The process uses 6 molecules of ATP and 6 of NADPH, after which the conversion of NADPH and ATP to ADP and NADP+ occur; these are returned to the light dependent reactions.
- A molecule of G3P, goes to the cytoplasm from this cycle, to form other complex molecules. Fixing sufficient carbon for this G3P export requires 3 revolutions of the cycle. Since two molecules of G3P are made per revolution, 3 turns make 6 G3Ps; 5 of these are used to regenerate RuBP for further fixation.
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