What is Photosynthesis ??
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- Photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds.
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★Photosynthesis is a process by which phototrophs convert light energy into chemical energy, which is later used to fuel cellular activities. The chemical energy is stored in the form of sugars, which are created from water and carbon dioxide.
★The process of photosynthesis occurs in two stages:
★Light Reaction of Photosynthesis (or) Light-dependent Reaction
- Photosynthesis begins with the light reaction which is carried out only during the day in the presence of sunlight. In plants, the light-dependent reaction takes place in the thylakoid membranes of chloroplasts.
- The Grana, membrane-bound sacs like structures present inside the thylakoid functions by gathering light and is called photosystems.
- These photosystems have large complexes of pigment and proteins molecules present within the plant cells, which play the primary role during the process of light reactions of photosynthesis.
- There are two types of photosystems: photosystem I and photosystem II.
- Under the light-dependent reactions, the light energy is converted to ATP and NADPH, which are used in the second phase of photosynthesis.
- During the light reactions, ATP and NADPH are generated by two electron-transport chains, water is used and oxygen is produced.
- The chemical equation in the light reaction of photosynthesis can be reduced to:
- 2H2O + 2NADP+ + 3ADP + 3Pi → O2 + 2NADPH + 3ATP
★Dark Reaction of Photosynthesis (or) Light-independent Reaction
- Dark reaction is also called carbon-fixing reaction.
- It is a light-independent process in which sugar molecules are formed from the water and carbon dioxide molecules.
- The dark reaction occurs in the stroma of the chloroplast where they utilize the NADPH and ATP products of the light reaction.
- Plants capture the carbon dioxide from the atmosphere through stomata and proceed to the Calvin photosynthesis cycle.
- In the Calvin cycle, the ATP and NADPH formed during light reaction drive the reaction and convert 6 molecules of carbon dioxide into one sugar molecule or glucose.
- The chemical equation for the dark reaction can be reduced to:
- 3CO2 + 6 NADPH + 5H2O + 9ATP → G3P + 2H+ + 6 NADP+ + 9 ADP + 8 Pi
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