Chloroplasts absorb light in the violet and blue wavelengths, and also in the red regions of the visible spectrum of light. This portion ofthe spectrum between 400nm and 700nm is also referred to as photosynthetically active radiation (PAR).
The inner side of the plastids is clearly divisible into
a colourless ground substance called stroma and
a membrane system consisting of closed flattened sacs called thylakoids.
Chlorophyll pigments occur universally in the plant kingdom, in photosynthetic protists, and virtually in all photosynthetic bacteria, except halobacteria.
The photosynthetic reactions can be grouped broadly into two categories.
Light reactions which are chemical processes occur only in the presence of light. In these reactions the light energy is absorbed and used by chlorophyll.
In dark reactions carbon dioxide is fixed and reduced by thermochemical mechanisms, resulting in the formation of carbohydrates. These reactions are not directly dependent on light.
Light-induced phosphorylation of ADP to form ATP is called photophosphorylation or photosynthetic phosphorylation.
The reaction by which water undergoes light dependent cleavage is called photolysis.
The light-driven reactions of photosynthesis, referred to as electron transport chain, were first formulated by Robert Hill in 1939.
In 1945, Melvin Calvin and his colleagues started a series of investigations that resulted in the overall understanding of the dark reactions of photosynthesis. They used the unicellular green alga Chlorella in their work.
The main aim of Melvin Calvin is to determine the pathway by which carbon dioxide became fixed into carbohydrates.
Photorespiration reactions are dependent on light and it also performs uptake of oxygen and release of carbon dioxide, so this process is called photorespiration.
Crassulacean Acid Metabolism occurs only in succulents and other plants that normally grow in dry conditions.
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