Question
Describe the main chemical changes which occur during photosynthesis in:
Light reaction
Light reaction
✓
Answer
The light reaction occurs in two main steps:
(1) Activation of chlorophyll - On exposure to light energy, chlorophyll becomes activated by absorbing photons.
(2) Splitting of water - The absorbed energy is used in splitting the water molecule into hydrogen and oxygen, releasing energy. This reaction is known as photolysis of water.
$2 H _2 O \xrightarrow{\text { energy of } 4 \text { photons }} 4 H ^{+}+4 e ^{-}+ O _2$
The fate of $H ^{+}, e ^{-}$and $( O )$ component are as follows:
The hydrogen ions $\left( H ^{+}\right)$obtained from above are picked up by a compound NADP (Nicotinamide adenine dinucleotide phosphate) to form NADPH.
$NADP ^{+}+ e ^{-}+ H ^{+} \xrightarrow{\text { enzyme }} NADPH$
The oxygen $( O )$ component is given out as molecular oxygen $\left( O _2\right)$.
$'2"O" -> "O"_2'$
The electrons ( $e ^{-}$) are used in converting ADP into energy rich ATP by adding one inorganic phosphate group $P _{ i }$.
$"ADP" + "P" -> "ATP"`$
This process is called photophosphorylation.
(1) Activation of chlorophyll - On exposure to light energy, chlorophyll becomes activated by absorbing photons.
(2) Splitting of water - The absorbed energy is used in splitting the water molecule into hydrogen and oxygen, releasing energy. This reaction is known as photolysis of water.
$2 H _2 O \xrightarrow{\text { energy of } 4 \text { photons }} 4 H ^{+}+4 e ^{-}+ O _2$
The fate of $H ^{+}, e ^{-}$and $( O )$ component are as follows:
The hydrogen ions $\left( H ^{+}\right)$obtained from above are picked up by a compound NADP (Nicotinamide adenine dinucleotide phosphate) to form NADPH.
$NADP ^{+}+ e ^{-}+ H ^{+} \xrightarrow{\text { enzyme }} NADPH$
The oxygen $( O )$ component is given out as molecular oxygen $\left( O _2\right)$.
$'2"O" -> "O"_2'$
The electrons ( $e ^{-}$) are used in converting ADP into energy rich ATP by adding one inorganic phosphate group $P _{ i }$.
$"ADP" + "P" -> "ATP"`$
This process is called photophosphorylation.
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