Question

Represent the equation of photosynthesis. Explain the steps involved in photosynthesis. In which way are the steps of photosynthesis different in desert plants.

Answer 1

Hint: Photosynthesis is the process of synthesis of food in the presence of sunlight as the energy is derived from solar radiation. This process is seen in photoautotrophic organisms like cyanobacteria. There are also chemoautotrophic organisms that synthesize food by deriving energy from chemical bonds.

Complete answer:
The equation of photosynthesis is as follows:
${6CO}_2+{12H}_{2}O\underset{Light}{\overset{Chlorophyll}{\to }}{C}_6{H}_{12}{O}_6+{6H}_{2}O+{6O}_2$
This equation represents how simple inorganic compounds like carbon dioxide and water are converted into glucose and oxygen in the presence of sunlight inside the green parts of plants that contain chlorophyll. There is water represented on both sides of the equation because the source of these two water molecules is not the same.
The steps involved in photosynthesis are as follows:
-Light reactions: These reactions are also known as photochemical reactions as they are directly driven by the sunlight and result in the production of ATP and NADPH. These reactions take place in the membrane system of the chloroplast. The following reactions make up the light reactions:
(i)Light absorption or photophosphorylation
(ii)Water splitting
(iii)Oxygen release
(iv)Formation of high energy chemical intermediates ATP and NADPH
-Dark reactions: These reactions do not occur in the dark, but depend on the products of the light reactions ATP and NADPH to take place. They are also known as carbon reactions as carboxylation takes place in these reactions. It takes place in the stroma of the chloroplast which results in the production of sugar. Dark reactions consist of the Calvin cycle which includes carboxylation, reduction, and regeneration by which ATP, NADPH, ${CO}_2$, and $H_{2}O$ are utilized in glucose formation.
The carbon fixation step is different in desert plants. There is a time lag between carbon fixation and the Calvin cycle so as to avoid water loss due to transpiration. This pathway is known as Crassulacean acid metabolism or CAM photosynthesis.

Note: -Another pathway which is known as the $C_4$ pathway is seen in some plants to avoid photorespiration.
-Such plants have a special type of anatomy in their leaves known as the Kranz anatomy.
-Photorespiration is the process where the oxygenase activity of RuBisCO takes place resulting in the release of ${CO}_2$ instead of its fixation.