Given below is the experimental set-up to establish that one of the atmospheric gases is essential for photosynthesis in plants. $(a)$ Name the atmospheric gas which is essential for photosynthesis. $(b)$ What is kept in the watch-glass in figure 'a' and why? $(c)$ Write the balanced chemical equation for the process of photosynthesis. $(d)$ When do the desert plants take up carbon dioxide and perform photosynthesis?

(N/A) The atmospheric gas essential for photosynthesis is carbon dioxide $(CO_2)$.
$(b)$ Potassium hydroxide $(KOH)$ is kept in the watch-glass. It is used to absorb carbon dioxide present in the bell jar.
$(c)$ The balanced chemical equation for photosynthesis is:
$6CO_2 + 12H_2O \xrightarrow{\text{Chlorophyll, Sunlight}} C_6H_{12}O_6 + 6O_2 + 6H_2O$
$(d)$ Desert plants take up carbon dioxide at night and prepare an intermediate product, which is acted upon by the energy absorbed by the chlorophyll during the day to perform photosynthesis.