Explain the experiment of $T$. $W$. Engelmann $(1843 - 1909)$.

(N/A) $\Rightarrow$ $T$. $W$. Engelmann used a prism to split light into its spectral components.
$\Rightarrow$ He then illuminated a green alga,$Cladophora$,which was placed in a suspension of aerobic bacteria.
$\Rightarrow$ The bacteria were used to detect the sites of $O_{2}$ evolution.
$\Rightarrow$ He observed that the bacteria accumulated mainly in the regions of blue and red light of the split spectrum.
$\Rightarrow$ Thus,the first action spectrum of photosynthesis was described.
$\Rightarrow$ This spectrum roughly resembles the absorption spectra of chlorophyll $a$ and $b$.