In a chlorophyll $a$ molecule,which of the following groups is attached to carbon atom $3$ of pyrrole ring $II$?

How does protochlorophyll differ from chlorophyll due to the lack of which component?

In the figure given below,the black line (upper) indicates the action spectrum for photosynthesis and the lighter line (lower) indicates the absorption spectrum of chlorophyll-$a$. Answer the following:
$(a)$ What does the action spectrum indicate? How can we plot an action spectrum? Explain with an example.
$(b)$ How can we derive an absorption spectrum for any substance?
$(c)$ If chlorophyll-$a$ is responsible for the light reaction of photosynthesis,why do the action spectrum and absorption spectrum not overlap?

Which of the following pigments is yellow in colour?

Carotenes present in chloroplasts help in .........

Leaves appear green because they...