Chlorophyll a occurs in

Chlorophyll occurs in all oxygen-liberating autotrophs.
Chlorophyll a is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light, and it is a poor absorber of green and near-green portions of the spectrum.
Chlorophyll is essential for most photosynthetic organisms to release chemical energy but is not the only pigment that can be used for photosynthesis. All oxygenic photosynthetic organisms use chlorophyll a but differ in accessory pigments like chlorophyll b.