They allow for many variations to exist in species. That's the answer
In light reactions, a molecule of chlorophyll absorbs one photon of light, causing a chlorophyll electron to transfer to a higher energy level. The energized electrons from the chlorophyll molecules flow down a transportation chain to a compound called nicotinamide adenine dinucleotide phosphate or NADP.
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Answer:
Mollusks can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. These classes are distinguished by, among other criteria, the presence and types of shells they possess.