The correct statement among the options provided is:
A. Plant and animal cells require oxygen to properly break down food molecules.
This is true because both plants (during cellular respiration) and animals require oxygen to break down food molecules effectively in a process called aerobic respiration.
B is incorrect because sunlight is specifically required for photosynthesis in plants, not for breaking down food in plants and animals.
C is also incorrect because while chloroplasts are involved in photosynthesis (in plants), cellular respiration occurs in the mitochondria of plant and animal cells.
Therefore, the answer is A.