Organisms need to obtain energy via cellular respiration primarily for C to grow and reproduce. Cellular respiration is a process that converts biochemical energy from nutrients into adenosine triphosphate (ATP), which is used to power biological processes necessary for growth, reproduction, and maintenance of cellular functions.
While ATP is broken down in various processes (option A), and glycolysis is a part of cellular respiration (option D), the ultimate purpose of obtaining energy through cellular respiration is to support growth and reproduction. Photosynthesis (option B) is specific to plants and some microorganisms that produce their own energy by converting light energy into chemical energy.