What is DNA primarily responsible for in living organisms?

DNA is primarily responsible for storing genetic information in living organisms. It contains the instructions needed for an organism’s growth, development, functioning, and reproduction. This genetic information is encoded in the sequence of nucleotides within the DNA molecule, which ultimately determines the traits and characteristics of an organism.

In the context of heredity, DNA is fundamental because it ensures that the hereditary information is passed down from one generation to the next during reproduction. Each organism’s unique genetic code is what allows for the vast diversity of life observed on Earth. Additionally, the information stored in DNA is used to synthesize proteins through processes such as transcription and translation, which are crucial for the organism's cellular functions.

The other options, while important functions in biology, do not accurately represent the primary role of DNA. Energy production is primarily handled by mitochondria in eukaryotes, catalyzing reactions is done by enzymes (which are typically proteins produced based on genetic instructions), and transporting molecules often involves different cellular structures and systems, such as membranes and transport proteins. Thus, the role of DNA as the repository of genetic information is central to its function in living organisms.