Final answer:
Most of an organism's DNA is carried by its chromosomes, which are located within the nucleus of eukaryotic cells. The nucleolus is involved in the synthesis of ribosomes, not in storing DNA. Prokaryotic DNA is located in the nucleoid region and not in a nucleus.
Step-by-step explanation:
The question concerns where a major portion of an organism's DNA is located. The correct answer to the question 'Most of an organism's DNA is carried by its _____.' is b. chromosomes. In eukaryotic organisms, chromosomes are found within the nucleus, which is a membrane-bound organelle. The nucleus contains the cell's genetic material in the form of chromatin. When the cell is about to divide, the chromatin condenses into chromosomes. Each chromosome bears many genes, which are units of hereditary information.
The nucleolus is also found within the nucleus, but rather than storing DNA, it's responsible for synthesizing ribosomes, which then travel out to the cytoplasm to perform protein synthesis. Both plant and animal cells have a nucleus with chromosomes, where the vast majority of the organism's genome is stored and organized. In contrast, prokaryotic organisms, such as bacteria, do not have a nucleus but rather a nucleoid area that contains their DNA.