Final Answer:
Chargaff disproved the tetranucleotide hypothesis by examining the base composition of DNA. b) He demonstrated that the ratio of adenine to thymine and guanine to cytosine was not consistent. Conclusion: DNA is composed of pairs of complementary bases.
Step-by-step explanation:
He observed that the ratios of adenine (A) to thymine (T) and guanine (G) to cytosine (C) were not consistent across species. In his experiments, Chargaff found that while the overall amount of DNA bases might vary, the quantity of adenine always roughly equaled that of thymine, and the quantity of guanine was approximately equal to that of cytosine.
Chargaff's findings laid the foundation for the discovery of the complementary base pairing in DNA. The consistent ratios of A to T and G to C indicated that these bases form pairs with specific complementary partners: A pairs with T, and G pairs with C. This insight became a crucial piece of evidence supporting Watson and Crick's double helix model of DNA, wherein the two strands are held together by hydrogen bonds between complementary base pairs. Thus, Chargaff's work refuted the tetranucleotide hypothesis and contributed significantly to our understanding of DNA's true composition and structure.
In summary, Chargaff's disproval of the tetranucleotide hypothesis was based on the consistent ratios of complementary bases in DNA, providing essential support for the concept of base pairing and ultimately confirming the double-stranded, complementary nature of the DNA molecule. Therefore, the correct answer is b) He demonstrated that the ratio of adenine to thymine and guanine to cytosine was not consistent.