Final answer:
Adenine cannot pair with guanine due to the number of hydrogen bonds required; Rosalind Franklin's X-ray diffraction experiments were crucial for DNA's double helix structure discovery; adenine and thymine are complementary; Watson and Crick were aided by X-ray images; the complementary sequence to A-T-T-G-C-T is T-A-A-C-G-A; species' DNA differs in base sequence.
Step-by-step explanation:
The structural problem that prevents adenine from pairing with guanine is b) The number of hydrogen bonds required. Adenine and guanine are both purines with a two-ring structure, making them too large to fit together within the DNA double helix.
Rosalind Franklin contributed to the understanding of DNA by c) Conducting X-ray diffraction experiments. These experiments provided critical images that helped in the discovery of DNA's double helix structure.
The relationship between adenine and thymine is c) They are complementary base pairs. They are connected by two hydrogen bonds and fit together perfectly to maintain the uniform shape of the DNA double helix.
The critical clue that aided Watson and Crick in solving the structure of DNA was a) X-ray diffraction images by Rosalind Franklin. These images provided essential details about DNA's helical structure and base pairing.
A DNA strand with the sequence A-T-T-G-C-T would be complementary to a) T-A-A-C-G-A. Each base on one strand pairs with a specific complementary base on the opposite strand, A with T and G with C.
DNA from one species differs from the DNA of another species in its b) Sequence of bases. This sequence determines the unique genetic information of each species.