Why do primers bind to panda DNA but not to DNA from bacteria or bamboo?

• A. DNA has specific base sequence and primers bind by complementary base-pairing
• B. Primers are universal for all organisms
• C. Bacteria DNA degraded in faeces
• D. Panda DNA more abundant than bacteria DNA

Answer: (A)

Primers bind by complementary base pairing to a specific DNA sequence. They are short sequences that are designed to match a particular region of the target DNA. Because panda DNA has the exact sequence that the primer was designed to recognize, the primer can pair up with that panda DNA and be extended by the DNA polymerase. DNA from bacteria or bamboo has different sequences, so the primer cannot form a stable, correct base-pairing interaction with those DNAs, and binding doesn’t occur.

This is why sequence specificity matters: even if all DNAs share some bases, the exact arrangement matters for a stable match at the annealing temperature used. The other ideas aren’t correct because primers are not universal for all organisms, and binding isn’t determined by how much DNA is present or by degradation status—it's all about having the exact complementary sequence.