Cell Biology - Study Mode

Explanation

Solution: DNA (Deoxyribonucleic acid) uses four "letters" or bases to write its instructions: adenine (A), guanine (G), cytosine (C), and thymine (T). RNA (Ribonucleic acid) is very similar, but it has a slight change in one of its letters. Let's look at the options: * Option A: thymine: DNA does have thymine (T). RNA doesn't use thymine. * Option B: uracil: RNA uses uracil (U) instead of thymine. DNA doesn't have uracil. * Option C: adenine: Both DNA and RNA have adenine (A). * Option D: guanine: Both DNA and RNA have guanine (G). The key difference is that DNA uses thymine (T), while RNA uses uracil (U) . Therefore, the correct answer is B: uracil.