Which type of microscopy was used to observe the first strands of DNA?

• A. Light microscopy
• B. Fluorescence microscopy
• C. Transmission electron microscopy
• D. X-ray crystallography

Answer: (D)

Verified step by step guidance

1. Understand the context: The question asks about the method used to observe the first strands of DNA, which refers to the technique that revealed the detailed structure of DNA molecules.
2. Recall the capabilities of each microscopy type: Light microscopy and fluorescence microscopy are useful for observing cells and some larger structures but lack the resolution to see DNA strands at the molecular level.
3. Transmission electron microscopy (TEM) provides higher resolution images of cellular ultrastructure but still does not directly reveal the atomic-level structure of DNA strands.
4. X-ray crystallography is a technique that uses X-ray diffraction patterns from crystallized molecules to determine the three-dimensional atomic structure of molecules like DNA.
5. Therefore, the first detailed observation and structural determination of DNA strands were achieved using X-ray crystallography, not traditional microscopy methods.