Introduction:
The question asks about the granular structures that were first observed under an electron microscope as dense particles in 1955, along with the scientist who made this discovery.

Answer:

Ribosomes and George Palade:
The correct answer is option A: Ribosomes, George Palade. Ribosomes are cell organelles responsible for protein synthesis. They were first observed as dense particles under an electron microscope in 1955 by George Palade, a Romanian-American cell biologist. Palade's discovery of ribosomes and his subsequent research on their structure and function significantly contributed to our understanding of protein synthesis.

Significance of the Discovery:
The discovery of ribosomes as granular structures was a significant breakthrough in the field of cell biology. It provided scientists with a better understanding of how proteins are produced within cells, shedding light on the fundamental processes that govern cellular function.

Role of Ribosomes in Protein Synthesis:
Ribosomes play a crucial role in protein synthesis. They are composed of ribosomal RNA (rRNA) and proteins and exist in two subunits - large and small. Ribosomes facilitate the translation of genetic information encoded in messenger RNA (mRNA) into the amino acid sequence of proteins. This process occurs in the cytoplasm of the cell.

George Palade's Contribution:
George Palade's discovery of ribosomes and his subsequent research on their structure and function earned him the Nobel Prize in Physiology or Medicine in 1974. His studies involved using electron microscopy techniques to visualize ribosomes and their association with various cellular components involved in protein synthesis.

Conclusion:
In summary, ribosomes were the granular structures first observed as dense particles under an electron microscope in 1955. The scientist credited with this discovery is George Palade. His work on ribosomes significantly contributed to our understanding of protein synthesis and earned him the Nobel Prize in Physiology or Medicine.