Correct Option: B. Ribosomes Detailed Explanation:

1. Understanding Protein Synthesis:
2. Proteins are essential macromolecules that perform a vast array of functions within living organisms, including structural roles, enzymatic activities, and signaling. The process of synthesizing proteins is known as translation, which occurs in the cytoplasm of the cell.
3. Role of Ribosomes:
4. Ribosomes are the primary organelles responsible for protein synthesis. They can be found either floating freely in the cytoplasm or attached to the endoplasmic reticulum (ER), forming what is known as rough ER. Ribosomes read the messenger RNA (mRNA) sequence, which is transcribed from DNA, and translate it into a specific sequence of amino acids, thereby forming a protein.
5. Mechanism of Protein Synthesis:
6. The process begins when mRNA, which carries the genetic code from DNA, binds to a ribosome. Transfer RNA (tRNA) molecules then bring specific amino acids to the ribosome, where the ribosome facilitates the formation of peptide bonds between the amino acids, creating a polypeptide chain. This chain eventually folds into a functional protein.

Why Other Options Are Incorrect:

• A. Mitochondria:
• Mitochondria are known as the "powerhouses" of the cell because they generate adenosine triphosphate (ATP) through cellular respiration. While they do have their own ribosomes and can synthesize some proteins (specifically those needed for mitochondrial function), they are not the primary site for protein synthesis in the cell. Their main role is energy production, not protein synthesis.
• C. Golgi Apparatus:
• The Golgi apparatus is involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles. It acts as a processing center for proteins that have been synthesized by ribosomes. However, it does not synthesize proteins itself; rather, it works with proteins that have already been made.
• D. Lysosomes:
• Lysosomes are membrane-bound organelles that contain digestive enzymes. Their primary function is to break down waste materials and cellular debris. They do not play a role in protein synthesis; instead, they are involved in the degradation of proteins and other macromolecules.

Summary of Key Points:

• Ribosomes are the primary organelles responsible for protein synthesis in cells.
• They translate mRNA into amino acid sequences, forming proteins.
• Other organelles like mitochondria, Golgi apparatus, and lysosomes have distinct functions unrelated to the synthesis of proteins.
• Understanding the specific roles of each organelle is crucial for grasping cellular functions and processes.

This comprehensive understanding of ribosomes and their role in protein synthesis is essential for any student studying biology, especially in the context of cellular functions and molecular biology.