The structure in cell concerned with the synthesis of proteins is the

Step 1: Analyze the question The question asks which cell structure is responsible for synthesizing proteins (building proteins from amino acids).

Step 2: Explain the concept Protein synthesis has two main stages:

• Transcription (in the nucleus): DNA is copied into mRNA.
• Translation (at the ribosome): the mRNA code is read, and amino acids are joined in order to form a polypeptide chain (protein).

The ribosome is the actual "factory" where amino acids are assembled into proteins. Ribosomes are made of rRNA and protein, and they may be free in the cytoplasm or attached to the rough endoplasmic reticulum.

Step 3: Evaluate each option

• A. Endoplasmic reticulum: It transports and processes proteins. The rough ER only has ribosomes attached to it, and the ribosomes do the synthesizing. The smooth ER makes lipids.
• B. Ribosome: It is the site of translation, where proteins are assembled. ✔
• C. Nucleus: It holds the DNA and controls the cell, but it does not assemble proteins.
• D. Plasma membrane: It controls what enters and leaves the cell.
• E. Golgi apparatus: It modifies, packages, and secretes proteins, but it does not make them.

Step 4: Answer The correct answer is B. ribosome.

Exam tip: Remember "Ribosome = Recipe reader, builds Protein." Also remember the pairing: Ribosome → Protein, Smooth ER → Lipids, Golgi → Packaging, Mitochondria → Energy.