18. The diagram below shows the rough endoplasmic reticulum of a cell as seen under the electron microscope. The structures labeled Z are the site of protein synthesis, Z is indicating
Answer: C
Z indicates ribosomes, which are the site of protein synthesis.
Ribosomes, labeled as Z in the diagram, are essential cellular structures responsible for synthesizing proteins. They can be found either free-floating in the cytoplasm or attached to the rough endoplasmic reticulum, where they play a crucial role in translating messenger RNA into polypeptide chains.
A) mitochondria
Mitochondria are organelles responsible for energy production through the process of cellular respiration. They are not involved in protein synthesis, which is the function of ribosomes, making this option incorrect.
B) chromosomes
Chromosomes are structures made of DNA that contain genetic information. They play a role in cell division and heredity but do not participate in the protein synthesis process directly, thus rendering this option incorrect.
C) ribosomes
Ribosomes are the correct answer as they are directly involved in protein synthesis. They translate the genetic code into proteins, and their presence on the rough endoplasmic reticulum is characteristic of a cell engaged in producing proteins for export or for use in the cell membrane.
D) centrosomes
Centrosomes are cellular structures that organize microtubules and are involved in cell division. They do not synthesize proteins and therefore do not relate to the function indicated by the label Z in the diagram.
Conclusion
Ribosomes are the only cellular components listed that are directly responsible for protein synthesis, aligning perfectly with the label Z in the diagram. All other options, including mitochondria, chromosomes, and centrosomes, have distinct functions unrelated to protein synthesis, confirming that C is the correct answer.