nucleus cytoskeleton endoplasmic reticulum plasma membrane
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Actin filaments are part of the contractile machinery in smooth muscle cells of eukaryotic organisms. Which organelle is responsible for contractile movement in these cells?
Possibilities:
- nucleus
- cytoskeleton
- endoplasmic reticulum
- plasma membrane

cytoskeleton