nucleus cytoskeleton endoplasmic reticulum plasma membrane
I gave my students this multiple choice 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?

Only one answer is correct among these 4 choices:
- nucleus
- cytoskeleton
- endoplasmic reticulum
- plasma membrane

Could you tell me which one is correct?

cytoskeleton