Consider this animal cell. Which organelle is labeled I? cell membrane ribosome endoplasmic reticulum nucleus

The right answer is the nucleus.

The nucleus is a large structure surrounded by a double membrane, the nuclear envelope, which separates it from the cytoplasm. The membranes fuse in a few places, leaving openings called "nuclear pores", allowing the exchange of molecules between the nucleus and the cytoplasm.

The nuclear envelope is continuous with the granular endoplasmic reticulum, which is therefore bonded to the nucleus.

Cell membrane is the coating around the cell, ribosomes are tiny dots inside the cell, ER is large and membrane-like folded inside the cell, and the nucleus is towards the middle and usually pretty large