Question

fill in the blank question
the

is a group of membranes that extend out from the nucleus throughout the cytoplasm with some parts being studded with ribosomes, some parts not.

Explanation:

The endoplasmic reticulum (ER) is a network of membranes extending from the nucleus into the cytoplasm. It has two regions: rough ER (studded with ribosomes) and smooth ER (not studded with ribosomes). This matches the description in the question.

Answer:

endoplasmic reticulum