Questions: A nuclear pore is best described as an opening in the that permits the passage of molecules into and out of the nucleus. nuclear envelope plasma membrane endoplasmic reticulum nucleolus

The answer is the first one: nuclear envelope.

Explanation for each option:

1. Nuclear envelope: Correct. The nuclear pore is an opening in the nuclear envelope, which is the double membrane structure that surrounds the nucleus. These pores regulate the passage of molecules such as RNA and proteins between the nucleus and the cytoplasm.

2. Plasma membrane: Incorrect. The plasma membrane is the outer membrane of the cell, not the nucleus. It controls the movement of substances in and out of the entire cell, not specifically the nucleus.

3. Endoplasmic reticulum: Incorrect. The endoplasmic reticulum (ER) is a network of membranes within the cell that is involved in protein and lipid synthesis. It is not directly involved in the passage of molecules into and out of the nucleus.

4. Nucleolus: Incorrect. The nucleolus is a structure within the nucleus where ribosomal RNA is produced and ribosome assembly begins. It does not have pores for the passage of molecules into and out of the nucleus.

Summary: A nuclear pore is best described as an opening in the nuclear envelope that permits the passage of molecules into and out of the nucleus.