Question

question: 3
a cell biologist compared the properties of rough endoplasmic reticulum (er) and smooth er. she found that one type of er is used for protein storage, and the other is used for lipid storage. what accounts for this difference?
a. smooth er works with the nucleus to synthesize protein.
b. rough er has ribosomes on its surface.
c. smooth er creates amino acids for ribosomes to form into proteins.
d. rough er forms proteins and transports them to the mitochondria.

Explanation:

To solve this, we analyze each option:

• Option A: Smooth ER does not work with the nucleus to synthesize protein; ribosomes (on rough ER) and the nucleus (via mRNA) are involved in protein synthesis. So A is incorrect.
• Option B: Rough ER has ribosomes on its surface. Ribosomes are the site of protein synthesis, so rough ER is associated with protein - related functions (like protein storage as per the question), while smooth ER is involved in lipid synthesis/storage. This option correctly explains the structural difference that leads to functional differences.
• Option C: Smooth ER does not create amino acids for ribosomes. Amino acids are obtained from the cell's environment or from the breakdown of molecules, and ribosomes use amino acids to make proteins, but smooth ER is not involved in this process. So C is incorrect.
• Option D: Rough ER forms proteins but does not transport them to the mitochondria. Proteins from rough ER are usually sent to the Golgi apparatus for further processing and then to other destinations, not the mitochondria. So D is incorrect.

Answer:

B. Rough ER has ribosomes on its surface.