Which of the following statements about a protein in the lumen of the ER is FALSE?A protein in the lumen of the ER is synthesized by ribosomes on the ER membrane.Some of the proteins in the lumen of the ER can end up in the extracellular space.Some of the proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system.Some of the proteins in the lumen of the ER can end up in the plasma membrane.

The endoplasmic reticulum, or ER, is the net-like branching tubule found in the cytoplasm. In animal cells, it makes up more than half of the cell's membrane since ER is membrane-bound. The space between the membranes of the ER that aids in the folding of proteins among many is called the lumen. The false statement is the last option; some of the proteins in the lumen of the ER can end up in the plasma membrane. The ER folds the proteins that enter its lumen and directs them to the Golgi bodies. The Golgi bodies package the proteins and send them to their final destination. The proteins are synthesized on the surface of ER and are then captured by the ER. They then get transported to cytosol, the lumen of other organelles, and secreted out into extracellular space as well. But only transmembrane proteins that are part of the ER are transported into the plasma membrane or membranes of other organelles. Hence the given statement is false. 2. A protein in the lumen of the ER is synthesized by ribosomes on the ER membrane. The proteins found inside the ER's lumen are categorized as transmembrane or water-soluble proteins captured from the cytosol. These proteins are secreted by the ribosomes located in the ER and are directed toward the ER with the help of specialized signals. Hence the given statement is accurate. 3. Some of the proteins in the lumen of the ER can end up in the extracellular space. Some water-soluble proteins entering the ER's lumen get secreted out. Hence the given statement is correct. 4. Some of the proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system. The endoplasmic reticulum captures two types of proteins from the cytosol, they are transmembrane and water-soluble proteins. The water-soluble proteins end up either outside the cell or other organelle's lumen.The false statement is some of the proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system.