Question

SER is mainly found in cells actively engaged in/SER is a site of
A) Secretion activity
B) Protein metabolism
C) Lipid metabolism
D) Catabolic activity

Answer 1

Before moving to the functionality of SER, let us first understand what is ER(endoplasmic reticulum). Within the cytoplasm of the eukaryotic cell, a membrane that forms a sequence of flattened sacs is known as endoplasmic reticulum. It plays a vital role in synthesis, modification, folding and transport of proteins.

Complete answer:
The main function of endoplasmic reticulum is to produce proteins for the cell.There are two types of endoplasmic reticulum,

1. RER: Rough endoplasmic reticulum, whose membrane has particles of ribosomes.
2. SER: Smooth endoplasmic reticulum, whose membrane does not contain ribosomes.
   Ribosomes are the tiny particles that consist of RNA along with some associated protein particles. It is regarded as the site of protein synthesis.
   Smooth endoplasmic reticulum helps in the synthesis of fat molecules or lipids that includes phospholipids and cholesterol that aids in manufacturing of new cellular membranes.

Additional information:

Secretion activity: The process of production and release of a substance by a cell or gland is called secretion. Golgi apparatus of a cell is responsible for the transportation, modification and packaging of proteins into vesicles prior to secretion. They play a vital role in secretion pathways.
Protein metabolism: Ribosomes are the site of protein synthesis in the cell. They are found in cytoplasm in free state and also found on the surface of rough endoplasmic reticulum. They are responsible for the process of translation, which involves the conversion of mRNA to protein.
Catabolic activity: It is a metabolic process which involves the breakdown of complex molecules like fatty acids into simpler units by the cell. This catabolic metabolism takes place in the mitochondria of the cell that releases energy(ATP) by oxidative phosphorylation.

Therefore the correct option is (c)Lipid metabolism.

Note: Smooth endoplasmic reticulum is formed by the shedding of ribosomes from the rough endoplasmic reticulum. RER is found close to the nucleus whereas SER is found near the cell membrane.