Cell The Unit of Life Test - 88

• The endoplasmic reticulum is the network of the membranous tube-like structure. It serves many functions, including the folding of protein molecules in sacs called cisternae and the transport of synthesized proteins in vesicles to the Golgi apparatus. 
• It provides strength to the cell cytoplasm. The ribosome is a large and complex molecular machine, found within all living cells, that serves as the site of biological protein synthesis (translation). 
• Ribosomes link amino acids together in the order specified by messenger RNA (mRNA) molecules. The endoplasmic reticulum is studded with ribosomes called rough endoplasmic reticulum involves the formation, modification, and transportation of protein. 
• Thus, the correct answer is option B.

A- The presence of DNA in mitochondria and chloroplasts can be explained through the theory of endosymbiosis. This theory was formulated by Lynn Margulis in 1960. According to Margulis aerobic bacteria were engulfed by anaerobic bacteria and can live together in a relationship where they can mutually benefit each other. Aerobic bacteria would handle the oxygen toxification for the anaerobic partner whereas the anaerobic partner protects the aerobic symbiote and ingested food. 

Both flagella and pili, are the extended part of the bacterial cell and behave like locomotory structure. Flagella are like a whip or tail-like while pili are best described as hair-like. Flagella actually extend from the interior of the cell body while pili are strictly surface appendages. They are made up of different proteins- flagellin (or flagella) and pilin (or pili). They serve different purposes for the cell. Flagella are used primarily for propulsion and movement but can also be used to sense certain chemicals and temperature. Pili are used more for surface recognition and can allow certain bacteria to come together and exchange DNA with one another.
So, the correct answer is option D.

The ribosomes in the eukaryotic cell are composed of the 80S type, with two subunits 60S and 40S. The ribosomes are attached to the surface of the endoplasmic reticulum with the help of glycoproteins, ribophorin I and II. The larger subunit 60S attaches with these glycoproteins to form an attachment with the ER. Thus, the correct answer is option A. 

Flagella is the locomotory structure in bacteria. The number and location of flagella are distinctive for each genus. There are four types of flagellar arrangement.

1. Monotrichous: Single polar flagellum, e.g., Vibrio cholerae.  
   
2. Amphitrichous: Single flagellum at both ends, e.g., Alcaligenes faecalis. 
3. Lophotrichous: Tuft of flagella at one or both ends, e.g., Spirilla.
4. Peritrichous: Flagella surrounding the cell, e.g., Typhoid bacilli.

The ribosomes are the cellular organelles which are involved in the translation of the mRNA to form protein. The ribosomes are attached to the surface of endoplasmic reticulum and involved in the production of proteins, enzymes and hormones. The smooth ER is associated with the production of the fats and lipids. These molecules are required by the cells for their structure as well as the functioning of the different biochemical pathways.

Mitochondria are the cellular organelles which are involved in the process of respiration. These organelles are double membrane-bound structure and are present in all the eukaryotic cells. They are absent in prokaryotic cells. The outer membrane is stretched but the inner membrane is folded to form the cristae which possess the oxysomes.  Thus, the correct answer is option D. 

The RER (rough endoplasmic reticulum) has many ribosomes bound to its surface. These are engaged in the synthesis of proteins are translocated into other organelles or the plasma membrane only after their synthesis is complete. Smooth ER (SER) acts as a storage organelle. It is important in the creation and storage of lipids and steroids. The ER sends many of its proteins and lipids to the Golgi apparatus. The Golgi apparatus consists of organized stacks of a disc like compartments called as Golgi cisternae. It receives lipids and proteins from the ER and dispatches them to a variety of destinations, usually covalently modifying them en route. Thus, the correct answer is option A.

Smooth ER is abundant in the liver, where it contains enzymes that metabolise various lipid-soluble compounds. These detoxifying enzymes inactivate a number of potentially harmful drugs (e.g., phenobarbital) by converting them into water-soluble compounds that can be eliminated from the body in the urine. The smooth ER is thus involved in multiple aspects of the metabolism of lipids and lipid-soluble compounds.