Cytoplasm and Its Components MCQ - Practice Questions with Answers

• It is crystal-colloidal complex that forms the protoplasm excluding its nucleoid. 
• Membrane-bound cell organelles are absent in cytoplasm. 
• The structures found in the cytoplasm are mesosome, ribosome and chromatophores. 

Mesosome 

• Infolding of the plasma membrane, consisting of vesicles, tubules and lamellae.
• Mesosome is comparable to mitochondria in eukaryotes. It contains respiratory enzymes.
• Mesosomes can be connected to nucleoid. If it is not joined to nucleoid, it is called chondroid.

Ribosome 

• These are small, membrane-less sub microscopic ribonucleoproteins.  
• Ribosomes are found freely in the cytoplasm or fixed to the plasma membrane.
• Ribosomes of bacteria are the 70s in nature. 
• Each ribosome has two subunits i.e. large subunit (the 50S) and a small subunit (30S). 
• Ribosomes are involved in protein synthesis. 

Chromatophores

• These structures are found in autotrophic bacteria.
• Chromatophores may be covered by a normal phospholipid membrane or by a proteinaceous membrane.
• Chromatophores are mainly involved in photosynthesis (they are a substitute of chloroplast). 
• Photosynthetic pigments like bacteriochlorophyll, bacteriopheophytin and carotenoids are found in chromatophores. 

Inclusion bodies
These are non-living structures found in the cytoplasm. These are of 3 types-

• Gas vacuole- found in cyanobacteria, purple and green bacteria. It consists of gas vesicles surrounded by a proteinaceous membrane. These gas vacuoles protect the bacteria from harmful radiations.
• Inorganic inclusions- these include volutin, sulphur, iron, magnetite granules. 
• Food reserve- the reserve food particles include cyanophycean starch, lipid globules, glycogen, neutral fats and protein granules. 

 Nucleoid: 

• Nucleoid represents the genetic material of bacteria and other prokaryotes. 
• Nucleoid includes single, supercoiled, the circular strand of DNA duplex. 
• DNA of prokaryotes is considered naked because it is not associated with histone proteins and also not enveloped by the nuclear membrane.
• The proteins in nucleoid are different from eukaryotic histone proteins. These are called polyamines or nucleoid proteins.

Extrachromosomal DNA in bacteria- Plasmid

• The plasmid is self-replicating, extrachromosomal, double-stranded and circular DNA found in bacteria.
• Plasmids can express specific characters such as antibiotic resistance in bacteria.
• Plasmids temporarily associated with nucleoid are known as episomes.