Question 1

What is a prokaryotic cell?

Accepted Answer

A prokaryotic cell is a cell that lacks a true, membrane-bound nucleus and membrane-bound organelles. Its genetic material — a single circular DNA molecule called the nucleoid — lies free in the cytoplasm. Bacteria and cyanobacteria (Kingdom Monera) are prokaryotes. They are typically 1–10 µm in size, smaller than eukaryotic cells.

Question 2

What is the nucleoid and how is it different from a nucleus?

Accepted Answer

The nucleoid (or genophore) is the region of the prokaryotic cytoplasm containing the single, circular, naked, supercoiled DNA molecule. Unlike a true nucleus, it has NO nuclear membrane, NO nucleolus and the DNA is not associated with histone proteins. It is therefore called an 'incipient nucleus'.

Question 3

What is a mesosome and what are its functions?

Accepted Answer

A mesosome is an infolding (extension) of the plasma membrane into the cytoplasm, in the form of vesicles, tubules and lamellae. Its functions include respiration, secretion, increasing surface area of the plasma membrane and enzyme content, formation of the cell wall, DNA replication and distribution of DNA to daughter cells during cell division.

Question 4

Why do prokaryotes have 70S ribosomes and not 80S?

Accepted Answer

Prokaryotic ribosomes are 70S, made of a 50S large subunit and a 30S small subunit (S = Svedberg unit, a measure of sedimentation rate). Eukaryotic cytoplasmic ribosomes are 80S (60S + 40S). Interestingly, mitochondria and chloroplasts also contain 70S ribosomes — evidence for the endosymbiotic theory of their bacterial origin.

Question 5

What is the difference between Gram-positive and Gram-negative bacteria?

Accepted Answer

Gram-positive bacteria have a thick peptidoglycan cell wall (20–80 nm) and no outer membrane, so they retain the crystal violet stain and appear purple. Gram-negative bacteria have a thin peptidoglycan wall (2–7 nm) plus an outer membrane containing lipopolysaccharide (LPS); they lose the crystal violet, take up the safranin counterstain, and appear pink/red. This difference, discovered by Christian Gram, is a key basis of bacterial classification.

Question 6

What are plasmids and why are they important?

Accepted Answer

Plasmids are small, circular, double-stranded DNA molecules that exist outside the main bacterial chromosome and replicate independently. They carry extra genes such as antibiotic resistance (R-factors) and can be transferred between cells by conjugation. In biotechnology, plasmids are the most widely used vectors for inserting foreign DNA into host cells (recombinant DNA technology).

Question 7

Is the prokaryotic cell an important NEET topic?

Accepted Answer

Yes. The prokaryotic cell is covered in the Class 11 chapter 'Cell: The Unit of Life' and links to 'Biological Classification' (Kingdom Monera). NEET regularly tests the absence of a nuclear membrane and organelles, the nucleoid, mesosome, 70S ribosomes, cell wall / peptidoglycan, Gram staining, plasmids, and flagellar structure. It is a high-yield, frequently examined topic.

Prokaryotic Cell — Bacterial Anatomy in 3D

Practice

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