Understanding Prokaryotic Cells

Prokaryotic cells are simple cell types that lack a true nucleus and other membrane-bound organelles. They include bacteria and archaea. Understanding the characteristics of prokaryotic cells is fundamental in biology.

The question asks which of the given statements is not true about prokaryotic cells. Let's examine each statement:

Analyzing Statements about Prokaryotic Cells

• Statement 1: Replication of DNA occurs in cytoplasm.

  In prokaryotic cells, the genetic material (DNA) is located in a region called the nucleoid, which is part of the cytoplasm. Since there is no nucleus, processes like DNA replication happen within the cytoplasm. This statement is true.

• Statement 2: Some of them are capable of nitrogen fixation.

  Nitrogen fixation is a process where atmospheric nitrogen gas (N₂) is converted into ammonia (NH₃), a form usable by living organisms. Many bacteria, which are prokaryotes, are capable of nitrogen fixation, such as Rhizobium and cyanobacteria. This statement is true.

• Statement 3: Plasmids do not occur in prokaryotic cell.

  Plasmids are small, often circular, double-stranded DNA molecules that are distinct from a cell's chromosomal DNA. They naturally exist in bacterial cells (prokaryotes) and some eukaryotes. Plasmids are quite common in prokaryotic cells and often carry genes that provide advantages like antibiotic resistance. Therefore, stating that plasmids do not occur in prokaryotic cells is incorrect. This statement is false.

• Statement 4: Organic compounds can be produced by some of them from inorganic precursors.

  Some prokaryotes are autotrophs, meaning they can produce their own food (organic compounds) from inorganic sources. Examples include photosynthetic bacteria (like cyanobacteria) that use light energy and chemosynthetic bacteria that use chemical energy to synthesize organic molecules from inorganic precursors like carbon dioxide. This statement is true.

Identifying the Incorrect Statement

Based on the analysis, three of the statements are true characteristics of prokaryotic cells, while one statement is false.

The statement that is not true is that plasmids do not occur in prokaryotic cells. Plasmids are indeed frequently found in prokaryotic cells.

Conclusion

The statement "Plasmids do not occurs in prokaryotic cell" is incorrect regarding prokaryotic cells.