Which of the following is not true about prokaryotic cells ?

Question

Accepted Answer

Option 3 is the correct answer because it states that "Plasmids do not occur in prokaryotic cells," which is not true. In fact, plasmids are small, circular, double-stranded DNA molecules that are commonly found in prokaryotic cells, particularly in bacteria. These plasmids are separate from the chromosomal DNA and can replicate independently. They often carry genes that confer advantageous traits, such as antibiotic resistance, which can be beneficial for the survival of the bacteria in certain environments.

Now, let's examine why the other options are incorrect:

1. **Replication of DNA occurs in cytoplasm**: This statement is true for prokaryotic cells. Unlike eukaryotic cells, prokaryotic cells do not have a defined nucleus. Therefore, all cellular processes, including DNA replication, occur in the cytoplasm. This is a fundamental characteristic of prokaryotic cells.

2. **Some of them are capable of nitrogen fixation**: This statement is also true. Certain prokaryotic organisms, such as some bacteria and archaea, have the ability to fix atmospheric nitrogen into a form that can be used by plants and other organisms. This process is crucial for the nitrogen cycle and supports the growth of many ecosystems.

4. **Organic compounds can be produced by some of them from inorganic precursors**: This statement is true as well. Some prokaryotic cells, such as autotrophic bacteria, can synthesize organic compounds from inorganic substances through processes like photosynthesis or chemosynthesis. This ability allows them to thrive in environments where organic nutrients are scarce.

In summary, Option 3 is the correct answer because it inaccurately states that plasmids do not occur in prokaryotic cells, whereas plasmids are indeed a common feature of these cells. The other options accurately describe characteristics or capabilities of prokaryotic cells.