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Nucleus and nucleoid are the dynamic centres of the cell. The cell is the basic structural and functional unit of all living organisms. It is the centre of the location of the genetic material called DNA (Deoxyribose nucleic acid). It may be in the form of chromosomes or chromatin reticulum surrounded by a nuclear membrane or simply a naked genetic material floating in the cytoplasm.
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Key Terms: Cell, prokaryotic cell, eukaryotic cell, nucleus, nucleoid.
Cell
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The cell is the basic structural and functional unit of all living organisms.
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Animal Cell
Types of Cells
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Prokaryotic cell
The cell without a definite nucleus is called the prokaryotic cell. Organisms belonging to Monera consist of prokaryotic cells. E.g., Bacteria and blue-green algae.
Prokaryotic cell
Eukaryotic cell
The cell with a definite nucleus surrounded by a nuclear membrane is called the eukaryotic cell. All organisms except those that belong to Monera consist of eukaryotic cells. E.g., Protista, fungi, plants and animals.
Eukaryotic cell
Nucleoid
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The region of concentration of genetic material in the cytoplasm of the prokaryotes is called the nucleoid. It consists of naked DNA without chromatin reticulum and nuclear membrane. It is the dynamic centre of the prokaryotic cell. It is also called genophore or the prokaryotic chromosome.
Nucleoid
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Nucleus
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The part of the eukaryotic cell with chromatin reticulum surrounded by a definite nuclear membrane is called the nucleus. It is the dynamic centre of the eukaryotic cell.
Nucleus
Difference between Nucleus and Nucleoid
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The difference between nucleus and nucleoid are tabulated as follows:
| Nucleus | Nucleoid |
|---|---|
| It is the characteristic feature of all eukaryotic cells. | It is the characteristic feature of all prokaryotic cells. |
| It is present in all living organisms except those that belong to monera. | It is present only in organisms that belong to Monera. |
| It is surrounded by a double membrane called the nuclear membrane. | It is not surrounded by any membrane. |
| It consists of a network of genetic material called chromatin reticulum and chromosomes. | There are no structures like chromatin reticulum and chromosomes in the nucleoid. |
| DNA is surrounded by a protein coat to form chromatin reticulum and chromosomes. DNA is packed by histone proteins. | DNA is naked without a protein coat.. DNA is not packed by histone proteins. |
Things to Remember
- Cell is the basic structural and functional unit of all living organisms.
- Cell without a definite nucleus is called the prokaryotic cell.
- Organisms belonging to Monera consist of prokaryotic cells. E.g., Bacteria and blue-green algae.
- Cell with a definite nucleus surrounded by a nuclear membrane is called the eukaryotic cell.
- All organisms except those that belong to Monera consist of eukaryotic cells. E.g., Protista, fungi, plants and animals
- The region of concentration of genetic material in the cytoplasm of the prokaryotes is called the nucleoid.
- The part of the eukaryotic cell with chromatin reticulum surrounded by a definite nuclear membrane is called the nucleus. It is the dynamic centre of the eukaryotic cell.
- The nucleus is surrounded by a nuclear membrane with nuclear pores.
- The nucleus consists of nucleoplasm, chromatin reticulum, and nucleosome.
- DNA is single-stranded in the nucleoid and double-stranded in the nucleus.
- The nucleus consists of many chromosomes and the nucleoid consists of a single chromosome.
- In the nucleus, DNA is associated with histone proteins, whereas it is not associated with histone proteins in the nucleoid.
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Sample Questions
Ques: What is the basic unit of life? What is its dynamic centre? (2 marks)
Ans: The cell is the basic structural and functional unit of all living organisms. The nucleus and nucleoid are the dynamic centres of the cell.
Ques: Where is the genetic material located in prokaryotic and eukaryotic cells? (2 marks)
Ans: The centre of the location of the genetic material is a nucleoid in prokaryotic cells. The centre of the location of the genetic material is a nucleus in eukaryotic cells.
Ques: What is the demarcating layer between cytoplasm and nucleoplasm? What is the dynamic centre of the cell? (2 marks)
Ans: The demarcating layer between cytoplasm and nucleoplasm is called the nuclear membrane. The dynamic centre of the cell is the nucleus.
Ques: Draw a neat labelled diagram of the nucleus? (2 marks)
Ans: The following is the diagram of the nucleus.
Ques: What are the chief differences between a prokaryotic cell and a eukaryotic cell? (3 marks)
Ans: Prokaryotic cell: The cell without a definite nucleus is called the prokaryotic cell. Organisms belonging to Monera consist of prokaryotic cells. E.g., Bacteria and blue-green algae.
Eukaryotic cell: The cell with a definite nucleus surrounded by a nuclear membrane is called the eukaryotic cell. All organisms except those that belong to Monera consist of eukaryotic cells. E.g., Protista, fungi, plants and animals
Ques: What is the difference between chromatin reticulum and chromosome? Where are they present? (3 marks)
Ans: The network of genetic material in the nucleus of eukaryotic cells is called the chromatin reticulum. The chromatin reticulum is condensed into thread-like structures called chromosomes during cell division. The chromatin reticulum is present in the nucleus. Chromosomes are present in the nucleus and the cytoplasm during cell division.
Ques: Describe the DNA of nucleoid and nucleus? (3 marks)
Ans: DNA is the chief genetic material in living organisms. It stores and transmits characters from parents to offspring. It is naked and single-stranded in nucleoids of prokaryotic cells. It is not packed in histone proteins in prokaryotic cells. It is sheathed and double-stranded in the Nucleus of eukaryotic cells. It is packed in histone proteins in eukaryotic cells.
Ques: Write any five differences between a nucleus and a nucleoid. (5 marks)
Ans: The following are the differences between a nucleus and a nucleoid:
| Nucleus | Nucleoid |
| It is the characteristic feature of all eukaryotic cells. | It is the characteristic feature of all prokaryotic cells. |
| It is present in all living organisms except those that belong to monera. | It is present only in organisms that belong to Monera. |
| It is surrounded by a double membrane called the nuclear membrane. | It is not surrounded by any membrane. |
| It consists of a network of genetic material called chromatin reticulum and chromosomes. | There are no structures like chromatin reticulum and chromosomes in the nucleoid. |
| DNA is surrounded by a protein coat to form chromatin reticulum and chromosomes. DNA is packed by histone proteins. | DNA is naked without a protein coat.. DNA is not packed by histone proteins. |
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