Nucleus MCQs Quiz | Class 9
This quiz covers Class IX Science (Code 086), Unit II: Organization in the Living World, specifically focusing on the Nucleus. The questions address the role of the nucleus as the control center, its structure, and the basic concept of genetic material. Click Submit to check your answers and download the PDF solution.
Understanding the Nucleus
The nucleus is often referred to as the “brain” or control center of the cell. It plays a critical role in cellular reproduction and directs the chemical activities of the cell. In Class 9 Science (Unit II), understanding the structure and function of the nucleus is essential for grasping how life is organized at the cellular level.
Key Structural Components
The nucleus is separated from the cytoplasm by a double-layered covering called the nuclear membrane. This membrane has pores (nuclear pores) that allow the transfer of material from inside the nucleus to the outside (into the cytoplasm).
- Nucleoplasm: The fluid substance inside the nucleus.
- Nucleolus: A spherical body within the nucleus involved in ribosome synthesis.
- Chromatin material: An entangled mass of thread-like structures visible when the cell is not dividing.
Genetic Material: DNA and Chromosomes
When a cell is about to divide, the chromatin material condenses into rod-shaped structures called chromosomes. Chromosomes contain information for inheritance of features from parents to the next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules.
| Component | Description |
|---|---|
| Chromosomes | Composed of DNA and protein; carry hereditary information. |
| DNA | Contains the instructions necessary for constructing and organizing cells. |
| Genes | Functional segments of DNA that determine specific traits. |
Prokaryotic vs. Eukaryotic Nucleus
In some organisms like bacteria, the nuclear region is poorly defined due to the absence of a nuclear membrane. This undefined nuclear region containing only nucleic acids is called a nucleoid. Such organisms are called prokaryotes (pro = primitive, karyon = nucleus). Organisms with a well-defined nucleus and nuclear membrane are called eukaryotes.
Quick Revision Points
- The nucleus controls cell metabolism and cell division.
- It contains the genetic material essential for inheritance.
- The nuclear membrane separates the nucleus from the cytoplasm.
- Chromatin condenses into chromosomes only during cell division.
Extra Practice Questions
- Why is the nucleus called the director of the cell?
- Differentiate between chromatin and chromosomes.
- What is the significance of nuclear pores?
- Name the protein found in chromosomes.
- Define nucleoid.
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