Structure of the Cell > Nucleus: “Brain” of the Cell

The nucleus is called the brain of the cell, as it controls all the activities of cells. It contains a double-layered nuclear membrane with pores that allow the transfer of material in and out of the cell.

• The nucleus contains chromosomes. Chromosomes contain information for the inheritance of features from parents to the next generation in the form of DNA (deoxyribonucleic acid) molecules.
• It controls all metabolic activities of the cell and also cell division. And involved in the transmission of hereditary characters from parents to offspring.
• The chromosome is available in the form of chromatin material in non-dividing cells. Whenever the cell is about to divide, the chromatin material gets organised into chromosomes and performs cell division.
• The nucleus plays a central role in cellular reproduction in unicellular organisms.
• Prokaryotes have an undefined nuclear region containing only nucleic acids and are called a nucleoid.

Nucleus

1. Aim: To observe cheek cells and identify the nucleus using methylene blue stain.

2. Requirements: clean glass slide, ice cream spoon, needle, methylene blue stain, cover slip, microscope.

3. Procedure

• Place a drop of water on a clean glass slide.
• Gently scrape the inner surface of your cheek with an ice cream spoon.
• Use a needle to transfer a small amount of the cheek cell material into the water drop on the slide.
• Spread the material evenly and add a drop of methylene blue stain.
• Carefully place a cover slip on the smear and observe under a microscope.
• Notice the blue-stained nucleus in the cells.

4. Observation: The blue nucleus is visible in cheek cells. In onion cells stained with iodine, a dark round spot (nucleus) is seen, surrounded by a double-layered membrane with pores.

5. Conclusion: The nucleus, visible as a dark spot, is surrounded by a membrane and contains chromatin fibres that become chromosomes during cell division. Genes are located on these chromosomes. The experiment demonstrates the structure and importance of the nucleus in cells.

The nucleoplasm contains a network of dark-coloured fibres called chromatin fibres.

• The nucleus is the largest, spherical organelle located centrally in the cytoplasm, enclosed by a double-layered membrane with pores.
• It contains nucleoplasm, one or more nucleoli, and a network of chromatin fibres.
• Nucleolus produces ribosomes and assists in protein synthesis by forming and storing RNA.
• Chromatin fibres (made of DNA) condense into chromosomes during cell division and carry hereditary information.
• The nucleus controls all cell functions, and its removal leads to cell death.