Class 9 Biology Fundamental Unit of Life Nucleus


The nucleus is small, round and membrane bound structure found in cell.

The fluid inside the nucleus surrounded by nuclear membrane is called nucleoplasm.

It controls the cell’s growth and reproduction because it contains cell's hereditary information.

It is covered by dual layer called nuclear membrane.

The nuclear membrane contains pores due to which materials can travel both inside the nucleus from its outer surrounding i.e. cytoplasm.

Fig. Nucleus of a Cell

The nucleus contains some thread like structures called chromatin. It exists during the resting stage of cell.

The chromatin contains DNA (Deoxy-ribo nucleic acid), RNA (Ribo Nucleic acid) and proteins.

The nucleus contains some rod shaped structures in a cell that contains the hereditary information. They are called chromosome.

They are formed when the chromatin condenses together when the cell is about to divide.

Chromosomes contain DNA and nuclear proteins.

They contain the hereditary information for inheritance of features from the parents to the offspring as DNA.

The DNA molecules contain the information for construction and organization of cells. Genes are the functional segments of DNA.

Human body has 23 pairs of sex chromosomes. A boy has one X chromosome and one Y chromosome whereas a girl has two X chromosomes.

The nucleus of cell divides itself to give rise to new offsprings.

Genes present in the chromosomes decide the hereditary characters.

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