What is the substance within a cell nucleus that consists of DNA and RNA called?

The substance within a cell nucleus that consists of DNA and RNA is known as chromatin. Chromatin is a complex of DNA and proteins found in eukaryotic cells, where it serves to package the DNA into a more compact structure, allowing for the efficient organization and regulation of gene expression. The DNA in chromatin is tightly coiled around histone proteins, enabling the molecule to fit within the confines of the nucleus.

In contrast, chlorophyll refers to the green pigment found in plants that is essential for photosynthesis, enabling them to absorb light energy. Cytoplasm is the jelly-like substance that fills the cell and surrounds the organelles, playing a crucial role in cellular processes. The nucleolus, located within the nucleus, is responsible for producing ribosomes and is not the substance that contains DNA and RNA itself. Thus, the defining characteristic of chromatin is its role in packaging genetic material, making it the correct answer.