Chromosomes
The interphase nucleus has a loose and distinct network of nucleoprotein fibers called chromatin. But during different stages of cell division, cells show structured chromosomes in place of the nucleus. Chromatin contains DNA and some basic proteins called histones, some non-histone proteins, and also RNA. A single human cell has an approximately 2-meter-long thread of DNA distributed among its forty-six (twenty-three pairs) chromosomes.
Differences between nucleus and nucleolus.
- The nucleus represents the whole eukaryotic complex that contains genetic information, while the nucleolus is a component of the nucleus.
- The nucleus is covered by a two-membrane envelope, whereas the nucleolus does not have a covering membrane.
- The nucleus controls the structure and working of cells, and the nucleolus synthesizes ribosomal subunits.
What is Nucleus? | Class 11 Biology
The cell is the basic structural and functional unit of living organisms. In biology, the cell has the same central position as that of an atom in the physical sciences. The bodies of living organisms are made up of microscopic units called cells. Cells have evolved a variety of different lifestyles. Many organisms, such as bacteria (both archaebacteria and eubacteria), protozoa(e.g., amoeba), and yeasts consist of single cells (called unicellular organisms) that have the ability to perform a function like self-replication. More complex organisms, called multicellular organisms, those consists of collections of cells that perform particular functions.
Term cell was discovered by Robert Hook in his book Micrographia. The size of the cell is 10-16 micrometers. The shape of the cell may be polygonal, disc-like amoebic, thread-like, cuboid or irregular, oval, hexagonal, circular, branched, elongated, etc. The cells are too small to be seen with naked eyes. So, it is studied with the help of microscopes.