(1) The basic structural and functional unit in people and all living things. Each cell is a small container of chemicals and water wrapped in a membrane.
Each cell in the human body – there are 100 trillion cells in each of us – contains the entire human genome, all the genetic information necessary to build a human being. This information is encoded within the cell nucleus in 6 billion base pairs, subunits of DNA, packaged in 23 pairs of chromosomes, one chromosome in each pair coming from each parent. Each of the 46 human chromosomes contains the DNA for thousands of individual genes, the units of heredity.
There are notable exceptions including the egg and sperm cells (each of which have only 23 chromosomes containing half the usual amount of DNA) and mature red blood cells (which no longer have a nucleus and so lack chromosomes and DNA).
(2) 1. the structural, functional and biological unit of all organisms
An autonomous self-replicating unit that may exist as functional independent unit of life (as in the case of unicellular organism), or as sub-unit in a multicellular organism (such as in plants and animals) that is specialized into carrying out particular functions towards the cause of the organism as a whole.
A membrane bound structure containing biomolecules, such as nucleic acids, proteins, and polysaccharides
There are two distinct types of cells: prokaryotic cells (e.g. bacterial cells) and eukaryotic cells (e.g. plant or animal cell). The main difference between the two is a well-defined nucleus surrounded by a membranous nuclear envelope present only in eukaryotic cells. Despite this difference they share a number of common features: the genetic information is stored in genes, proteins serve as their main structural material, ribosomes are used to synthesize proteins, adenosine triphosphate is the main source of metabolic energy to sustain various cellular processes, and a cell membrane that controls the flow of substances into and out of the cell.