NCERT Book Class 11 Biology Chapter 10 Cell Cycle and Cell Division

120 BIOLOGY

C HAPTER 10
C ELL C YCLE AND C ELL D IVISION
10.1 Cell Cycle Are you aware that all organisms, even the largest, start their life from a
10.2 M Phase single cell? You may wonder how a single cell then goes on to form such
large organisms. Growth and reproduction are characteristics of cells,
10.3 Significance of
indeed of all living organisms. All cells reproduce by dividing into two,
Mitosis
with each parental cell giving rise to two daughter cells each time they
10.4 Meiosis divide. These newly formed daughter cells can themselves grow and divide,
giving rise to a new cell population that is formed by the growth and
10.5 Significance of
division of a single parental cell and its progeny. In other words, such
Meiosis
cycles of growth and division allow a single cell to form a structure
consisting of millions of cells.

10.1 C ELL CYCLE

Cell division is a very important process in all living organisms. During
the division of a cell, DNA replication and cell growth also take place. All
these processes, i.e., cell division, DNA replication, and cell growth, hence,
have to take place in a coordinated way to ensure correct division and
formation of progeny cells containing intact genomes. The sequence of
events by which a cell duplicates its genome, synthesises the other
constituents of the cell and eventually divides into two daughter cells is
termed cell cycle. Although cell growth (in terms of cytoplasmic increase)
is a continuous process, DNA synthesis occurs only during one specific
stage in the cell cycle. The replicated chromosomes (DNA) are then
distributed to daughter nuclei by a complex series of events during cell
division. These events are themselves under genetic control.