Cell Division and Growth
Date _____
Name __________________
Introduction
The cell cycle allows multicellular organisms to grow and divide and single-celled organisms to reproduce.
Figure one Caption: A sea urchin begins life as a single cell that (a) divides to form two cells, visible by scanning electron
microscopy. After four rounds of cell division, (b) there are 16 cells, as seen in this SEM image. After many rounds of cell division,
the individual develops into a complex, multicellular organism, as seen in this (c) mature sea urchin.
Key Points
- All multicellular organisms use cell division for growth, maintenance, and repair of cells.
- Single-celled organisms use cell division as their method of reproduction.
- Somatic cells divide regularly; all human cells (except for the cells that produce eggs and sperm) are
somatic cells.
- Somatic cells contain two copies of each of their chromosomes (one copy from each parent) a total of
46.
- The cell cycle has two major phases: interphase and the mitotic phase.
- During interphase, the cell grows and DNA is replicated; during the mitotic phase, the replicated DNA and
cytoplasmic contents are separated and the cell divides.
Important terms
interphase - The stage in the life cycle of a cell where the cell grows and DNA is replicated
mitotic phase - Replicated DNA and the cytoplasmic material are divided into two identical
cells
somatic cell - Any normal body cell of an organism that is not involved in sexual reproduction
The Cell Cycle
The cell cycle consists of interphase and the mitotic phase.
During interphase, the cell grows and the nuclear DNA is
duplicated. Interphase is followed by the mitotic phase. During
the mitotic phase, the duplicated chromosomes are segregated
and distributed into daughter nuclei. The cytoplasm is usually
divided as well, resulting in two daughter cells
Date _____
Cell Division and Growth
Name __________________
A human, as well as every sexually-reproducing organism, begins life as a fertilized egg or zygote. Trillions of
cell divisions subsequently occur in a controlled manner to produce a complex, multicellular human. In other
words, that original single cell is the ancestor of every other cell in the body. Once an organism is fully grown,
cell reproduction is still necessary for repair. For example, new blood and skin cells are constantly being
produced. All multicellular organisms use cell division for growth, maintenance, and repair of cells. (Figure 1).
Cell division is tightly regulated because the occasional failure of regulation can have life-threatening
consequences. Single-celled organisms use cell division as their method of reproduction.
While there are a few cells in the body that do not undergo cell division, most somatic cells divide regularly. A
somatic cell is a general term for a body cell: all human cells, except for the cells that produce eggs and sperm
(which are referred to as germ cells), are somatic cells. Somatic cells contain two copies of each of their
chromosomes (one copy received from each parent). Cells in the body replace themselves over the lifetime of a
person. For example, the cells lining the gastrointestinal tract must be frequently replaced when constantly
“worn off” by the movement of food through the gut. But what triggers a cell to divide and how does it prepare
for complete cell division?
The cell cycle is an ordered series of events involving cell growth and cell division that produces two new
daughter cells. Cells on the path to cell division proceed through a series of precisely timed and carefully
regulated stages of growth, DNA replication, and division that produces two identical (clone) cells. The cell
cycle has two major phases: interphase and the mitotic phase (Figure 2). During interphase, the cell grows and
DNA is replicated. During the mitotic phase, the replicated DNA and cytoplasmic contents are separated and
the cell divides.