Divide and Conquer
Growth
One of the characteristics of life is the ability to grow. In
multicellular organisms, growth is generally associated with
getting “bigger.” Physical changes that take place during the
transition in life between a young organism to a mature
organism may involve significant increases in size. How
does this growth happen? Growth is the result of events that
occur at the cellular level. Individual cells increase in size
as they use nutrients and energy to build new cellular
components. These nutrients are taken into the cell through
the cell membrane and are metabolized.
When the cell is small, areas in the cell where metabolic
activity occurs are very near to the membrane through which
the materials are being transported. However, as cells
increase in size, the interior portions of the cell become
farther and farther from the membrane. The distance from
where nutrients enter the cell to where they are used
increases. As a result, the functioning of the cell becomes
less efficient. Waste substances accumulate in the cells.
They must be moved from the interior of the cell where they
are formed to outside the cell. The larger the cell is, the
longer that takes. And the longer that takes, the more energy
is used.
Adapted from The Matter of Life, LE 11
chromosome.
Following chromosome duplication and
separation, division of the cytoplasm occurs and two
daughter cells are formed.
Repair and Maintenance
Repair and maintenance of a healthy organism relies on the
ability of cells to divide in order to replace worn-out or
damaged structures. When overexposure to the sun causes
skin damage, for example, the injured and dead skin cells are
sloughed off and cell division soon replaces the lost cells.
Similarly, cell division is essential in wound healing. In a
human adult, cell division replaces approximately 200
million worn-out cells per minute!
For many years, scientists believed that muscle cells and
nerve cells had a limited capacity to regenerate themselves
when damaged or destroyed. A body builder's muscle mass
increases not as a result of cell division, but rather because
of an increase in the size of the individual cells in the
muscle. Similarly, scientists believed that damage to nerve
cells almost always resulted in the permanent loss of
essential functions. Recent research, however, gives new
hope to individuals who suffer damage to their nerves or
muscles. 
For many types of cells, the method for dealing with this
problem is to divide and form two smaller cells ("daughter
cells") out of one oversized cell. By dividing into two
smaller cells, the large cell increases its surface-to-volume
ratio. This then increases the efficiency with which
substances can reach all cellular components in the interior
of the cell.
Divvying Up the Goods
The mechanism of cell division is a precisely orchestrated
event that occurs in the same pattern in every eukaryotic
cell. (There is, however, some variation in cells that
eventually form eggs and sperm cells – we'll study that
later.) Cell division requires that the cell (1) duplicate all the
information that the daughter cells will need to carry out the
exact same metabolic activities and life sustaining functions
as the starting cell; (2) transfer this information to the
daughter cells; and (3) provide the daughter cells with
enough of the cellular machinery to be able to sustain
themselves until they are making their own cellular parts and
products. How does this happen?
All of the information needed by a cell to carry out its
functions is stored in its DNA. In eukaryotic cells the DNA
in association with certain proteins is located in the nucleus
within structures called chromosomes. The first step, long
before cell division, is to ensure that the chromosomes are
faithfully duplicated, for it is these structures that will carry
all the required information to the daughter cells to ensure
that they are exactly like the starting cell.
The chromosomes are then sorted in such a way to ensure
that each daughter cell receives one copy of each
Analysis Questions
Directions: Answer the following Q's in your journal.
1. Describe what might happen to a cell that grew very large
but was unable to divide.
2. Why is it important that DNA copies are distributed
equally during cell division?
3. Why is it important that each daughter cell receive
enough cellular organelles such as mitochondria and
ribosomes? List which processes a cell might be unable
to accomplish if it were lacking one of these organelles.
4. Explain why cell division requires both energy and
building blocks.
5. Name a specific disease or condition caused by nerve or
muscle damage.