Cell growth & Division:
Living things grow by producing more cells, not by existing cells getting bigger. There
are two reasons for this:
 The larger a cell becomes, the more demands the cell places on its DNA.
 The cell has more trouble moving enough nutrients and wastes across the cell
membrane.
o Nutrient and waste exchange depends on the surface area of the cell or cell
membrane, but the rate at which nutrients are used up and waste is
produced depends on the volume of the cell.
o When the surface area of a cell increases, the volume increases much more
rapidly meaning more nutrients are needed for the cell and more wastes
are produced than can be handled by the cell membrane.
Cell Division- the process by which a cell divides into 2 new daughter cells.
 In eukaryotic cells there are 2 stages to cell division.
o Mitosis- division of the cell nucleus
o Cytokinesis- division of the cytoplasm
Chromosomes: carry the genetic information that is passed from 1 generation of cells to
the next.
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Condense into compact, visible structures during the beginning of cell division
Each chromosome is replicated at the beginning of cell division therefore each
chromosome consists of 2 identical sister chromatids.
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When the cell divides the sister chromatids separate from each other and one goes
to each of the 2 new cells.
Each chromatid is attached to an area called the centromere that is usually
located near the middle.
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The Cell Cycle:
During the cell cycle, a cell grows, prepares for division and divides to form 2 daughter
cells, each of which then begins the cycle again.
Interphase- the in-between period of growth, divided into 3 phases:
 G1 phase: cell growth takes place here and new proteins and organelles are made.
 S Phase: chromosomes are replicated and new DNA molecules are made
 G2 phase: shortest of the 3 phases, organelles and molecules required for cell
division
Mitosis: “M Phase” divided into 4 phases.
 Prophase

o Takes as much as 50-60% of the time of mitosis
o Chromosomes become visible
o Centrioles, 2 tiny structures located in the cytoplasm near the nuclear envelope,
separate and go to opposite sides of the nucleus.
o
o Spindle, a fanlike microtubule structure that helps separate the chromosomes,
forms
o
o Chromosome attach to the spindle at their centromeres
o Nucleolus disappears and nuclear membrane breaks down
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Metaphase
o Lasts only a few minutes
o Chromosomes line up across the center (middle) of the cell
o
Anaphase:
o Centromeres split and sister chromatids separate to become individual
chromosomes.
o
Telophase:
o Chromosomes begin to unwind
o Nuclear envelope reforms around the chromosomes
o Spindle breaks apart
o Nucleolus becomes visible in each daughter nucleus
o
Cytokinesis: division of the cytoplasm
 Usually occurs at the same time as Telophase
 In most animal cells the cell membrane is drawn inward and
pinches the cytoplasm into 2 nearly equal parts
 In plant cells a cell plate gradually forms until it develops into a
separating membrane then a cell wall appears.
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Uncontrolled cell growth
Cancer: a disorder in which some of the body’s own cells lose their ability to control
growth.
 These cells do not respond to signals that regulate the growth of most cells
 Can be caused by various things
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