Download CELLULAR GROWTH 3 Reasons Why Cells Are Small

CELLULAR GROWTH
Cells grow until they reach their size limitations,
then they either stop growing or divide
3 Reasons Why Cells Are Small
1. Surface Area to Volume
a. Surface area refers to the area covered
by the plasma membrane
b. Volume refers to the space taken up by
the inner contents of the cell
As a cell grows the volume increases more rapidly
than the surface area. The surface area to
volume ratio decreases. Cells would have
difficulty moving materials across the cell.
2. Transport of Substance- Once inside the
cell materials move by diffusion and
transport proteins. Cells remain small to
maximize the ability to transport nutrients
and waste products
3. DNA Overload- The ability of the cells to
communicate instructions for cellular
functions would be harmed if cells were too
large.
THE CELL CYCLE
Once cell becomes too large it must either stop
growing or divide. Most cells will eventually
divide
 Prevents cells from becoming too large
 Is a method for cells to reproduce
 Provides a method for organisms to grow
 Provides a method to heal from injuries
The end result of the cell cycle is two identical
cells
Cell Cycle
Interphase
Interphase—90% of cell cycle
S
(DNA synthesis)
G1
(Cell growth)
G2
(growth and
preparation for
mitosis)
Cytokinesis
Mitosis
Control of
Cell Cycle
A. Cell Growth G1 checkpoint
Determines if the cell is ready to divide
B. DNA synthesis G2 checkpoint
DNA synthesis is checked
C. Mitosis checkpoint
Signals the start of First Growth Phase
1. First Growth Phase (G1)
cell grows and carries on normal function.
Major portion of cell’s life
nerves and some muscle cells spend entire life in
this phase
2. Synthesis Phase (S)
DNA is copied; each chromosome has a pair of
chromatids
3. Second Growth Phase (G2)
Microtubules are rearranged and preparations
made for the nucleus to divide
4. Mitosis
Process where the nucleus divides into 2 nuclei
and each one has the same number of
chromosomes
5. Cytokinesis
Process where cytoplasm divides and a new cell is
produced