Unit 6 Biology Notes Cell Size

Objective 9:
Explain why cells
must be small in
order to survive
and function
DNA in the nucleus controls cell activities
The nucleus can only control a limited amount
of active cytoplasm—so the cell can’t get too
Size of cell membrane
Cells obtain nutrients and rid themselves of
waste through the cell membrane
As cell increases in size, the need for materials
as well as the waste production increases—so
surface area of the cell membrane must
increase in order to bring in enough materials
and rid the cell of its wastes.
2. Size of cell membrane
As the cell gets larger, though, the surface
area (of the cell membranes) to volume (of
the cell) ratio gets smaller.
So…if a cell is small, it has a better chance of
exchanging enough materials to support its
Objective 8:
Describe how cell
division benefits
survival of
Multicellular organisms grow (get
bigger/increase in size) because of an
increase in the number of cells
In multicelluar organisms, injuries can be
mended by making new cells.
In order to maintain certain tissues,
organisms make new cells
New organisms are made by cell division
Maintain a high surface area to volume ratio
for material exchange
Objective 3: Describe DNA replication (When,
Where, How, Why)
When does DNA replicate?
before the cell divides
Where does DNA replicate?
How does DNA replicate?
1. Enzymes unzip DNA strand (DNA polymerase)
2. New nitrogen bases pair up with each exposed
3. Result is 2 identical DNA molecules
(each new DNA molecule has one old strand and
one new strand)
Why does DNA replicate?
to make 2 identical molecules of DNA
to have DNA in each of the new cells
Objective 4: Describe
the major events in
the cell cycle.
Objective 5: Compare
the relative amount of
time for interphase
and cell division to
Objective 6: Order
and describe the four
major events of
Objective 7: Describe
the outcome of
mitotic cell division.
◦ Cells spend most of their time here
◦ Normal cell activities occur
Cell grows
Cell makes new organelles
Protein synthesis
DNA replicates
 *Once a cell copies its DNA, it usually completes the rest
of the cell cycle.
Cell Division
a. Nuclear Division (mitosis)
b. Cytoplasmic Division

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