Name: ______________________________
Cell Division
Directions: Read and Highlight then answer the questions.
What has to happen for a cell to divide? Maybe some addition and subtraction?
Just kidding. When we talk about the division of a cell, we are talking about how
a cell reproduces. For cells to divide they have to recreate themselves much like
a copier recreates all of the homework I hand out. Ok, maybe it isn’t that simple,
but it does follow a similar idea. When a cell copies itself, it is an exact copy. But
that is just one step in the process. If you look at the picture to the right, you
can see a cell dividing. In order to divide, one cell goes through a process of
copying the organelles inside with one very specific organelle making certain the
copying goes just right (chromosomes). What happens if the copying goes wrong
though? Or worse yet, what if our cells stop copying all together?
1. When a cell copies itself…
a. It has equal parts of both parents.
b. It’s an exact copy of the parent cell.
c. It is completely different than the parent cell.
d. It dies off creating a new cell.
Imagine the first stages of life. In humans, an egg is fertilized
(birds and bees stuff ) forming the first cell. But humans are
made up of trillions of cells, so where do the new cells come
from? Remember that according to cell theory, all cells must
come from existing cells. From that one cell, an entire baby will
develop. And that’s not just for humans. Every living species
(eukaryotic at least) on earth goes through a similar process of
copying itself.
How does a new life go from one cell to so many? Simply put, the
cell divides in half, creating two cells. Then those two cells divide,
for a total of four cells. The new cells continue to divide and
divide. One cell becomes two, then four, then eight, and so on.
Each division can take anywhere from 20 minutes to 24 hours to
occur.
2. A cell reproduces going from 1 cell to 2 cells to 4 cells to 8 cells and on to which of the following correct
answers?
a. 16 to 32 to 64 to 128 and so on.
b. 12 to 24 to 48 to 96 and so on.
c. 10 to 14 to 18 to 22 and so on.
d. 24 to 72 to 216 to 648 and so on.
Besides the development of a baby, there are many other reasons that cell division is necessary for life:
 To grow and develop, you must form new cells. Imagine how often your cells must divide during a growth
spurt. Growing just an inch requires countless cell divisions.
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Cell division is also necessary to repair damaged cells. Imagine you cut your finger. After the scab forms, it
will eventually disappear and new skin cells will grow to repair the wound. Where do these cells come
from? Some of your existing skin cells divide and produce new cells.
Your cells can also simply wear out. Over time you must replace old and worn-out cells. Cell division is
essential to this process. Every 20 years, your body recreates itself making an entire new you.
3. What would happen if the cells in your body stopped going through reproduction?
a. Nothing because your cells don’t need to reproduce.
b. You would stay the same size forever.
c. You would die because your body couldn’t heal itself.
d. You would slowly shrink as older cells died off.
The Cell Cycle
The process of cell division in eukaryotic cells (remember eukaryotic cells have a nucleus) is carefully
controlled. The cell cycle is the lifecycle of a cell, with cell division happening at the end of the cycle. This cycle
has a series of steps that lead to cell division.
The cell cycle can be divided into two main components, interphase and mitosis. Interphase is when cells
perform their everyday functions just like we did in the cell factory. During interphase, cells spend most of
their time creating a 2nd set of organelles. Mitosis is when the cell prepares to
become two cells.
This life cycle is like a clock as cells spend most of their time in interphase (the letter
“I” in the picture to the right) and only a small amount of time in mitosis (lighter color
“M”). As a clock, interphase would be go from midnight all the way to 11:00 pm (23
hours). Mitosis would then go from 11:00 PM to midnight (1 hour). Once the cell
finishes mitosis, it goes back into interphase getting ready to repeat the process again.
4. What step of the cell cycle is the longest?
a. Mitosis
b. Interphase
c. Cytokinesis
d. Restphase
5. Why do they call a cell’s life a “cell cycle”?
a. Because it starts over each time a new cell is reproduced.
b. Because it turns on and off just like washing machine cycle.
c. Because it ends after reproduction never to start again.
d. Because cells create a 2nd set of organelles.
6. Interphase used to be considered the “resting” stage of the cell cycle. Why is this not correct?
a. Because cells are unable to rest during interphase.
b. Because cells are busy making protein in the ribosome during interphase.
c. Because cells can only respond or adapt during interphase.
d. Because cells are creating a 2nd set of organelles during interphase.