Download why don`t cells grow indefinitley

WHY DON’T CELLS GROW INDEFINITELY?
Many cells grow until they reach a certain size and then divide. Why don’t cells grow indefinitely, until they become the size
of basketballs? What problems arise when a cell grows larger? Why does a cell divide into two smaller cells when it reaches a
certain size? These are all questions that scientists have attempted to resolve.
Cell division is a necessary part of the life of any multi-cellar organism and allows for growth, repair, and formation of cells for
reproduction. Growth of an organism occurs mainly by an increase in the number of cells rather than by the enlargement of
individual cell. This process seems to be controlled by simple physical laws.
PROCEDURE:
1. Cut out the four cell models. Fold and glue together all sides of each model. You will have four structures that resemble
open boxes. Imagine that each cell model has a sixth side and is a closed body.
These models represent a cell at three different stages of growth. The youngest state in growth is represented by the model
that is 1 unit to a side. The latest stage in growth is represented by the model that is 4 units to a side.
2. Examine Table 1. Next to the row marked formulas, write in the mathematical formulas that can be used to calculate the
value described in the heading of each column. Use s as the length of one side of your models.
3. Use your formulas to calculate values (except for the mass) for each of the four cell models. Record your values in Table 1.
4. Fill and level each cell model with sand.
5. Determine the mass of each sand filled cell model by using the scale. Record masses in the last column of Table. 1.
6. Calculate the ratio of total surface area to volume for each model cell. To do this, divide the cell’s total surface area by its
volume. Place your answers in Table 2.
7. Calculate the ratio of total surface area to mass for each model cell. To do this, divide the cell’s total surface area by its
mass. Place your answers in Table 2.
OBSERVATIONS
Table 1.
Measurements of cell models
Formulas
Cell size
(Length of one
side)
1
2
3
4
Area of one face
(Square units)
Total surface area
of cell (Square
units)
Volume of cell
(Cubic units)
Distance from
center to edge
(Units)
Mass of cell
(Grams)
Table 2.
Cell size (Length of
one side)
Ratios of Cell-Model Measurements
Total surface area to volume
Total surface area to mass
1
2
3
4
1. Which two formulas of your cell models best represent the contents (inside) of an actual cell?
2. As a cell grows larger, will it need more or less nutrients in order to survive?
- Explain your answer.
3. Which organelle of a cell is in charge of controlling what enters and exits a cell?
4. Which of the measurements of your cell models best represents the organelle answered in question #3?
5. As a cell grows larger, does the surface area-to-volume ratio get larger, get smaller, or remain the same?
6. As a cell grows larger, what happens to the surface area-to-mass ratio?
7. Which cell model has the greatest surface area-to-volume and surface area-to-mass ratio?
8. Give one reason why cells cannot survive when the surface area-to-volume ratio and surface area-to-mass ratios become too
small (look at previous questions).
9. How many cells with s=1 would fit into a cell with s=3?
10. Which has more total surface area, one cell with s=3 or 27 cells, each with s=1?
11. What could a cell do to a cell’s plasma membrane to increase the surface area-to-volume and surface area-to-mass ratios?
(Hint: How can you fit something large into a smaller space????)
12. As the length of a side doubles in a cell, what happens to the distance that nutrients must travel to reach the center of the
cell?
13. Look back over the lab and the questions you have answered. Describe at least two reasons why cells don’t grow
indefinitely.
1 unit
3 units
2 units
4 units