Download Why Don`t Cells Grow Indefinitely? Cell Size 1617

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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 multicellular 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 cells. This process seems to be controlled by simple physical laws.
1.
Label the following organelles in Cell B: Cell membrane, cytoplasm, endoplasmic reticulum, Golgi
apparatus, mitochondria, nucleus, vacuole. If more than one, use additional lines to identify them all.
2. Are the two cells plant or animal cells? How can you tell?
3. Circle Cell A or Cell B for each of the following:
a. Has a larger surface area?
b. Has more cell membrane?
c. Has a larger volume?
d. Has more mitochondria?
e. Would take longer for a glucose molecule to get through the cell
membrane and to the mitochondria?
f. Would take longer for a carbon dioxide molecule produced in the
mitochondria to get out through the cell membrane?
g. Which cell has more channels in the cell membrane to transport
molecules into and out of the cell?
Cell A
Cell A
Cell A
Cell A
Cell B
Cell B
Cell B
Cell B
Cell A
Cell B
Cell A
Cell B
Cell A
Cell B
BY THE NUMBERS
Effect of Cell Size on Cell Dimensions and Ratios
Cell
Area of One
Side (cm2)
Total Surface Volume of
Area (cm2)
Cell (cm3)
Surface Area
: Volume
Ratio
Index
(SA ÷ V)
Distance
from edge
to center
(cm)
A (1 cube)
B (8 cubes)
C (64 cubes)
4. Describe the change in the surface area of the cube (or circle) each time the length of the side (or diameter) doubles.
5. Describe the change in the volume of the cube (or circle) each time the length of the side (or diameter) doubles.
6. As a shape gets larger, which increases faster? Surface Area or Volume (Circle your answer.)
7. How does the surface area-to-volume ratio change as cell size increases?
8. What kind of relationship does the Index have with cell size?
With ratio?
PUTTING IT ALL TOGETHER
Anything that the cell takes in, such as oxygen or food, or lets out, such as carbon dioxide, must pass through the
cell membrane. The cell contents, including the nucleus and the cytoplasm, use food and oxygen and produce
wastes.
9. Which column of the table would represent a quantity regarding the cell membrane?
10. Which column of the table would represent a quantity regarding the cell contents?
11. As a cell grows larger and accumulates more contents, will it need more or less cell membrane to survive?
Explain.
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. As a cell grows larger, does the surface area-to-volume ratio get larger, get smaller, or remain the same?
(circle your answer) How might this affect the diffusion of materials throughout a cell?
14. Is it more desirable for a cell to have a small or large surface area-to-volume ratio? Explain in terms of cell
functions.
15. How does a cell’s Index affect its ability to stay alive?
16. How can the surface area-to-volume ratio be increased in a large cell?
17. Explain why one cell (see Model 1) might need more mitochondria than another, and why one cell type might
need more mitochondria than another.
18. Is bigger always better for a cell?
19. A cylinder with a diameter of 1 cm and a length of 3.5 cm has a surface area of 12.57 cm2 and a volume of 2.75
cm3. How do the surface area, volume and surface area-to-volume ratio of this cylinder compare to the 2 cm cube?
21. Why would a cylindrical shape be more efficient for large cells like nerve or muscle cells?