Download The Need for Cell Division

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The Need for Cell Division
You will need eight sugar cubes and a ruler
to try this comparison.
All large plants and animals, including yourself, are composed of many
cells rather than one large cell. Why? Cells can grow, but there is•l limit.
Eventually every cell reaches a size at which it must divide.
1. Predict whether many small cells or one
large cell would be more effective at
exchanging nutrients and wastes. See if
you still agree with your prediction after
you have completed this activity.
Is Smaller Better?
Think about how hir chemical messages travel in a large cell, compared
with a small ctll. Before the nucleus can tell the organdIes in the
cytoplasm what to do, it must lirst receive messages from the cell’s
surroundings. The bigger the cell is, the longer it takes for messages to
reach the nucleus, and for the rest of the cell to receive instructions from
the nucleus. Cells nust be small for these chemical messages to travel
quickly, so the cells can react to changes in their environment. Just one
example of why this is important is shown in Figure 1.
Cells also need a constant supply of nutrients to work well. Waste
products must he removed from the cell. Molecules enter into and pass
out of cells through the cell membrane. The more cell membrane there
is compared to the volume of the cell, the more efficient the cell is in
taking in nutrients and eliminating waste. The amount of cell membrane
can be described in terms of the surface area of the cell.
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Sunlight triggers a
chemical message that
travels to the nucleus.
Unit 1
0 The nucleus sends
the
a message to
ribosomes, telling them
to make melanin.
O
Measure the length and width of a sugar
cube in millimetres. The cube
represents a small cell.
•
Calculate the surface area of a single
sugar cube. To calculate surface area,
find the area of each face and then find
the sum of those areas.
To find the surface area of eight sugar
cubes, multiply the surface area of the
single cube by eight.
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The melanin blocks
sunlight, preventing
sunlight from damaging
cells below.
•
Arrange eight sugar cubes to form
a large cube. This block of sugar cubes
represents one large cell.
•
Measure the length and width of the
large cube. Calculate the surface area
of the large cube.
•
Compare the surface area of the eight
individual cubes with that of the large
cube. Which is greater?
2. Which has more cell membrane for
nutrients and waste materials to pass
through: one large cell or eight
small cells?
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Area of A = length x width
Surface area of cube = 6 x area of A
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hi! iuit’I
For most people, exposure to the Sun
makes the skin darker This happens
because our skin cells produce a
special protein called melanin. What
wouLd happen if it took a long time for
the nuclear message to reach the
ribosomes?
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Comparing the Surface Areas of Small and Large Cells
Some Big, Some Small
Understanding Concepts
Some cells in your body are larger than
others. For example, cells in fat tissue are
bigger than cells in muscle tissue. Do you
know why? If you compare the sizes of cells
and their functions, you will find that cells
that must do a lot of work are usually smaller
than cells that are not as active. The more
active a cell is, the more nutrients it needs
and the more wastes it produces. Many small
cells together are more efficient at
exchanging nutrients and waste than one
large cell. This is because a group of small
ceJls have a greater surface area than a single
large cell.
1. Which size of cell is most efficient
at transporting messages from
its surroundings to its nucleus:
small or large? Explain.
2. Which size of cell would be more
efficient at transporting nutrients
in and waste materils out—big
or small?
3. Explain why highly active cells,
such as muscle cells, tend to
be small.
Exploring
4. Which cell has the greater
Iti
surface area if their volumes
are the same:
(a) a cell shaped like a sphere
or a cell shaped like a cube?
(b) a cell with a smooth
surface or one with
many projections?
a
&lls, hssne.c, Organs, and .Sys/ems
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