Answer:
Explanation:
If cells are the main structural and functional unit of an organism, why are they so small? And why are there no organisms with huge cells? The answers to these questions lie in a cell's need for fast, easy food. The need to be able to pass nutrients and gases into and out of the cell sets a limit on how big cells can be. The larger a cell gets, the more difficult it is for nutrients and gases to move in and out of the cell.
As a cell grows, its volume increases more quickly than its surface area. If a cell was to get very large, the small surface area would not allow enough nutrients to enter the cell quickly enough for the cell's needs. This idea is explained in Figure below. However, large cells have a way of dealing with some size challenges. Big cells, such as some white blood cells, often grow more nuclei so that they can supply enough proteins and RNA for the cell's requirements. Large, metabolically active cells often have lots of cell protrusions, resulting in many folds throughout the membrane. These folds increase the surface area available for transport of materials into or out of the cell. Such cell types are found lining your small intestine, where they absorb nutrients from your food through protrusions called microvilli.
Scale of Measurements
1 centimeter (cm) = 10 millimeters (mm) = 10-2 meters (m)
1 mm = 1000 micrometers (µm) = 10-3 m
1 µm = 1000 nanometers (nm) = 10-6 m
1 nm = 10-3 µm
A small cell , has a larger surface-area to volume ratio than a bigger cell. The greater the surface-area to volume ratio of a cell, the easier it is for the cell to get rid of wastes and take in essential materials such as oxygen and nutrients. In this example, the large cell has the same area as 27 small cells, but much less surface area.
Imagine cells as little cube blocks. If a small cube cell like the one in Figure above is one unit (u) in length, then the total surface area of this cell is calculated by the equation:
height × width × number of sides × number of boxes
1u × 1u × 6 × 1 = 6u2
The volume of the cell is calculated by the equation:
height × width × length × number of boxes
1u × 1u × 1u × 1 = 1u3
The surface-area to volume ratio is calculated by the equation:
area ÷ volume
6 ÷ 1 = 6
A larger cell that is 3 units in length would have a total surface area of
3u × 3u × 6 × 1 = 54u2
and a volume of:
3u × 3u × 3u × 1 = 27u3
The surface-area to volume ratio of the large cell is:
54 ÷ 27 = 2
Now, replace the three unit cell with enough one unit cells to equal the volume of the single three unit cell. This can be done with 27 one unit cells. Find the total surface area of the 27 cells:
1u × 1u × 6 × 27 = 162u2
The total volume of the block of 27 cells is:
1 × 1 × 1 × 27 = 27u3
The surface-area to volume ratio of the 27 cells is:
162 ÷ 27 = 6
An increased surface area to volume ratio means increased exposure to the environment. This means that nutrients and gases can move in and out of a small cell more easily than in and out of a larger cell.
