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All living organisms are composed of cells. A cell is a small, membrane-bound compartment that contains all the chemicals and molecules that help support an organism's life. An understanding of the structure of cells is one of the first steps in comprehending the complex cellular interactions that direct and produce life.
Cells can be thought of as the building blocks of organisms. Some organisms are composed of a single cell. Others, like ourselves, are composed of trillions of cells that work together to perform the more complex functions that make us different from bacteria. There are different types of cells with specific structures that are necessary for their role in the larger organism. These differences reflect differences in the functions that each of these classes of cells is required to perform. It is difficult to imagine that humans are descendants of a single cell, but this is an accepted theory in the scientific world. Before we can understand how multiple cells can work together to create complex biological functions, it is necessary to understand what biological functions single cells are capable of performing on their own to sustain life.
Cell Size
Across all organisms, life requires the constant exchange of macromolecules and inputs of energy. Surface area-to-volume ratios affect this as many reactions and exchanges occur on the plasma membranes that form these surfaces. As cells increase in volume, this surface area-to-volume ratio decreases and yet the need for resources increases. These limitations can restrict cell size and shape.
Relevant equations:
Volume of a Sphere: \(V = (4/3)πr^3\)
Volume of a Cube: \(V = s^2 \)
Volume of a Rectangular Solid: \(V = lwh \)
Volume of a Cylinder: \(V = πr^2h\)
Surface Area of a Sphere: \(SA = 4πr^2 \)
Surface Area of a Cube: \(SA s = 6s^2 \)
Surface Area of a Rectangular Solid: \(SA = 2lh + 2lw + 2wh \)
Surface Area of a Cylinder: \(SA = 2πrh + 2πr^2 \)
Where: r = radius l = length h = height w = width s = length of one side of a cube
