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Surface area is how much exposed area
Area

Area is a quantity expressing the two-dimensional size of a defined part of a surface, typically a region bounded by a closed curve. The term surface area refers to the total area of the exposed surface of a 3-dimensional solid, such as the sum of the areas of the exposed sides of a polyhedron....
 an object has. It is expressed in square units. If an object has flat faces
Face (geometry)

In geometry, a face of a polyhedron is any of the polygons that make up its boundaries. For example, any of the square s that bound a cube is a face of the cube....
, its surface area can be calculated by adding together the areas of its faces. Even objects with smooth surfaces, such as spheres, have surface area.


ace area is important in chemical kinetics
Chemical kinetics

Chemical kinetics, also known as reaction kinetics, is the study of reaction rate of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction mechanism and transition states, as well as the construction of ma...
. Increasing the surface area of a substance generally increases the rate
Reaction rate

The reaction rate or rate of reaction for a reactant or product in a particular chemical reaction is intuitively defined as how fast a reaction takes place....
 of a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
.






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Surface area is how much exposed area
Area

Area is a quantity expressing the two-dimensional size of a defined part of a surface, typically a region bounded by a closed curve. The term surface area refers to the total area of the exposed surface of a 3-dimensional solid, such as the sum of the areas of the exposed sides of a polyhedron....
 an object has. It is expressed in square units. If an object has flat faces
Face (geometry)

In geometry, a face of a polyhedron is any of the polygons that make up its boundaries. For example, any of the square s that bound a cube is a face of the cube....
, its surface area can be calculated by adding together the areas of its faces. Even objects with smooth surfaces, such as spheres, have surface area.


In chemistry

Surface area is important in chemical kinetics
Chemical kinetics

Chemical kinetics, also known as reaction kinetics, is the study of reaction rate of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction mechanism and transition states, as well as the construction of ma...
. Increasing the surface area of a substance generally increases the rate
Reaction rate

The reaction rate or rate of reaction for a reactant or product in a particular chemical reaction is intuitively defined as how fast a reaction takes place....
 of a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
. For example, iron
Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
 in a fine powder will combust
Combustion

Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering....
, while in solid blocks it is stable enough to use in structures. For different applications a minimal or maximal surface area may be desired.

In biology


The surface area-to-volume ratio (SA:V) of a cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 imposes upper limits on size, as the volume increases much faster than does the surface area, thus limiting the rate at which substances diffuse from the interior across the cell membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
 to interstitial spaces or to other cells. If you consider the math, you'll see the relation between SA and V much more intuitively: V = 4/3 p r3; SA = 4 p r2, where r is the radius of the cell. Do the math and the resulting ratio becomes 3/r. If a cell has a radius of 1 µm, the SA:V ratio is 3. Increase the cell's radius to 10 µm and the SA:V ratio becomes 0.3. With a cell radius of 100, SA:V ratio is 0.03. Using the previous simple example, we can see how the surface area falls off steeply with increasing volume.

What limitations does this place on a living cell? For small cells, SA:V ratio allows for relatively good exchange of nutrients and wastes. For larger cells and organisms, SA:V ratio forces the cell or organism to find more efficient ways to exchange nutrients and waste products, e.g. specific conduits that carry blood, hormones, lymph, etc. from deep regions to the surface of an organism.

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See also

  • Synthetic geometry
    Synthetic geometry

    Synthetic geometry is the branch of geometry which makes use of theorems and synthetic observations to draw conclusions, as opposed to analytic geometry which uses algebra to perform geometric computations and solve problems....