Compartmentalization in Cells

Each cell can be regarded as a compartment by itself since it is bound on all the sides by a cell membrane. It separates the protoplasm within the cell from the surrounding environment. As a result, the cell is able to retain specific molecules and carry out certain reactions in an orderly manner. This situation provides the cell with specific advantages. Apart from isolating the cell contents from outside, the cell membrane allows exchange of materials selectively.

In animal cells the cell membrane helps in recognizing the cells of the same kind, with the help of specific molecules attached to the surface.

The cells in higher organisms contain many membrane bound structures called cell organelles, which form compartments within the cytoplasm. Such a compartmentalization helps in carrying out specific functions in specific areas of the cytoplasm. There are also organelles that are not bound by membranes, like the ribosome. Cells containing membrane-bound organelles like mitochondria, chloroplasts, Golgi complex and endoplasmic reticulum, are called as eukaryotic cells.

Units of Measurement in Cytology

The cells and their compounds like cell organelles are measured in terms of the fractions of a millimeter, because of their extremely small size. The commonly used terminologies for these units are micron, nanometer and Angstrom.

a) A micron or micrometer is one thousandth of a millimeter

b) A nanometer or millimicron is one thousandth of a micron

c) An Angstrom unit is one tenth of a nanometer

The relationship between these units is as shown below.

fig. 12.8 - Relationship between units of measurement

fig. 12.9 - Size Range of Microscopic Structures