Unit-2: Cellular Organization:
This is the second unit topics of CSIR NET Life Sciences examination syllabus. Unit name is Cellular Organization. Just navigate the links on the given topics.
Basics of Cellular Organization:
Life exhibits varying degrees of organization. Atoms are organized into molecules, molecules into organelles, and organelles into cells, and so on. According to the Cell Theory, all living things are composed of one or more cells, and the functions of a multicellular organism are a consequence of the types of cells it has. Cells fall into two broad groups: prokaryotes and eukaryotes. Prokaryotic cells are smaller (as a general rule) and lack much of the internal compartmentalization and complexity of eukaryotic cells. No matter which type of cell we are considering, all cells have certain features in common, such as a cell membrane, DNA and RNA, cytoplasm, and ribosomes. Eukaryotic cells have a great variety of organelles and structures.
Cell Size and Shape:
The shapes of cells are quite varied with some, such as neurons, being longer than they are wide and others, such as parenchyma (a common type of plant cell) and erythrocytes (red blood cells) being equal dimensional. Some cells are encased in a rigid wall, which constrains their shape, while others have a flexible cell membrane (and no rigid cell wall).
The size of cells is also related to their functions. Eggs (or to use the latin word, ova) are very large, often being the largest cells an organism produces. The large size of many eggs is related to the process of development that occurs after the egg is fertilized, when the contents of the egg (now termed a zygote) are used in a rapid series of cellular divisions, each requiring tremendous amounts of energy that is available in the zygote cells. Later in life, the energy must be acquired, but at first, a sort of inheritance/trust fund of energy is used.
Cells range in size from small bacteria to large, unfertilized eggs laid by birds and dinosaurs. The realtive size ranges of biological things is shown in Figure 1. In science we use the metric system for measuring. Here are some measurements and convesrions that will aid your understanding of biology.
- 1 meter = 100 cm = 1,000 mm = 1,000,000 µm = 1,000,000,000 nm
- 1 centimenter (cm) = 1/100 meter = 10 mm
- 1 millimeter (mm) = 1/1000 meter = 1/10 cm
- 1 micrometer (µm) = 1/1,000,000 meter = 1/10,000 cm
- 1 nanometer (nm) = 1/1,000,000,000 meter = 1/10,000,000 cm