CELL BIOLOGY

Cell Biology

1. Levels of Organization

Living things are highly organized and structured, following a hierarchy that can be examined on a scale from small to large. The atom ( such as oxygen, hydrogen, carbon, nitrogen,..) is the smallest and most fundamental unit of matter. Atoms form molecules ( such as monosaccharide, amino acid, glycerol, ...) which is a chemical structure consisting of at least two atoms held together by one or more chemical bonds. Many molecules that are biologically important are macromolecules. There are 4 important kinds of macromolecules in living organism: carbohydrate, protein, nucleic acid and lipid. The aggregates of macromolecules lead to the formation of organelles. When organelles surrounded by membranes and carry out indispensable functions, these are called cell. All living things are made of cells; the cell itself is the smallest fundamental unit of structure and function in living organisms. This requirement is why viruses are not considered living: they are not made of cells. To make new viruses, they have to invade and hijack the reproductive mechanism of a living cell; only then can they obtain the materials they need to reproduce. Some organisms consist of a single cell ( called prokaryote) and others are multicellular ( called eukaryote).  Prokaryotes are single-celled or colonial organisms that do not have membrane-bound nuclei or organelles; in contrast, the cells of eukaryotes do have membrane-bound organelles and a membrane-bound nucleus.

Cells combine to make tissues, which are groups of similar cells carrying out similar or related functions. Collections of tissues grouped together performing a common function resulting in the formation of organs. Organs are present not only in animals but also in plants. An organ system is a higher level of organization that consists of functionally related organs. Mammals have many organ systems. For instance, the circulatory system transports blood through the body and to and from the lungs; it includes organs such as the heart and blood vessels.

Organisms are individual living entities. For example, each tree in a forest is an organism. Single-celled prokaryotes and single-celled eukaryotes are also considered organisms and are typically referred to as microorganisms.

2. Why cell is the basic unit of life? 

Reason: 

Cell is able to maintain its structure and reproduce. In order world, cells are the basic units of life capable of doing all the required biochemical processes that a normal cell has to do in order to live. The basic needs for the survival of all living organisms are the same. All living organisms need to respire, digest food for obtaining energy, and get rid of metabolic wastes. Cells are capable of performing all the metabolic functions of the body. Hence, cells are called the functional units of life.

to be continuous....