Human body is one of the complex systems on earth. Before discussing the various systems of body, it is essential to analyze the building blocks of human body. A brief idea about the cells is given below.
The cell: The cell is the basic structural and functional unit of all living organisms. It is the smallest thing that is classified as a living thing and is often called the building block of life. Humans are multi-cellular organisms. Each organ of our body is an aggregate of many different specialized cells. These cells are held together by intracellular supporting structures.
All the cells have a membrane that envelops the cell, separates its interior from its environment and maintains the electric potential of cell. Inside the cell, a salty cytoplasm takes up most of the cell volume. The entire cell possesses DNA which are the hereditary material of genes and RNA containing the information necessary to build various proteins. The cytoplasm of a cell is surrounded by a cell membrane called plasma membrane.
The cell membrane is said to be semi-permeable and it can either let a substance (molecule or ion ) pass through freely, pass through to a limited extend or not pass through at all. Two different kinds of genetic material exist in a cell. They are deoxi-ribonucleic acid (DNA) and Ribonucleic acid (RNA). The biological information contained in an organism is encoded in its DNA sequence. In humans the nuclear genome is divided into 23 pairs of linear DNA molecules called chromosomes.
Mitochondria are self replicating organelles that occur in various numbers, sizes and shapes. Mitochondria generate the cell energy and re called the ‘power house’ of a cell. Ribosome is a large complex of RNA and protein molecules. Each cell consists of a centrally located nucleus(cell core) surrounded by cell body(cytoplasm).The nucleus is separated from the cytoplasm a nuclear membrane and the cytoplasm is separated from surrounding fluids by cell membrane. Cell nucleus houses the cell chromosomes. It is in cell nucleus that almost all DNA replication and RNA synthesis occur. Lysosomes contain digestive enzymes which digest food particles and engulfed viruses or bacteria.