Cells, Tissues, Organs, Organ Systems made up the 4 level of organisation of an organism.
A cell is the smallest structural and functional unit of a living organism. Bacteria are unicellular consisting of a single cell. Human are multicellular. A group of similar cells having the same embryologic origin and performing similar functions is known as Tissue.
They are a collection of specialised cells in an extracellular matrix. The human body is made up of four major types of tissues
An organ is defined as a structure formed by two or more primary tissue types that execute one or more common functions. Some organs are composed of four types of primary tissues. The organs are of two types: coiled hollow organs and compact or parenchymal organs. The organs which has important functions are heart, brain, liver, lungs, kidneys, endocrine glands etc.
On the other hand, a system is defined as a group of organs that perform a common function or set of functions of the body and are viewed as a unit. Each system performs a specific function. Examples; The digestive system is concerned with digestion, Nervous system controls locomotion and other activities including intellectual functions.
Eukaryotic and Prokaryotic cells
There are two type of cells existing: Eukaryotic and Prokaryotic cells.
Eukaryotic cells are made up of:
- Plasma membrane.
- Protoplasm (Made up of the nucleus and the cytoplasm).
- The Nucleus (Limited by an envelope known as the Nuclear membrane, encloses the genetic material in the form of DNA).
- The Cytoplasm (Made up of the Morphoplasm which contains the organelles and the Paraplasm that contains inclusions).
Prokaryotic cells differs from eukaryotic cells in that
- They do not have nuclear membrane.
- Have smaller size.
- They proliferate by binary fission as opposed to eukaryotes who multiply by mitosis.
- They possess 70S ribosomes as opposed to the 80S in eukaryotes.
- There is discontinuous genes in prokaryotes as opposed to continuous genes in eukaryotes. .