INTRODUCTION
CELL
All the living things are composed of cells. A single cell
is the smallest unit that has all the characteristics of life.
Cell is defined as the structural and functional unit of the
living body
General Characteristics of Cell
Each cell in the body:
1. Needs nutrition and oxygen
2. Produces its own energy necessary for its growth,repair and other activities
3. Eliminates carbon dioxide and other metabolic wastes
4. Maintains the medium, i.e. the environment for its survival Cell
5. Shows immediate response to the entry of invaders like bacteria or toxic substances into the body
6. Reproduces by division. There are some exceptions like neuron, which do not reproduce.
TISSUE
Tissue is defined as the group of cells having similar
function. There are many types of tissues in the body. All
the tissues are classified into four major types which are
called the primary tissues. The primary tissues include:
1. Muscle tissue (skeletal muscle, smooth muscle and
cardiac muscle)
2. Nervous tissue (neurons and supporting cells)
3. Epithelial tissue (squamous, columnar and cuboidal
epithelial cells)
4. Connective tissue (connective tissue proper, cartilage,
bone and blood).
ORGAN
An organ is defined as the structure that is formed by two or more primary types of tissues, which execute the functions of the organ. Some organs are composed of all the four types of primary tissues. The organs are of two types, namely tubular or hollow organs and compact or parenchymal organs. Some of the organs in the body are brain, heart, lungs, stomach, intestine, liver, gallbladder, pancreas, kidneys, endocrine glands, etc.
SYSTEM
The organ system is defined as group of organs that work together to carry out specific functions of the body. Each system performs a specific function. Digestive
system is concerned with digestion of food particles. Excretory system eliminates unwanted substances.Cardiovascular system is responsible for transport of substances between the organs. Respiratory system is concerned with the supply of oxygen and removal of carbon dioxide. Reproductive system is involved in the
reproduction of species. Endocrine system is concerned with growth of the body and regulation and maintenance of normal life. Musculoskeletal system is responsible for
stability and movements of the body. Nervous system controls the locomotion and other activities including the intellectual functions.
COMPOSITION OF CELL MEMBRANE
Cell membrane is composed of three types of substances:
1. Proteins (55%)
2. Lipids (40%)
3. Carbohydrates (5%).
FUNCTIONS OF CELL MEMBRANE
1. Protective function: Cell membrane protects the
cytoplasm and the organelles present in the cytoplasm
2. Selective permeability: Cell membrane acts as a
semipermeable membrane, which allows only some
substances to pass through it and acts as a barrier
for other substances
3. Absorptive function: Nutrients are absorbed into the
cell through the cell membrane
4. Excretory function: Metabolites and other waste
products from the cell are excreted out through the
cell membrane
5. Exchange of gases: Oxygen enters the cell from the
blood and carbon dioxide leaves the cell and enters
the blood through the cell membrane
6. Maintenance of shape and size of the cell: Cell membrane
is responsible for the maintenance of shape
and size of the cell.
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More studies https://en.wikipedia.org/wiki/Cell_(biology)