Category: Biology Second Paper

Each cell has a specific lifespan. Cell lifespan depends on environmental conditions and genetic regulation or genetic clock. The life span of bacteria is a few hours. The life span of intestinal lining cells is 2-4 days. The average lifespan of a human cell is 10-12 days. White blood cells live for 1-15 days, platelets for 8-12 days and red blood cells for 120 days. Muscle and blood cells live throughout life.

Amoeba, protozoa, bacteria, algae and fungi are made up of single cells. Organisms are composed of a few to several thousand cells. The number of cells in a newborn human baby is about 2×10¹². Human body has 100 trillion cells. A human weighing 80 kg has approximately 60×10¹⁵ (6-10 lakh crore) cells.

Most cells are microscopic and 20-30 micrometers. A typical body cell is about 10 µm in size and weighs 1 ng. The smallest cell is Mycoplasma (Mycoplasma gallisepticum, PPLO-Pleuro Pneumonia Like Organism) with a diameter of 0.1 micrometer. The largest cell is the ostrich egg (17×12.5 cm). The smallest cell in the human body is the sperm and the largest cell is the egg (diameter 0.1 mm). The diameter of red blood cells is 7-8 micrometers. A human pea neuron cell is 1.37 meters long (from the base of the spinal cord to the big toe). Acetabularia algae are the largest cells in the plant kingdom. Its length is 5-10 cm. The longest cell is the bark fiber of Bochmeria nivea plant. Its length is 55 meters. The cells of plant fibers such as cotton, jute, palm etc. are quite long.

Different cells have different shapes. They can be round, oval, oblong, round, oblong, flat, pointed, macule shaped, polygonal, irregular etc. Branched filaments are seen in some cells.

The word Cytology is formed from two Greek words kytos meaning cell and logos meaning discussion. Cytology means discussion of cells. The branch of biology that deals with the size, shape, type, physical and chemical structure, division, growth, development and biological functions of cells is called Cytology. The father of cytology is Robert Hooke (1635-1703). But the father of modern cytology is Carl P. Swanson (1911-1996).

1. Cell is the structural and functional unit of living organism.
2. It is the basic unit of life.
3. It is covered by a semipermeable membrane.
4. New cells are formed from old cells.
5. It can grow in a controlled manner. After obtaining certain shape divides and increases in number.
6. It maintains the homeostatic state of the body.
7. Cells contain all the structural and molecular components for life. It contains cytoplasm.
8. It has adaptability. It can be adapted and transformed as needed.
9. Essential substances can move through it.
10. It can respond to any stimulus. It has the ability to respond to changes in the environment.
11. Cells have their own energy production systems. The energy produced is stored as ATP.
12. Cells contain nitrogen-containing polymeric material that enables replication.
13. All cells are self-reproducing.
14. Inherited cells contain signals for hereditary characteristics. It passes from one cell to another.
15. It causes body metabolism.
16. Every cell has a definite life span and cell death occurs after a certain period of time.
17. Cells obtain energy by absorbing essential raw materials from the environment and synthesize organic molecules.
18. It is able to maintain internal balance.
19. It contains all the genetic information and transmits it from generation to generation.

In 1658, Jessner observed the structure of proteases and gave the first idea about cells. He named it Foraminifera. In 1665, Robert Hooke, an engineer of the British Royal Society of London, observed that a wooden ship was stationary but floated in water. A thin section of the shell was observed under a self-made microscope with 30x magnification and he saw numerous tiny honeycomb-like cells or cells. He saw that these kuthuris were like small cells or ivashas for the accommodation of monks or priests of ashrams and inmates of jails. So he named these tiny cells cells. He published all the observed information in the book called Micrographia. The discovery of the cell marked the beginning of cytology. Today it is known as cell biology or molecular biology.

In 1674 Dutch scientist Antonie Van Leeuwenhoek first observed protozoa, bacteria, red blood cells, sperm etc. Important information about the cell was provided by – Grew (1682), Wolff (1759), De Mirbel (1802), Ocken (1805), Lamarck (1809) and Drochet (1824).

In 1825, French scientist Francis Rashpal said that all cells are created from pre-existing cells. In 2019, American scientist William Kalin and his colleagues discovered a mechanism for sensing and adapting cells to oxygen abundance. In 1931, German scientists Max Knol and Ernst Ruska noted the microscopic structure of cells and organelles. Scientists believe that cells appeared 3.5 billion years ago.

In 1920, Alixander Operin and J.B.S Harold said, organic molecules or amino acids were formed by the friction of methane (CH4), ammonia (NH3), hydrogen (H2) and water (H2O) in the atmosphere.

In 1953, Stanley Miller and Harold Urey produced amino acids in the laboratory by passing an electric current through a mixture of methane, ammonia, hydrogen and water.

Many people think that the first life is RNA. Proteins are then made from RNA. This idea is known as the RNA-World hypothesis.

1. Amino acids were formed by the friction of atmospheric methane (CH4), ammonia (NH3), hydrogen (H2) and water (H2O) due to lightening.
2. Carbon compounds and polymers were formed from amino acids in the deep sea.
3. A phospholipid bilayer was then formed with the polymer.
4. RNA was created from polymers.
5. Proteins were created from RNA (RNA-World).
6. Early cells were created from proteins.
7. The nucleus of the primitive cell is well formed and enveloped by the cell membrane to become a true cell.
8. Aerobic bacteria entered true cells, transformed into mitochondria, and evolved into animal cells.
9. Photosynthetic bacteria entered animal cells, transformed into chloroplasts, and evolved into plant cells.

Primordial cells are created from the original source. The original cell’s DNA becomes the nucleus and forms the true cell. Aerobic bacteria enter true cells and transform into mitochondria and form animal cells. Photosynthetic bacteria enter animal cells and transform into chloroplasts and form plant cells. Endosymbiosis is the process by which bacteria enter and survive in nucleated cells.

1. According to Jean Brachet (1961), the cell is the basic structural unit of an organism.
2. According to Loewy & Siekevitz (1963), a cell is a unit of biological function which is surrounded by a permeable membrane and is self-reproducing.
3. According to C. P. Hickman (1970), the cell is the unit of biological structure and function and is the smallest biological unit capable of self-regulation and reproduction.
4. According to Swanson and Webster (1978), the cell is the basic unit of physical existence of life.
5. According to De Roberties (1979), the cell is the basic structural and functional unit of an organism.
6. According to the Merriam Webster dictionary, a cell is a microscopic lump of protoplasm covered by a semipermeable membrane, containing one or more nuclei and other cell organelles and their components, capable of performing the basic functions of life either singly or by interaction with other cells, and is the smallest independent functioning structure of life. constitutes a unit.

The word Cell is formed with the Latin word Cellula meaning little box. Cell means small cell. The structural and functional unit of an organism is called a cell. In order to keep the body’s movement normal, various biochemical processes are carried out in the cells – photosynthesis, growth, protein synthesis, DNA and RNA synthesis, hormone and enzyme synthesis etc. Hence cell is called the functional unit of living organism. It is called the life-forming unit.