The cell is the structural and functional unit of the body of living organisms and often has the ability to reproduce itself. It is that smallest organized form of various substances in which all those activities take place which collectively we call life.
The English word for ‘cell’ is derived from the Latin word ‘ cellula ‘ which means ‘a small room’. The body of some organisms like bacteria is made up of a single cell, they are called unicellular organisms while some organisms like human body is made up of many cells, they are called multicellular organisms. The cell was discovered by Robert Hooke in 1665 AD
All the biological activities of living things take place within the cells. Within the cells are the necessary genetic information that controls the functions of the cell and the information is transferred to the next generation of cells.
The systematic study of cells is called Cytology or ‘ Cell Biology ‘.
History of Invention and Research
Robert Hooke in 1665 observed beehive-like cells based on a study of a thin layer of cork in the bottle and named them cells. This fact appeared in his book Micrographia. Robert Hooke used the word kosha on the basis of recesses.
- 1674 Antoine von Leeuwenhoek made the first study of living cells.
- He saw a living cell in a tooth scrap.
- In 1831 , Robert Brown discovered the ‘nucleus and nucleolus’ in the cell.
- A scientist named Tarochit presented the idea of cell theory in 1824, but it is attributed to botanist Matthias Jakob Schleiden and zoologist Theodor Schwann who properly Introduced the cell theory (in 1839) and stated that ‘cells are the structural unit of plants and animals’.
- 1855 : Rudolf Virchow put forward the idea that cells always arise from the division of cells.
- 1953 : Watson and Crick announced the ‘double-helix structure’ of DNA for the first time.
- 1981 : Lynn Margulis presented a paper on ‘Symbiosis in Cell Evolution’ in cell sequence evolution.
- In 1888 , Waldeyer named the chromosome.
- 1883 : I named the Swimper (Chloroplast) Schimper.
- In 1892 , Weissman clarified the difference between somatoplasm and germplasm.
- 1955 : The ribosome was discovered by GE Palade.
There are two types of cells,
- Prokaryotic cells and
- Eukaryotic cell
1. Prokaryotic :-
Prokaryotic cells are usually independent whereas eukaryotic cells are found in multicellular animals. There is no distinct nucleus in a prokaryotic cell . The rudimentary nuclei found in these are called nuclei which are scattered in the cytoplasm. This type of cell is found in bacteria and blue-green algae.
Eukaryotic cell type is found in all higher plants and animals. Organized nucleus is found in all eukaryotic cells which is covered by a sheath.
Cells are living beings and perform all the functions that living beings perform. Their shape is very small and the shape is spherical, oval, columnar, pubescent, flagellated, polygonal etc. They are surrounded by a jelly-like object. This covering is called the cell membrane or cell-membrane. This membrane is selectively permeable, which means that this membrane allows a substance ( molecule or ion ) to pass through freely, in a limited amount. Allows it to happen or stops it altogether. It is also sometimes called ‘plasma membrane’. The following structures are found within it:-
(1) Nucleus and nucleus
(3) Golgi complex or Golgi apparatus
(4) Particle Formula
(5) Endoplasmic branch
(6) Chromosomes and genes
(7) Ribosomes and Centrosomes
The structure of all types of cells, plant and animal cells is almost the same except for some special differences. They are made up of both living and non-living units. A normal cell or typical cell has three main parts, cytoplasm, cytoplasm and nucleus. The cytoplasm is the outermost covering or enclosure of the cell. In a plant cell, the cell wall and the cell membrane together form the cytoplasm. Cell wall is not found in animal cell, so cell membrane is the outermost covering. The part between the cell membrane and the nucleus is called cytoplasm, it contains various organelles. The nucleus is a round and dense structure found inside the cell. the nucleus of the cell’s brain’ is called. Just as the brain controls all the functions of the body, similarly all the functions of the cell are controlled by the nucleus.
There is usually only one nucleus in a cell, but sometimes more than one nucleus is also found. It is the center of operation for all the functions of the cell. When a cell divides, it also divides. The nucleus is a fluid inside the cell, often floating in the cytoplasm. Although it does not have a fixed location, yet it is mostly located almost in the central part. In some cells its position is basal and in some it is also peripheral. The shape of the nucleus is spherical, circular or oval. However, sometimes it can be cylindrical, ellipsoidal, flat, branched, pear-like, lanceolate, etc. Within it are found the nucleolus and chromosomes. The covering of the nucleus is called the nuclear membrane or nucleolemma.
One or more nuclei are found in each nucleus. The nucleus disappears at certain stages of cell division, but reappears later. Ribonucleic acid (Ritioncleric acid or RNA) and certain types of enzymes are found in large quantities within the nucleus. Nuclei play an important role in mitosis or mitosis.
It is a thick liquid that is known by local names; For example, the cytoplasm found in the space between the plasma membrane and the nucleus is called the cytoplasm and the protoplasm found inside the nuclear membrane is called the nucleoplasm. This part of the cell is extremely conscious and the center of all biological processes of the cell. That is why it is called ‘living’. Biologists call it the ‘physical basis of life’. Modern biologists have done a chemical analysis of the protoplasm and have found out by which components it is formed, but till date no scientist has succeeded in transmitting life (protoplasm) in it. Such is the mysterious substance of nature.
Protoplasm is made up of carbon, hydrogen, oxygen and many organic and inorganic substances. The water content in this is about 80%, proteins 15%, fats 3% and carbohydrates 1% and inorganic salts 1. There are many types of protoplasm, such as colloid, granular, fibrillar, reticular, alveolar, etc.
Golgi complex or apparatus
This organ is named after its discoverer, Camillo Golgi, who first discovered it in 1898. This organ is usually found near the nucleus, singly or in groups. It is made up of three elements or components: flat sacs, large vacuoles and vesicles. It looks like a kind of network. Their main function is cellular secretion and storage of proteins, fats and certain enzymes.
They are shaped like granules or rods. These organelles are located in the cytoplasm. Their number can be up to five lakhs in different animals. Their size ranges from 1/2 micron to 2 micron. In rare cases, they can be up to 40 microns in length. Many of their functions have been described, which depend on their shape. However, their main function is called cellular respiration. They are called the ‘power plant’ of the cell, because they supply the required energy.
This reticulum extends into the cytoplasm in the form of vesicles and tubules. Its position is usually between the nuclear membrane and the plasma membrane, but it is often spread throughout the cell. This reticulum is of two types: smooth surfaced and rough surfaced. Its surface is rough because the particles of ribosomes are scattered on it. Many of its functions have been reported, such as mechanical support, exchange of materials, intracellular transport, protein synthesis, etc.
The word is derived from the words chrom and soma , which mean color bodies . Chromosomes are found in pairs within the nucleus and are shared with the nucleus during cell division. The living beings located in these are said to be the carriers of the paternal qualities of the ancestors, their number is fixed in organisms, which can range from a couple of pairs to several hundred pairs. Their size ranges from 1 micron to 30 microns (long). Their shape is generally like the letter S of the English language. Among these , nucleo -proteins ( nucleo-o- proteins ) are mainly found. Some special types of patrisutras are also found, which are calledLampbrush chromosomes and polytene chromosomes have been termed .
Genes are considered as carriers of hereditary characters. Chromosomes or patriosomes are made up of histone proteins and deoxyribonucleic acid DNA and ribonucleic acid RNA . Genes are made by one of these, DNA. When the life of a new organism is initiated as a result of cell division, then these same genes along with the paternal and physiological properties are passed from the parents to the offspring. This exchange takes place through the genes located in the mother’s ovum and the father ‘s sperm . In the month of June 1970 , Indian scientist based in America, Shri Hargobind Khuranahad had unprecedented success in generating artificial genes. He received the Nobel Prize in 1978 .
These structures obtained in the form of microscopic gullies can be seen only under electron microscope. They are made up of 50% protein and 50% RNA. These are especially found above the endoplasmic reticulum. Proteins are synthesized in them.
These are found near the nucleus. A special part of them is called the centrosphere, within which a pair of centrioles is found. During cell division, these separators determine the pole of the cell and produce flagella-like structures in some cells.
Fungi are mostly found in plants. These are a type of pigment granules, which are scattered everywhere in the protoplasm. The chloroplast bearing color is called chloroplas. Due to this, greenness is seen in the trees. Plants do photosynthesis because of chlorophyll. According to some scientists, fungi are transferred directly to the daughter cells during cell division in the form of cytoplasmic inheritance.
- The process of cell division was first reported to Virchau in 1855 AD.
- Cell division takes place in three ways.
- Amitosis: In bacteria, blue green algae, yeast, amoeba and some other protozoa, etc., which have undeveloped cells, ‘mitosis’ takes place.
- Mitosis: Mitosis occurs only in somatic cells.
- In 1882 AD, this division of the cell was named Mitosis (mitosis) by ‘Walter Fleming’.
- Mitosis takes place in 5 stages namely interphase, prophase, metaphase, anaphase and telophase.
- The period between two cell divisions in which the cell prepares itself for division is called interphase.
- Prophase is the first stage of division. By the end of this the nucleus disappears.
- The ‘chromosomes’ come in metaphase at the equatorial plate.
- Anaphase is the shortest period (2-3 minutes) to complete. chromatids in it
- Let us take the shape of UV or L.
- The final stage of mitosis is telophase.
- Mitosis results in the birth of two daughter cells from one parent cell.
- Each daughter cell formed as a result of mitosis has the same number of chromosomes as the parent cell.
- Due to division, organisms grow and develop. In some micro-organisms, the process of asexual reproduction takes place through this division.
- Through mitosis, new cells are formed in the body, thus the body is repaired and wounds are healed.
- It is also called reduction division.
- This division was named ‘Meiosis’ in 1905 AD by Farmer and Moore.
- Towards meiosis was made by Weissman and its first detailed study was done by Strausswerger in 1888 AD.
- This division takes place only in sex cells.
- There are two stages of meiosis (meiosis-I and meiosis-III)
- There are four stages in meiosis-I division, prophase-I, metaphase-I, anaphase-I and telophase-I.
- Protoplasm is found in the cell, which the scientist Huxley described as the physical basis of life.