Cells are the fundamental and structural unit of living organisms. All living organisms are made up of cells while non-living things do not have cells.
Cytology: It is called study of cell given by O’Herturig
Introduction to cell biology
Cell biology consist of detailed study of :
1.Structural
2.Genetical
3.Physiological
4.Bio-chemical composition
5.Evolution
6.Cell reproduction
Cell was first discovered by Robert Hook. Robert Hook discovered a cell in spanish cork oak (Quercus suber).The discovered dead cells actually he did not discover. But he discovered a cell wall.In cell hollow space were termed as cellula.the structure looks like honey bee web.
He firstly discovered living cells in bacteria, yeast, protozoa,RBC,sperms cells.He he called those living cells as Animalcule.(Animal like)
According to Corti, each cell is composed of a living substance called protoplasm . The word protoplasm was discovered by Jan Evangelista Purkinje.
Robert Brown discovered the nucleus.
Cell theory:
The cell theory was discovered by M.J Schleiden and Theodor schwann.
Mathias Schleiden was german botanist.He found cells in plant.He examined a large no. of plants and observed that all plants are made of different kinds of cells which form tissue.
Theodor Schwann, british zoologist,observed in animal cells and explained that cells have a thin outer membrane called plasma membrane.Schwann proposed the hypothesis that body of plant and animal are composed of cells and product of cells.
According to cell theory of a cell in cell biology :
1.Structural
2.Functional unit of living beings
3.Hereditary unit
4.New cell always arises from preexisting cell
5.Composed of nucleus and protoplasm
Schleiden and Schwann together formulated the cell theory.this theory could not explain how the new cells are found.(Drawback of cell theory) Rudolf virchow first explained that cells divided and new cells are formed from pre-existing cells.(omnis cellula -e-cellula) .He modified the hypothesis of schleiden and schwann and gave a final shape to the cell theory.
Exception of cell theory:
1. Viruses are an exception to this theory because viruses lack cell organisation i.e.it as not have nucleus protoplasm cellular organelles etc.
2.Bacteria and blue green algae . it doesn't have a nucleus.
3.Body of protozoa is not divided into cells.but according to cell theory the body is made up of cells. Protozoans do not have cells; they have the entire body.
4.Amoeba cannot be divided, which means it does not have cells . If cells are present then the body can be divided.(i) Rhizopus fungi are multinucleated (ii) vorticella algae are coenocytic.
5.According to modern scientist all the cellular organism monera and protista xanthophyta (vaucheria) ,phycomycetes (rhizopus are exception of cell theory)
Types of cell :
On the basics of nucleus
1.Prokaryotic
2.Eukaryotic
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| PROKARYOTIC CELL |
Bacteria have following
1. Envelop
2. Nucleoid
3.Plasmid
4.Mesosomes
5.Flagella
6.Pili / fimbriae
7.Chromatophores
8.Stored food
Explanation structure and the function:
1.Cell envelope:
Glycocalyx is the covering that surrounds the cell membrane of the bacterias.it is made up of glycoprotein and glycolipid.glycocalyx may or may not be present. Cell wall and cell membrane present in almost all bacteria .Exceptions are also found as mycoplasma.Glycocalyx is the outermost layer in some bacteria. It is a mucilaginous layer made up of cellulosic polysaccharide.It is a secret mucilaginous layer to provide stickiness so it helps in attachment.Avoid desiccation (drying) from adverse
Condition, protect bacteria from toxic substances ,help to protect bacteria from viruses ,and prevent mostly pathogenic bacteria.
2.Cell wall:
It is the property by which bacteria were considered a s plants.Cell wall is permeable so it is called as dead.Bacteria cells are Hard,permeable, provide shape, dead.made up of peptidoglycan /murein/muramic acid.Inner most layer of cell envelope called membrane.
3.cell membrane:
Cell membrane is living because it is selectively permeable.It is made up of phospholipid and it has living properties.
4.Nucleoid:
The nucleoid (meaning nucleus-like) is an irregularly-shaped region within the cell of a prokaryote that contains all or most of the genetic material like circular dna ,covering histone absent with compared to eukaryotes. In contrast to the nucleus of a eukaryotic cell, it is not surrounded by a nuclear membrane.
5. Plasmid
Pieces or fragments of bacteria DNA are found in cytoplasm. These fragments are called chromosome DNA are called plasmid , bacteria with plasmid resistant capacity against antibiotic.when plasmid join with main DNA then called as episome.
6. Mesosomes:
Infolding of plasma membrane and invegination. Extension of plasma membrane to cytoplasm evgination is the outergrowths, invgination is the inner growth. Mesosomes help in respiration. cell formation, increase surface area and DNA replication.
7.Flagella
Origin is cell membrane and outgrowth of cell wall may be motile, non motile ,transmitted through air water etc.
They have 3 parts.
Basal body: embedded in cell membrane flagella is made up of globulin called flagellin
Hook embedded in cell wall
Hollow outermost structure called filament hook originates from the basal body.
8.pili:
Pili is a hair-like appendage found on the surface of bacteria
Longer pili is conjugation pili made of pilin protein, smaller pili is work for adhering purpose. Pili are not meant for location or movement
9.Chromatophores:
Membrane bound organelles , in photosynthesis bacteria membrane ,flat disc like structure are found that contain chl and carotene
Chromatophores are mainly formed from cell membrane chromophores are mainly found in BGA, maximum amount of oxygen is evolved through BGA i.e. chromatophores.
10. Reserve food:
Animal stored food in the form of glucose and in plants store food in the form of starch.
Different small gas vacuoles combine to form large vacuoles .Gas vacuoles provide buoyancy. For photosynthesis plant has to come on the surface of water so gas vacuoles provide buoyancy to the plant to perform photosynthesis .