Cell the Unit of Life

Chapter-8 Cell: The Unit Of Life
What is a cell?
Cell is the basic or fundamental structural and functional unit of an organism.

What is cell biology?
The branch of biology that deals with the study of cell structure and function is called cell biology.

DISCOVERIES;
Who discovered cell?
Robert Hooke observed a live cell in 1665. He observed the cell(actually the cell walls) in the slice of cork under his compound microscope ,coined the term cell, recorded his observations in micrographic.

What is the contribution of Anton Von Leewenhoek to biology?
1)Obsevation of live cells of baacteria and protozoans called them as animal cules in 1667.
2)Discovery of Electron Microscope. First microscope which perfects the techniques of grinding microscope(bacteria).

What is the contribution of Rudolf Virchow?
Rudolf Virchow in 1885 put forward the theory of cell lineage and stated that cells always develop from pre-existing cells by cell division (Omnis cellula e cellula).

CELL THEORY
Who proposed the cell theory?
Matthias Schleiden a German botanist observed all the plants are composed of different kinds of cells which forms the tissues of the plant in 1838 and Theodere Schwann a British Zoologist studied different types of animal cells that had a outer layer called Plasma Membrane in 1839.
Theodere Schwann and Matthias Schleiden formulated the cell theory.
Features of cell theory:
1)All organisms are made up of cells and their product.
2)Cell is the structural and functional unit of life.
3)A Cell originates from a pre-existing cell, by the process of cell division.
Modern cell theory: * Also called as the Cell Principle or Modern cell theory. * Modified by Schwann and Rudolf Virchow
Main features of modern cell theory * Cell contains cell organelles. * Cell live independently but organelles cannot. * Cell is capable of not only maintaining itself but is also able to propagate itself. * Life exists in the form of the cells only. * Cell is not only the storehouse of heriditary information but also the vehicle of expression. * All organisms are made of cells and their products. * Cell is the basic structural and functional unit of all living organisms. * A cell originates from a previously existing cell, by the process of cell division. * A cell basically have a similar structure, with protoplasm bound by a membrane and with nucleus and cell organelles. * All cells posses similar chemical composition and metabolic activities. * Cell id the store house of heriditary information.

OBJECTIONS: * Viruses are noncellular as they lack protoplasm and do not have cell division. * The Protozoans like ameoba are acellular as their body is composed of single cell. * Organisms like Rhizopus are coenocytic as they have a multinucleated body and lacks differentiation into cells. * RBC of mammals ,Seive tubes cells do not have nucleus and hence are enucleated.

AN OVERVIEW OF CELL
What is cytology?
Cytology id the branch of science which deals with the structure ,function and reproduction of cells.
What do you mean by Totipotent?
The potential of an individual of forming a whole individual from a single cell.
Where we can observe the cells?
1)The onion cell which is a typical plant cell has a distinct cell wall as its outer boundary and just within it is the cell membrane.
2)the cells of human cheeks has an outer membrane as the delimiting structure of the cell.
Nucleus:
Each cell is a dense membrane bound structure called the nucleus.

Where is the genetic material DNA found?
Nucleus contains chromosomes which in turn contains the genetic material ,DNA.

One important differences between prokaryotic and eukaryotic cells? Prokaryotic Eukaryotic Cells that lack a membrane bound nuclei | Cells that have a membrane bound nuclei |

An Overview of cell: * In both prokaryotic and eukaryotic cells a semi fluid matrix called cytoplasm occupies the volume of cell. The cytoplasm is the main arena of cellular activities in both the plant and animal cells .Various chemical reactions occur in it to keep the cell in the living state. * The eukaryotic cells have other membrane bound distinct structures called organelles like the endoplasmic reticulum , the golgi complex, lysosomes, mitochondria, microbodies and vacuoles. The prokaryotic cells lack such membrane bound organelles. * Ribosomes are non membrane bound organelles found in all all cells-both prokaryotic as well as eukaryotic. Ribosomes are found not only in the cytoplasm but also within the two organelles chloroplasts (in plants) and mitochondria on the rough endoplasmic reticulum. * Animal cells contain another non membrane bound cell organelle called centriole which helps in cell division.

Cell size: * Cells are generally microscopic and the cell size varies greatly. * Prokaryotic cells measure 0.1 micrometer to 5 micrometer. Eukaryotic cell can measure from 1 micrometer to several centimeters. * Smallest cell is that of mycoplasma gallisepticum ,which are only 0.3 micrometer wjile the bacteria could to be 3 to 5 micrometer. * Largest cell is that of Ostrich egg, measures 17*15 cm wide. * Among multicellular organisms , human red cells are about 7.0 micrometer in diameter. * Nerve cells are some of the longest cells .
Cell shape: * Shapes of cells vary greatly. * In plants, generally cells have a definite shape due to the presence of a rigid cell wall. * Most of the plant cells are spherical or polyhedral (many sided as in parenchyma . It may be cylindrical as in green algae . Needle shaped as in fibres etc. * Animals exhibit a greater diversity in cell shape. They are column -like as in epithelial cells, fibre -like elongated as in muscle cells, biconcave shaped like RBC etc. * The shape of the cell may vary with the function they perform.
Unicellular and multicellular organisms: * All organisms whose body is made of single cell are called Unicellular. * Eg: Ameoba, Euglena. * All organisms whose body is made of several cell are called Multicellular. * Eg :Plants, Animals.

Eukaryotic and Prokaryotic cells:
Eukaryotic cells: are cells with True nucleus where the genetic material is bound by a nuclear membrane .All the organisms with such a nucleus is called prokaryotes. Eg: higher plants and animals including humans.
Prokaryotic cells: are cells with a primitive nucleus, where the genetic material is not bound by a such a nucleus is also called nucleiod or incipient nucleus. Eg: Bacteria, Blue green algae and PPLO(Pleuro Pneumonia Like Organisms) as mycoplasma.

Ultra structure of a Prokaryotic cell(Bacterial cell):