THE CELL ,DISCOVERY OF CELL AND CELL THEORY:
Q.No.
Who invented the first microscope ? Who discovered the cell ?
Answer :
As the cell is microscopic structure , its discovery is directly related with the invention of the microscope .
FIRST MICROSCOPE:
Etymology:
The word microscope has been derived from two Greek words mikros mean little and skopein mean to look at.
H. Jansen invented the first and most useful microscope in 1590. This microscope would magnify the objects thirty times .
THE CELL:
CYTOLOGY:
The branch of biology , which deals with the study of cells , is called Cell Biology .
DISCOVERY OF CELL:
Etymology:
The word cell has been derived from Latin word cella meaning to cover.
Robert Hooke reported the discovery of cell in his famous publication Micrographia in 1665. He took a piece of cork and cut it into thin sections and studied them under his self - made compound microscope . He observed that the cork is composed of minute honeycomb like compartments , which he termed as cells . According to Hooke , cell is an empty space bound by thick walls .
DISCOVERY OF NUCLEUS:
In 1831 , Robert Brown observed a spherical body , the nucleus , in the cells of orchid's plants . It showed that cell is not an empty space .
Q.No. Who proposed the cell theory ? What are the main points of cell theory ?
Answer : DEVELOPMENT OF CELL THEORY:
A German zoologist Theodor Schwann ( 1838 ) and a German botanist Matthias Schleiden ( 1839 ) , working independently , came out with a theory , called the Cell Theory.
CELL THEORY:
Definition According to cell theory , all living , organisms are composed of cells and cell products .
The salient features of cell theory in its present form are :
1 . All organisms are composed of one or more cells .
2 . All cells arise from pre - existing cells .
3 . Cell is the basic structural as well as functional unit for all organisms .
Q.No. Write a note on magnification and importance of microscope .
Answer :
RESOLUTION:
The human naked eye can differentiate between two points , which are at least 1.0 mm apart . This is known as resolution of the eye . This resolution can be increased with the aid of lenses .
COMPOUND MICROSCOPE:
A compound microscope is a typical laboratory microscope with at least different magnification powers
RESOLUTION OF COMPOUND MICROSCOPE:
In a typical compound microscope the resolution is 2.0 m , which is about 500X that of naked eye . The typical ocular lenses could be 5X and 10X , but others also exist . Likewise different types of objective lenses viz . 20X , 40X , 100X etc exist .
CALCULATION OF MAGNIFICATION:
The magnification power of microscope is determined by multiplying X values of ocular lens and X value of objective lens . Therefore , a microscope with 10X ocular lens and 40X objective lens will have ( 10X40 = 400X ) 400X magnifying power . The resolution will , however , remain the same , which is 500X that of the naked eye .
SOURCE OF ILLUMINATION IN COMPOUND MICROSCOPE:
The source of illumination in compound microscopes is visible light .
SOURCE OF ILLUMINATION IN ELECTRON MICROSCOPE:
In electron microscope , the source of illumination is a beam of electrons and the resolution of microscope ranges between 2-4 Angstrom , which make it 500X greater than that of the compound microscope and 250,000X greater than that of the naked eye . This means that two points , which are 2-4 Angstrom apart , can be differentiated with the help of electron microscope .
IMPORTANCE OF MICROSCOPE:
The revelation of complexity of structure of various cellular organelles is closely linked with the development of microscopy and improvement in the resolution power of the microscope .
Q.No. What are the methods to study the structure of a generalized cell ?
Answer :
Methods:
Structure of a cell can be studied by different methods i.e. microscopy and cell fractionation .
MICROSCOPY:
Structure of a cell can be studied under light microscope as well as electron microscope . Electron microscope magnifies the objects too much and reveals minute details . Structure of a cell as revealed by electron microscope is called its ultra structure .
CELL FRACTIONATION:
The modern technology enables us to isolate various components of cells including its organelles by a process of cell fractionation during which , the tissues are homogenized or disrupted with special instruments Various parts of the cells are separated by density gradient centrifugation . This separation is achieved by spinning the homogenized or disrupted cells in a special medium in a centrifuge at medium speed . The various cellular parts separate out in different layers depending upon their size and weight , and density of the medium . Some cellular components require very high speeds for separation from other parts of the cells . This is achieved through ultracentrifugation .
Q.No. What are the components ( parts ) of a generalized cell ? Write a detailed on structure and functions of plasma membrane .
Answer :
COMPONENTS OF A CELL:
A cell consists of the following basic components :
1. Plasma membrane
2. A cell wall ( in plant cell only )
3. Cytoplasm , containing cell organelles
4. Nucleus , with nuclear or chromatin material .
PLASMA MEMBRANE:
Plasma membrane or cell membrane is the outer most boundary of the cell but in plant cells , it is covered by a cell wall .
CHEMICAL COMPOSITION:
Cell membrane is chemically composed of :
a . 60 80 % Protein
b . 20-40 % Lipids
In addition there is a small quantity ( 2-10 % ) of carbohydrates .
STRUCTURE:
Unit Membrane:
It was proposed earlier that cell membrane is composed of lipid bilayer sandwiched between inner and outer layers of protein. This basic structure is called the unit membrane and is present in all the cellular organelles.
Fluid Mosaic Model:
The modern technology has revealed that lipid bilayers are not sandwiched between two protein layers. The protein layers are not continuous and are not confined to the surface of the membrane but are embedded in lipid layers in a mosaic manner. This discovery led to the proposal of Fluid Mosaic Model. This model at present is the most accepted one. Cell membrane also contains charged pores through which movement of materials takes place, both by active and passive transport.
FUNCTIONS OF PLASMA MEMBRANE:
1. Mechanical Support: Plasma membrane provides mechanical support and external form to the protoplasm.
2. Selectively Permeable Membrane: Plasma membrane offers a barrier between the cell contents and their environment, allowing only selective substances to pass through it, thus it is known as differentially permeable or selectively permeable membrane.
3. Transport of Material: Transport of materials is one of the vital roles it plays for the cell. Transport is of two basic types:
a. Non-Facilitated Transport
b. Facilitated Transport
a. Non-Facilitated Transport: The substances, which are lipid soluble, cross it more easily than others, e.g. fatty acids, oil droplets, phospholipids. It is called non-facilitated transport.
b. Facilitated Transport: Many small gas molecules, water, glucose etc. being neutral can easily cross while ions, being charged particles, have some difficulty in crossing. These substances are carried across the membrane with the help of specialized protein. So, it is called facilitated transport. It is of two types:
1. Passive Transport: The transport of molecules across the membrane along concentration gradient (from higher conc. to lower conc.) without the use of energy is called passive transport.
2. Active Transport: The transport of molecules across the membrane against concentration gradient (from lower conc. to higher conc.) with the use of cnergy is called active transport. ATP provides the energy used for this movement.
Endocytosis:
Etymology:
The word Endocytosis has been derived from Two Greek words endos mean within cytos mean cell .
In many animal cells, the cell membrane helps to take in materials by in folding in the form of vacuoles. This type of intake is termed as endocytosis.
It is of two types:
a. Phagocytosis:
Etymology:
The word Phagocytosis has been derived from two Greek words phagein mean to eat and cytos mean cell.
If the large solid particles are taken in the cell then the process is called phagocytosis (to engulf solid particles).
b. Pinocytosis: If the large liquid particles are taken in the cell then the process is called pinocytosis (to take in liquid material).
Exocytosis: if the material is transported from the cell to the outside, then such process is called exocytosis e.g. transport of secretions or waste products across the membrane.
Nerve Impulse: In neurons (nerve cells) the cell membrane transmits nerve impulses from one part of the body to the other to keep coordination.
0 Comments