In our day to day life, we come across severalthings. Have you ever wondered what each of these things is made up of ? You mayobserved that some things appear to be madeof similar repetitive unite. The respective unitsare called “building block" of these things
Robert Hooke (1635-1703) anEnglishman, first discovered the cell in1664 while examining a slice of corkunder a microscope. Hook observedthat a slice of cork is made up of tinyhoneycomb-likecompartments, arranged one on top ofthe other. He called thesecompartments ‘cells’ . It was much laterthat scientists discovered that livingthings are made up of cels.
Today biologists study living things based on celltheory proposed by tow German scientists, Matthias Schleiden and Theodor Schwann. Thecell theory states that1) All organisms are made of one or more cells2) Cells arise from pre-existing cellsYou may be amazed to know that irrespective ofnumber of cells an organism is made up of, celltheory applies to every organism in the world.
Organisms that consist of many cell are calledunicellular organisms. Examples are amoeba,Paramoecium, Euglena.
Organisms whose body consist of many cell arecalled multicellular organisms. Examples are plants animals and human beings
Cells exist in different shapes. They can be disc-shaped, polygonal, rectangular, branched, or evenirregular. The shape of a cell depends on the onthe specific function it performs. Most cells are microscopic and cannot be seenwith a naked eye. Cell size may vary frommicrometer to a few centimeters. The generallyrange in size from 0.1 to 0.5 micrometers. TheLargest cell is the egg of an ostrich 170 millimeterin diameter.
Most cells can viewed with the help of a compound microscope. The object to be viewedunder the microscope is generally referred to asto the specimen. A thin glass sheet of glass calledcalled a microscopic slide which is used to hold asample of the specimen. A second much thinner,sheet of glass called cover slip.Purpose of cover slip:-1) It protects the microscope’s objective lens bypreventing it from coming into contact with thespecimen sample.2) It helps to create an even thinness for the sample.
Through cell may differ in shape size, all of themhave the same basic structure, referred to as thegeneralized cell structure or generalized cell. Thecell has both living and non living parts. Theliving parts of a cell that have a definite shapefunction are called organelles.
1) Cell membrane2) Cytoplasm3) Nucleus4) Golgi apparatus5) Vacuole6) Lysosome7) Endoplasmic reticulum8) Ribosome9) Centrosome10) Plastid11) Mitochondria (power house of the cell)
Although plants and animals cell have the samestructure, there are certain differences betweenthem. We are going to discuss this in the nextslide.
PLANTS CELL ANIMALS CELL Cell wall is present Cell wall is absent. Cytoplasm is not as Cytoplasm is dense dense as in an animal Vacuole is generally cell. absent. If present small A large vacuole is in size. present. Plastid are absent. Plastids are usually Centrosome is present. present. Centrosome is absent.