CELL THEORY TYPES OF CELLS Robert Hooke 1665

CELL THEORY & TYPES OF CELLS

ØRobert Hooke -1665 observed the slices of cork tissue under compound microscope ØHe saw honey comb like arrangement composed of small compartments. ØHe coined the term cell for individual units

Robert Brown- 1831 observed a spherical body in each cell and called it as nucleus

CELL THEORY üM. J. Schleiden and Theodore Schwann concluded that all living tissues-plant and animals are composed of individual cellular units and they proposed the cell theory üCell theory states that all organisms are composed of one or more cell and üThe cell is the structural and functional unit of the life

THREE TENETS TO THE CELL THEORY Rudolf Virchow states that a new cell can arise only by the division of a pre-existing living cell The three tenets to the cell theory are as described below: 1. All living organisms are composed of one or more cells. 2. Thecell is the basic unit of structure and organization in organisms. 3. Cells arise from pre-existing cells.

MODERN THEORY- CELL THEORY v. Energy flow occurs within cells v. Heredity information (DNA) is passed on from cell to cell v. All cells have the same basic chemical composition

PROTOPLASM THEORY §Proposed by Hertwig in 1892 §It states that the cell contains a viscous, colourless, translucent, col loidal susbstance called protoplasm §Protoplasm means first substance

§The term protoplasm was coined by Purkinje in 1840 §Protoplasm is also called substance of life, or physical basis of life

• Protoplasm shows all the activities like metabolism, movement , growth homeostasis, reproduction etc • As long as protoplasm carries metabolic activities it is alive. • The moment activities stop, protoplasm no longer live and soon disintegrates

GERM PLASM THEORY o. Proposed by August Weismann in 1892 o. The body of organism is formed of two types of cells namely somatic cells and germ cells o. Cytoplasm present in the somatic cells is called somatoplasm and in germ cells is called germplasm

§Somatoplasm dies with death of animal §But Germ plasm is carried to the next generation §The Reproductive cells are said to be germ cells

ORGANISMAL THEORY §Proposed by Laurence Picken in 1960 §It states that cell is an organism §Unicellular organism is small, much less differentiated mass of protoplasm §Multicellular organism is large, highly differentiated mass of protoplasm

ORGANISMAL THEORY ØIt states that cytoplasm of one cell is connected to the neighbouring cell by cytoplasmic strand called plasmodesmata ØThis theory is not accepted because it is applicable only to plants

SHAPE AND SIZE OF CELL Shape varies depends upon the functional requirement of organism and environmental conditions irregular like amoeba, spherical, cuboidal, spindle, oval, etc

STRUCTURE OF A CELL §cell has three distinct regions namely cell wall, protoplasm and vacuole §cell wall and vacuoles are non-living components §protoplasm is differentiated into nucleus and cytoplasm §nucleus is surrounded by nuclear membrane

STRUCTURE OF A CELL cytoplasm is surrounded by cell or plasma membrane cytoplasm is differentiated into outer ectoplasm and inner endoplasm encloses various cell organelles main cytoplasmic organelles are mitochochondria, plastids, golgi complex, endoplasmic reticulum, ribosomes, lysosomes, flagella, centroso

STRUCTURE OF A CELL plant cell has an outermost envelop called cell wall is absent in animal cell

FUNDAMENTAL PROPERTIES OF CELL 1. Membrane A cellular membrane, also called a plasma membrane, surrounds all cells. give the cell shape, and to keep the internal components confined and separate from the extracellular fluid that surrounds all cells 2. The nucleus serves two main functions. It holds the genetic material, known as deoxyribose nucleic acid or DNA. It also coordinates the activities of the cell 3. The cytoplasm serves several important cellular functions. cytoplasm provides cells with shape. The cytoplasm dissolves cellular waste products. It also facilitates movement and conducts electricity.