CELL AND ITS THEORY By Dr. A. Jayaprakash.pptx

Gives an overall content about cell theory

1. CELL & ITS THEORY Dr. A. Jayaprakash

2. CELL BIOLOGY Cell biology  (also  cellular biology  or  cytology ) is a branch of  biology  that studies the structure,  function , and behavior of  cells . All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and functioning of organisms. Cell biology is the study of structural and functional units of cells. Cell biology encompasses both   prokaryotic  and  eukaryotic cells  and has many subtopics which may include the study of  cell metabolism ,  cell communication ,  cell cycle ,  biochemistry , and  cell composition .

3. CELL A cell is the structural and fundamental unit of life. The study of cells from its basic structure to the functions of every cell organelle is called Cell Biology. Robert Hooke (1665) was the first Biologist who discovered cells. All organisms are made up of cells. They may be made up of a single cell (unicellular), or many cells (multicellular ). They range in size from 0.0001 mm to nearly 150 mm across. Mycoplasmas are the smallest known cells. Cells are the building blocks of all living beings. They provide structure to the body and convert the nutrients taken from the food into energy.

4. Cells are complex and their components perform various functions in an organism. They are of different shapes and sizes, pretty much like bricks of the buildings. Our body is made up of cells of different shapes and sizes. Cells are the lowest level of organization in every life form. From organism to organism, the count of cells may vary. Humans have more number of cells compared to that of  bacteria . Cells comprise several cell organelles that perform specialized functions to carry out life processes. Every organelle has a specific structure. The hereditary material of the organisms is also present in the cells.

5. Discovery of Cells Robert Hooke discovered the cell in 1665. Robert Hooke observed a piece of bottle cork under a compound microscope and noticed minuscule structures that reminded him of small rooms. Consequently , he named these “rooms” as cells. However , his compound microscope had limited magnification, and hence, he could not see any details in the structure. Owing to this limitation, Hooke concluded that these were non-living entities.

6. Later Anton Van Leeuwenhoek observed cells under another compound microscope with higher magnification. This time, he had noted that the cells exhibited some form of movement (motility). As a result, Leeuwenhoek concluded that these microscopic entities were “alive.” Eventually, after a host of other observations, these entities were named as animalcules. In 1883, Robert Brown , a Scottish botanist, provided the very first insights into the cell structure. He was able to describe the nucleus present in the cells of orchids.

7. Characteristics of Cells Cells provide structure and support to the body of an organism. The cell interior is organized into different individual organelles surrounded by a separate membrane. The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth. Every cell has one nucleus and membrane-bound organelles in the cytoplasm .

8. Mitochondria , a double membrane-bound organelle is mainly responsible for the energy transactions vital for the survival of the cell and called as the power house of the cell . Lysosomes digest unwanted materials in the cell. Endoplasmic reticulum plays a significant role in the internal organization of the cell by synthesizing selective molecules and processing, directing and sorting them to their appropriate locations.

9. CELL THEORY The CELL THEORY states that all organisms are composed of similar units of organization called cells. The concept was formally articulated in 1839 by Schleiden & Schwann and has remained as the foundation of modern biology. The idea predates other great paradigms of biology including Darwin's theory of evolution (1859), Mendel's laws of inheritance (1865), and the establishment of comparative biochemistry (1940 ). Ultrastructural research and modern molecular biology have added many tenets to the cell theory, but it remains as the preeminent theory of biology. The Cell Theory is to Biology as Atomic Theory is to Physics.

10. In 1838, Matthias Schleiden , a German botanist, examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant. At about the same time, Theodore Schwann (1839), a British Zoologist, studied different types of animal cells and reported that cells had a thin outer layer which is today known as the ‘plasma membrane ’. He also concluded, based on his studies on plant tissues , that the presence of cell wall is a unique character of the plant cells. On the basis of this, Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells .

11. Schleiden and Schwann together formulated the cell theory. This theory however , did not explain as to how new cells were formed. Rudolf Virchow (1855 ) first explained that cells divided and new cells are formed from pre-existing cells. He modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape.

12. Cell theory as understood today is : All organisms are composed of one or more cells. The cell is the basic unit of life in all living things. All cells are produced by the division of preexisting cells . A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena.

13. Modern Cell Theory Modern cell theory consists of the 3 basic components of cell theory, plus 4 additional statements: The cell pass information from cell to cell during cell division using DNA. All cells have basically the same chemical composition and metabolic activities. All cells have basically the same chemical & physiological functions (movement , digestion, etc.). Cell activity depends on the activities of structures within the cell (organelles , nucleus, plasma membrane ).

14. Types of Cells Cells are similar to factories with different labourers and departments that work towards a common objective. Various types of cells perform different functions. Based on cellular structure, there are two types of cells: Prokaryotes Eukaryotes