Tiêu đề Cell_ The Unit Of Life.pdf ✅

NEET : Biology [ 6 ] www.allen.in BASIC COMPONENTS OF A CELL : HISTORY OF CELL : • Robert Hooke – Discovered and termed cell. He observed cell wall of dead cells in cork slice. • Anton Von Leeuwenhoek – Saw and described a live cell e.g. Bacteria, Algal cells, sperms. • Robert Brown – Discovered nucleus. • The invention of the microscope and its improvement leading to the electron microscope revealed all the structural details of the cell. 03. CELL THEORY • 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. • Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells. • 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 (Omnis cellula-e cellula). He modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape. • Cell theory as understood today is: (i) All living organisms are composed of cells and products of cells. (ii) All cells arise from pre-existing cells. Plasma membrane – delimiting (boundary) structure of cell and medium for exchange. Cytoplasm – semi fluid matrix. Main arena for all cellular activities (metabolism) Genetic material – DNA Ribosomes – protein factory of cell. Universal organelle. Fig : Structure of cell