Question

PREPARE A MODULE FOR CELL STRUCTURE AND PRESENT IT IN THE CLASS

Answer 1

Answer:

Cell Theory The cell theory, or cell doctrine, states that all organisms are composed of similar units of organization, called cells. The concept was formally articulated in 1839 by Schleiden and 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). Fact File The average human being is composed of around 100 Trillion individual cells. It would take as many as 50 cells to cover the area of a dot on the letter “i”. First Cells Seen in Cork “I took a good clear piece of Cork and with a Pen­knife sharpen’d as keen as a razor … cut off … an exceeding thin piece of it, and placing it on a balck object Plate … and casting the light on it with a deep planoconvex Glass, I could exceedingly plainly perceive it to be all perforated and porous … these pores, or cells, were not very deep, but consisted of a great many little Boxes, separated out of one continued long pore by certain Diaphragms … Nor is this kind of texture peculiar to Cork only; for upon examination with my Microscope, I have found that the pith of an Elder, or almost any other Tree, the inner pul or pith of the Cany hollow stalks of several other Vegetables: as of Fennel, Carrets, Daucus, Bur­docks, Teasels, Fearn … & c. have so much kind of Schematisme, as I have lately shown that of Cork.” ­Robert Hooke (first report on the existence of cell, 1665) from Microphagia While the invention of the telescope made the Cosmos accessible to human observation, the microscope opened up smaller worlds, showing what living forms were composed of. The cell was first discovered and named by Robert Hooke in 1665. He remarked that it looked strangely similar to cellula or small rooms which monks inhabited, thus deriving the name. However what Hooke actually saw was the dead cell walls of plant cells (cork) as it appeared under the microscope. Hooke’s description of these cells was published in Micrographia. The cell walls observed by Hooke gave no indication of the nucleus and other organelles found in most living cells. Figure 1.1 The cells observed by Hook in the honeycomb structure of a cork tissueUsing handcrafted microscopes, Anton van Leeuwenhoek was the first person to observe and describe single celled organisms, which he originally referred to as animalcules (which we now refer to as microorganisms). He was also the first to record and observe muscle fibres, bacteria, spermatozoa and blood flow in capillaries (small blood vessels). Fact File In 1681, Anton van Leeuwenhoek examined his own stool samples during times of diarrhea. In his runny stool, he found little animals. Leeuwenhoek described Giardia being a slow moving animal, but able to make quick motions with their “paws.” Today, we know this is a helical motion that is caused by flagella. Formulation of Cell Theory In 1838, Theodor Schwann and Matthias Schleiden were enjoying after­dinner coffee and talking about their studies on cells. It has been suggested that when Schwann heard Schleiden describe plant cells with nuclei, he was struck by the similarity of these plant cells to cells he had observed in animal tissues. The two scientists went immediately to Schwann’s lab to look at his slides. Schwann published his book on animal and plant cells (Schwann 1839) the next year, a treatise devoid of acknowledgments of anyone else’s contribution, including that of Schleiden (1838). These discoveries of Schleiden and Schwann introduced the cell theory. This theory states that: 1. All living things are made up of one or more cells. 2. The cell is the fundamental, structural and functional unit of all living organisms. In 1855, third statement on the cell theory was added by Rudolf Virchow. It states that: 3. All living cells come from pre­existing cells, by division. This ability of cells to divide and form new cells is the reason for the reproduction and growth of all organisms.