Chapter 3-4 - Chapter 3-4 CELLULAR FORM and FUNCTION...

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Chapter 3-4: CELLULAR FORM and FUNCTION Concepts of Cellular Structure Development of the Cell Theory. 1663 Robert Hooke observed empty cell walls of cork and coined the term “CELL”. He also observed living cells. During the nineteenth century, Theodor Schwann concluded that all animals are made of cells. Spontaneous generation had been the prevailing view for centuries, but in 1859 Loius Pasteur conducted experiments that finally laid the idea of spontaneous generation to rest. During the 20 th century, the ideas and rules of modern cell theory emerged. Cell Shapes. Cell shape varies widely: Squamous cells are flat and thin. Polygonal cells have irregular shapes with four, five or more sides. Cuboidal cells are cube-shaped. Other shapes include columnar, spheroid to ovoid, discoid, fusiform, or stellate. Epithelial cells that line organs have a basal side upon which the cell rests, lateral sides that are adjacent to nearby cells, and an exposed upper (apical) surface. Cell Size Cell size is expressed in micrometers. Most human cells range from 10-15 micrometers, but an egg cell may be 100 micrometers. Cell size is limited due to surface area-to-volume relationships.
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Perspective on cells. The resolution of the light miscroscope prevented early scientists from seeing the organelles. With the advent of the transmission electron microscope, biologists were able to see far more details inside the cells. The scanning electron microscope views minute surface details. The Cell Surface. The plasma membrane. The electron microscope revealed that the plasma cell membrane is made up of two layers. The current model of membrane structure is called the fluid- mosaic model. It suggests that the plasma membrane is made up of mobile globular proteins in a layer of phospholipids. Membrane lipids. 1. Phospholipids are amphiphilic, with a hydrophilic phosphate containing head and two hydrophobic fatty acid tails. 2. In the plasma membrane, the phospholipids are oriented with the heads out and the tails to the inside, forming a phospholipids bilayer. The hospholipids are not fixed into position. 3. Twenty percent of the membrane lipids are cholesterol, which lends stability to the phospholipids.
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