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BIOLOGY – CHAPTER FIVE Cells first observed in 1600 by Robert Hooke (cork) 1820’s: nucleus first observed by Robert Brown Theodore Shawann later proposed that that all animals and plant cells have a nucleus and that cells that make up multicellular organisms retain independence. Rudolf Virchow discovers that all cells come from pre-existing cells. Basic cellular theory: o All organisms are composed of one or more cells o The cell is the smallest unit that has the properties of life o Cells only arise from the growth and division of pre-existing cells Single cells can vary in size, from 5 micrometers (smallest bacteria) to 30 micrometers (the largest cells of multicellular organisms) Light microscopes are used to view larger cells, while electron microscopes are used to view smaller cells and cellular functions. Cells are small because, as the diameter of the cell increases, the volume of the cell increases much faster than the surface area of the cell. The volume of a cell determines how much chemical activity can occur in the cell. The surface area of the cell determines the amount of substances that can enter and exit the cell. A cell with a large volume could not maintain the required levels of waste and nutrient exchange for cell life. Some cells increase their surface area by flattening themselves or by folding their cell membranes upon themselves (eg, intestinal cells). Genes – segments of DNA that code for specific individual proteins. Cytoplasm contains cystol, a solution containing ions and organic molecules. Organelles – small, organized structures important for cellular function. Plasma membrane – bilayer of lipids with embedded protein molecules. Select water-soluble substances can penetrate the cell membrane through the use of transport proteins channels. (eg, ions and molecules) Most of the cells functions occur in the cytoplasm The cytoplasm also conducts stimulatory signals from outside of the cell into the cells interior and then carries out chemical reactions that respond to these signals and converts chemical and light energy into forms that can be used by the cell.
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