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BIOA01H3 (202)
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Chapter 4

chapter 4

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University of Toronto Scarborough
Biological Sciences

My Notes Chapter 4Lecture2 41 What features of cells make them the fundamental unit of life y Cells are the building blocks of life y Cell theory Cells are the fundamental units of lifeAll organisms are composed of cellsAll cells come from preexisting cells y Cell theory has three important implicationsStudying cell biology is in some sense the same as studying lifeLife is continuousThe origin of life on Earth was marked by the origin of the first cells y Cells are tiny y Surface areatovolume ratio for any cell organism or geometrical solid the ratio of surface area to volume this is an important factor in setting an upper limit on the size of a cell or organism can attain y As an object increases in volume its surface area also increasesTwo biological reasonsThe volume of a cell determines the amount of chemical activity it carries out per unit of timeThe surface area of a cell determines the amount of substances the cell can take in from the outside environment and the amount of waste products it can release to the environment y Resolution the distance apart two objects must be in order for the eye to distinguish them as separate Microscopes improve resolution so that cells and their internal structures can be seen y Two types of microscopesA light microscope uses glass lenses and visible light to form a magnified image of an objectAn electron microscope uses electromagnets to focus an electron beam much as a light microscope uses glass lenses to focus a beam of light y Plasma membrane the membrane that surrounds the cell regulating the entry and exit of molecules and ionsEvery cell has a plasma membraneRolesAllows the cell to maintain a more or less constant internal environmentA selfmaintaining constant internal environment the state known as homeostasisActs a selectively permeable barrier preventing some substances from crossing it while permitting other substances to enter and leave the cellAs the cells boundary with the outside environment the plasma membrane is important in communicating with adjacent cells and receiving signals from the environmentThe plasma membrane often has proteins protruding from it that are responsible for binding and adhering to adjacent cells y Prokaryotes organisms whose genetic material is not contained within a nucleus the bacteria and archaeaorganisms whose cells contain their genetic material inside a nucleus y Eukaryotes The genetic material DNA of eukaryotic cells is contained in a special membraneenclosed compartment called the nucleusNucleus in cells the centrally located compartment of eukaryotic cells that is bounded by a double membrane and contains the chromosomes
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