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Exam_1_Key - Bio 101-004. Principles of Biology Exam 1 26...

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Bio 101-004. Principles of Biology Exam 1 Name_____ KEY ________________ 26 September 2007 In the fainting goats review we started at the level of the muscle and only referred to the presence of nerve cells (neurons) that bring chemical signals to the muscle cell membrane. Now let’s look more closely at the nerve cell itself. Neurons “depolarize” by a brief, localized change in ion concentrations between the inside and the outside of the cell. This depolarization moves from the cell body to the axon terminal, down the axon. 1. Which term describes the tonicity of the inside of the cell compared to the outside of the cell with respect to sodium ions. (circle one) Isotonic / Hypotonic / Hypertonic ( fewer Na+ ions inside than outside ) 2. Why can’t ions diffuse through the cell membrane? (Explain in a few words) Since they have a charge (plus in the case of sodium), ions cannot move through the non- polar center of the cell membrane where all the hydrophobic tails cluster. 3. When the sodium channel opens, Na+ ions move from the outside to the inside of the cell. Why do they not flow the other way? Diffusion across an elcetrochemical gradient: molecules always move from high to low concentration areas. Being charged, sodium ions also repel each other, (like charges repel), driving them from high to low areas of charge. 4. Ion Channels in the cell membrane are made predominantly _____ protein ___________ of what macromolecule? 5. (For each blank, choose POLAR or NON-POLAR) If you could look down on the top of this ion channel molecule as it rested in the cell membrane, you would find that the channel itself (in the middle / interior of the molecule) was ____ polar ______ and the outside of of the molecule (in contact with the center of the membrane) was ____ non-polar ________. Fig. 1. Top: A nerve cell (neuron). Cell body (left); Axon (long
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Exam_1_Key - Bio 101-004. Principles of Biology Exam 1 26...

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