# Adrian week 2 key x - IA Adrian Bahn Friday 2:00-2:50...

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IA: Adrian Bahn Friday 2:00-2:50 Peterson 104 Week 2 Questions 1. What is the concentration of pure water in 1 Liter? How about 500 mL? 1 mL? The concentration of pure water is always 55 M. The MW of H2O is 18 g (O = 16, H = 1), and 1 g of water = 1 mL. Since 18 g of water is 1 mole of water, and 18 g of water is 18 mL of water, 1000 mL / 18 = 55, there are 55 moles per 1 liter of water. The concentration remains the same whether it is 500 mL or 1 mL because it is still just pure water; you are not adding anything to the water or changing its composition. 2. A neuron is placed in a 200 mOsm permeable glucose solution also containing 300 mOsm of impermeable NaCl. The cell’s osmolarity is 300 mOsm. What is the initial and final osmolarity (hyper, iso, hypo) and what is the tonicity of the solution? The initial osmolarity of the solution is hyperosmolar because the total osmolarity is 500 mOsm (200 glucose + 300 NaCl). However, the final osmolarity is hypoosmolar because the neuron will absorb all of the glucose through GLUT 3 , making the cell’s osmolarity greater than 300 mOsm, while the solution remains 300 mOsm from the impermeable NaCl. The glucose does not establish equilibrium because the cell does not allow glucose to leave (through phosphorylation to glucose-6- phosphate). The tonicity of the solution is then hypotonic; water will go into the cell.

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IA: Adrian Bahn Friday 2:00-2:50 Peterson 104 3. If you replaced a cell’s lipid bilayer composition to be mainly very short- chain unsaturated fatty acids, what factors of Fick’s Law would be affected? What if they were very long-chain saturated fatty acids?
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• Fall '07
• French
• Electric charge, Ion, Adrian Bahn

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