AnsCellProbs3 - inside the bacterial cells The cells are...

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ANSWERS TO CELL PROBLEMS 13. a and c 14. NaCl dissociates, so the effective osmotic concentration is 0.3 M. 15. Urea and glycerol are smaller molecules than glucose, and they enter the cell faster. As they enter the cell, water also will enter the cell by osmosis, and the cell will expand. If the concentration of solute (urea or glycerol) becomes the same inside and out, then the difference in total concentration of solutes is as great as if the cells were placed in water. 16. Yes, assuming that its plasma membrane is intact. 17. A. No, cell A had the higher pressure and the higher osmotic concentration. B. Yes, both cells have the same pressure and the same osmotic concentration. 18. A. 0.29 M B. 0.58 M 19. The medium has a concentration of solutes higher than the concentration
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Unformatted text preview: inside the bacterial cells. The cells are not growing, perhaps because the medium lacks an essential nutrient. 20. Glucose does not cross a membrane rapidly, because it takes an input of energy to associate the hydrophilic glucose molecule (dissolve it) in the hydrophobic lipid phase. That energy is analogous to activation energy of a chemical reaction. The channel allows the glucose to cross without acquiring the energy (or as much energy). There is, however, no chemical reaction during the crossing. 21. Many enzymes need a particular pH and sometimes a specific cofactor (metal ion, small organic molecule). You may have purified it away from its cofactor. You may have irreversibly denatured the enzyme during purification. You may have associated it (possibly covalently) with an inhibitor....
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