Be sure to clearly state the principles addressed in

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explanation of those results based on the principles involved. (Be sure to clearly state the principles addressed in your discussion.) 1993: Membranes are important structural features of cells. (a) Describe how membrane structure is related to the transport of materials across a membrane. (b) Describe the role of membranes in the synthesis of ATP in either cellular respiration or photosynthesis. 2000 Feedback mechanisms are used by organisms to maintain the steady-state physiological condition known as homeostasis. Choose three of the following and for each, explain how feedback mechanisms maintain homeostasis. a) Blood glucose concentration b) Calcium ion concentration in blood c) Body temperature in mammals d) Osmolarity of the blood e) Pulse rate in mammals 2002: The following experiment was designed to test whether different concentration gradients affect the rate of diffusion. In this experiment, four solutions (0% NaCl, 1% NaCl, 5% NaCl, and 10% NaCl) were tested under identical
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AP BIOLOGY 4 conditions. Fifteen milliliters (mL) of 0% NaCl were put into a bag formed of dialysis tubing that is permeable to Na + , Cl - and water. The same was done for each NaCl solution. Each bag was submerged in a separate beaker containing 300mL of distilled water. The concentration of NaCl in mg/L in the water outside each bag was measured at 40-second intervals. The results from the 5% bag are shown in the table below. CONCENTRATION IN mg/L OF NaCl OUTSIDE THE 5% NaCl BAG Time (seconds) NaCl (mg/L) 0 0 40 130 80 220 120 320 160 400 (a) On the axes provided, graph the data for the 5% NaCl solution. (b) Using the same set of axes, draw and label three additional lines representing the results that you would predict for the 0%, 1% and 10% NaCl solutions. Explain your predictions. (c) Farmlands located near costal regions are being threatened by encroaching seawater seeping into the soil. In terms of water movement into or out of plant cells, explain why seawater could decrease crop production. Include a discussion of water potential in your discussion. 2005: Water potential in potato cells was determined in the following manner. The initial masses of six groups of potato cores were measured. The potato cores were placed in sucrose solutions of various molarities. The masses of the cores were measured again after 24 hours. Percent changes in mass were calculated. The results are shown below. Molarity of Sucrose in Beaker Percent Change in Mass 0.0 M 18.0 0.2 5.0 0.4 -8.0 0.6 -16.0 0.8 -23.5 1.0 -24.0 (a) Graph these data on the axes provided. From your graph, find the apparent molar concentration (osmolarity) of the potato core cells. (b) What are the components of water potential, and why is water potential important for the movement of water in plants? (c) Predict what would happen to typical animal cells placed in 0.0 M and 1.0 M sucrose solutions, and explain your prediction.
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