Prelim_1___Key_with_Grading_Notes

Prelim_1___Key_with_Grading_Notes - BioEE 2610, Fall 2008...

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BioEE 2610, Fall 2008 PRELIMINARY EXAM I - KEY 1. [15 pts] (a) low; (b) wet; (c) permafrost (due to very low annual temp) [Explanation: there is little precipitation in the tundra but the soil is wet because the permafrost prevents water from percolating down through the soil.] Grading note: 5 pts for each answer 2. [10 pts] Dead organisms raining down from above (mainly from the photo zone). [Ultimately, this energy can be traced back to photoautotrophs (and then the sun).] Grading notes: Point breakdown for complete and partial answers - 8 points for dead organisms; 2 points for acknowledging that the dead organisms came from surface waters; 5 points for the sun; 5 points for recognizing that organisms using sun energy die, providing food when they sink 3. [15 pts] Water moves from the roots, up through trunk, stems, leaves and then out into the atmosphere through stomata in the leaves. Transpiration from the leaves is due to the lower water potential of the air relative to the leaves. Water is “pulled” up from the roots to replace this due to the cohesive property of water, and its high tensile strength. When air is injected into the xylem – the water column above the air bubble is no longer attached to the water below the bubble. As the water column above the bubble moves upwards due to water loss from transpiration, air comes in the hole to replace it. Grading Notes: 10 points for correctly describing: a) water potential gradients (most importantly due to pressure potential); and b) cohesion/adhesion/tension properties of water. 5 points for recognizing that water movement will be disrupted and won't continue past the air hole. Partial credit: 3 point deduction if
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Prelim_1___Key_with_Grading_Notes - BioEE 2610, Fall 2008...

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