{"id":167,"date":"2018-06-04T19:33:06","date_gmt":"2018-06-04T19:33:06","guid":{"rendered":"http:\/\/sites.warnercnr.colostate.edu\/ocheltw\/?page_id=167"},"modified":"2018-06-27T20:17:26","modified_gmt":"2018-06-27T20:17:26","slug":"310-assignment-9","status":"publish","type":"page","link":"https:\/\/sites.warnercnr.colostate.edu\/ocheltw\/teaching\/f-rs-310\/310-assignment-descriptions\/310-assignment-9\/","title":{"rendered":"310 Assignment #9"},"content":{"rendered":"

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FRS310<\/strong><\/p>\n

Assignment #9<\/strong><\/p>\n

Leaf Size, Angle, and Color <\/strong><\/p>\n

40 Points Possible<\/strong><\/p>\n

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Introduction<\/strong><\/p>\n

Throughout the semester we\u2019ve talked quite a bit about boundary layers and about how the angle of sun hitting a surface (either earth or a leaf) impacts the amount of energy absorbed.\u00a0 In this lab we are going to test the impact of leaf size on the boundary layer and the impact of leaf angle and leaf color on the energy absorbed by leaves.<\/p>\n

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Boundary Layer<\/em> \u2013 Remember that the boundary layer is a layer of air directly adjacent to a surface that is unperturbed air, or air the is not moving very much. The still air of the boundary layer acts as a resistance to the movement of molecules and energy, making the passage of water vapor and heat extremely slow through this layer. \u00a0If the boundary layer is very thin, then water vapor and heat can still move relatively quickly through this layer.\u00a0 But, if the boundary is extremely thick, then it really slows down the movement of heat and water from the surface of interest.\u00a0 We also talked briefly about the thickness of the boundary layer in relation to leaf size.\u00a0 The longer the air is in contact with a leaf surface (ie. larger leaf), the thicker the boundary layer gets (See figure below).<\/p>\n

[\/vc_column_text][vc_single_image image=”171″ img_size=”large”][\/vc_column][\/vc_row][vc_row][vc_column][vc_column_text]Leaf Angle<\/em> \u2013 We talked about beam spread in the second or third week of lecture, and although we first discussed this concept in relation to the angle that the sun hits earth\u2019s surface, the concept can also apply to leaf angle.\u00a0 If a leaf is positioned perpendicular to the incoming light (so a horizontal leaf), then it is going to absorbed the maximum amount of radiation.\u00a0 If, however, it is oriented at, say, a 45-degree angle relative to incoming radiation then the energy in each wave will be spread out over a larger portion of the leaf.\u00a0 When talking about conifer adaptations, we discussed how they could change leaf angle in order to minimize the amount of UV light absorbed by leaves.\u00a0 And we will also talk about beam spread as it relates to leaf temperature in desert ecosystems.<\/p>\n

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Leaf Color<\/em> \u2013 In the next couple of weeks we\u2019ll talk more about the adaptations of plants to desert ecosystems, and one of the adaptations is leaf color. To start, it is helpful to know that a perfect \u2018black body\u2019 is a theoretical object that absorbs all of the energy that \u2018hits\u2019 it, and the closer in color\/shade to a \u2018black body\u2019 that an object gets, the more energy that it absorbs. So, leaves that are a lot lighter in color would reflect more of the incoming energy than dark leaves.\u00a0 Many species common to desert ecosystems have \u2018canescent\u2019 leaves, or leaves that have a silver or greyish appearance.\u00a0 One advantage of this color adaptation is that it decreases the energy absorbed by the leaf and may impact leaf temperature.<\/p>\n

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Objective<\/strong><\/p>\n

The objective of this lab activity is to investigate the impact of leaf size, angle and color on the temperature of simulated leaves.\u00a0 This activity corresponds with information we are covering in lecture about desert ecosystems, but also applies to plants growing in other ecosystem types.<\/p>\n

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Student Learning Outcomes<\/strong><\/p>\n

After completing this assignment students will be able to:<\/p>\n