24_Prelim_2_Review - 1 Review for Prelim 2 Light and...

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Unformatted text preview: 1 Review for Prelim 2 Light and Nutrient Requirements Photosynthesis depends solely on the availability of water, CO 2 and sun light . Primary production , which involves the synthesis of complex organic compounds, depends also on the uptake of plant nutrients for the construction of complex molecules needed to form new cellular components. Consequently , primary production depends not only on sun light, but also on the availability of plant nutrients in the surrounding water. Net Primary Production The reactions needed to construct new complex molecules and to provide basic metabolic needs consumes oxygen and generates CO 2- which is exactly the opposite of what happens during photosynthesis. Collectively the generation of CO 2 by this process is referred to at respiration . The difference between the amount of CO 2 consumed by photosynthesis and the amount of CO 2 produced by respiration is called net primary production . 2 Light-Dependency of Primary Production 1. At light levels below the compensation light level , phytoplankton cells do not have sufficient light to photosynthesize fast enough to meet their basal metabolic needs and so cell respiration exceeds photosynthesis leading to negative values of net primary production. 2. At low light levels, phytoplankton are light limited . 3. At optimal light levels, phytoplankton are light saturated 4. At very high light levels, phytoplankton are photoinhibited 5. The depth at which the ambient light intensity is equal to the compensation light intensity is called the compensation depth Nutrient-Dependency of Primary Production 1. The amount of nutrient needed for growth by an individual phytoplankton cell is proportional to the cells mass or, equivalently, to the cells volume . 2. The amount of nutrient that can be transported into a cell is proportional to the cells surface area . 3. Small cells have a larger surface area to volume ratio than do larger cells so smaller cells can grow better a lower nutrient concentrations Subtropical Gyres exhibit year-round low rates of primary production 3 A Persistent Lens of Warm Low-Nutrient Surface Water in the Subtropical Gyre, and the Associated Depression of the Thermocline to Greater Depths, Causes Year-Round Low Nutrient Conditions in the Subtropics and Low Levels of Primary Production Throughout the Year The Equatorial Pacific and Equatorial Atlantic exhibit elevated rates of primary production due to upwelling of nutrient rich water from depth Equatorial Upwelling of Cold Nutrient-Rich Deep Water in the Eastern Equatorial Pacific and Atlantic Easterly Trade Winds Cause Surface Waters to Pile Up in the West Themocline is Deep in the West and Shallow in the East Proximity of Thermocline Near the Surface in the East Enhances Coastal Upwelling of Cold and Nutrient-Rich Deep-Water to the Lighted Region of the Surface Ocean and Thus Enhances Biological Productivity in this Area 4 Coastal Regions 1. Tidal Mixing in Shallow Continental Shelf Regions...
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24_Prelim_2_Review - 1 Review for Prelim 2 Light and...

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