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Evaluation of effects on the environment
This question related to an investigation into the need for carbon dioxide in photosynthesis and presented the candidates with the diagram of the apparatus used. In general it was answered more proficiently on this paper than on the Foundation Tier. In part (a) many candidates thought that the purpose of the investigation was to test for starch rather than demonstrating the need for carbon dioxide. In part (b) some knew that hot or boiling alcohol was needed to remove chlorophyll from a leaf and almost all correctly gave iodine as the chemical used to identify starch. When asked to explain why part of the leaf was yellow -brown after testing, most did state that starch was absent. They also went on to link this to the removal of carbon dioxide by sodium hydroxide and the consequent lack of photosynthesis. Full marks were frequently awarded. In parts (c) and (d) most answers recognised the purpose of the container of water as a control. Many referred to its importance in allowing light to reach the leaf for photosynthesis. However, few seemed to understand its value in ensuring that the only limiting factor being tested was carbon dioxide.
Many factors influence the evolution of herbicide resistance in weed populations (reviewed in ). To design effective resistance management strategies for the long term, UC and other scientists are conducting basic research on weed biology and on ecological and evolutionary processes in weed populations.
The excretion of PCP from the body surface was minor.
Many cases of herbicide resistance in weeds are identified after growers, land managers or pest control advisers observe weed control failures with treatments that were once effective. These weeds are generally brought to the attention of local or statewide Cooperative Extension personnel. If the herbicide application method is ruled out as the cause of poor weed control (i.e., incorrect product, rate, timing, placement, etc.), researchers often conduct field or greenhouse tests to verify and quantify the level of resistance. Plants from the suspected herbicide-resistant population are treated with the herbicide of interest at rates ranging from below normal doses to doses well above those legally allowed in the field (see photos, below). The response (i.e., plant growth or mortality) of the putative resistant population is then compared with the response of the known susceptible, or wild-type, population. Resistance is confirmed if the herbicide affects the two (or more) populations of the same species in markedly different ways with respect to plant growth and survival. In many cases, an estimate of the level of resistance also is made from these data. For example, if the susceptible population is controlled at one-half the field rate, but the resistant population survives at twice the field rate, it would be described as having a fourfold (2 / 0.5 = 4) level of resistance.
6CO + 6H O ® C H O + 12O (in the presence of light energy and chlorophyll) Aim- The aim of the experiment is to determine what effect light intensity has upon the rate of photosynthesis of Canadian Pondweed (Elodea)....
The limited effects of this exposure are considered briefly here.
Braun & Sauerhoff (1976) administered a single oral dose of 10 mg PCP/kg body weight in corn oil to 3 male and 3 female rhesus monkeys and calculated the half-life for absorption to be 3.6 h in males and 1.8 h in females.
However, levels of dioxins in the milk- or body-fat of cows orally treated with technical-grade PCP (10 mg/kg body weight per day) were about 1000 times higher than those in blood, indicating a substantial accumulation (Firestone et al., 1979).
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(1972) Effects of soil on the activity of pentachlorophenol.
"despite high chronic exposures to PCP, individuals in the wood treatment group of workers had not undergone any serious health effects from this exposure.
(1968) Effect of organic compounds on photosynthetic oxygenation.
The workers were divided into 3 groups: a high exposure group handling wet-treated lumber; a medium exposure group with no manual contact with treated lumber; and a control group with no exposure to PCP, T4CP, or related chemicals.
(1979) Reviews of the environmental effects of pollutants: XI.
Occupational exposure Clinical studies have identified a number of toxic effects of short-term PCP exposure in man, some of which are also characteristic of acute intoxication (section 9.1).
Combined effect of diuron and simazine on …
Most California rice is produced in monoculture systems due to impeded soil drainage, which limits rotation to other upland crops (). Rice fields are kept under continuous flood conditions during the growing season, primarily for the control of grass weeds (). Although this system favors sedges and other water-tolerant weeds, selective herbicides such as molinate and bensulfuron provided highly effective weed control for several years. However, in the early 1990s, after repeated use, resistance to the ALS-inhibiting herbicide bensulfuron became widespread among weedy species in rice. By 2000, several additional weed biotypes with resistance to ALS inhibitors, thiocarbamates or ACCase inhibitors had evolved and were causing significant weed management, economic and environmental issues in the rice cropping system. UC researchers, extension personnel and industry partners have devoted considerable efforts to understanding and managing herbicide-resistant weeds in rice.
Combined effect of diuron and simazine on ..
The word equation for photosynthesis is: Light [IMAGE]Carbon Dioxide + Water Glucose + Oxygen Chlorophyll Although most of the glucose produced is converted into insoluble starch for storage in the stem, leaves or roots, some is used immediately by the plant to provide via respiration....
PAM fluorometry demonstrated rapid effect of diuron on ..
Introduction: "Photosynthesis is the conversion of light energy to chemical energy that is stored in glucose or other organic compounds; it occurs in plants, algae, and certain prokaryotes" (Campbell, G-16).
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