Biology+173+-+Quiz+2+-+2012 - Bio173 Quiz2 GSI Name 1 Is...

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Unformatted text preview: Bio173 Quiz2 GSI _____________________________ Name _________________________________ 1) Is competition good or bad for organisms? Explain. (two points) Bad. Competing organisms get less of the shared resource, so neither grows as well as it would with no competition What is the difference between interspecific competition and intraspecific competition? (two points) Intra- is competition between members of the same species Inter- is competition between different species In comparing a pot with 50 tomato plants to a pot with 25 tomato and 25 rye plants, what result would we see if intraspecific competition was stronger than interspecific competition? (one point) Tomatoes in 50T pots < tomatoes in 25T/25R pots 2) What does the variance of a sample say about the population? Use words, not an equation. (one point) Variance is how much individuals differ from the mean for the population What does a high p- value (p>0.05) say about two populations being compared? (one point) They are not significantly different 3) The following questions come from this research article: Dickson & Foster, Ecology Letters (2011) 14: 380–388 a. One observation in plant ecology is that the number of species present in an area (species richness) is low when nutrients are poor. When the soil is modestly fertilized, both total plant biomass and the number of different species per acre increase. Explain this. (two points) When soil nutrients are poor, only the organism best adapted to nutrient scarcity will survive. Competitive exclusion. With added nutrients, competition is somewhat reduced. Resource partitioning allows more different kinds of organisms to survive. Higher overall nutrients lead to higher overall biomass. b. When soil is intensely fertilized and watered, biomass continues to increase, but now species richness declines. Competition for light is believed to be responsible. Explain the logic of this hypothesis. (one point) Soil nutrients no longer are the limiting factor(s), light is. The best competitor for light will dominate. Competitive exclusion, as above. c. Dickson & Foster found that shading plants decreased species richness in a wet year but increased it in a dry year. Is this result compatible with the hypothesis in part b? Explain. (two points) Also talk about why the drought result is different than the wet result (one point) plant biodiversity 385 Fertilization, light and 2003 (Drought) 2004 (Wet) 12 9 6 3 0 – Shade + Shade 2003 (Drought) 2004 (Wet) 12 2003 (Drought) 2004 (Wet) 12 In wet years, you see decreases in richness when light is limiting (shade) 9 6 3 0 – Fertilizer (e) 15 Sown species richness Sown species richness (b) 15 Yes, compatible. (d) 15 Sown species richness Sown species richness (a) 15 In drought, water becomes the limiting factor. Shade lessens water stress. + Fertilizer 2003 (Drought) 2004 (Wet) 12 4) Tetracycline binds to bacterial ribosomes but not eukaryotic ribosomes. Why 9 9 does this make it a useful antibiotic? (one point) 6 6 It will stop protein synthesis in bacteria but not humans. 3 3 0 0 – Tie back + Tie back – a cell + become resistant to tetracycline and the cost Describe two different ways Fertilizer couldFertilizer t(c) 15 cell (compared to (f) 15et-sensitive cell) in each case. (four points) o the at 2003 (Drought) 2004 (Wet) 2003 (Drought) 2004 (Wet) Sown species richness 12 12 Any two of: block entry, transport out, cleave antibiotic, or mutate 9 9 ribosome (not avoid pathway!) of sown plant species richness to shade ion (d), vegetation tie-backs (b) and pping (c) and fertilization (f) (lines are e from the absence to the presence of the rror). Sown species richness 6 6 Cost = use up a.a. or NTPs, extra energy expenditure, reduced function 3 3 0 rent study measured light levels explained much in species richness than did the fertilization and in previous studies measured light penetraot fully explain the decline in total plant richness (Rajaniemi 2002; Stevens & Carson 2002; 3). The glasshouse study (Hautier et al. 2009) – Clipping + Clipping 0 – Fertilizer + Fertilizer from the deeper soil conditions typically found in the field. Whatever the reasons for the differences between the glasshouse and field results, it does not appear that light levels completely mediate the effects of fertilization on plant richness in the field. If decreases in plant richness are at least partly independent of light under fertilized conditions, especially under variable environmental 5) Each student provided a sample of intestinal E. coli, which we transferred to antibiotic plates to see the pattern of antibiotic resistance. In broad terms, what did we hope to learn by comparing survey data to the resistance results? (one point) We wanted to see if differences in resistance results could be explained by differences in history (survey results) In the plasmid loss experiment, why did we grow the bacteria in media containing no antibiotic? (one point) We wanted to see if resistant cells were at a disadvantage when there was no selection for maintaining resistance. Also in the plasmid loss experiment, why is it a clear sign of error when substantially more colonies appear on the antibiotic plate compared to the plain plate? (one point) Equal numbers of cells were inoculated on each plate. All live cells should survive on plain plate, antibiotic can’t help more than 100% grow. 6) Draw a dilution scheme that will yield countable numbers of bacteria from a flask with an estimated initial titer of 5 x 107 bacteria. Be clear with labels, volumes transferred, expected numbers on plate, etc. Also, be sure to account for the uncertainty of the initial titer (four points) The most common right answer will probably be six 1/10 dilutions followed by plating 0.1 ml from tubes 4, 5 and 6. Follow their dilution series carefully. They get full credit so long as it yields 30- 300 colonies. Students lose a point for plating inappropriate volumes (anything outside 50- 200 µl). Students lose a point if they do not “bracket” the target plate (plate from multiple dilutions) and another point if the middle plate (#5) is not the one that achieves the targeted dilution). Other math errors lose points according to severity. ...
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