Tutor profile: Rehnuma K.
How does an author achieve his/her purpose stylistically?
By using a variety of rhetorical strategies throughout the passage. Rhetorical strategies include, but are by no means limited to: ethos, pathos, logos, metaphors, analogies, syntax, diction, aphorisms, apostrophes, euphemisms, abstractions.
A student needs to create a 250 mL 1M solution of sucrose (C12H22O11) from a stock solution of 30M sucrose. She will use this solution to test an enzyme catalyzed reaction at standard PVT. (a) How should she proceed to create a solution of sucrose from the stock such that it equals 1M? (b) What is the molar mass of sucrose? (c) How does an enzyme catalyze a reaction? What is ONE property of an enzyme that applies to the entire class as a general basis for classification? (d) The student will use beta-3-galactosucralase to catalyze the breakdown of sucrose into two molecules of galactose. This enzyme has an optimal pH of 5.5. She can select from one of three indicators: (a) Proteiodidyline turns from red to blue in the presence of proteins in a pH range of 4.5 to 6.5; (b) Galactodyline turns from blue to bright orange in the presence of simple sugars in a pH range of 3.2 to 7.6; (c) Isosaccharidyne turns from blue to red in the presence of simple sugars in a pH range of 7.8 to 11.2. Which indicator should the student use to check whether or not the enzyme is functioning and why?
(a) The dilutions formula (C1)(V1) = (C2)(V2) should be used to calculate the initial volume (V1) of the solution needed for the dilution. (30M)(V1) = (1M)(.25L). Solving for V1 results in .0083L, but since the question asked for the volume in mL, .0083 must be multiplied by 1000 in order to convert back into mL. .0083L*1000 = 8.3 mL. 8.3 mL of 30M stock solution of sucrose should be dissolved in 241.7 mL water in order to create a 250 mL 1M solution. (b) The molar mass of sucrose is 342.30. There are 12 carbon atoms, so the atomic mass of carbon must be multiplied by 12: 12.011*12 = 144.132 There are 22 hydrogen atoms, so the atomic mass of hydrogen must be multiplied by 22: 1.008*22= 22.176 There are 11 oxygen atoms, so the atomic mass of oxygen must be multiplied by 11: 15.99*11= 175.89 Adding these values gets us the molar mass of sucrose: 342.198 grams. (c) An enzyme catalyzes a reaction by lowering the activation energy of the reaction. An enzyme cannot be used up during the course of the reaction. It must be reusable. (d) The student should use Galactodyline. If the enzyme is working, then sucrose should be broken down into a simpler sugar, galactose in this case. Galactodyline can test the presence of simple sugars, unlike Proteiodidyline. The enzyme also works best at a pH of 5.5, which means any number way beyond this range will denature the protein. Galactodyline changes color within the optimal range of the enzyme, meaning that it is best for testing for sugar and pH at the same time.
2014 AP Biology Free-Response Question 8: A research team has genetically engineered a strain of fruit flies to eliminate errors during DNA replication. The team claims that this will eliminate genetic variation in the engineered flies. A second research team claims that eliminating errors during DNA replication will not entirely eliminate genetic variation in the engineered flies. (a) Provide ONE piece of evidence that would indicate new genetic variation has occurred in the engineered flies. (b) Describe THREE mechanisms that could lead to genetic variation in the engineered strain of flies. (c) Describe how genetic variation in a population contributes to the process of evolution in the population.
(a) Evidence indicating that genetic variation has occurred in the engineered flies would include observing recombinant phenotypes in the offspring of the engineered flies during a cross breed. For example, if an engineered female fly with red eyes and a yellow body is crossed with an engineered male fly with sepia eyes and an ebony body, progeny with red eyes and an ebony body (or sepia eyes and a yellow body) would indicate that crossing over and recombination created new genetic variations in the fly population. (b) Sexual reproduction is one mechanism by which the engineered strain of flies can still accumulate genetic variation without mutations. Crossing over events at meiosis is another mechanism that produces genetic variation. Nondisjunction is another way to introduce genetic variation within a species without the need for mutation. (c) Genetic variation is the foundation on which natural selection acts. Genetic variation leads to new phenotypes, some of which may work better in changing environments. These phenotypes may be selected for or against, leading to a shifting gene pool, thus leading to evolution.
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