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2SEX

BaP only

EFFECT OF ENVIRONMENTAL FACTORS ON DNA

Treatment Mean Percent of DNA with Double-Strand Breaks

Untreated control 9.8 2.4

9.7 3.2

UVA only 10.1 3.4

UVA and BaP 35.1 5.0

2. Environmental mutagens can affect DNA in cells. Benzo[a]pyrene (BaP) is a mutagen that is commonly found in urban air pollution. Researchers claim that the effect of UVA radiation (UVA), another known mutagen, is amplified by the presence of BaP. To test their claim, the researchers exposed cultured eukaryotic cells to either BaP, UVA radiation, or both mutagens. The researchers then determined the percent of chromosomal DNA that contained damage in the form of double-strand breaks. The results are shown in the table.

(a) On the template below construct a graph using the data in the table to represent the effect of UVA and BaP on DNA.

(b) Using the results from all treatments, describe the effect of BaP alone and UVA alone compared with the effect of the combined treatment of BaP and UVA on DNA.

(c) Predict the most likely effect on cell division for a cell containing DNA with double-strand breaks. Justify your prediction.

(d) Point mutations alter the DNA sequence at a single nucleotide. Describe how point mutations affect the genetic makeup of the population AND impact the evolution of the population.

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10.1

9.4

19.6

28.5

Createanappropriatelylabeledgraphtoillustratethesamplemeansofthethreepopulationswithin95%confidence,+/-2SEM.

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CreateanappropriatelylabeledbargraphtoanalyzetheeffectofpHontheoxidaseactivity.WhatistheoptimalpH?

BIOLOGY

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BIOLOGY Section II

8 Questions Planning Time------10 minutes Writing Time------80 minutes

Directions: Questions 1 and 2 are long free-response questions that require about 22 minutes each to answer and are worth 10 points each. Questions 3–8 are short free-response questions that require about 6 minutes each to answer. Questions 3–5 are worth 4 points each and questions 6–8 are worth 3 points each.

Read each question carefully and completely. Write your response in the space provided for each question. Only material written in the space provided will be scored. Answers must be written out in paragraph form. Outlines, bulleted lists, or diagrams alone are not acceptable.

1. Catechol, a natural substance found in plants, reacts with oxygen to produce benzoquinone and water, as represented by the chemical equation above. The reaction is catalyzed in plants by the enzyme polyphenol oxidase. Accumulation of benzoquinone in plant tissue results in the gradual appearance of a brown color.

A student observes that lemon juice (pH 2)(pH 2) slows the browning of apple slices. The student claims that lemon juice slows the browning process by altering the activity of polyphenol oxidase. To test the claim, the student distributes equal amounts of a dilute catechol solution to 6 identical test tubes. The pH of each solution was adjusted as shown in the table, and the initial absorbance was recorded. Equal amounts of polyphenol oxidase were added to each reaction tube. After 10 minutes at room temperature the absorbance of 389 nm light (A389) was measured for each sample. Solutions containing greater concentrations of benzoquinone absorb more light. The changes in A389A389 are shown in the table below.

POLYPHENOL OXIDASE ACTIVITY

Test Tube pH Change in A389 After

Incubation with EnzymeA 1.0 0.06B 3.0 0.09C 5.0 0.23D 7.0 0.83E 9.0 0.32F 11.0 0.10

(a) On the axes provided, construct an appropriately labeled bar graph to analyze the effect of pH on polyphenol oxidase activity.

(b) Based on the experimental results, estimate the optimal pH of the enzyme. Explain your estimate by connecting the experimental results to the structure and function of proteins.

(c) Propose an appropriate control treatment for the experiment, and describe how the control treatment would increase the validity of the results.

(d) Genetic engineering can be used to disrupt specific genes in the genome of an organism. Predict how the browning of apple slices would be affected in a strain of apples that was genetically engineered to lack functional copies of the gene encoding polyphenol oxidase. Justify your response.

.09

.22

.38

.87

1.46

.11

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9/6/2018 Interpreting Error Bars - BIOLOGY FOR LIFE

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Interpreting Error Bars

What is an Error Bar?

An error bar is a line through a point on a graph, parallel to one of the axes, which represents the uncertainty orvariation of the corresponding coordinate of the point.  In IB Biology, the error bars most often represent the standarddeviation of a data set.  Click here to learn what the standard deviation is (/standard-deviation.html) or here to learnhow to add standard deviation error bars to a graph in Excel 2016 (/graphing-with-excel.html). Example graphs with error bars:

Why Include Error Bars on a Graph?

Error bars can communicate the following information about your data:

How spread the data are around the mean value (small SD bar = low spread, data are clumped around themean; larger SD bar = larger spread, data are more variable from the mean).

The reliability of the mean value as a representative number for the data set.  In other words, how accuratelythe mean value represents the data (small SD bar = more reliable, larger SD bar = less reliable).  It's important tonote that just because you have a larger SD, it does not indicate your data is not valid.  Biological measurementsare notoriously variable.

The likelihood of there being a signi�cant difference between between data sets.  More on this below...

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What do Error Bars Indicate about Statistical Signi�cance?

A "signi�cant difference" means that the results that are seen are most likely not due to chance or sampling error.  Inany experiment or observation that involves sampling from a population, there is always the possibility that anobserved effect would have occurred due to sampling error alone.  But if result is "signi�cant,"  then the investigatormay conclude that the observed effect actually re�ects the characteristics of the population rather than just samplingerror or chance.   The standard deviation error bars on a graph can be used to get a sense for whether or not a difference is signi�cant. Look for overlap between the standard deviation bars:

The standard deviation is NOT a statistical test, rather the standard deviation is a measure of variability.  To assessstatistical signi�cance, the sample size must also be taken into account.  Therefore, while standard deviation error barscan give you a clue about statistical signi�cance, you must actually perform a statistical test (/statistics.html) to draw avalid conclusion.  For more, you can read the article "Error bars in experimental biology(https://drive.google.com/�le/d/0B7EoydxcWA7pT2NVZlFyQ3JNMkk/view?usp=sharing)."

"When we try to pick out anything by itself, we �nd it hitched to everything else in the Universe."  

  John Muir,      1911

When standard deviation errors barsoverlap quite a bit, it's a clue that thedifference is not statisticallysigni�cant.  You must actuallyperform a statistical test to draw aconclusion. 

When standard deviation errors barsoverlap even less, it's a clue thatthe difference is probably notstatistically signi�cant.   You mustactually perform a statistical test todraw a conclusion.

When standard deviation error barsdo not overlap, it's a clue that thedifference may be signi�cant, butyou cannot be sure.  You mustactually perform a statistical test todraw a conclusion.

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