Biology

Blessed2016

HomeworkIntroductiontotheScientificProcess_Full.docx

Home >Biology homework help >Biology

Lab Exercise 1: Introduction to the Scientific Process, Data and Communication

Homework/Assignment

I. Metric System Practice Problems – identifying abbreviations

What does each of the following abbreviations stand for?

1. nm =

2. mL =

3. µm =

4. µg =

5. kg =

II. Metric-to-Metric Conversion Practice Problems

When converting within the metric system think in terms of the base unit. Whatever your starting point, convert to the base unit and then to your final units. Learn the factors listed in Table 1.

Example: How many nm in 6.8 µm?

The factor for micrometer is 10-6, this means there are 10-6 meters in a micrometer.

6.8 m

(10 -6 m)

(1 m )

= 6.8 x 10-6 m

Once you have converted to the base unit, convert to your final units. What is the factor for nanometers?

(1 nm)

-6

6.8 x 10 m

(10-9 m)

= 6800 nm

This is written as 6.8 x 103 nm in scientific notation

A quicker way to do the problem is to write it a one equation and set it up so the units cancel out as shown below:

6.8 m (10-6 m) (1 nm)

(1 m) (10-9 m) = 6800 nm

Remember

1) When multiplying numbers with exponents, add the exponent value. When dividing numbers with exponents, subtract the exponent values. In the previous example 6.8X10-6 m/ 10-9 m. -6 – (-9) = 3. Therefore the final answer is 6.8 X103.

2) Always include the appropriate units in your answer. Example: The above answer is 6800 nm, not just 6800. The units will NOT always be written for you. UNITS ARE IMPORTANT.

Another example: How many millimeters in 1.5 x 106 nanometers?

1.5 x 106 nm

(10-9 m)

(1 nm)

= 1.5 x 10-3 m

1.5 x 10-3 m

(1 mm)

(10-3 m)

= 1.5 x 100 mm = 1.5 mm

There are 1.5 mm in 1.5 x 106 nm

HW Problems

1. How many mm in 1.5 cm?

Once you have an answer, look at a metric ruler. Does your answer make sense?

2. How many µm in 1.8 mm?

3. 120 µm = nm

4. How many g in 9.7 kg?

5. How many µL in 25 nL?

6. How many kg in 59.04 g?

7. How many m in 4336 µm?

8. How many mm in 21,678 nm?

9. An adult human has on average 5,000 mL of blood; this equates to L (scientific notation is not necessary).

10. If the average human heart has a mass of 300 grams, what is its mass in milligrams?

11. A protist measures 10 µm in length; this equates to mm.

III. GRAPHING PRACTICE PROBLEMS

Graph 1: The following data were collected during a study of the effect of water pH on tadpole survival.

The Effect of Water pH on Tadpole Survival

pH OF WATER	NUMBER OF SURVIVING TADPOLES
8.0	45
7.5	69
7.0	78
6.5	88
6.0	43
5.5	23

1. What is the dependent variable?

2. What is the independent variable?

3. Is the independent variable quantitative?

4. Is the independent variable continuous?

5. What kind of graph would be best to use? Circle one below.

BAR GRAPH LINE GRAPH

6. Explain your graph choice.

7. Use TAILS (Title, Axes, Intervals, Labels, Scale) checklist and graph the data.

Once you have completed the graph answer the following questions.

8. What is the optimum water pH for tadpole development?

9. Between what two pH readings is there the greatest change in tadpole number?

Graph 2: The following data were collected during a study of the tadpole populations in nearby lakes.

Survey of Tadpole Populations in Maryland Lakes

LAKE	NUMBER OF TADPOLES PER LITER LAKE WATER
Needwood	145
Frank	69
Little Seneca	78
Pine	288

1. What is the dependent variable?

2. What is the independent variable?

3. Is the independent variable quantitative?

4. Is the independent variable continuous?

5. What kind of graph would be best to use? Circle one below.

i. BAR GRAPH LINE GRAPH

6. Explain your graph choice.

7. Use TAILS (Title, Axes, Intervals, Labels, Scale) checklist and graph the data.

Graph 3: The following data were collected during a drug trial testing antibiotics on methicillin- resistant Staphylococcus aureus

The Effect of Different Dosages of Antibiotics on S. aureus growth

	*Percent inhibition of S. aureus* growth (as compared to saline)**
Dosage (mg)	DAPTOMYCIN	LINEZOLID	DALFOPRISTIN
0.25	10	15	8
0.50	35	45	38
1.00	70	90	76
1.50	100	100	100

1. What is the dependent variable?

2. If an experiment is done properly, a researcher can test different variables at the same time. What are the independent variables in this experiment?

3. Are the independent variables quantitative?

4. Are the independent variables continuous?

5. What kind of graph would be best to use? Circle one below.

BAR GRAPH LINE GRAPH

6. Explain your graph choice.

7. Use TAILS (Title, Axes, Intervals, Labels, Scale, Legend) checklist and graph the data.

Lines of best fit (graphs 4 and 5) -positive and negative correlations

Graph 4. The following data represents the chirp frequencies of crickets at different temperatures.

Temperature-dependence of cricket chirp frequencies in south central Maine

Temp (°C)	# of Chirps/14 sec
5.0	2
5.6	3
7.2	4
7.2	4
7.2	7
7.2	8
10.0	10
10.0	10
10.6	12
11.1	14
12.8	15
15.6	20
17.8	24
18.3	25
18.3	26
20.0	28
23.9	36
25.6	40
27.8	40
29.4	44

Data modified from: http://abacus.bates.edu/~ganderso/biology/resources/writing/HTWtablefigs.html#linegraph

1. What is the dependent variable?

2. What is the independent variable?

3. Are the independent variables quantitative?

4. Are the independent variables continuous?

5. Explain the reason(s) for using a line graph (line of best fit) for this data.

6. After completing the graph, write a brief conclusion based on the data.

7. Use TAILS (Title, Axes, Intervals, Labels, Scale) checklist and graph the data.

Graph 5. The following data represents the distance travelled by DNA fragments on an agarose gel.

Size-dependent migration distances of DNA fragments in an agarose gel

Length of DNA fragments (bp)	Distance travelled (mm)
2000	11
1500	20
1000	29
750	39.5
500	48.5
300	59.5
150	70
50	76

Source of data: General Biology (BIOL 101) lab manual.

1. What is the dependent variable?

2. What is the independent variable?

3. Use TAILS (Title, Axes, Intervals, Labels, Scale) checklist to graph the data and answer the questions on the next page.

4. Write a brief conclusion based on the data represented in the graph.

5. Compare graphs 4 and 5 and discuss the differences in the conclusions that you have drawn based on the data represented in the lines of best fit.

6. Use the data on the distance travelled by three DNA fragments provided in the table below, to determine their lengths. Use the data in the line of best fit (standard curve) to determine the lengths of the three DNA fragments.

Size-dependent migration distances of DNA fragments in an agarose gel

Distance travelled (mm)	Length of DNA fragments (bp)
38
23
71.5

Source of data: Modified from General Biology (BIOL 101) lab manual.

7. Explain how you used the line of best fit to determine the DNA lengths for the three fragments.

Using a Spectrophotometer

Spectrophotometry is one of the most useful methods of quantitative analysis in various fields such as chemistry, physics, biochemistry, material and chemical engineering and clinical applications. A spectrophotometer is used to measure the amount of light that a sample absorbs. The instrument operates by passing a beam of light through a sample and measuring the intensity of light reaching a detector. As the beam of light passes through a solution, it can encounter a molecule of solute, and there is a chance the molecule will absorb the light. The spectrophotometer can calculate how much light has been absorbed at different wavelengths.

Visible light, the light your eyes can detect, travels in waves that vary between 390 – 750 nanometers. Our brain interprets the various wavelengths of light as different colors. When visible light is passed through a prism it is separated into its various wavelengths, and we see the rainbow colors: red, orange, yellow, green, blue, and violet.

The amount of light a molecule will absorb depends on the wavelength of light. Different molecules absorb different wavelengths of light. A spectrophotometer is used to determine what wavelengths of light a molecule absorbs. If a molecule does not absorb light, we say the light is reflected or transmitted. If transmittance is 100 % , this indicates an absorbance of 0%. When a molecule reflects a wavelength of light, it bounces off the substance, and then we see that color of light. The spectrophotometer has special filters that can separate white light into individual wavelengths. The basic principle is that each compound absorbs light over a certain range of wavelengths.

Figure 1

Figure 1 illustrates the basic structure of spectrophotometers. Visible light (a light bulb) passes through a prism, which splits the light into its different wavelengths. A specific wavelength can be selected to pass through the substance in a cuvette. The amount of light absorbed by the

substance is displayed on the spectrophotometer. (Modified from UC Davis ChemWiki licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.)

Click on the link below for a simulation with colored solutions. Click on the Beer’s Law tab to get started.

https://phet.colorado.edu/sims/html/beers-law-lab/latest/beers-law-lab_en.html

In today’s activity you will be using the spectrophotometer to measure the amount of light that is absorbed by fruit/vegetable extracts at various wavelengths. The objective of this activity is for you to learn to use a spectrophotometer and to describe the relationship between wavelengths of light, light absorption, and color of a substance. You are measuring the amount of light absorbed by the fruit/vegetable extract at different wavelengths of visible light. The wavelengths you are testing correspond to specific colors.

Before a spectrophotometer can calculate the amount of light absorbed, you need to show the spectrophotometer what 0 absorbance looks like – a negative control. A cuvette that contains only the solvent for your sample is used as reference or blank cuvette. The blank cuvette is inserted into the spectrophotometer and you adjust the reading to 0 absorbance. You must use the blank cuvette before the sample cuvette every time you make a change to the spectrophotometer.

The videos below explain how this is done

How to use a spectrophotometer video 1

How to use a Genesys Spectrophotometer video 2

For remote classes : Look at the set of data for different food extracts in the table below. Copy the values for the extract your group picks in the table provided on page 26, answer the questions below and plot a graph using this information, to complete the assignment in class or as homework.

wavelength	purple cabbage	spinach	carrot	Blueberry
350	0.068	0.0795	0.065	0.03
400	0.051	0.599	0.123	0.05
450	0.052	0.573	0.454	0.032
500	0.076	0.324	0.525	0.085
550	0.111	0.127	0.120	0.42
600	0.076	0.141	0.08	0.22
650	0.020	0.217	0.065	0.08
700	0.010	0.112	0.064	0.021
750	0.004	0.058	0.01	0.001

Student Activity

Which extract did your group select?

What variable will be manipulated or changed with the use of the spectrophotometer?

What variable will be measure with the use of the spectrophotometer?

Review the information about the spectrophotometer and your answers to the above questions. What do you think will happen when you measure the absorbance of the extract in the spectrophotometer? Your answer to this question should be testable and falsifiable. This is your hypothesis for this experiment.

Hypothesis

Data Collection

When designing an experiment it is important to think about how you will record the data you will be collecting. Often the data are recorded in a table and then presented in a graph. Graphs provide a compact method of synthesizing all of the data into a single image (http://www.ncsu. edu/labwrite).

A Table to record your results

For this experiment we have designed a table for you, however in future activities you may need to design your own table.

Title of Table 1: Absorbance values of extract at different wavelengths of visible light.

The independent Variable is _____________	The dependent Variable is _____________

Graphing your Results

a. What is the independent variable?

i. Does this go on the X-axis or Y-axis?

b. What is the dependent variable?

i. Does this go on the X-axis or Y-axis?

c. Is the independent variable quantitative?

d. Is the independent variable continuous?

e. What kind of graph would be best to use? Circle one below.

BAR GRAPH LINE GRAPH

f. Explain your graph choice.

g. Use the TAILS checklist and graph the data on the following page.

· Title

· Axes

· Intervals

· Labels

· Scale

Conclusion:

Do your results support your hypothesis?

Should you accept or reject your hypothesis? Explain.

What color of light corresponds to the lowest amount of light absorbed?

If the light is not being absorbed, what is happening to it?

Explain the relationship between the color of a substance and the wavelengths of light the substance absorbs.

Why do you think green plants are green? What wavelength of light is being reflected or transmitted?

GRAPHING DATA: Follow these guidelines

USE TAILS to help you remember how to graph properly:

T = Title: Use a descriptive title that includes the independent and dependent variables. The following formats are useful:

The Dependent variable as a function of the Independent variable The Dependent variable depends on the Independent variable

The Relationship between the Independent variable and the Dependent variable The Effect of the Independent variable on the Dependent variable

A = Axes: The independent variable is usually placed on the X- axis (horizontal axis). The independent variable is what the experimenter changes and is different between different groups or samples.

The dependent variable is usually placed on the Y- axis (vertical axis). The dependent variable changes as a result of changes in the independent variable and is usually what is being measured. Axes of your graph should be on the first printed line of the graph paper, NOT INSET.

I = Intervals: Spacing between one number and the next on each axis. Use regular intervals such as 0.5, 1, 2, 5, 10, 20 or 100.

Not every line needs to labeled.

Both axes do not have to have the same interval.

L = Labels (units): Each axis will usually need units, which should be put in parentheses.

Examples: Time (min). O2 produced (ml/hr)

Exceptions: Some variables do not have units (Ex. pH or SA/V ratio).

S = Scale: The minimum and maximum on each axis for the data being graphed.

The lowest number or minimum on the axis should be a bit lower than lowest data point. The highest number or maximum on the axis should be a bit higher than highest data point. The minimum does not always have to be zero (unless it is a bar graph or one in math class). The graph should fill up most of the graph paper being used.

Line of Best Fit:

-The line should closely follow the trend of the data.

-It does not have to pass through every data point, if a data point does not follow the general trend.

- Not all line graphs are straight. They may curve, increase or decrease and then straighten out, be bell-shaped, etc. Follow the data.

Legend (or key): Use when graphing data with multiple groups and/or two independent variables in the experiment.

*The different lines should be the independent variable that you want use for comparison, usually what is different between the different groups.

To distinguish lines, draw dotted or dashed lines, use different colors, or different symbols.

Tables: need informative titles and should be different than your graph titles.