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Microscopic Explorations

Performance Assessment – Lab

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BE PREPARED

Materials

Class materials:

3 50 ml beakers
1 100 ml graduated cylinder 1 ml red food coloring
1 ml blue food coloring 100 g sugar
150 g sand
150 g salt
100 ml rubbing alcohol 100 ml vegetable oil
130 ml water
15 weigh dishes
15 scoopula spatulas
25 plastic droppers

Group materials

1 100 ml beaker containing sand
1 100 ml beaker containing salt
1 100 ml beaker containing sugar
1 100 ml beaker containing rubbing alcohol 1 100 ml beaker containing vegetable oil 1 100 ml beaker containing water
1 Elodea leaf slide
1 Pinus stem slide
1 Colon slide
1 Human Blood slide

Pair materials

1 microscope
9 glass slides
9 coverslips

Individual materials

Student Data Record

TEACHER PREPARATION

1. The table below illustrates the equipment and supplies needed for the class to perform the investigation. The equipment and supplies will be divided among five tables. Step 2 provides directions for the preparation of materials for each table. Step 3 provides directions for the preparation of “CRIME SCENE SAMPLES” the entire class will share during the Investigation.

2. For each table, prepare the following materials:

a. Fill a 100 ml beaker with 30 grams of sand. This can be approximated by filling a 100 ml up to the 20 ml mark with sand. Label the beaker “SAND.”

b. Fill a 100 ml beaker with 20 grams of sugar. This can be approximated by filling a 100 ml up to the 20 ml mark with sand. Label the beaker “SUGAR.”

c. Fill a 100 ml beaker with 30 grams of salt. This can be approximated by filling a 100 ml up to the 20 ml mark with sand. Label the beaker “SALT.”

d. Fill a 100 ml beaker with 20 mls of rubbing alcohol. Label the beaker “RUBBING ALCOHOL.”

e. Fill a 100 ml beaker with 20 mls of water. Label the beaker “WATER.”

f. Fill a 100 ml beaker with 20 mls of vegetable. Label the beaker “OIL.”

g. Place 5 microscopes at the table.

h. Place one of the following slides at each table:

- - - - Elodea Leaf
        
        Pinus Stem slide
        
        Colon slide
        
        Human Blood slide

3. Prepare the Evidence Specimens for the class.

a. Using a graduated cylinder, pour 10 ml of water into a 50 ml beaker. Add 2 drops of red food coloring and 2 drop of blue food coloring to the water. Label the beaker “EVIDENCE SPECIMEN 1.”

b. Obtain a 20 g sample of sugar. This can be approximated by filling a 50 ml beaker up to the 20 ml mark. Label the beaker “EVIDENCE SPECIMEN 2.”

c. Using a graduated cylinder, pour 20 ml of water into a 50 ml beaker. Label the beaker “EVIDENCE SPECIMEN 3.”

d. Place the three “EVIDENCE SPECIMENS” at the distribution point.

4. Divide the class into pairs. Divide pairs among the five tables.

Instruction:

1. Direct one pair at each table to obtain the following necessary materials from the distribution point: three (3) weigh dishes, three (3) scoopula spatulas, five (5) plastic droppers, nine (9) glass slides, and nine (9) coverslips from the distribution station.

Procedure:

1. Tell students that their main goal in this Investigation is to use what they know about lenses, refraction, magnification, microscopes, and specimen preparation to determine the identity of three unknown samples from a crime scene.

2. Begin the Performance Assessment by either reading the opening passage from the Scientist Data Record aloud or encouraging students to read the passage independently.

READ:

Mrs. Wong and Mr. and Mrs. Miller live by the beach. On Monday morning Miss Wong decides to visit the Millers. She walks out the back door of her house through the sand to the Miller’s house. On her walk, she passes her niece and some of her friends. They are playing baseball in the lot next to the Miller’s house. When she arrives at the Miller’s she sees that the window in the kitchen door is broken. As she peers through the window she sees some broken glass on the kitchen floor. There are some other substances on the floor. Mrs. Wong can’t tell what one substance is, but she thinks the others are sand and blood. Concerned for her neighbors, Mrs. Wong runs back to her house and makes a call to the police.

The police arrive at the Millers along with a forensics team. The police chief talks to Mrs. Wong. He tells her that there have been several robberies in the area. The thief disguises himself as a delivery man for the neighborhood grocery store. The thief pretends to be an employee of the grocery store with groceries that people have ordered and asked to have delivered to their home. Part of his disguise is a bag of groceries containing salt, oil, fruits, and vegetables. In many of the robberies, the thief enters the home by breaking a window. In the process of the break-in, he tracks sand into the house and often spills his bag of groceries leaving salt and oil on the floor.

The forensics team that arrives with the police begins to collect samples of the substances for analysis. They also plan to investigate the house to look for any other evidence of a crime. When they are finished, they will take the samples they collect back to their lab to analyze and identify.

Imagine that you are a part of the forensics team that visits the Millers. When you return to the lab, you must analyze and try to identify the samples taken at the Miller’s home. Your findings will be used to determine whether a crime has been committed at the Miller’s home.

3. Briefly review the contents of the passage and outline the specific goals of this project to the class. Read aloud the goals from the list on the Scientist Data Record.

4. With the students, walk through the five steps in the project. Encourage students to draw on their understanding of refraction, magnification, resolution, field of view, slide preparation, and microscopy from the first five investigations.

5. Students will need to prepare slides of the Crime Scene Samples and the solid and liquid known samples. In order to limit the number of glass slides and coverslips used during the investigation, the Performance Assessment has been designed so that the student pairs at each table share the responsibility for specimen preparation. Nine glass slides and coverslips have been provided for this purpose. In addition, Crime Scene Samples should be placed at a distribution point where students from each table can obtain a small portion for use at their table.

6. Remind students that they are to work in pairs for this Investigation, but will need to share the samples of the Crime Scene Samples, the known samples, and the glass slides and coverslips. Three weigh dishes, scopulas, and plastic droppers have been provided for students to obtain portions of the Crime Scene Samples. One pair from each table should use these pieces of equipment to bring samples of the Crime Scene Samples from the distribution point to their tables. Students will also be expected to share the known samples (both liquids, solids, and slides) that are at each table. The scoopula spatulas and plastic droppers can also be used when working with the solid and liquid known samples.

7. Allow students to complete their Performance Assessments. You may wish to informally or formally evaluate students as they work on their performance assessments. An evaluation rubric for the Performance Assessment has been provided to aid in the evaluation process.

8. Once students have completed and recorded their analyses, read the following passage to them.

READ:

Your supervisor at the forensics lab reviews your work. She too has analyzed the samples and was able to obtain some additional known substances to use for comparison. She agrees with your conclusions that two of the Crime Scene Samples were sugar (Crime Scene Sample 2) and water (Crime Scene Sample 3) and that Crime Scene Sample 1 was not blood. In addition, she has identified that Crime Scene Sample 1, the purplish liquid, was Kool-Aid.

She also tells you that the detectives that were working on the case found out that the Millers had left their house suddenly when they received a call from the hospital stating that their daughter had been in a minor car accident. Before they received the phone call, Mrs. Miller had been making Kool-Aid and had spilled some sugar on the counter. She had also made some ice cubes for the Kool-Aid and in her rush to get to the hospital had spilled some water from the ice cube tray on the floor. Because they were anxious to get to the hospital, the Millers had not bothered to clean up the sugar and water before they left. They had also forgotten to put the pitcher of Kool-Aid in the refrigerator.

After they left for the hospital, some of the children playing baseball accidentally hit a baseball through the kitchen window. The children told the detectives that they had gone to the Millers to apologize, but no one was home. They said they left a note on the kitchen door explaining what had happened. The detectives determined that the baseball must have also hit the glass pitcher of Kool-Aid on the kitchen counter. The Kool-Aid and the glass from the pitcher and the broken window fell on the kitchen floor. They also thought that the note the children had left on the door must have blown away before the police arrived at the house, as it was a very windy day at the beach.