ANALYZE IT

Note: Questions marked with a triangle (∆) are included to enrich students’ understanding. These questions do not appear in students’ SDRs but should be used as additional discussion points during the PostLab.

As a class, discuss the effect of staining on the characteristics of the specimen.

• ∆ Did your cheek cells appear different from the prepared cheek cell slide? If so, in what way? Student answers will vary. Students may feel that their cheek cell slide contained fewer cells or that the cells from their slide were a different size than the cells on the prepared slide. Students should notice a distinct difference in the color of the cells. The cells in their own slide were clear and did not contain much color. However, the cells observed on the prepared slide were stained dark pink, with purple nuclei.

• ∆ The prepared slide was stained. How did the staining affect your observations of the cheek cells? Student answers will vary. The staining allowed students to observe the cheek cells more easily. The cells were easier to locate on the slide, and students could easily observe the cells’ nuclei on the prepared slide.

• ∆ Think back to your observations in Investigation One. Were any of your observations due to the staining of a specific specimen? If students observed color on a slide, their observations were most likely due to the staining of the specimen, rather than the actual color of a cellular structure.

As a class, discuss the effect of sectioning on the characteristics of different specimens.

• ∆ Did the celery appear different depending on the way it was cut, or sectioned? Yes. When a cross-section of the celery was made, the celery was crescent-shaped. We were able to view small circles scattered across the specimen where the string-like fibers were cut. When a longitudinal section of the celery was made, it was long and rectangular. No small circles were visible. Rather, long stripes stretched across the specimen.

• ∆ Did the longitudinal section slide appear different from the cross-section slide of the corn stem? How did this compare to the celery sectioning? Student answers will vary. Just as the celery appeared different depending on the way it was sectioned, so the corn stem appeared differently.

Note: The cross-section of the stem contained many large, somewhat circular cells that appear empty. In various sections of the specimen, students observed clusters of smaller cells and ducts. The longitudinal section of the corn stem contained may long, narrow, rectangular cells which appear empty. In various sections of the specimen, students observed stripes of cells and ducts which are stained purple or red. Although students observed the same structures in each section, the appearance of the structures was changed by the way each specimen was sectioned.

Instruct students to complete the Analysis Question in their SDRs then discuss it as a class. Use the suggested response below to guide students’ answers.

• Why would it be important for a scientist to know what kind of sectioning was used to prepare a specimen for observation under a microscope? Student answers will vary. Because sectioning can drastically change the appearance of the cells under the microscope, it is important to know what sectioning technique is used. If the type of sectioning is not known or incorrectly identified, it could lead to the misidentification of cells. When comparing cells from different specimens, it would be important to use the same type of sectioning for each so that the differences observed between the cells are actual structural differences within the cell and not the consequence of different sectioning.

GET FOCUSED

Instruct students to complete the Focus Questions in their SDRs then discuss them as a class. Use the suggested responses below to guide students’ answers.

• How does staining affect the appearance of a specimen? Student answers will vary. Staining of specimens may add artificial color to the cells to allow various structures to be more easily viewed. For instance, the staining of the prepared cheek cell slide allowed students to observe the cheek cells more easily. The cells were easier to locate on the slide, and students could observe more detail in the cells on the prepared slide.

• How does sectioning affect the appearance of a specimen? Student answers will vary. Observations of the size, shape, and arrangement of cells can be affected by the sectioning of the specimen. Student observations of the size, shape, and arrangement of cells were possibly affected by the sectioning of the specimen. In order to conclusively answer this question, students would need to compare each type of tissue sectioned in several different ways.