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Cellular Organization

Investigation 2 – Lab

 

 

 

 

 

 

 

MINDSET

This Investigation is designed to:

  • help you understand that staining and sectioning of a specimen can change the appearance of cells and tissues,
  • promote the idea that knowledge of staining and sectioning is important in helping to identify structures and functions of cells, and
  • familiarize you with identifying the nucleus, cytoplasm, and cell membrane in stained and unstained animal cell specimens.

BE PREPARED

Student Preparation for the Investigation includes having students gather the following materials. This preparation takes place on lab day after student lab groups have settled at their assigned lab tables.

Note: The materials are listed in students’ SDRs. They are also listed below for your reference.

Each student group needs the following:

  • (1) slide with the label covered (corn stem slide)
  • (1) scalpel
  • (1) human cheek slide
  • (1) 100 ml beaker filled with 50 ml of water

Each student needs the following:

  • (1) toothpick
  • (1) glass slide
  • (1) plastic dropper
  • (1) paper towel
  • (1) coverslip

Note: The plastic dropper, glass slide, and coverslip should be placed on each of the paper towels. The celery may be placed on one of the paper towels.

Direct one student from each lab group to collect the materials listed in their SDRs.

INVESTIGATE

  • Briefly review the experiment they performed in Investigation One.

Note: You observed six slides under a microscope and compared the characteristics of the cells in each slide. Students may have compared color, size, shape, and arrangement of cells.

  • The characteristics of the cells you observed in Investigation One were specific to those cells because of the nature of the cell or due to the preparation of the slides. When the slides were prepared, two factors, staining and sectioning, may have influenced the characteristics of the cells when viewed under the microscope.
  • In Investigation Two, you will investigate two procedures, sectioning and staining, used in creating slides. In doing so, you should answer the following questions:
    • How does sectioning affect the appearance of a specimen?
    • How does staining affect the appearance of a specimen?
  • Reflect on the PreLab video as you move through the procedural steps.
  • During the Experiment, every procedural step is important. If one step is skipped, data can become invalid. To help you keep on track, read each step thoroughly, complete the step, then check it off (Read it – Do it – Check it).
  • Complete all of the procedural steps in your SDR.

Note: The procedural steps are listed below for your reference.

Scientists often stain the specimens on a slide so that the specific parts of the specimen can be more easily observed. In Trial 1, you will create a wet mount slide of your own cheek cells in order to investigate the effect of staining on a slide.

Trial 1:

  1. Prepare a wet mount slide of your cheek cells.Cellular 2 Lab Slide Prep
    1. Use a plastic dropper to place a drop of water on the glass slide.
    2. Gently scrape the inside of your cheek with the flat side of a toothpick.
    3. Place the toothpick in the water drop on your slide and gently move the toothpick in the water.
    4. Place one edge of the coverslip on the slide. Tilt the opposite edge down until it is resting on the water.
    5. If the slides contain air bubbles, gently tap on the coverslip. This may remove air bubbles.
  1. Place one of the wet mount slides of cheek cells prepared by students in your group on the microscope.
  2. Use the 10X objective to locate the cells. Refer to the procedure, Microscope Use and Operation, if you need help.
  3. Observe the cells under the 40X objective. Do not use the 100X objective on a wet mount slide, because the oil may move under the coverslip and ruin the specimen.
  4. Record: Draw what the cheek cells look like.
  1. Look at other cheek cell slides that students in your group made. What similarities and differences do you see?
  1. View the prepared slide of the human cheek cells. Use the 10X and the 40X objectives.
  2. Record: Draw what the prepared cheek cells look like under the 40X objective.
  1. Compare and contrast the prepared slide with the slides you created. How are the slides similar or different?

During Trial 2 you will investigate slide preparation by learning about sectioning. Observe your piece of celery. When scientists prepare slides, they may cut, or section, the specimen in a variety of ways. Depending on how the specimen is cut, it may appear different when viewed under the microscope.

Trial 2:

  1. Cellular 2 Lab Cross PrepPrepare a cross-section of the piece of celery.
  2. Cut the stalk in half by cutting across the width of the stalk.
  3. Cut off as thin a slice as possible from one of the halves. You should be able to almost see through the slice.
  4. Observe the cross-section without the microscope.
  5. Record: Draw the cross-section and describe your observations.
  1. Place the piece of celery on a slide, and prepare a wet mount. If you need help, refer to the procedure, Wet Mount Slide Preparation.
  2. View the slide under the microscope using the 4X, 10X, and 40X objectives.
  3. Record: Draw what the cross-section looked like under the microscope. Be sure to label drawings with the magnification (objective) used.
  1. Prepare a longitudinal section of the piece of celery. Cellular 2 Lab Long Prep
  2. Cut one of the remaining pieces in half by cutting through the length of the stalk.
  3. Cut as thin a slice as possible from the length of one of the halves. You should be able to almost see through the slice.
  4. Observe the longitudinal section without the microscope.
  5. Record: Draw the longitudinal section and describe your observations.
  1. Shorten the length of the specimen so that it fits on slide.
  2. Place the specimen on a slide, and prepare a wet mount. If you need help, refer to the procedure, Wet Mount Slide Preparation.
  3. View the slide under the microscope using the 4X, 10X, and 40X objectives.
  4. Record: Draw what the longitudinal section looked like under the microscope. Be sure to label drawings with the magnification (objective) used.
  1. Compare and contrast the cross-section and the longitudinal section of the celery. How are the slides similar or different?
  1. Record: Observe the slide with the covered label using the microscope. Draw or write your observations below.
  1. The slide you observed contains specimens of a corn stem. Based on your observations with the celery, make a prediction of what you are seeing in the prepared slide.

CLEAN UP

Be sure to clean up your lab bench after your experiments.

Place the glass slide containing your own cheek cells and the toothpick in a paper towel and dispose of them.