Biology

Worksheet 6 Lab – Light Microscopy, the Cell Cycle and Mitosis

Objective: The objective of this lab is to introduce you to the concepts of light microscopy, the cell cycle and mitosis.

Reading Assignment: Read 4.1,8.2 and 8.4; Cells (Visualizing Cells), Eukaryotic Cell Cycle and Cell Division from the textbook Essentials of the Living World.

Fill out the worksheet Lab 6. Once you have completed the worksheet you need to submit it using Blackboard.

Take Quiz 6. This quiz covers the information from sections 4.1, 8.2 and 8.4.

For this lab, you will be using a virtual microscope:

Link to virtual microscope: https://www.udel.edu/biology/ketcham/microscope/scope.html

Step 1. Follow the tutorial in the “Getting Started” section by clicking on start tour. Please note that a green checkmark will appear in the “At view” and “Through view” checklist when the task has been done correctly.

Step 2. Click on the “Control lighting” tab to turn on and adjust your lighting.

Step 3. Click on the “Pick a slide” tab and follow the instructions. Choose the Letter “e” slide.

Step 4. Click on the “Switch objectives” tab and follow the instructions. Choose the 4X (scanning objective).

Step 5. Click on the “Reposition slide holder” tab and follow the instructions.

Step 6. Click on the “Adjust focus” tab and follow the instructions. Then click “more” and switch views.

Step 7. Click on the “Adjust oculars” tab and follow the instructions.

Step 8. Click on the “Fine tuning” tab and follow the instructions.

Step 9. Click on the “Switch objectives” tab and follow the instructions. Use both the 10X (low power objective) and 40X (high power objective) to view the image.

Exercise 1 – Letter “e” slide

Step 10. Rotate the objectives so that the 4X (scanning) objective is in place. Center and bring the image into focus.

Step 11. The slide with the letter “e” is placed on the compound light microscope so that to the naked eye the “e” appears right-side-up and correctly oriented left-to-right.

Answer the following questions.

Describe two characteristics of the image as it appears under the microscope.

a.)______________________________________________________________________

b.)______________________________________________________________________

A total magnification of 100X requires the use of the 10X ocular lens with which objective?

___________________

What adjustment knob is used with high power? ___________________

Exercise 2 – Onion root tip slide

Step 12. Review “Essential Biological Process 8A and B” on page 135, 138 and 139 of your textbook.

Step 13. Search on the internet to find images (unlabeled photographs of a microscope slide) of an onion root tip cell in different phases of mitotic division. Insert images and label an onion root cell in InterphaseProphaseMetaphaseAnaphase and Telophase. For Telophase also include an image of an animal cell (Ascaris or whitefish mitosis for example).

Upload photo for Interphase here.

Upload photo for Prophase here.

Upload photo for Metaphase here.

Upload photo for Anaphase here.

Upload photo for (plant) Telophase here.

Upload photo for (animal) Telophase here.

Exercise 3 – Onion root tip slide

Step 14. Remove the “e” slide and insert the Onion root tip slide.

Step 15. Rotate the objectives so that the 4X (scanning) objective is in place. Center and bring the image into focus.

Step 16. With the image in focus, move up in magnification to the 40X objective and observe the cells within the red circle on the slide.

Step 17. Within the red circle, randomly choose 50 cells and determine what phase of mitosis they are in. Record your results in the table provided. Note: you will have to use the controls to move the slide in order to see 50 cells, but make sure to stay within the red circle.

Step 18. Calculate the % of cells in each phase (cells in a phase divided by total cells (50) counted) and record your results in the table provided.

Step 19. Calculate the # of minutes in that phase using the formula below and record your results in the table provided.

**It takes, on average, 24 hours (1440 minutes) for a cell to complete the cycle. You can calculate the amount of time spent in each phase by using the following formula:

% of cells in a stage x 1440 minutes = # of minutes in that stage

Total % of cells counted Time in each stage
Interphase
Prophase
Metaphase
Anaphase
Telophase
Total 50

Step 20. Answer the following questions.

During which part of the cell cycle does DNA replicate?

From the info in your table, which phase is the longest? Is this expected?

From the info in your table, which phase is the shortest? Is this expected?

During which phase(s) are chromosomes composed of sister chromatids?

During which phase(s) are daughter chromosomes present?

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