Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Cut each pipe cleaner in half to make 6 pieces.
2. Put each color of pipe cleaner in separate beakers or container on a supply table.
3. Break each piece of chalk in half and place all of the pieces in a beaker or container.
4. Place the assorted beads into an open container and keep it at the demonstration table or teacher desk.

Safety Precautions

Although the materials in this activity are considered non-hazardous, please follow all normal laboratory safety procedures.

Lab Hints

Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students.|The Engage, Explore and Explain sections can reasonably be completed in one 50-minute class period. The Elaborate and Evaluate sections will require at least one additional day, depending on the level of the class.|Answers to the questions in the Explore section should be discussed before students move on to the Explain section. Doing so will help them understand the simulation better.|The Elaborate section should not be given to any student group until the Engage, Explore and Explain sections have been completed and discussed. If several groups are lagging behind the others, assign groups that are finished to help them.|A compound microscope should be available for student use in the Evaluate section. Whitefish blastula slides may be used in addition to onion root tips for a comparison of plant and animal cell mitosis.

Teacher Tips

• Using a constructivist approach to teach draws on student’s prior knowledge and skills, such as reading and comprehension, to help them understand new material.

• This learning strategy requires the teacher to constantly listen and monitor student groups as they are working in order to guide them in their thinking. Monitoring also keeps students on-task and assists in answering questions without giving away answers.
• An additional Explore activity might be to use mitosis models of plant and/or animal cells. Cover up any numbers present on the models, then have students put the models in the correct order from the start (interphase) to the finish (telophase). When ordered correctly, their text can be used to identify the phase names, one to two major events, etc.
• The Elaborate section of this activity will help you discover which part(s) of the process of mitosis students do not fully understand. Be vigilant in monitoring the groups as they work. Students should be held accountable for their learning in this section by listening to their explanations as they practice.
• In the Evaluate section, be aware that some students may have difficulty finding the phases of mitosis in onion root tip cells under a microscope. They may not understand that the chromosomes actually move, as depicted in their diagrams.
• Several alternatives to having students use microscope slides in the Evaluate section are:
  1. Use prepared slides and a microprojector or Videoflex camera to show students cells and have them identify the phase name, one major event, etc.
  2. Use a slide projector to show photographic slides, if available, of cells in various mitotic phases.
  3. Find micrographs of cells undergoing mitosis on the Internet and make a PowerPoint slide show. Have students write the phase names, etc. as you present the slides.
  4. Let students make a “mitosis” movie by drawing cell diagrams, similar to those done in the Elaboration section, complete with moving (animated) chromosomes (colored clay on a white board) and a script that names and explains each phase.
  5. Allow student groups to find cell micrographs, not diagrams, of mitotic cells and then make their own PowerPoint presentation describing the cell cycle and the process of mitosis—its purpose, phases and end result.

• The beads (centromeres) used in this kit to hold the pipe cleaners together are special UV detecting beads and may be used when discussing the electromagnetic spectrum.

Further Extensions

1. These same materials plus straws, cut into short pieces, may also be used to help students learn the process of meiosis (gamete formation).
2. Use the short pieces of straws as connectors to attach cut pieces of pipe cleaners to each other to demonstrate the phenomenon of “crossing over” that occurs when homologous pairs of chromosomes form tetrads.
3. Tape or a rubber band will be needed to hold the tetrads together.

Answers to Questions

Explore

1. What did you have to do to complete Procedure 5? Be specific.

   We had to go get more pipe cleaners from the supply container.

2. Which answer—a, b, c or d—in the ENGAGE section is most closely related to the way you completed Procedure 5? Explain.

   Answer d because we had to go “in the house” (the supply container) and get more “chips” (pipe cleaners).

3. What do the pipe cleaners represent?

   Chromosomes

4. What do the circles of chalk represent?

   Cells

5. Assuming the pipe cleaners and circles represent the structures indicated in 3 and 4, what would happen in “real life” after the circle with the pipe cleaners on the left but before the circle on the right would contain pipe cleaners?

   There would have to be more chromosomes and the cell would have to divide to make another cell.

6. What is the process you are trying to understand in this activity?

   Mitosis, because without this process, organisms could not grow larger in size nor heal themselves after an injury.

1. Write the name of each step or phase of mitosis.

Prophase, Metaphase, Anaphase, Telophase

2. After the name of each phase, write one or two major events that occur in that phase.

Prophase—the nuclear membrane disappears, chromosomes become more visible

Metaphase—the chromosomes line up on the equator of the cell and spindle fibers attach to centromeres

Anaphase—chromatids are pulled to opposite sides of the cell by the spindle fibers

Telophase—the nuclear membranes reform, spindle fibers disappear, chromosomes become less visible; the cytoplasm is divided separating the two new cells during cytokinesis

3. Write the name of the phase that is not part of mitosis but is a critical part of the cell cycle.

Interphase

4. What important event, essential to the process of mitosis, occurs in the phase listed in Question 3?

A cell’s chromosomes are replicated (copies are made) so that each new cell has an exact copy of the original chromosomes.

Post-Lab

Based on what was learned in this activity:

1. Why is mitosis necessary?

Mitosis is necessary so that every cell, when it divides, reproduces new “daughter” cells with the exact same number and kind of chromosomes that were present in the original cell.

2. What is the end result of mitosis? Be specific.

Two new “daughter” cells that are identical to the original cell in terms of number and kind of chromosomes present.

3. Mitosis is also referred to as asexual reproduction. Why? Be specific.

Asexual reproduction does not involve the exchange and mixing of the genetic information from the parents. Therefore, the offspring of asexually-reproducing organisms are clones of the parent organism. Mitosis produces two exact copies or clones, of the original cell.

4. 1. In your own words, define cytokinesis.

      The process that occurs near the end of telophase that separates the cytoplasm into two cells.

   2. What would happen if cytokinesis never occurred?

      Organisms would not be able to grow or heal themselves as rapidly or efficiently because the cells would be too big.

5. Of the five characteristics of living things listed below, which of them would require the process of mitosis? Explain.

1. Responds to stimuli
2. Reproduces
3. Makes and uses chemical energy (metabolism)
4. Maintains a stable internal environment, like temperature (homeostasis)
5. Grows

Letter e would be correct because growth is due to an increase in the number of cells and mitosis is the process that causes growth. Letter a could also be correct if the response to a stimulus was, for example, the healing of the skin after a cut. Letter b could also be correct if an organism reproduces asexually, without producing sex cells (gametes).

Introduction

As we grow or when we sustain any kind of injury to our skin, bones, etc., the process of growing and healing always involves an increase in the number of individual cells. How does this happen? By constructing simplified, simulated cells containing chromosomes, mitosis (asexual reproduction) and cytokinesis (division of the cytoplasm), the process will be more fully understood.

Concepts

• Mitosis

• Cytokinesis

Background

A Doritos^® corn chip commercial once stated, “Crunch all you want, we’ll make more!” Imagine that one day, while munching and crunching a snack-size bag of Doritos outside your house, a good friend shows up. What would you do? (Circle one answer.)

1. Hurry and finish the bag without offering your friend any.
2. Offer your friend some of the chips from your bag.
3. Give the rest of the bag to your friend.
4. Go in the house and get your friend a second bag of chips.

Materials

Procedure

Explore

1. Lay the paper horizontally on the desk or tabletop.
2. Use the chalk to draw a circle which fills the left half of the paper (see Figure 1).
3. Place three pipe cleaners inside the circle.
4. Draw a second circle, the same size as the first, on the right side of the paper.
5. Place three pipe cleaners, the same size and color as the pipe cleaners in the left circle, inside the second circle.

Elaborate

1. Remove the pipe cleaners from the previously drawn circles and rub the chalk marks off the paper.
2. Begin with Interphase and use chalk to make a series of five “cell” drawings on the paper. Six pipe cleaners and three beads will be used to simulate chromosomes and to show their movements. Show each “cell” in a different phase and explain the diagrams. Note: Use the accompanying diagrams on this page or a textbook to assist you.
3. After one partner has completed a series of all drawings, rub off the chalk marks on the paper and let the other partner draw his or her set of diagrams and explain them.
4. When both partners have practiced enough so that each can draw all five phase diagrams, name the phases, and describe one event that occurs during each phase, without referring to this page, using notes or receiving help from others, you are ready for the EVALUATE section.
5. When finished, put all materials—pipe cleaners, chalk, beads—inside a zipper-lock bag. Rub the chalk marks off the paper and return the bag and paper to the supply area.

Evaluate

Demonstrate your knowledge of mitosis by doing the following without discussion.

1. Get a sheet of notebook paper and number from 1 to 5 on the left side.
2. Obtain a microscope and using the 40X objective, locate a cell on the onion root tip slide that appears to be in one of the four phases of mitosis or in Interphase.
3. When a desired cell is found, place the tip of the microscope pointer on the cell. Write down the name of the phase next to one of the numbers on the paper and write one major event that occurs during that phase. If the microscope eyepiece does not have a pointer, make a drawing of the selected cell.
4. Have the instructor verify, by looking through the microscope, that the name of the phase for that cell and the major event(s) described for that phase are correct.
5. Repeat steps 2–4 until all the phases, including interphase, have been found and correctly identified.

Post-Lab Questions

1. Why is mitosis necessary?
2. What is the end result of mitosis? Be specific.
3. Mitosis is also referred to as asexual reproduction? Why? Be specific.

4. 1. In your own words, define cytokinesis.
   2. What would happen if cytokinesis never occurred?

5. Of the five characteristics of living things listed, which of them would require the process of mitosis? Explain.

1. Responds to stimuli
2. Reproduces
3. Makes and uses chemical energy (metabolism)
4. Maintains a stable internal environment, like temperature (homeostasis)
5. Grows

Student Worksheet PDF

10686_Student1.pdf