Pose the following questions to students,
- “What is the biggest animal ever to have lived?” (It is believed to be the blue whale; it is even larger than any dinosaur that has been found. They can reach over 100 feet long and weigh over 200 tons, which is 400,000 pounds.)
- “If you had a huge balance and you put a blue whale on one side and daphnia on the other, how many daphnia would it take to balance the scale?” Have students pair or group and make a guess. The answer is: about 90,000,000,000 daphnia (2 milligrams) equal one blue whale (200 tons).
- “Which animal has bigger cells, the daphnia or the blue whale?” (All living things—prokaryotes/bacteria excluded have cells of roughly the same size.)
- “Which one started out as a single egg cell fertilized by a single sperm cell?” (both)
- “Which one has gone through cell division more times?” (blue whale)
Tell students that today they will learn about the way that cells grow and divide to make additional cells. The name of the process is mitosis. All living things (except bacteria) go through mitosis to grow bigger, then continue to carry out mitosis at a slower rate to replace some dead or damaged cells.
Tell students that the goal of mitosis is to start with one cell that has all the DNA directions and end with two cells that each has a copy of all the DNA directions. Ask, “What is something in everyday life that you would need to sort through and organize if someone wanted a full set of what you have?” (Answers will vary; examples include papers, music, pictures, movies, and string for sewing.) Have one student give a detailed walkthrough of how s/he would give someone a set of such items. Prompt the student while s/he describes the process so that the following is clearly identified: copying of originals and sorting items into two piles. Tell students that cells need to do a similar type of sorting of their chromosomes (sets of DNA) when they divide during mitosis so that each cell gets a full set.
Distribute copies (colored if possible) of Mitosis Phases Sorting to each group of students (S-7-4-2_Mitosis Phases Sorting.docx). The handout should be precut so that each group receives a pack of the five diagrams. Explain to students that the five diagrams are pictures of a cell sorting its chromosomes, but that they are not in order and that they should place them in what they think would be the proper sequence.
After the groups have placed them into a reasonable order ask the class, “Which of the diagrams are you fairly confident you have in the correct spot and why?” (Answers will vary.) “Which of the diagrams did you have difficulty placing in the correct spot and why?” (Answers will vary.) The goal of this is to get students to critically look at the different phases and think about them before drawing them in the next activity. Write the following on the board: Prophase, Metaphase, Anaphase, Telophase, Cytokinesis. Have students make corrections to their sequence by putting them into this order, using the letters at the top of each diagram. Explain that this is the proper order and you will now walk them through each step as they draw.
Hand out the Mitosis and Meiosis Drawing Packet (S-7-4-2_Mitosis and Meiosis Drawing Packet and KEY.docx). Ideally, give each student (or pair) a red, orange, dark blue, and light blue colored pencil or marker. Any colors work but it will be best for meiosis later if they use a pair of similar colors and another pair of similar colors (for example dark and light green and dark and light brown). Use the Drawing Mitosis PowerPoint presentation or draw each phase onto the board (S-7-4-2_Drawing Mitosis Presentation.pptx). Have students copy the pictures into their packet. At the onset, point out that two of the chromosomes should be large and two should be small, so that they can be distinguished from one another. If desired, additional concepts and vocabulary can be added to the notes section on the right side. Remind students that the different phases are all part of one continuous process and that in real life the cell doesn’t necessarily pause between each phase.
When finished, ask students, “Why do cells go through mitosis?” (for growth and replacement of damaged cells) Tell students, “A typical adult human is made of approximately 100 trillion cells. How many cells does a person start with?” (one fertilized egg or zygote) “At least how many times does the process of mitosis have to happen to form an adult from a fertilized egg?” (100 trillion, plus much more to replace dead/damaged cells along the way)
Have students write the following phases of mitosis on a piece of a paper:
After each word, have students write a very brief (up to 4 words) summary of what happens in each phase of mitosis. Have students come up with a mnemonic device to remember PMATC in order. Have them write it on the bottom of their paper. Time permitting, have some students share their mnemonic devices. Collect their papers for assessment.
- Students who may be going beyond the standards can add labeled figures to their mitosis drawing packet. Reasonable additional items include centrioles, spindle fibers, and centromeres. Students could find these additional items from their textbook, other textbooks, or an online search.
- Give students who might need extra practice the printed diagrams that they sorted in the earlier activity. Students can copy the diagrams onto their sheet if they get behind the general pace of the class during the drawing of the stages.