Cell Division in the Onion Root Tip Adapted from M. Arias

Objectives for this lab AP Essential Knowledge: 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization Science Practices Science Practice 2: The student can use mathematics appropriately. Science Practice 3: The student can engage in scientific questioning to extend thinking or to guide investigations within the context of the AP course. Science Practice 4: The student can plan and implement data collection strategies appropriate to a particular scientific question. Science Practice 5: The student can perform data analysis and evaluation of evidence.

Lab 7: Mitosis & Meiosis

Review: The Cell Cycle Cells grow and divide. As one cell enters Mitosis, two cells exit which are exact replicas or clones of the original “parent” cell. Cells that no longer need to divide exit the cell cycle in G1(ex. neurons, muscle cells, fat cells do this). Purpose: to replenish dead or dying cells, to allow an organism to grow and develop

Objectives for this lab AP Essential Knowledge: 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization Science Practices Science Practice 2: The student can use mathematics appropriately. Science Practice 3: The student can engage in scientific questioning to extend thinking or to guide investigations within the context of the AP course. Science Practice 4: The student can plan and implement data collection strategies appropriate to a particular scientific question. Science Practice 5: The student can perform data analysis and evaluation of evidence.

Interphase A cell spends the majority of its lifetime in interphase. Cell grows and carries out normal cell processes DNA replicates Prepares for cell division Onion root tip Plant cell

4 Stages of Mitosis: Plants & Animal Cells Prophase: Chromosomes condense and form visible bodies. Nuclear envelope breaks down. Onion root tip whitefish Metaphase: Chromosomes line up in the middle of the cell. Spindle fibers attach to the centromeres. Anaphase: Centromeres split. Sister chromatids separate and are pulled to opposite sides of the cell. Telophase: Nuclear envelope reappears. Cytokinesis The cytoplasm and all its contents divide

Lab 7: Mitosis & Meiosis Concepts Part 1 and 4: Modeling –mitosis interphase prophase metaphase anaphase telophase –meiosis meiosis 1 –separate homologous pairs meiosis 2 –separate sister chromatids –crossing over in prophase 1 I PMAT

Lab 7: Mitosis & Meiosis Description Part 5: –crossing over in meiosis farther gene is from centromere the greater number of crossovers observed crossing over in fungus, Sordaria –arrangement of ascospores

Sordaria analysis % crossover total crossover total offspring = distance from centromere % crossover 2 =

Lab 7: Mitosis & Meiosis Description for today’s portion of the lab –Two treatment groups of plant root tips were compared one group was treated with lectin (increases cell division) the other was a control group that had not been treated with lectin (we used cards for these). Chi-square analysis was used

Lab 7: Mitosis & Meiosis Today’s Lab –Based on the description of the lab that you read in your Bellwork and your prior knowledge, what do you expect to see in the two groups of onion root tips (lectin treated and non-lectin treated)?

Objectives for this lab AP Essential Knowledge: 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization Science Practices Science Practice 2: The student can use mathematics appropriately. Science Practice 3: The student can engage in scientific questioning to extend thinking or to guide investigations within the context of the AP course. Science Practice 4: The student can plan and implement data collection strategies appropriate to a particular scientific question. Science Practice 5: The student can perform data analysis and evaluation of evidence.

Mitosis in the Onion Root Tip Today’s lab activity: –examine the tip of an onion root –Count the number of cell in interphase and the number of cell in mitotic phases Root tips are useful to observe mitosis because the cells are frequently dividing as the root grows.

What your root tips might look like

Procedure: Preparing Root Tip 1.Place 3 onion root tips in 1M HCl for 4 minutes 2.Transfer the tip to Carnoy’s fixative for 4 minutes 3.Remove a slide from the Coplin jar containing 70% ethanol, dry it. 4.Place the tip on the slide and cut off the distal 2 mm portion of the tip; discard the remainder of the tip. 5.Cover the root tip with carbol-fushin stain for 2 minutes. 6.Blot off excess stain and cover the tip with 1 drop of water 7.Gently tease the root tip apart with a dissecting probe. Place the cover slip over the root tip 8.Firmly press down on the cover slip with the eraser end of a pencil. DO NOT TWIST

Procedure: Counting Data 1.Find the cells using the scanning lens (4x), then the low power (10x) and then the high power (40x). Remember to use ONLY the fine adjustment (small) knob when you are using the 40x lens!! 2.Look for well stained, distinct cells 3.Within the field of view, count cells in each phase. Repeat the counts in the other two root tips 4.Collect class data for each group. TipInterphaseMitoticTotal 1 2 3

Class Data Control TipInterphaseMitoticTotal Class Data Lectin TipInterphaseMitoticTotal 1 2 3

Data Analysis Perform a Chi Square Goodness of Fit test on the data. Use page S89 in your labbook to calculate your expected values

Extension What other environmental factors could we test this way? How would the experimental design differ from this one? What do you hypothesize would be the results?

Objectives for this lab AP Essential Knowledge: 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization Science Practices Science Practice 2: The student can use mathematics appropriately. Science Practice 3: The student can engage in scientific questioning to extend thinking or to guide investigations within the context of the AP course. Science Practice 4: The student can plan and implement data collection strategies appropriate to a particular scientific question. Science Practice 5: The student can perform data analysis and evaluation of evidence.

Lab 7: Mitosis & Meiosis Conclusions –Mitosis cell division –growth, repair –making clones longest phase = interphase each subsequent phase is shorter in duration –Meiosis reduction division –making gametes –increasing variation crossing over in Prophase 1

Conclusion Questions 1.Summarize the procedure for this lab. 2.The cells in the root of an onion are actively dividing. How might the numbers of cells found in this region differ from a different part of the plant? 3.What stage were the majority of the cells in the water treated root tips? 4.What happens when cell division is interrupted? 1.What process must take place before mitosis can begin? 5.What process must take place before mitosis can begin?

Conclusion Questions 6.Why is mitosis important? Where does mitosis take place? 7.Give an example of cells in your body that divide slowly or do not divide at all. 8.What is cancer? How does cancer affect the rate of mitosis? 9.How would a slide of cancerous cells look different from this one? 10.What type of cells in your body do not divide by mitosis?

Acknowledgements: M. Arias Images taken from the following sites: tip-mitosis-lab/ s/PDFs/GIB-RootingforMitosis.pdf