4.05 lab

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Jan 9, 2024

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Cell Cycle Lab Report Instructions: For this lab activity, you will examine a section of an onion root tip under a compound light microscope to determine the approximate amount of time spent in each stage of a cell’s life cycle. At the end of your lab activity, you will complete chi-square testing using some of your data. Submit your lab report to your instructor when completed. Title: Cell Cycle of Onion Roots Objective(s): Determine the amount of time an onion root tip spends in each stage of its cell’s life cycle. Hypothesis: I predict that the cell cycle of the onion root will spend the most time in interphase, because it prepares the cell for division and allows it to grow before the cycle, therefore this stage will have the highest time. Procedure: Access the virtual lab and complete both examinations of onion root tip cells. The materials are listed for you. However, you are responsible for providing a brief summary of the steps you followed during the experimental procedure. Materials: Cell Cycle Virtual Lab Summary of Steps: 1. For this lab i observed a part of the onion root tip through a compound light microscope. 2. The roots were cut and separated into small sections on the microscope slides, staining so you can see the chromosomes more, and covering the slide with a cover slip. 3. For each slide I classi±ed the cells on what phase it’s in, and then counted the amount of cells in each phase. 4. I used the amounts to predict how long a dividing cell takes in every phase.

Data: Table 1 Record any observations about the cells you observed. What does the cell look like for each stage? What is a distinguishing visible feature of each stage of the cell cycle? Description of cell Interphase I noticed each cell in interphase has squiggly lines or chromatin (~) scattered around the cell. Mitosis Prophase I noticed each cell in prophase the squiggly lines came together to form x’s that also scatter around the cell. This would be the visibility of the chromatin to the chromosomes because of the microscope. Metaphase I noticed each cell in metaphase had x’s along the middle of the cell and spindle ±bers connecting to them. (this feature seems to be the beginning of the division) Anaphase I noticed each cell in anaphase has the same feature as the metaphase cells, but the ±bers pull the chromosomes/x’s and separate to each side of the cell. There was also some kind of ripple in the walls between the separation. Telophase I noticed each cell in the telophase have the same squiggly lines as interphase had, but the ripple in the walls of the cell are more de±ned (it seems that the cell is dividing/pulling into two separate ones) Table 2 Record the number of cells you observed in each part of the lab activity.

Number of Cells in Trial 1 Number of Cells in Trial 2 Interphase 17 11 Mitosis Prophase 3 5 Metaphase 2 4 Anaphase 2 3 Telophase 1 2 Table 3 In this table, list the number of cells in interphase for each trial, then add up all the other stages under the mitosis column. Place these numbers in the chart below: Interphase Mitosis Trial One- Control 17 25 Trial Two- Treated 11 25 Calculations

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Calculate the percentage of the cell cycle spent in each stage for both trials. Number of cells in given stage ÷ total number of cells counted × 100 = % of the cell cycle spent in this stage. Record your percentages below: Interphase Prophase Metaphase Anaphase Telophase Trial 1 68% 12% 8% 8% 4% Trial 2 44% 20% 16% 12% 8% Conclusion: Write a conclusion statement that addresses the following questions: Based on my data collected, I can infer the most time a cell spends in its life cycle in an onion root s interphase. I believe this because during interphase is where the most activities occur so it takes longer. The longest stage was interphase and the shortest was telophase. I believe interphase takes the longest because more happens ( cell growth, replication of chromosomes, cell division preparation), and telophase takes the hottest because all it has to do is divide the sister chromatid into daughters. My data does support this because for both trials most of the cells took the longest in interphase (68% and 44% of the time) and the least in telophase (4% and 8%)! Some sources of error that could impact the results of this investigation if it were repeated in a physical laboratory could be the type of root, and conditions (like temperature. :) Lab Reflection Questions Answer the re²ection questions using what you have learned from the lesson and your experimental data. It will be helpful to refer to your class notes. Answer questions in complete sentences. 1. What differences can you see when you compare the nucleus of a dividing cell with that of a non-dividing cell? Some di³erences I can see when I compare the nucleus of a dividing cell with a non-dividing cell is that in dividing cells you can see the nucleus and in non-dividing cells you can’t; and the stages prophase, metaphase, anaphase and telophase can also be seen!

2. If your observation had not been restricted to the tip of the onion root, how would the results be different? If my observation included the rest of the onion, how would the results be di³erent because the rest of the plant is more developed than the root, so I believe most of the cells would be in the later stages. 3. If you need assistance on chi-square hypothesis testing for the question below, refer to the pre-lab activity of your lesson. Agriculturalists investigating a poorly growing onion crop discovered it was infected with a fungal pathogen. The fungus secreted a lectin-like protein in the soil surrounding the onions’ roots. Lectins often accelerate mitosis in root systems, but this abnormal growth creates weaker plant tissues. Three samples of 25 cells each were observed from the struggling onion crop. The observed number of cells in each part of the cell cycle are shown below: Interphase Mitosis Sample One 11 14 Sample Two 9 16 Sample Three 12 13 a) State the null and alternative hypothesis related to the data. The crops with weaker plant tissues due to fungal pathogen infection will not a³ect the number of cells in each part of the cycle.

b) Calculate the chi-square values for interphase and mitosis using your trial one data in table 3 as the expected data (e). These cells are normal, onion root tip cells. Use the sample data above as the observed values (o). These samples were exposed to lectin. 10.4 was my calculation c) Using the chi-square table, determine the critical value for interphase and mitosis of the struggling onion crop using the chi-square values in (b). It would be 0.01 because 3-1=2 and the closest value to 10.4 under 2 is 9.21! p- value Degrees of Freedom 1 2 3 4 5 6 7 8 0.05 3.84 5.99 7.82 9.49 11.07 12.59 14.07 15.11 0.01 6.64 9.21 11.34 13.28 15.09 16.81 18.48 20.09 Based on the chi-square and critical value, draw a conclusion about the null hypothesis. Based on the chi-square and critical value, 9.21 is less than 10.4 so the null hypothesis can;t be rejected! :)

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