Onion Root Tip Lab 50 pts http www
Onion Root Tip Lab 50 pts http: //www. biology. arizona. edu/c ell_bio/activities/cell_cycle/cell_c ycle. html
Objectives l l Identify cells in different stages of the cell cycle. Calculate how long a cell stays in a particular stage of the cell cycle. l l l Calculate percentages. Translate this into real time. Infer why a cell would spend the amount of time it does in each stage. Essential Questions l l How long does a cell spend in each stage of the cell cycle? Why does the cell spend so much of its time in a particular stage?
Somatic Cell Division
Plant (Lily) Cell Division
Human Karyotype
Human Karyotype
Chromosomes & Chromatids Eukaryotic Chromosomes l In G 1, our cells start to express genes. This happens throughout the life of a cell, but it starts in G 1. l Genes are stored on regions of DNA contained in structures called chromosomes. Human Chromosome #1 NCBI https: //www. ncbi. nlm. nih. gov/genome
Chromosomes & Chromatids l A chromosome is one unbroken structure of DNA. l l It can be single-stranded (before S phase or after anaphase) or double stranded (after S phase is complete). Each chromatid is made of a single, long molecule of DNA containing 1 set of genes. Depending on the stage in the cell cycle being studied, chromosomes are identified or illustrated as single columns of 1 chromatid (as they would be in G 1 or Anaphase)… …or as “X”s (as they would be after replication) l In this state, it’s actually 2 identical chromosomes formed after the original has been replicated during the S phase, joined in the center. Each of the two thick strands of a fully condensed, duplicated chromosome (illustrated here) are called a chromatid.
Chromosomes & Chromatid Eukaryotic Chromosomes l During replication the DNA of every chromatid and all genes associated with them is copied. l The identical pairs of chromatids formed after replication are called sister chromatids. l l Why do the sister chromatids need to be identical? l l The sister chromatid stay attached until anaphase of mitosis. During cell division, the sister chromatids are separated at the centromere, and one ends up in each daughter cell. They need to be identical so the daughter cells will have the exact same genes and do the exact same things. Centromere: The region that holds two sister chromatids together. CENTROMERE
Fig. 12 -4 0. 5 µm 1 Chromosome is also 1 chromatid DNA molecules Chromosome arm Centromere Chromosome duplication (including DNA synthesis) 2 sister chromatids Connected at centromere = 1 chromosome Separation of sister chromatids occurring in anaphase 2 chromosomes: 1 chromosome as 1 chromatid Per cell Sister chromatids Centromere
Interphase Plant Mitosis. Prophase – Overview • Nucleolus is clearly visible. • Nucleus is intact • Chromosomes are not defined. • Can’t tell if it’s G 1 -S-G 2. • Chromosomes are marbling (starting to condense) • Nucleus is breaking down Metaphase … MIDDLE Anaphase … AWAY EQUATOR • Chromosomes (condensed) align down the equator (in the middle) • No nucleus. Chromatids = Fingers. • Sister chromatids are moving away from each other. • Moving toward opposite poles, pulled by spindle fibers to centrosomes. Telophase Cytokinesis …LOOKS LIKE INTERPHASE Chromatids = Fists. • Chromatids (also called chromosomes) are organized into two forming nuclei on opposite sides. • Cell plate forms • Looks just like interphase, only smaller.
Plant Mitosis -- Review Prophase Interphase Cytokinesis Interphase Metaphase Anaphase Telophase
l In order to examine cells in the tip of an onion root, a thin slice of the root is placed onto a microscope slide and stained so the chromosomes will be visible. Root tip cells are good to look at because they divide often and allow us to see cells in the different stages. The cells you'll be looking at in this activity were photographed with a light microscope and then digitized so you can see them.
On to the exercise l Today, you are going to study an onion root tip picture to 1 st identify which stage the cells are in and 2 nd calculate the time cells spend in different phases of the cell cycle. l Review the major phases of the cell cycle. l l Interphase Mitosis l Prophase l Metaphase l Anaphase l Telophase Cytokinesis We’ll be concentrating on these because these are the only ones we can tell the difference between. l We can’t tell the difference between interphase and cytokinesis cells.
Pre-Lab Get into groups, then pair up. On the back of your ½ sheet of notes. Identify cells 1 -8 in your groups. You have 4 minutes to pair up and solve. Word Bank - Telophase - Interphase - Prophase - Anaphase - Metaphase 1 Metaphase 2 Prophase 3 Telophase 4 Interphase 5 Interphase 6 Interphase 7 Anaphase 8 Interphase
Pre-Lab Get into groups, then pair up. On the back of your ½ sheet of notes. Determine the % of cells that are in interphase. You have 2 minutes to solve. # in interphase 12 Total number of cells 22 = . 55 X 100 = 55 %
Prediction/Hypothesis l The first question is how do you think you can determine a realistic amount of time a cell spends in a particular stage of the cell cycle based on a still image? l Part I: It depends on the % of cells in each stage at any particular point in time. l For example, for these cells, if 50% are in interphase we can guesstimate that these cells spend 50% of their time in that phase. l Every cell should exhibit this behavior because they are the same type of cell. l Cells are living and change through time so we assume that… l By calculating the % of cells seen in an image at any given time, we can get an idea of how much time cells spend in each stage over their lives. l Remember, the cell cycle is cyclical.
Prediction/Hypothesis l The first question is how do you think you can determine a realistic amount of time a cell spends in a particular stage of the cell cycle based on a still image? l Part II: It depends on the how ling it takes for this species to go completely through the cell cycle. l For example, if this species takes 48 hours to go through the cell cycle, 50% of it’s life is in interphase, meaning 24 hours would be spent in interphase. l Again, every cell should exhibit this behavior because they are the same type of cell. l Cells are living and change through time so we assume that… l By multiplying the percentage of cells in a stage by the total time for this species’ cell cycle we can calculate the amount of time a cell spends in each stage. l Remember, the cell cycle is cyclical.
Make your prediction. l l The cell cycle you drew and the book reference suggests that cells spend about _____% of their lives in interphase. We have an idea of how long a cell spends in interphase, but how long in Prophase? , Metaphase? Anaphase? Telophase? Predict how long onion cells spend in each stage of the cell cycle. l Remember, this hypothesis will serve as a prediction that can be tested. l Keep in mind the question: How long does a cell spend in each stage of the cell cycle? Your prediction will be an educated guess on how many hours (out of 24) does a onion root tip cell spend in each phase.
l Fill in the top row. l All 5 boxes need to add up to 24 hours. Interphase Prophase Metaphase Anaphase Telophase Predicted time in phase Fill Out. These should add to 24. Total 24 hrs Number of cells (Data) 77 Percent of cells (Results) 100% Actual calculated time 24 hrs
The Method l l You will study the picture, each taken from a larger sample of an onion root tip that was photographed during natural development. By determining the number of total cells in each phase and dividing this number by the total number of cells one could calculate and predict a general average of how long each particular cell stays in each stage.
Decide which phase each numbered cell is. IF YOU THINK THE CELL IS IN 1. Anaphase CYTOKINESIS THEN COUNT IT AS 2 CELLS IN INTERPHASE 2. Interphase 3. Telophase OR ONE CELL IN TELOPHASE. 4. Prophase 5. Metaphase 3 1 IF YOU CAN’T TELL (it’s too dark or washed out) ASSUME IT’S IN INTERPHASE 5 THE NUCLEOLUS IS THE FEATURE OF A CELL IN INTERPHASE 2 4
The Assignment l l l In this activity, you will be presented with cells from the tip of an onion root. You will classify each cell based on what phase it is in. At the end PREDICT you will count up the cells found in each phase and use those numbers to predict how much time a dividing cell spends in each phase. You can base your calculation on a total cell cycle of Label each cell and COUNT (verify) 24 hours. We will use the data we gather in order to determine the % of cells in each phase, yes, but CALCULATE % also to predict the amount of time a cell spends in these phases, on average based upon a 24 hour life. TRANSLATE INTO You will use a small sample size for time, but this TIME experiment has been repeated thousands of times with thousands of root tips and has been ANSWER found to be a good predictor of average cellular QUESTIONS activity.
Decide which phase each numbered cell is!!! IF YOU THINK THE CELL IS IN 1. Anaphase The Logic: CYTOKINESIS THEN COUNT IT If we can calculate the % of cells AS 2 CELLS IN INTERPHASE 2. Interphase in each stage from a given 3. Telophase sample now, this % will apply to 4. Prophase the whole organism all the time; OR ONE CELL IN TELOPHASE. 5. Metaphase meaning if we took the same 3 THE NUCLEOLUS IS THE PREDICT COUNT CALCULATE % TRANSLATE INTO TIME ANSWER QUESTIONS picture any time in the future some cells will be in different phase, but the % will be the same. 1 FEATURE OF A CELL IN INTERPHASE IF YOU CAN’T TELL (washed out or too dark) ASSUME IT’S IN INTERPHASE 2 4 5 THESE ARE 2 CELLS IN INTERPHASE YOU HAVE THE REST OF CLASS TO WORK ON THIS It’s due If you have questions, ask. When you are finished you can check in with me and use the rest of time to complete “Mitosis Notes”
If you haven’t done so already, copy this table onto a piece of paper. You can enter data in this table as you go along, or at the end of the activity. Interphase Prophase Metaphase Anaphase Telophase Predicted time in phase Total 24 hrs Number of cells (Data) 77 Percent of cells (Results) 100% Actual calculated time 24 hrs
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