Name: ______

Teacher______

Class and Period______

Date______

Lab 4 Onion Root Tip Lab

(Based on the following: http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html)

Background: In this lab, you are going to determine the relative amount of time spent in different phases of the cell cycle. Growth in an organism is carefully controlled by regulating the cell cycle. In plants, the roots continue to grow as they search for water and nutrients. These regions of growth are good for studying the cell cycle because at any given time, you can find cells that are undergoing mitosis.
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. The cells you'll be looking at in this activity were photographed with a light microsope and then digitized. /
Although slicing the onion root captures many cells in different phases of the cell cycle, keep in mind that the cell cycle is a continuous process. Scientists have divided the process into 5 phases, each characterized by important events, but these divisions are still arbitrary. / (An animal cell during interphase)

The life cycle of the cell is typically divided into 5 major phases. The phases are listed below, along with the major events that occur during each phase; these cells are from an animal, not a plant.

/ Interphase. The cell is engaged in metabolic activity and performing its duty as part of a tissue. The DNA duplicates during interphase to prepare for mitosis (the next four phases that lead up to and include nuclear division). Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible.
/ Prophase. Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes. The nuclear membrane dissolves, marking the beginning of prometaphase. Proteins attach to the centromeres creating the kinetochores. Microtubules attach at the kinetochores and the chromosomes begin moving.
/ Metaphase. Spindle fibers align the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate. This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.
/ Anaphase. The paired chromosomes separate at the kinetochores and move to opposite sides of the cell. Motion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules.
/ Telophase. New membranes form around the daughter nuclei while the chromosomes disperse and are no longer visible under the light microscope. Cytokinesis or the partitioning of the cell may also begin during this stage.

In this activity, you will be presented with cells from the tip of an onion root. The purpose is to classify each cell based on what phase it is in and to predict how much time a dividing cell spends in each phase. The prediction of how much time is spent by a dividing cell can be found by counting the cells found in each phase and use those numbers to calculate the number of minutes spent in each phase based on a total cell cycle of 12 hours (720 minutes).

Mitosis Onion Root Tip Lab Tips Sheet

The organism you are making observations of in this lab is an onion of the genus Allium. The pictures you cut out and identify the phase of the cell in the cell cycle are from the tip of the root at the end of the onion that was in the ground. The cells are in a special type of tissue found in plants called meristem. Meristematic tissue is like embryonic tissue in that it is made of rapidly dividing, small, immature cells that are not specialized into any particular type of tissue yet. This makes meristematic tissue perfect for this lab.

However the pictures at the beginning of the lab that look like they are of round cells are NOT onion cells. They are not even plant cells. These cells are generic animal cells (those model cells that get drawn in textbooks as examples, but no cell like that actually exists). This is important because mitosis in animal cells and plant cells is different. The key difference you need to observe occurs during telophase/cytokinesis. The animal cells develop the cleavage furrow that looks like a pinching in of the membrane, or a fold like in a peach, due to the constriction of a ring of protein around the equator of the cell that eventually cuts it in two. Plant cells have to reform the cell wall; therefore, the plant cell lays down a row of vesicles from the Golgi that forms the cell plate and eventually the new cell wall.

The WORDS with those pictures that describe each phase, ARE GOOD for helping you determine the different phases the cells are in. Below is a little more help:

The Procedure:

INTERPHASE – these cells either have the nucleolus visible, OR no white space visible because the DNA (chromatin) has not condensed enough to leave space between the separate chromosomes

or

PROPHASE – the nucleolus is never visible (it has disassembled) and white space is visible between the condensing chromosomes

METAPHASE – these are the easiest cells to recognize. The condensed chromosomes are lined up across the middle of the cell

ANAPHASE – the cells are moving toward the other side of the cell. When they are not yet at the poles and/or if there is no cell plate forming yet, it is anaphase

TELOPHASE – the chromosomes are at the poles and the cell plate is forming (or a cleavage furrow if it’s an animal cell)

The Calculations Table: Remember that the row of boxes in the table should add up to the number in the total column.

Remember: Scientific drawings are accurate sketches of the entire field of view, titled, include the magnification, have all labels down the right hand side and a ruler is used to draw straight, horizontal lines that do not cross each other.

(cut these out)


Name: ______

Teacher______

Class and Period______

Date______

Onion Root Tip Lab

Purpose: (write a one sentence statement explaining the purpose of the lab). (PRE-LAB)

______

Hypothesis:

If there are more cells present in interphase than any other phase, then interphase is the longest phase.

Safety:

·  Follow rules for microscope use.

·  Wear goggles if staining your own slide.

·  Use caution when using scissors.

·  Use caution when using glue.

Materials/Equipment:

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Scissors

tape

Prepared onion root tip slide

Microscope

Pencil

Colored pencils

Calculator

ruler

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Procedure:

1. Cut out cells from page 3. (PRE-LAB: IT IS RECOMMENDED THAT YOU DO THIS STEP AS YOUR PRE-LAB AND BRING TO CLASS IN A BAGGIE ON LAB DAY)

2. Arrange the cut out cells into their appropriate column in Data Table 1 on page 6. You should find 20 in interphase, 10 prophase, 3 metaphase, 2 anaphase, and 1 telophase. Notice that the table is labeled with an appropriate title and number.

3. Once you have the cells in their correct column and have the correct number for each, tape your cells down. Please use tape sparingly!

4. Next, look at the prepared slide of an allium root tip or at the picture of an allium root tip slide on the projector screen.

5. Make an appropriate scientific drawing in the space provided (figure 1 on page 7) by drawing what is seen in the field of view in PENCIL and color in COLORED PENCIL.

6. Write a title it above with the name and write the magnification below (400x) since it was on high power.

7. Then using proper labeling techniques, make appropriate labels according to the instructions. Label lines should be straight—use a RULER! Label lines should ONLY go out to the RIGHT.

Data:

Data Table 1. Cell Cycle Observations in Onion Root Tip Cells

INTERPHASE / PROPHASE / METAPHASE / ANAPHASE / TELOPHASE

In your own words write an explanation of Data Table 1. Include whether this is quantitative data, qualitative data or both quantitative and qualitative and explain why.

______

Look at an Allium root tip under the microscope or from a picture taken through a microscope.

In your own words describe what you see in your field of view by describing what the cells in the following stages look like to you. Be sure to include the phase names: interphase, prophase, metaphase, anaphase, and telophase.

______

Analysis: Determine the percent of cells in each stage from the cells in Table 1 and the relative amount of time spent in each phase as indicated in Table 2 below. Interphase has been done for you. You must SHOW YOUR WORK!

Table 2. Time Spent in Each Stage of the Cell Cycle

Interphase / Prophase / Metaphase / Anaphase / Telophase / Total
Number of cells / 20 / 10 / 3 / 2 / 1 / 36
Percent of cells / (20/36) x 100 = 55.6% / / / / / 100%
Time in each phase / (20/36) x 720 = 400 / 720 min

Conclusion Question:

1. Discuss all of your results and reference your data (restate the results of Table 1 and Table 2). (As shown in Table 1…; As and use your analysis to EXPLAIN WHAT THE RESULTS MEAN (According to Table 2…) DISCUSS EVERY SINGLE PIECE OF INFORMATION THAT IS THERE—YOU WILL WRITE A LOT. Write in present tense. No pronouns. Here’s a few hints to help you think about what you should be getting out of the data and analysis.

·  Explain what your observations imply.

·  Were there more cells in a particular phase, if so which phase? What does this mean about the time cells spend in that phase? Why do they spend the most time in this phase?

·  In which phase were there the least amount of cells? In which phase did the cells spend the least amount of time? Why are these the same phase?

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Name______

Per_____

RUBRIC - Onion Root Tips Lab

(2 formative grades)

Pre-Lab: (5 points)

Purpose: ______/5 pts

·  complete sentence, starting with “The purpose of this lab is to…”

·  no pronouns

Data: (45 points)

Table 1 ______/45 pts

·  Cells glued/taped neatly ______/4

·  Cells placed in appropriate columns ______/36

·  Explanation of type of data ______/5

Figure 1 ______/10 pts

·  Description of what is seen ______/10

Analysis: (16 points)

Table 2 ______/16 pts

·  all 12 boxes complete ______/8

·  work shown ______/8

Conclusion: (34 points)

In own words; in paragraph form

·  Discussed all results, referencing data tables and figures ______/16 pts

·  Used analysis to explain what the results mean ______/16 pts

·  In present tense; no pronouns ______/2 pts

TEACHER DESCRETION: Even though all of the above may be included in your lab you could possibly lose points for items such as writing in sentence fragments, inaccurate calculations, items not in correct order, messy work, not using class time wisely, etc. Points Lost (if any): up to 10 points ______

Points Missed: ______

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