Download CELL CYCLE and THE LENGTH OF EACH PHASE

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Lab Onion Root Tip
Do NOT take home!!
Introduction:
A single fertilized human egg cell will divide to form two cells. These two cells will each divide into two cells. In time,
trillions of cells are produced. The cycle of growth and division takes place in three major stages:
1. Interphase: The life and times of the cell (including growth and prep for division).
2. Mitosis: The division of nuclear material, in which each new cell obtains the same number of
chromosomes and the same DNA code as the original cell. It occurs in four phases.
3. Cytokinesis: The division of the cytoplasm to create two new cells. After cytokinesis, each cell enters
the stage of interphase.
Purpose:
In this investigation, you will
 Locate cells in prepared onion root slides that are in the process of interphase and dividing mitosis.
 Identify cells in interphase and in each of the four stages of mitosis in the onion root tips by comparing them
with diagrams.
 Study the changes which occur in a cell as it undergoes the cell cycle.
Materials:
Microscope
Prepared Slide of Onion Root Tip (Alium)
Lens Paper
Procedure:
1) Observe the prepared onion root tip slide using correct
microscope procedures.
2) The dividing cells will be found near the root tip. Find the
region of dividing cells just above the root cap.
3) Using the “Rules for Lab Drawings,” draw one example of
each phase of the Cell Cycle using high power. Draw one cell
demonstrating a phase on its own half-sheet of white paper.
4) Label the appropriate structures on each of the drawings of
the phases. Only draw what can be seen, however, when appropriate, label the area the structure would appear.
chromosome
chromatin
spindle fibers
metaphase plate
nucleus
cell plate
nucleolus
poles
5) Attach the white sheets to the back of the lab notebook pages using ONE piece of tape or staple (left side of
notebook).
6) On the corresponding right hand page, answer phase appropriate Analysis Questions, in complete sentences.
Revised 2014/2015 Turner
Pre-Lab Questions:
From the Introduction:
1. What are the 3 major stages of the Cell Cycle?
From the Procedures:
1. Where are the dividing cells found on the onion root tip specimen?
2. What rules will you be using to get full credit on your drawings?
3. What structures will you be labeling?
4. Where will the sheets be attached?
5. Where will the questions be answered?
ANALYSIS QUESTIONS FOR ONION ROOT TIP LAB
Answer phase appropriate questions, in complete sentences, on the right side of your notebook next to the drawing
(attached to the left side of your notebook) representing that phase.
Interphase
1. Are a nucleolus and a nuclear membrane present in the cell?
2. Are distinct rod-shaped structures called chromosomes easily observed in the nucleus at this time?
3. What term is used to describe nuclear contents (the form of the DNA) during interphase?
4. What important event occurs to DNA during interphase?
Prophase
5. Are chromosomes now visible during prophase?
6. Describe the changes that have occurred to the nucleolus and nuclear membrane from interphase to prophase.
7. Explain why chromosomes can now be observed but were not observable during interphase.
Metaphase
8. Describe where the chromosomes are now located in relation to the cell.
9. What are the fibers called that become more visible during this phase?
10. What term is used to describe the structure at which each fiber attaches to a chromosome?
Anaphase
11. In metaphase, chromosome pairs were lined up along the cell’s center. Describe what is occurring to each chromosome
pair during anaphase.
12. Toward what area of the cell are the chromosomes being directed?
13. What structure is responsible for the movement of chromosomes during this phase?
Telophase
14. What cell parts begin to reappear during this phase?
15. Explain how the number of chromosomes found in each daughter cell compares to the number found in the original
cells before mitosis. (HINT: re-read the Introduction if you are unsure).
16. To prepare for cytokinesis, what forms in a plant cell that will eventually become a cell wall?
Cytokinesis & Summary
17. How many cells have now formed from an original cell?
18. Explain the purpose of the cell cycle and mitosis for eukaryotes.
19. Why does the number of cells increase rather than the size of the cells in order for an organism to grow?
20. What evidence do you have from your experience that cells spend the majority of their time in Interphase?
Revised 2014/2015 Turner