Mitosis: (onion roots) Root cells are good for observing mitosis; this is because they’re in the tip of the root which is an area of the plant that grows quickly. This results in more cells going through mitosis all at once, also allowing us to examine the different stages of mitosis. Stages:
1. Interphase: DNA replicates, but has not formed the condensed structure. They remain as loosely coiled chromatin. The nucleus is still intact.
2. Prophase: The DNA molecules progressively shorten and condense by coiling, to form chromosomes. The spindle fibres are pulled to opposite sides/poles of the cell.
3. Metaphase: The spindle fibres attach themselves to the centromeres of the chromosomes.
4. Anaphase: The spindle fibres shorten and the centromere splits, separated sister chromatids are pulled along behind the centromeres.
5. Telophase: The chromosomes reach the poles of their respective spindles. Nuclear envelope reform before the chromosomes uncoil. The spindle fibres disintegrate.
1. Place some premixed 1 molar Hydrochloric acid and Acetic Orcein in the watch glass.
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Be careful not to get this mixture on your skin or clothing. * Hydrochloric acid (HCL) breaks down the middle lamella and softens the cells tissue and the cell will lose its 3-D shape.
2. In to this mixture place the terminal (end) 3 or 4 mm of a garlic root (remove the rest of the root). * The cut end needs to be removed in order to avoid random errors.
3. Place on the 40oC heating blocks to warm. In a short time (a few minutes) the root tip will feel soft when touched with a mounted needle (Do not let it dry out completely). Heat it in order to speed up the process of the cell wall breaking down, and also for the stain to spread quicker. The stain will bind with the DNA, and it will become more visible.
4. Now, using forceps or the mounted needle, pick up the softened root tip and transfer it in to a clean slide.
5. Add a few drops of Acetic Orcein
6. Using a mounted needle macerate (Squash) the root tip.
7. Once this procedure is complete, apply a clean cover slip to the slide and heat it gently on the 40oC heating blocks for 10 seconds to intensify the stain.
- This will spread the stain and allow it to bind with the DNA.
8. Then invert the slide on a blotting paper and push down ward firmly, applying pressure with your thumb over the cover glass. This should flatten the cells and disperse them so they can be observed under the microscope.
- This will help flatten it to cell thick.
- Depending upon how effective your squash has been you may either use this or a pre-prepared slide to observe the stages of mitosis in the root tip; you will use either one to identify and record the different stages of mitosis.
Variables: Independent Variables: The slide itself, however, we don’t know anything about the slide.
Dependent Variable: The percentage of cells in each stage of mitosis. Controlled Variables: No. of cells counted. The magnification power used. Were my results valid and reliable? Valid: To ensure my results were valid, I compared my results with the other classes’ results, who were also undertaking the same experiment. Also, I compared them to other results I’ve have online, and made sure they both agree. Reliability: My results were reliable because, 20 other different students in my class also did the experiment, and my results are the average of them all.
Errors: I have identified some systematical errors, such as; students consistently looking at the wrong section of the root, as opposed to the growing section. We do not want this as it will damage our results—However, if one individual does this then it will become a random error along with students confusing stages together. e. g. If you look at the attached data; student ‘TW’ overestimated the telophase cells, and underestimated the prophase cells. This is a prime example of a random error in my results. Trends and patterns: I have identified several trends and patterns in my results, for example; the interphase stage took the longest.
I expected this to be the case because interphase has along of stage within itself, so it is understandable for it to take considerable more time than the rest. Also, I have noticed that anaphase took the shortest amount of time, as it is just the centromeres splitting and separating. Process of Mitosis: If a group of cells is dividing rapidly, a high proportion of the cells will be undergoing mitosis. A group of cells that is not dividing will have all cells in interphase of the cell cycle. The amount of cell division occurring in a tissue can be quantified using the mitotic index.
The mitotic index is used for studying tumour growth in cancer patients. Using the formula below, calculate the mitotic index for your root tip preparation. If you have time, compare this value with the mitotic index of an area of cells away from the root tip and comment on your findings. e. g. Mitotic Index = number of cells containing visible chromosomes total number of cells in the field of view Data analysis: #DIV/0! = Mean. // #DIV0! Of the phases; 13. 126315. – Precision: To the nearest cell (1dp) Title: % of time spent in each phase cycle.