Monocotyledonous plants have large chromosomes, which are nicely visible in the experiments. The meristematic tissues that are enabled at the tip of the roots provide a good source for the study of the process of mitosis. Onions are monocotyledonous plants possessing large chromosomes, hence their root tip is used for studying.
Cell division is required for maturation, growth, maintenance of the tissues, repairing of cells and others. The aim of the experiment is to study and demonstrate the process of mitosis through the preparation of the mount of an onion root tip.
For the maturation, growth, maintenance of tissues, repairing and synthesizing of cells, the division of the cells is essential. There are two types of cell division, one is mitosis and other meiosis.
Prophase is the first stage of mitosis whereupon the division of the cells is initiated. In this stage, the coiling and the thickening of the chromosomes occurs. The process progresses with the shrinking and disappearance of the nucleolus and the membrane of the nucleus takes place. In the final stage of the prophase, the cluster of fibre manages to form the spindle fibres.
In the metaphase, the chromosomes turn thick at first. Then the two chromosomes from each of the chromosomes appear distinct. All the single chromosomes are fastened to the spindle fibres located on its controller. The chromosomes make their alignment at the centre of the cell in a line. In the anaphase, every chromatid pair detaches from the centromere and proceeds to the other end of the cell via the spindle fibre. In this stage the cell membrane also begins to compress at the centre of the place.
The last stage of mitosis is known as the telophase. In this stage the chromatids reach the other end of the cell.
Figure 1: Different Stages of Mitosis
The spindle fibre starts disappearing. The fibres of the chromatin formation take place as an outcome of the uncoiling of the daughter chromosomes. The formation of the two daughter nuclei at the two ends takes place because of the formation of the nucleolus and the membrane of the nucleus. This is the end stage whereupon the splitting of the cell or the process of cytokinesis takes place.
After the end of mitosis, the next stage known as the interface takes place. The interface is also a kind of the cell cycle that is non-dividing and is in between two consecutive divisions of the cell. In many cases, the cell spends most of its time in interface. It consists of the G1, S and the G2 stages.
The materials that are required for the experiment are
Compound microscope
Glass slide
Blade
N/10 hydrochloric acid
Needle
Burner
Dropper
Watch glass
Water
Filter paper
Coverslip
Acetocarmine stain
Aceto alcohol (glacial acetic acid, and ethanol in the ratio of 1:3)
Onion root peel
Vials
Forceps
At first, an onion must be kept on the tile followed by snipping off the dry roots with a sharp blade. After this, the bulbs need to be placed in the beaker containing water for the growth of the root tips.
After a few days, have the new roots trimmed and placed in the watch glass. Through the use of the forceps, shift it into a vial having the aceto alcohol. Let the root tips be in it for one whole day.
Get one root and keep it in the new glass slide. Thereupon the N/10 hydrochloric acid must be added with the help of a dropper at the tip of the root. Two to three drops of the acetocarmine stain must also be added now.
Now heat it lightly on a burner such that the stain does not get dried up. The additional stain must be treated with the filter paper. The extra stained part of the root should be trimmed with the help of a blade.
Remove the additional less stained part and keep the more stained part. A drop of water must be added now and a coverslip should be mounted.
After this, the coverslip must be taped softly with an unsharpened end of the needle such that the meristematic tissue under the tip of the root under the coverslip is squeezed nicely and gets straightened as a fine thin layer.
After this, it can be stated that the onion root tip cell slide is prepared and the different stages of mitosis is examined. At this moment the slide is also prepared for examination under the compound microscope.
Figure 2: Mitosis cell in the Root tip of Onion under a microscope.
After keeping the stained root tip slides under the stage of the compound microscope, the alterations and modifications are noticed. Henceforth, the different stages of the root cells can be noticed that is prophase, metaphase, anaphase, and telophase.
Mitosis and meiosis are two distinct processes of cell division.
Temporary mounting involves putting a specimen in water.
Mitosis is important for cell growth.
Mitosis is an important procedure in the cell and the growth and development of the organism. Onion roots are one of the favourite subjects because it is monocotyledonous with dense chromosomes. The different phases can easily be noticed under the microscope that is prophase, metaphase, anaphase and telophase.
Q1. What are the other materials that can be used in the mitosis study?
Ans. Other cells that can be used are shoot apex of the plant, gills of fish. Additionally, tadpole larvae can also be used.
Q2. From where does the spindle fibre originate?
Ans. In the case of plant cells, it originates from cytoplasm. In the case of animals, it develops in centrioles.
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