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Mitosis is the process of cell division, where one parent cell splits into two daughter cells. A temporary mount is also known as a wet mount. In a temporary mount, the specimen under observation is put in water, or glycerine in-between the slide and the coverslip, and is observed. The onion root tip is an ideal cell specimen used to study mitosis since the root tip is characterized by the presence of a meristematic cell. Further onion is monocotyledon in nature, thus it is easier to study the nature and changes in the chromosomes. The process of preparing a temporary mount of the onion root tip, along with a brief overview of mitosis is given below.
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Key Terms: Mitosis, Phases of Mitosis, Onion Root, Meristematic Cells, Monocotyledon, Chromosomes, Cell Division, Cells, Tissues, Temporary Mount
What is Mitosis?
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We know that each and every living organism is made up of a basic unit, a cell. New cells must be produced for an organism to maintain the regular life processes like, growing, maturing, and retaining tissue. All cells in an organism are made up of pre-existing cells that have been divided. Cell division is necessary for life to continue. Mitosis and meiosis are the two basic processes of cell division. Mitosis is critical to life because it generates new cells for growth, and eliminates the dead cells.
Mitosis is the biological process which includes the division of a parent cell into two daughter cells after the nucleus of a eukaryotic cell divides in two. Cytokinesis and karyokinesis are the two activities that occur during cell division. Karyokinesis is the process of nucleus division, while cytokinesis is the process of cytoplasmic division. Mitosis is affected by factors like temperature, and time. Mitosis can be divided into four phases.
Mitosis
Read More: Difference Between Karyokinesis and Cytokinesis
Phases of Mitosis
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Mitosis can be subdivided into four phases, they are:
Prophase
During prophase, the chromosomes come together and undergo thickening. Then they undergo coiling. This marks the beginning of mitosis. The nucleolus and its nuclear membrane shrink and vanish. The commencement of the formation of a bunch of fibres to form a spindle marks the end of the prophase.
Metaphase
In metaphase, the chromosome thickens, and each chromosome's two chromatids become apparent. It also has a centromere, at its centromere, each chromosome attaches to spindle fibres. The chromosomes are then positioned at the cell's midline.
Anaphase
Each chromatid pair separates from the centromere and moves to opposite ends of the cell through the spindle fibres during anaphase. And then, at the centre of the cell, the membrane begins to pinch. This marks the beginning of the final phase, telophase.
Telophase
In this phase, the Chromatids arrive at the cell's opposite poles. Then the daughter chromosome uncoils to generate chromatin fibres, and the spindle formed earlier dissolves and vanishes. The nucleolus and nuclear membranes reform, and two daughter nuclei emerge at opposing poles. During this stage, cytokinesis, or cell partitioning, may also commence. This produces two daughter cells.
Interphase is the stage or phase that occurs after mitosis is completed. Between two subsequent cell divisions, it is the non-dividing phase of the cell cycle. The majority of a cell's life is spent in interphase.
Phases of Mitosis
Aim
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Studying mitosis by preparing a temporary mount of an onion root tip.
Material Required & Apparatus
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There are a few things needed before initiating the process of preparing a temporary mount of the onion root tip. The things needed to carry out the process are
- Blade
- Beaker
- Forceps
- Vials
- Glass slide and coverslip
- Onion with dry roots
- Water
- Hydrochloric acid
- Aceto-alcohol mixture
- Acetocarmine stain
- Filter paper
- Microscope
Read More: Mitosis Stages
Procedure
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- Place a slice of onion on the tile.
- Using a sharp blade, carefully remove the dried roots.
- Place the bulbs in a beaker filled with water to grow root tips.
- It may take 3–6 days for new roots to sprout.
- 2–3 cm of freshly formed roots should be cut off and dropped into a watch glass.
- Transfer them to the vial containing newly made aceto-alcohol fixative using forceps (1:3: glacial acetic acid: ethanol).
- Allow the root tips to soak for 24 hours in the fixative.
- Take one root with a forceps and set it on a clean glass slide.
- Apply one drop of N/10 HCl to the root tip using a dropper, then 2–3 drops of acetocarmine stain.
- Warm it up a little on the stove. Kindly ensure that the strain doesn't dry out.
- Using filter paper, carefully blot the excess stain.
- Cut the significantly more stained tip piece of the root with a blade, keep it on the slide, and discard the rest.
- Put one drop of water on the root tip after that. Using a needle, attach a coverslip to it.
- Now, touch the coverslip slowly with the blunt end of a needle to appropriately compress and then disperse the meristematic tissue of the root tip beneath the cover slip as a thin layer of cells.
- Finally, the different phases of mitosis can be studied under a microscope.
Things to Remember
- A temporary mount involves the specimen to be put in water, or glycerine in-between the slide and the coverslip, and observed.
- The onion root tip is a really good cell specimen that is used to study mitosis as the root tip is characterized by the presence of a meristematic cell.
- Mitosis and meiosis are the two basic processes of cell division.
- Mitosis is essential for life because it generates new cells for growth, and eliminates the dead cells. It involves the division of a parent cell into two daughter cells after the nucleus of a eukaryotic cell divides in two.
- The material required to carry out the process of preparation of a temporary mount of onion root is Blade, Beaker, Forceps, Vials, Glass slide and coverslip, Onion with dry roots, and Water.
- The process to prepare a temporary mount of onion root cells includes 14 steps, starting from trimming the dry route of the onion, growing them, and then treating them with chemicals, and staining them.
Read More: Preparing a Temporary Mount of a Leaf Peel to Show Stomata
Sample Questions
Ques. What is temporary mounting or wet slide preparation? (3 Marks)
Ans. In this process, the specimen is placed in a drop of water or another liquid that is kept between the slide and the cover slip by surface tension in a wet mount. This method is often used to examine the movement and activity of microscopic organisms that thrive in pond water or other liquid media.
Ques. What is a dry mount? (3 Marks)
Ans. The object is simply placed on the slide in a dry mount, which is the most basic type of mounting. A cover slip can be placed on top of the specimen to protect it from the microscope's objective and to keep it steady and flat. Pollen, feathers, hairs, and other specimens can be successfully viewed using this technique.
Ques. What is a strewn mount? (3 Marks)
Ans. The process of making palynological microscope slides by suspending a concentrated sample in distilled water, placing the samples on a slide, and allowing the water to evaporate is known as strewn mounting.
Ques. Why is onion root cell an ideal choice to study mitosis? (3 Marks)
Ans. The most ideal material for studying mitosis is the meristematic cells found in the root tips. Because monocotyledonous plants' chromosomes are larger and more apparent, onion root tips are utilised to research mitosis. The time taken for mitosis to occur is variable depending on the type of cells and organism. Temperature and time both have an impact on mitosis.
Ques. Why do we need coverslips while studying a slide? (3 Marks)
Ans. The smaller glass coverslips are frequently used to keep specimens in place. The cover slip's main purpose is to keep solid specimens flat and liquid samples moulded into a flat layer of uniform thickness. This is required because high-resolution microscopes can only focus in a relatively small area.
Ques. What other cells can be used to study mitosis? (3 Marks)
Ans. Other cells which can be used to study mitosis are
- Tadpole larvae's tails.
- Fish epithelial cells in the gills.
- Any vertebrate's bone marrow tissue.
- Any herbaceous plant's root tip cells.
- Plants' shoot apices.
- Larvae of grasshoppers.
Ques. Explain the staining process used to study mitosis in the onion root cells? (3 Marks)
Ans. Initially apply one drop of N/10 HCl to the root tip using a dropper, then add 2–3 drops of acetocarmine stain. Warm it up a little on the stove. Use filter paper, and carefully blot the excess stain.
Then, cut the significantly more stained tip piece of the root with a blade, keep it on the slide, and discard the rest. Put one drop of water on the root tip after that. Using a needle, attach a coverslip to it. Touch the coverslip with the blunt end of a needle to compress and disperse the meristematic tissue of the root tip beneath the cover slip as a thin layer of cells. And finally, observe it.
Ques. Why were the onion root cells treated with HCl? (2 Marks)
Ans. HCl being a strong acid can easily hydrolyse and dissolve the middle lamella between the cells. This makes it easier to study the changes in the chromosomes.
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