Question

Anvi wanted to study the cells in root tip. For this, she prepared onion root tips by putting the onion

bulb on the mouth of the glass tumbler. She observed the growth of roots for a few days till they grew

nearly to an inch. Later she has taken the onion out and had cut some of the root tips.

She observed the root tip under a microscope by preparing a glass slide using water, glycerine, cover

slip. She then made a record of her observations. Later she marked the cut ends with a marker and

placed the onion on the glass tumbler and kept it aside for few days. After few days she observed the

roots of onion again. d)wriite any one precaution to be taken while doing the above activity?​

Answer 1

Aim Of The Experiment

To study and demonstrate mitosis by preparing the mount of an onion root tip cells.

Theory Of The Experiment

For entities to mature, grow, maintain tissues, repair and synthesize new cells, cell division is required. Cell division is of two types:

Mitosis

Meiosis

Mitosis

In mitosis, the nucleus of the Eukaryotic cells divides into two, subsequently resulting in the splitting of the parent cells into two daughter cells. Hence, every cell division involves two chief stages:

Cytokinesis – Cytoplasm division

Karyokinesis – Nucleus division

Stages Of Mitosis

The various stages of mitosis are:

1. Prophase

The process of mitosis is initiated at this stage wherein coiling and thickening of the chromosomes occurs

Shrinking and hence the disappearance of the nucleolus and nuclear membrane takes place

The stage reaches its final state when a cluster of fibres organizes to form the spindle fibres.

2. Metaphase

Chromosomes turn thick in this phase. The two chromatids from each of the chromosomes appear distinct

Each of the chromosomes is fastened to the spindle fibres located on its controller

Chromosomes align at the centreline of the cell

3. Anaphase

Each of the chromatid pair detaches from the centromere and approaches the other end of the cell through the spindle fibre

At this stage, compressing of the cell membrane at the centre takes place

4. Telophase

Chromatids have reached the other end of the cell

The disappearance of the spindles

Chromatin fibres are formed as a result of uncoiling of daughter chromosomes

The appearance of two daughter nuclei at the opposing ends due to the reformation of the nucleolus and nuclear membrane

At this phase, splitting of the cell or cytokinesis may also occur.

Post mitosis, the next stage is referred to as interphase which is part of the cell cycle that is non-dividing and between two consecutive cell divisions. A cell spends most of its life in the interphase. It comprises the G1, S and G2 stages.

Why is onion root tip used to demonstrate mitosis in this experiment?

It is because of the meristematic cells that are situated in the tip of the roots that render the most desirable and suitable raw material to study the different stages of mitosis. Onion is a monocot plant. Monocotyledonous plants possess large chromosomes that are clearly visible. Hence, their root tips are used. The period of time taken for mitosis varies as it is dependent on the cell type and type of species.

Is mitosis influenced by any factor? If yes, name them.

Yes, mitosis, the cell cycle is affected by various factors such as time and temperature.

Materials Required

Compound microscope

Acetocarmine stain

Water

Burner

N/10 Hydrochloric acid

Filter paper

Coverslip

Aceto alcohol (Glacial acetic acid and Ethanol in the ratio 1:3)

Glass Slide

Onion root peel

Forceps

Blade

Watch glass

Dropper

Needle

Vial

Procedure Of The Experiment

Place an onion on a tile

With the help of a sharp blade, carefully snip the dry roots of the onion

Place the bulbs in a beaker containing water to grow the root tips

It may take around 4 to 6 days for the new roots to grow and appear

Trim around 3 cm of the newly grown roots and place them in a watch glass

With the help of forceps, shift it to a vial holding freshly prepared aceto-alcohol i.e., a mixture of glacial acetic acid and ethanol in the ratio 1:3.

Allow the root tips to remain the vial for one complete day

With the help of forceps, pick one root and set in on a new glass slide

With the help of a dropper, allow one drop of N/10 HCl to come in contact with the tip of the root. Additionally, add around 2 to 3 drops of the acetocarmine stain.

Heat is lightly on the burner in such a way that the stain does not dry up.

Excessive stain can be carefully treated using filter paper

The more stained part of the root tip can be trimmed with the help of a blade.

Discard the lesser stained part while retaining the more stained section.

Add a droplet of water to it

With the help of a needle, a coverslip can be mounted on it

Gently tap the coverslip with an unsharpened end of a needle in order for the meristematic tissue of the root tip present under the coverslip to be squashed properly and to be straightened out as a fine cell layer

The onion root tip cells’ slide is now prepared and ready to be examined for different stages of mitosis

Observe and study mitosis by placing the slide under the compound microscope. Focus as desired to obtain a distinct and clear image.

Observations and Conclusion

The slide containing the stained root tip cells is placed on the stage of the compound microscope, changes taking place are noted and sketched.

The different phases of mitosis, such as prophase, metaphase, anaphase and telophase can be observed.

Answer 2

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