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CP5 - Prepare and stain a root tip squash to observe the stages of mitosis
Core practical 5 - prepare and stain a root tip squash to observe the stages of mitosis
Aim : to prepare slides of actively dividing plant tissue, observe the stages of the cell cycle
and determine the duration of the stages of mitosis in relation to the whole cell cycle.
Introduction
Mitosis is the phase of the cell cycle where the nucleus of a cell is divided into 2 nuclei with
an equal amount of genetic material in both the daughter nuclei. It succeeds the G2 phase
and is succeeded by cytoplasmic division after the separation of the nucleus. (Byjus, 2017)
Interphase is known as the preparation for mitosis as it is essential to maintain genomic
integrity. It includes the G1, S and G2 phases during which the cell synthesises new cell
components such as organelles, membranes and new DNA. The formation of new cell
proteins occurs throughout the interphase whereas DNA synthesis occurs only during the S
phase. The individual chromosomes are unravelled to allow access to the genetic material
for new proteins to be synthesised. (University Of York Science Education Group. Nuffield
Curriculum Centre, 2015)
Mitosis is split into 5 stages : prophase, prometaphase, metaphase, anaphase and
telophase. In prophase, the chromosomes condense making them visible under the
microscope and the mitotic spindle begins to form. Then in prometaphase, the nuclear
envelope starts to break down and the microtubules extend from the centromere to attach to
the kinetochores of the chromosomes. (Khan Academy, 2015)
Microtubules that don’t bind to kinetochores can grab on to microtubules from the opposite
pole, stabilising the spindle. More microtubules extend from each centrosome towards the
edge of the cell, forming a structure called the aster. (Khan Academy, 2015)
In metaphase, the chromosomes are lined up along the equator of the cell, then the sister
chromatids are separated from each other and pulled towards the opposite end of the cell in
anaphase. The last stage of mitosis is telophase where two new nuclear membranes form
around each set of chromosomes and the chromosomes begin to decondense. This is
succeeded by cytokinesis, cytoplasmic division, where the cell is pinched by a contractile
ring made of actin filaments. This results in 2 new cells each with a complete set of
chromosomes identical to those of the mother cell. (Khan Academy, 2015)
Staining is a part of histology which allows for the visualisation of tissue structure and
characteristic changes the tissue may have undergone. The histological stains chosen for a
given specimen depends on the investigational question at hand.(Gurina and Simms).
Toluidine blue is an acidophilic metachromatic dye that selectively stains acidic tissue
components and has an affinity for nucleic acids. Therefore it binds to nuclear material of
tissues with high DNA and RNA content.(Sridharan and Shankar)
Hypothesis : We will be able to observe cells and their chromosomes in various stages of
the cell cycle. A lower number of cells will be undergoing mitosis as interphase is the longest
phase of the cell cycle.
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