mitosis practical Flashcards
what is the purpose of using strong HCl
hydrolyses pectin in the middle lamella allowing cells to be separated and squashed into a layer one cell thick
also helps stain diffuse into cells by breaking down cell walls
what is the purpose of using stain
to increase contrast allowing the chromosomes in the nucleus to be visible
why are root tip cells used
this contains meristem tissue which is actively growing and dividing in roots
why is it important that the root tips are firmly squashed before viewing them with a microscope
to produce a layer that is one cell thick
this reduces the likelihood of cells “hiding behind each other” and makes it easier for light to penetrate for viewing
how do you calculate mitotic index
number of cells in mitosis/ total number of cells
why is it important to repeat using several fields of view
ideally, many cells should be examined to ensure a representative sample
counts should also be repeated to ensure figures are correct (in case of human error)
magnification equation
= image size / actual size of image
what are artefacts, examples
things visible down a microscope that aren’t a part of the cell or specimen being viewed
usually made during the preparation of the specimen
examples: dust, air bubbles and fingerprints
describe how to prepare and stain a root tip to observe the stages of mitosis
cut around 2mm from the tip of a growing root
prepare a boiling tube containing 10ml HCl and put it in a water bath
transfer the root tip to the boiling tube and incubate for 5 minutes
rinse the root tip with cold water using a pipette, leave it to dry
use a mounted needle to macerate the tip and spread the cells out thinly
adds a few drops of the stain and place a coverslip over the cells, pushing down firmly to squash the tissue
difference in results
water availability
temperature
nutrient availability
genetic differences
how the behaviour of chromosomes causes changes in the amount of DNA per cell
DNA initially decreases
the first decrease is due to DNA replication
2nd decrease is due to sister chromatids separating
describe how the student could have prepared a microscope slide to view the cells in a root tip
cut a small section of the root tip and place it on a microscope slide
use a mounted needle to spread the section, making it thin to allow light through it
add a few drops of the stain, leave for a few minutes and press the cover slip on firmly
describe how the student could have prepared a microscope slide to view the cells in a root tip
cut a small section of the root tip and place it on a microscope slide
use a mounted needle to spread the section, making it thin to allow light through it
add a few drops of the stain, leave for a few minutes and press the cover slip on firmly
safety precautions
HCl is corrosive so eye protection should be worn
wear gloves
describe how to observe the cells in a prepared slide using a light microscope
place the slide used onto the stage and select the lowest objective lens
bring the stage up by using the coarse adjustment knob
to get the image in focus, adjust the fine adjustment knob
to get a higher magnification to see the cell structure better, select a higher objective lens
