Required practical 2 Flashcards
Viewing cells from plant root tips
What is the aim of this investigation
. Prepare a microscope slide of meristem tissue from an onion root.
You should add a stain to be able to see the chromosomes
Look at slide under microscope and identify any cells showing signs of mitosis
Hydrochloric acid is included in this experiment, what can you do to be safe
It is corrosive so wear gloves and eye protection eg goggles
Also, leave the beaker on a bench mat and don’t carry it around with acid in it
How do you make the microscope slide with onion
. Stand beaker on bench mat add add 10ml of HCl that is 5mol/dm3 that has been heated to 60 degrees in a waterbath
. Put some paper towel on the bench mat to label it
. Place 2cm of root tip in the acid and leave for 15 minutes
. Set up microscope while waiting
. Rinse root tip in distilled water in the watch glass
. Cut off root tip (1mm) and place on microscope slide
. Cover the section with toluidene blue stain and macerate/mush it with the needle to separate the cells
. Use a white piece of paper to aid colouration of roots
. Keep mushing until tissue is broken and cells are stained dark blue
. Put a cover slip over and gently spread the material under it and blot with filter paper between finger and slide
. Start on lowest magnification, and focus with course focussing nob then fine nob
. Look at the cells, and if you can see the chromosomes
After you have carried out the experiment what do you do
Take pictures of the cells under the microscope then print out to see which ones are going through mitosis
Carry out mitotic index by counting up cells going through mitosis, and divide by the total number of cells in the picture
Why do you lower the cover slip carefully
Because you don’t want any air bubbles to get in which would distort the slide under the microscope
Why do you add a stain eg toluidine blue?
It makes the chromosomes visible so you can see which cells are undergoing mitosis
Where can cells in plants undergoing mitosis be found
In meristem root tips and shoots
What is the mitotic index
Ratio of cells undergoing mitosis to the total number of cells in the sample
Scalpel is used, how is it dangerous
It is sharp so may cut you which could be dangerous
If it occurs clean the wound with antiseptic and cover with plaster
Why is hydrochloric acid added to the cells
It hydrolyses the lining between cell walls (maceration)
So the stain can diffuse in to stain the chromosomes
What should you do when counting cells to ensure the mitotic index is reliable
Use large number of cells for a big sample size
Count multiple times to make sure you have the right number
Why do you press down the cover slip
To make a thin single layer of cells
So light can pass through
