Core Practical 5 - Prepare and stain a root tip squahs to observe the stages of mitosi

Define what is mitosis

mitosis is the nuclear cell division that produces two genetically identical daughter cells

• it occurs in all body cells apart from gametes

• produces two diploid cells (has 46 chromosmes)

Devise a method for : Prepare and stain a root tip squash to observe the stages of mitosis

1. using a water bath heat HCl acid at 60^oC for 15 minutes, use a thermometer to ensure that it has reached the correct temperature

2. using a scalpel cut 5mm of garlic root tip and place in the warm HCl for 5 minutes - start a timer

3. once done, rinse the garlic root tips in distilled water for 5 minutes

4. blot the root tips dry using paper towels then use forceps to transfer onto a micrscope slide

5. add 1 drop of acetic orcein stain using a pippette and leave for 2 minutes (use a timer)

6. lower the cover slip at an angle to prevent any air bubbles from forming

7. cover the slide with several layers of paper towels then press firmly onto the slide o ‘squash’ the root tips - maceration

8. place the slide under the microscope with the lower magnification

9. use the fine focus knob and the coarse adjustment knob to get the cells into focus and clear

10. calculate the mitotic index

Explain why the following techniques are used when producing a root tip squash to observe cell division:

• adding hydrochloric acid

• adding a stain to the root tip

• adding hydrochloric acid - this breaks down the middle lamella to produce a thin layer of cells

• adding a stain to the root tip - makes the chromosomes visible so the stages of mitosis can be identified

Devise an investigation to study the effect of temperature on the rate of nuclear division in a plant meristem. (5)

1. grow 4 garlic plant of the same species in different temperatures : 10^oC , 20^oC , 30^oC and 40^oC

2. use the same age garlic plant and the same length of a root tip

3. use a scalpel to cut 5mm of root tip from the garlic plant ensuring using a ruler that they are of the same length

4. heat the hydrochloric acid in a water bath to 60^oC for 15 minutes

5. place the root tip in HCl for 5 minutes - start a timer

6. rinse using distilled water for another 5 minutes and blot dry using paper towels

7. place the root tip on a microscope slide then add 1 drop of acetic orcein stain and leave for 2 minutes

8. lower the cover slip at an angle to prevent any air bubbles then wrap the slip and cover slip in several layers of paper towels, ‘squash’ the slide to get a thin layer of cells - maceration

9. place the slide on the stage and view under the microscope, then count the number of cells in field view and cells in mitosis

10. calculate the mitotic index

11. repeat for root tips grown in different temperatures

12. comapre the mitotic index of each of them