RP2 -Preparation Of Stained Squashes Of Cells From Plant Root Tips

Question 1

describe how to prepare squashes of cells from plant root tips

Answer 1

1) cut a thin slice of root tip using scalpel and mount onto a slide
2) soak root tip in hydrochloric acid then rinse
3) Stain for DNA
4) Lower coverslip using a mounted needle at 45 degrees without trapping air bubbles
5) squash firmly by pressing down on a glass slip but do not push sideways

Question 2

Explain why a root tip is used

Answer 2

where mitosis occurs

Question 3

explain why a stain is used

Answer 3

to distinguish chromosomes

Question 4

explain why the cover slip needs to be squashed

Answer 4

to create a single layer of cells
so light passed through to make chromosomes visible

Question 5

explain why the coverslip should not be pushed sideways

Answer 5

avoid breaking chromosomes

Question 6

give two reasons why the roots should be soaked in acid

Answer 6

• to stop mitosis
• to separate cells

Question 7

describe how to set up and use an optical microscope

Answer 7

1) clip slide onto stage and turn on light
2) select lowest powering objective lens
3) use coarse focusing dial to move stage close to lens and turn coarse focusing dial to move stage away from lens until imagine comes into focus
4) adjust fine focusing dial to get clear image
5) swap to higher power objective lens then refocus

Question 8

what are the rules of scientific drawing

Answer 8

• look similar to image
• draw on same scale
• no sketching
• no shading
• include a magnification scale
• label with straight uncrossed lines

Question 9

explain how the stages of mitosis can be identified

Answer 9

prophase :
- chromosomes visible because condensing
- but randomly arranged
metaphase :
- chromosome lined up on equator
anaphase :
- chromatids at poles of spindle
- chromatids V shaped
telophase :
chromosomes in 2 sets

Question 10

what is a mitotic index

Answer 10

proportion of cells undergoing mitosis
mitotic index = number of cells under going mitosis / total number of cells in sample

Question 11

explain how to determine a reliable mitotic index from observed squashes

Answer 11

• count cells in mitosis field of view
• count only whole cells
• divide this by total number of cells by field of view
• repeat with many fields of view selected randomly
• calculate a reliable mean

Question 12

suggest how to calculate the time cells are in a certain phase of mitosis

Answer 12

) identify proportion of cells in named phase at any one time - number of cells in that phase / total number of cells observed
2) multiply by length of cell cycle