Required Practical 2- Mitosis Flashcards
Where in plants can cells undergoing mitosis be found
Meristem tissue at shoot and root tips
Mitotic index?
Ratio of cells undergoing mitosis to total number of cells in a sample
Formula for mitotic index?
Number of cells with visible chromosomes/number of cells in sample
Why only use cells in tip?
Because the tip is the only part of the plant which is actively undergoing mitosis (contain meristem tissue)
Purpose of blue stain?
Stain chromosomes to make chromosomes visible- show which cells are undergoing mitosis
Why treat with acid and heat?
Used to break up cellulose wall- allow stain to permeate tissue + make it easier to squash tissue of microscope slide and to STOP mitosis
Why are cells squashed? How should you do it?
Flattens- to get thin, single layer of cells allowing light through so chromosomes are visible
Gently to avoid damage to cells
Why are root tips heated to 60°C for 15 mins?
-increase kinetic energy of molecules
-increase rate of reaction with acid
-denaturing proteins
-soften cells + stop mitosis
Why different results obtained when mitotic count repeated with different garlic root tip?
-may have been different ages
-may have been different types- genetic differences
-chance
-water + nutrients may have been less available to one root
Why place root tip in hydrochloric acid?
To make cells more permeable so stain can bind to DNA
Why push down and not sideways with coverslip?
So cells are spread and to prevent chromosomes from breaking if pushed sideways
Why is an optical microscope used?
Has high enough magnification to view chromosomes
Why root tip of onion, garlic or shallot?
Easy to grow in large numbers
Outline procedure to prepare root tip slide
1.Warm 1M HCI to 60°C in a water bath.
2. Cut a root tip using a scalpel and add to the HCI. Leave
for 5 minutes.
3. Remove from HCI and wash with distilled water.
4. Cut the tip of the root tip sample and place on a slide.
5. Add a few drops of stain to make chromosomes visible.
