Unit: Cell and Molecular Biology (AH): Structure, function and growth of prokaryotic and eukaryotic cells
Title: Staining a root tip and calculating its mitotic index
TEACHER/LECTURER GUIDE
Type and purpose of activity
This experiment can be used to:
• provide evidence for assessment of Outcome 3
(For advice on marking Outco me 3 report, please contact the SAPS Scotland office.)
• develop knowledge and understanding of the process of mitosis
• develop problem solving skills and in particular Outcome 2 PCs: (b) infor mation is accurately processed, using
calculations where appropriate (d) experimental procedures are planned, designed and evaluated appropriately
Background information
• In this activity stud ents will prepare and stain root tips. To achieve an Outco me 3 students must either have TWO
different sources of root tips OR stain one type of root tip with two different stains. A comparison between EITHER
the root types OR the stains will then be possib le.
• This practical is best carried out in the morning to get good results.
• Two recommende d sources of roots are garlic and hyacinth. The garlic cloves, bought normally for cooking purposes,
will produce roots at any time of year. Hyacinth bulbs can be bought at Garden Centres during autumn and winter.
Both garlic cloves and hyacinth bulbs will produce ample roots for the experiment.
• Suitable stains for studying the stages of mitosis in root tips are lactopropi onic orcein and toluidene blue.
• The mitotic index is the fraction of cells in a microscope field which contain condensed chromosomes. This index will
be calculated for each slide prepared.
• Preparation of the plant materials and the stains is covered in the Technica l Guide.
• To make this activity non-seasonal, it is possible to ‘fix’ the r oot tips when available and then store them until required .
Fixing of root tips is only covered in the Technical Guide.
Classroom management
Students are asked to mark the root tip one or two days prior to staining the root tips. This will enable them to link rate
of growth with mitotic index.
Microscopic exam ination of the slides:
Students should examine severa l slides and ca lculate the mitotic index for each one. Prep ared slides co uld also be
available.
Supply of materials
In order to satisfy the core skill in problem solving, students will be required to identify an d obtain resources required
for themselves. Further advice on supply of material is given in the Technical Guide.
Extension work
Try to vary the mitotic index of the plant tissue e.g. cutting the root tips and keeping them at 0°C for 24 hours may
increase the mito tic index. The experimental method can be varied e.g. varying the temperature or concentration o f
acid; varying the time the root tip is in the acid ; squashing the root tip with a coverslip ins tead of macerating; varying
the age of the root used; preparing the stains differently (e.g. different dilutions, different pHs); heating the
lactopropionic orcein slide gently; investigating a possible link between rate of growth of root and mitotic index.
Acknowledgements
• Information and adv ice from Dr Kwiton Jong, Royal Botanic Garden, Edinburgh, is gratefully acknowledg ed.
Information was also received from Ashby Merson-Davies, Sevenoaks School, Kent.
• This experiment was produced by the SAPS Biotechnology Scotland Project. Funding for the project was provided by
SAPS, Unilever and The Scottish Office. Support was also provided by Edinburgh University, Quest International, the
Scottish CCC, the Higher Still Development Unit and SSERC.
