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This content is taken from the National STEM Learning Centre's online course, Teaching Practical Science: Biology. Join the course to learn more.

Skip to 0 minutes and 10 seconds This experiment requires warmed acid. Before you start put 2cm3 of hydrochloric acid in a test tube in a water bath at 60°c and leave for at least 2 minutes to reach the temperature. Garlic bulbs produce roots quickly. When they are suspended like this you can see the roots. For the best results pick roots which are no longer than 1cm, white and have a firm rounded head. These will have lots of dividing cells. Select your roots and put into the warmed hydrochloric acid. This will break down the calcium pectate between the cells allowing the stain to enter the cell.

Skip to 1 minute and 0 seconds Leave this for 5 minutes.

Skip to 1 minute and 6 seconds Remove the root tips from the acid and place in a small bottle containing 5cm3 of ice cold water for 4-5 minutes.

Skip to 1 minute and 25 seconds The next stage is to prepare the slide. Remove the roots from the water and dry on filter paper. The root tips will be fragile.

Skip to 1 minute and 38 seconds Transfer one root tip to a clean microscope slide.

Skip to 1 minute and 46 seconds Cut about 4-5 mm from the growing end. Keep the rounded end. Roll the mounted needle across the root tip to break up the material, spreading the material out as thinly as possible. Add one small drop of toluidine blue stain onto the material. Leave for 2 minutes to allow the stain to be absorbed. Lower the coverslip onto the material and blot away excess stain. Press gently to spread out the root tip.

Skip to 2 minutes and 34 seconds Put the slide onto the microscope stage and view under low power objective x10.

Skip to 2 minutes and 43 seconds Look for small square cells with no wall thickening and no vacuoles. Within these cells you should see threadlike chromosomes.

Identifying required skills for practicals

In the previous video you identified the technical skills required to undertake a practical technique. In this step we’ll look at a complete practical and ask you to consider how individual skills are developed in preceding years.

This video shows a reliable method for carrying out a root tip squash. This is a complex practical involving many skills you may use with high level students aged 15-16 to demonstrate the stages of mitosis but it is a required practical for advanced level biology.

To ensure your students have the appropriate skills to allow them to be successful with this practical we need to prepare them and allow enough opportunities for them to practice the skills involved in the process. Just as you identified the skills needed to carry out a successful serial dilution you are going to do the same for a more complex practical so that we can move onto thinking about how we can map the skills across a five year curriculum


  1. Download the planning grid template [Word].
  2. Watch the video and make a list of the skills involved in carrying out this practical activity. You will be using this list in the next activity to develop progression throughout the curriculum.
  3. Put your list of skills into the first column of the planning grid.

Planning grid with year group across top and space for practical skills to be listed on the left

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This video is from the free online course:

Teaching Practical Science: Biology

National STEM Learning Centre