Core Practical 6: root tip squash

Cell Structure, Reproduction and Development · Mitosis and the cell cycle · note 2 of 3

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Core Practical 6: root tip squashSpec 3.15

In short

In Core Practical 6, a root tip is warmed in hydrochloric acid, stained with a chromosome stain such as acetic orcein and squashed into a thin layer on a slide. Under a light microscope, cells from the growing region can be seen in different stages of mitosis. The root tip is used because it contains meristem cells that are dividing.

Core practical:

Core practical 6: prepare and stain a root tip squash to observe the stages of mitosis.

Root tips (for example onion, garlic or broad bean) are used because the meristem just behind the tip is the region where cells are dividing rapidly by mitosis.

Cut about 2 to 3 mm from the end of a growing root tip with a scalpel and place it in warm (about 60 °C) 1 M hydrochloric acid for about 5 minutes. The acid softens the tissue by breaking down the middle lamella between cells, so that the cells can be separated, and it kills the cells, fixing them in their stage.
Rinse the root tip in water and place it on a clean microscope slide.
Add a few drops of a stain that binds to chromosomes, such as acetic orcein, and leave for a few minutes. Spread out the tissue with a mounted needle.
Lower a coverslip on at an angle. Cover it with a piece of filter paper and press down firmly with a thumb, without sliding the coverslip sideways, to squash the tissue into a thin layer of cells.
View under a light microscope, starting at low power to find the region with small, square, densely stained cells, then at high power to identify the stage of each cell.
Make labelled drawings of cells in each stage and count the cells in each stage in several fields of view.

Variables to control when comparing roots: same type of plant, same length of root tip, same time in acid and stain, same temperature.
Risks: 1 M hydrochloric acid is an irritant, so wear eye protection; hot water baths can scald; acetic orcein stains skin and clothing and is an irritant; scalpels are sharp, so cut away from the body on a hard surface.
Reliability: count a large number of cells (at least several hundred) and repeat on several root tips to reduce the effects of chance.

Exam tip:

Explain each step, not just the order. The squash gives a layer one cell thick, so light can pass through, and the acid separates the cells and stops further division.

Drawing of a stained root tip squash under the microscope with cells labelled in interphase, prophase, metaphase, anaphase and telophase, and a 20 µm scale bar. — In a root tip squash most cells are in interphase, because it is the longest part of the cell cycle.

Written and checked against the Edexcel International AS Level Biology (XBI11) specification · Updated October 2026

Frequently asked questions

What happens in each stage of mitosis?

In prophase the chromosomes condense and the nuclear envelope breaks down. In metaphase they line up on the equator. In anaphase the centromeres divide and sister chromatids are pulled to opposite poles. In telophase nuclear envelopes re-form and the chromosomes uncoil.

Why is mitosis important?

Mitosis produces two genetically identical daughter cells, so it is how multicellular organisms grow and replace damaged or worn-out cells. It is also the basis of asexual reproduction, in which offspring are genetic clones of one parent.

How do you make a root tip squash?

Warm a 2 to 3 mm root tip in 1 M hydrochloric acid at about 60 °C, rinse, stain with acetic orcein and squash it under a coverslip to make a single layer of cells. Then view it under a light microscope to find cells in each stage of mitosis.

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