Zoe Schnepp
Page created by Zoe Schnepp

This is an experiment aimed at A-Level students studying chemistry or biology. We’ll be looking at the toxic effect of table salt on cress seeds and using our data to plot a dose-response curve.

Toxicology and the harmful effects of chemicals is something you could come across in many different degree courses, including chemistry, biology, biochemistry, medical and dental sciences, environmental sciences and pharmacology. This project could give you something really nice to write about for your UCAS statement.

Image of some cress seedlings grown from solutions of table salt in water at different concentrations.

Introduction to toxicology

Toxicology is a field of science that allows us to study the harmful effects of chemical substances on living organisms and the environment. It’s essential in many industries, from understanding the effect of trace compounds in the environment to learning about pharmaceutical side effects.

You can learn how chemicals enter the body, what type of adverse effects they might cause and how they can interact in the video below. Or if you prefer, you can find a webpage or text version of the information here.


The experiment

Watch the experiment here or you can find written instructions here.



My results, after 6 days of growth are shown in this table:

Table of results


You can use your data of ‘number of seeds not germinated’ (y axis) and concentration of salt solution (x axis) to plot a dose-response curve.

I plotted this and fitted a line using Origin. You can download a free trial version of the software here.

More info on what a dose-response curve shows and how to plot it will be added here shortly…

I’ll also upload information on how to use your data to work out the NOAEL (more to come shortly!)


Going further

  • What other concentrations do you think might be useful to trial? What is the effect of a really low concentration? Can you determine the concentration at which there is no observable effect on the cress seeds?
  • What other ‘toxins’ could you try? How about sugar, alcohol (parental permission please), vinegar, washing-up liquid? Disclaimer: I have no idea how these other things would work but would love to see your results! Share on Twitter or Instagram!
  • Can you find anything that actually promotes growth? What happens with plant food? Is there an initial promotion followed by a toxic effect at high concentration?
  • What are the main sources of error in this experiment?



This work is licensed under a Creative Commons Attribution 4.0 International License.