I'm a secondary biology teacher in Midlothian putting together activities for the new National 3 & 4 biology courses and wondered if you had an off the shelf water culture experiment you could point me towards to demonstrate the effects of various nutrients (N, P and K in particular) missing from the culture medium? The guidance we have from SQA suggests an experiment with Lemna in water culture.

You will find a discussion of this topic at:-

http://www.saps.org.uk/saps-associates-area/ask-the-experts/396-what-is-the-quickest-way-to-demonstrate-nutrient-deficiencies

(You will need to register as an associate (for free) to read this page.)

You can buy a set of Sach's Water Culture solutions.  This is a set of about 6 different mixtures to enable you to make up solutions which are short of
particular mineral nutrients.  These should be straightforward to get from your normal laboratory supplier.

These pages may also help:-

http://www.saps.org.uk/secondary/teaching-resources/744-using-duckweed-in-the-lab

and

http://www.saps.org.uk/students/projects/232-student-projects-investigations-with-lemna-minor

(which explains how to measure the "doubling time" (an interesting way of quantifying the growth rate))