Steps 1 and 2

Auxins are a group of hormones in plants that are involved in various processes and one of these processes is cell elongation which is the way that plants grow and bend.

Indole-3-acetic acid (IAA) is one such auxin and this experiment is an investigation into how it affects the growth of shoots and roots at various concentrations.

28th Feb - Week 1

 Step 1

Production of 7 different concentrations of IAA and one Control of distilled water.

This was done by serial dilution of an initial IAA solution which was at 0.01% concentration. That's 0.01 parts per hundred which, if you multiply both figures by 10,000, is the same as 100 (or 10²) parts per 1,000,000

Written as 10² ppm, if you dilute this by a factor of 10 each time, for six times, you get further IAA concentrations of 10ppm, 1ppm, 10^-1ppm, 10^-2ppm, 10^-3ppm and 10^-4ppm.

This was done by pouring 10ml of the initial solution into a test tube and pouring 9ml of distilled water into each of 6 more test tubes.

Then 1ml of the initial solution was taken from the first tube and added to the distilled water in the second tube thereby diluting it by a factor of 10 to form 10ppm. The tube was so labelled. 

Then 1ml of this tube's solution was added to the distilled water in the next tube thereby diluting this by a further factor of 10 to 1ppm. This tube was labelled 1ppm.

This process continued until the last of the six tubes had a total of 10ml of solution in it. 1ml of this solution was removed and discarded.

An 8th and final tube had 9ml of distilled water only poured into it to act as a control, to see what would occur if there was no IAA present in order to better gauge what was happening in the other 7.

Step 2

Preparation of 8 Petri dish cultures

8 Petri dishes were each lined with round cross-hatched acetate and 5 radish seeds placed in a row at the intersection of two lines. Lining the seeds up like this is to allow an easier comparison of their respective shoot and root lengths. A round piece of filter paper was placed over each set of seeds.

Each of the Petri dishes had been labelled in the same parts per million (ppm) as the test tubes.

From each corresponding tube 2ml of the solution was dropped on the filter paper and it was gently pressed in place to ensure that there were no air bubbles which could result in a seed drying out.

Finally, each dish was spread with a piece of absorbant cotton wool and the remaining 7ml of solution in each case was poured onto the cotton wool and the 2nd half of the dish put in place..

The dishes were sealed with tape to prevent leakage. Then were then all placed in a stack, taped together and placed with the dishes standing on their edges in an incubator for 2-3 days at 25 degrees C.