Pelargonic acid is a contact herbicide that disrupts cell-surface membranes, but the level of disruption can vary between plant species.
Scientists investigated the effect of pelargonic acid on barley plants (a crop) and chickweed plants (a weed).
They grew plants of both species in greenhouse chambers. They allocated plants of each species to one of two groups:
After spraying, they cut 40 discs from the leaves of plants in each group and placed them in flasks containing 15 cm3 of de-ionised water. After 5 minutes, they measured the concentration of ions released into the water from the leaf discs to determine membrane disruption.
Their results are shown in the table below:
| Group | Treatment | Mean concentration of ions in water / arbitrary units (Barley) | Mean concentration of ions in water / arbitrary units (Chickweed) |
|---|---|---|---|
| C | Water | 15 | 32 |
| P | Pelargonic acid | 19 | 64 |
| LSD | 6 | 8 |
The lowest significant difference (LSD) is the smallest difference between two means that would be statistically significant at P≤0.05P \le 0.05P≤0.05.
Give three environmental variables that should be controlled when growing the plants before treatment with the sprays.
Evaluate the use of pelargonic acid as a herbicide on a barley crop that contains chickweed as a weed. Use all the information provided in the table.
Suggest one reason why the scientists ensured the temperature remained constant during incubation and one reason why the leaf discs were shaken.
