Gibberellins are a group of plant hormones that are involved in the elongation of plant stems. A student investigated the effect of two different concentrations of a gibberellin, known as GA₃, on stem elongation of 10-day old pea seedlings. The student was given a stock solution of GA₃ with a concentration of 2.85 × 10⁻⁴ moldm⁻³.

1. (a)Describe a method the student could use to make a solution of GA₃ with a concentration of 1.90 × 10⁻⁶ moldm⁻³ and state the dilution factor used.[2]
2. (b)In the investigation, the student: • used the two concentrations of GA₃: 2.85 × 10⁻⁴ moldm⁻³ (high concentration GA₃) and 1.90 × 10⁻⁶ moldm⁻³ (low concentration GA₃) • applied the high concentration GA₃ to one batch of 10-day-old pea seedlings • applied the low concentration GA₃ to another batch of 10-day-old pea seedlings • applied distilled water to a third batch of 10-day-old pea seedlings, as a control • standardised all other variables • measured the length of the stem of each seedling every two days until the seedlings were 20 days old • calculated the rate of stem elongation in cm day⁻¹. State one way in which the student could standardise the measuring of stem length.[1]
3. (c)(i)Complete Table 2.1 by calculating the rate of stem elongation in cm day⁻¹ for the seedlings with low concentration GA₃ added.[1]
4. (c)(ii)A scientist stated that they did not have enough confidence in the results in Table 2.1 to make any conclusions. State one reason to support the statement made by the scientist.[1]
5. (c)(iii)Describe how the student could modify the investigation to increase confidence in the results.[1]
6. (d)Complete Table 2.3 to show the calculated values for SE and mean ± 95% CI for the data from far-red light for GA₁ (batch 4).[2]
7. (e)Use Fig. 2.1, Table 2.2 and Table 2.3 to state three conclusions about the effect of different wavelengths of light on the concentrations of GA₁ and GA₈ in plants.[3]