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A student investigated the effects of indoleacetic acid (IAA) on the growth of oat seedlings (young plants) - AQA - A-Level Biology - Question 3 - 2019 - Paper 2
Question 3
A student investigated the effects of indoleacetic acid (IAA) on the growth of oat seedlings (young plants). The student: - removed the shoot tip from each seed... show full transcript
Worked Solution & Example Answer:A student investigated the effects of indoleacetic acid (IAA) on the growth of oat seedlings (young plants) - AQA - A-Level Biology - Question 3 - 2019 - Paper 2
Step 1
Explain why the student removed the shoot tip from each seedling.
Answer
The student removed the shoot tip from each seedling because the shoot tip is responsible for producing indoleacetic acid (IAA), which promotes growth. By removing the tip, the experiment ensured that any observed growth response could be attributed directly to the varying concentrations of IAA introduced in the Petri dishes.
Step 2
Explain why the student added glucose solution to each Petri dish.
Answer
The glucose solution was added to each Petri dish to provide a source of energy for the seedlings. Glucose is essential for cellular respiration, which is necessary to produce ATP for growth and other metabolic processes.
Step 3
Step 4
Describe and explain the results shown in Table 1 and suggest how the results might have differed if lengths of root had been used.
Answer
The results in Table 1 indicate that as the concentration of IAA increases, the mean change in length of the shoot also increases. This demonstrates a positive correlation between IAA concentration and growth. If lengths of root had been used, the results might have differed, as roots may respond differently to IAA than shoots. Higher IAA concentrations could potentially lead to reduced root elongation or even inhibition of growth.
Step 5
Complete Table 2 with the volumes of stock IAA solution and distilled water required to produce 40 cm³ of 10 ppm IAA solution.
Answer
To prepare a 10 ppm IAA solution from a stock solution of 1 g dm⁻³, you can use the formula:
dilution = (C1 × V1) = (C2 × V2)
where C1 = concentration of stock solution, V1 = volume of stock solution needed, C2 = final concentration, and V2 = final volume.
Using this:
- C1 = 1000 ppm (1 g/l)
- C2 = 10 ppm
- V2 = 40 cm³
Substituting the values:
the volume of stock = (C2 × V2) / C1 = (10 ppm × 40 cm³) / 1000 ppm = 0.4 cm³.
Therefore, the volume of distilled water needed = 40 cm³ - 0.4 cm³ = 39.6 cm³.
Thus, the completed Table 2 would include:
| Concentration of IAA solution / parts per million | Volume of stock IAA solution / cm³ | Volume of distilled water / cm³ |
|---|---|---|
| 10 | 0.4 | 39.6 |