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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 1
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 1
Step 1
Explain why the student removed the shoot tip from each seedling.
Answer
The student removed the shoot tip because this part of the plant is responsible for producing indoleacetic acid (IAA), which plays a crucial role in regulating growth and elongation of the shoots. By cutting off the shoot tip, the student aimed to initiate a response to different concentrations of IAA added to the Petri dishes.
Step 2
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 using a stock concentration of 1 g dm^-3, we need to calculate the required volume of stock solution.
-
First, convert 10 ppm to grams:
Since 1 ppm = 1 mg per liter, 10 ppm = 10 mg per 40 cm³ (which is 0.04 L). -
The stock concentration is 1 g dm^-3, which is equivalent to 1000 mg per 1000 cm³ (or 1 L).
- Therefore, 1 g = 1000 mg in 1000 cm³, which gives us a concentration of 1 mg/cm³.
-
To obtain 10 mg, we use the formula:
Volume = Mass / Concentration
Volume = 10 mg / 1 mg/cm³ = 10 cm³. -
The total volume is 40 cm³, which means the volume of distilled water required is:
Volume of distilled water = Total volume - Volume of stock solution
Volume of distilled water = 40 cm³ - 10 cm³ = 30 cm³.
In conclusion, Table 2 will be completed as follows:
| Concentration of IAA solution / parts per million | Volume of stock IAA solution / cm³ | Volume of distilled water / cm³ |
|---|---|---|
| 10 | 10 | 30 |