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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 seedling ... 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 the tip produces indoleacetic acid (IAA), which affects the concentration of IAA in the plant. This action allows for accurate measurements of the impact of various concentrations of IAA on growth by eliminating the variable effect of the tip's natural hormone production.
Step 2
Complete Table 2 with the volumes of stock IAA solution and distilled water required to produce 40 cm³ of 10 ppm (parts per million) IAA solution.
Answer
To obtain 10 ppm IAA solution:
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First, determine the total amount of IAA needed for 10 ppm in 40 cm³:
10 ext{ ppm} = rac{10 ext{ grams}}{1,000,000 ext{ cm}³}
Hence, for 40 cm³, the mass of IAA required is:
ext{Mass of IAA} = 10 imes rac{40}{1000000} = 0.0004 ext{ g}
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Since the stock solution is 1 g/dm³ (which is equivalent to 1 g per 1000 cm³), we find out how many cm³ of stock solution will contain 0.0004 g:
ext{Volume of stock IAA solution} = rac{0.0004 ext{ g}}{1 ext{ g/1000 cm³}} = 0.4 ext{ cm³}
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Now calculate the volume of distilled water needed:
Thus, fill in Table 2 as follows:
| Concentration of IAA solution / parts per million | Volume of stock IAA solution / cm³ | Volume of distilled water / cm³ |
|---|---|---|
| 10 | 0.4 | 39.6 |