Photo AI
Scientists investigated stomatal density on leaves of one species of tree - AQA - A-Level Biology - Question 9 - 2020 - Paper 1
Question 9
Scientists investigated stomatal density on leaves of one species of tree. Figure 9 shows three examples of the square fields of view the scientists used to calcul... show full transcript
Worked Solution & Example Answer:Scientists investigated stomatal density on leaves of one species of tree - AQA - A-Level Biology - Question 9 - 2020 - Paper 1
Step 1
Calculate the mean stomatal density in the three fields of view in Figure 9.
Answer
To calculate the mean stomatal density, count the number of stomata in each field of view provided in Figure 9. Assuming the stomata counts are as follows: 200, 180, and 150, we can calculate:
Mean stomatal density = ( \frac{200 + 180 + 150}{3} = \frac{530}{3} = 176.67 )
Rounding this, we get approximately 177 stomata per mm².
Step 2
Give a null hypothesis for this investigation and name a statistical test that would be appropriate to test your null hypothesis.
Answer
Null hypothesis: There is no association between the concentration of carbon dioxide and the stomatal density.
Statistical test: Spearman’s rank correlation coefficient would be appropriate to test this hypothesis.
Step 3
From 1910 to 2000, the carbon dioxide concentration in the atmosphere increased from 300 parts per million to 365 parts per million. Use Figure 10 to calculate the mean rate of change in stomatal density from 1910 to 2000.
Answer
To calculate the mean rate of change in stomatal density over a 90-year period:
Rate of change = ( \frac{final stomatal density - initial stomatal density}{number of years} )
If the initial density was estimated at 10 stomata per mm² and the final density was 15 stomata per mm² (as per Figure 10), the formula becomes:
Rate = ( \frac{15 - 10}{90} = \frac{5}{90} = 0.0556 ) stomata per mm² per year, which translates to approximately 0.56 stomata per mm² per 10-year period.
Step 4
Evaluate his suggestion.
Answer
The journalist's suggestion that increases in atmospheric carbon dioxide concentration could lead to less transpiration can be evaluated from several perspectives:
- Increased carbon dioxide generally leads to reduced stomatal conductance as plants attempt to conserve water.
- However, fewer stomata could increase leaf temperature, potentially leading to increased transpiration rates.
- Other factors such as leaf size, temperature, and humidity also play critical roles in transpiration rates.
- Overall, more research is needed to determine the precise relationship between carbon dioxide levels and transpiration.