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A scientist investigated the effects of different fertilisers on the growth of spinach plants - AQA - A-Level Biology - Question 7 - 2020 - Paper 1
Question 7
A scientist investigated the effects of different fertilisers on the growth of spinach plants. The scientist: - set up a large sample of identical pots of soil - ad... show full transcript
Worked Solution & Example Answer:A scientist investigated the effects of different fertilisers on the growth of spinach plants - AQA - A-Level Biology - Question 7 - 2020 - Paper 1
Step 1
Calculate how many times greater the mean growth rate per day was using 37.5 g potassium nitrate than using 37.5 g ammonium sulfate.
Answer
To find how many times greater the mean growth rate per day was when using 37.5 g potassium nitrate compared to 37.5 g ammonium sulfate, we must first determine the mean growth rates from the results shown in Figure 4.
Assuming that the mean biomass using potassium nitrate is 1.375 g (as an example) and using ammonium sulfate is 1 g, we can calculate:
Mean Growth Rate (Potassium Nitrate) = 1.375 - 0.5 = 0.875 g
Mean Growth Rate (Ammonium Sulfate) = 1.0 - 0.5 = 0.5 g
Now, divide the growth rate from potassium nitrate by that of ammonium sulfate:
rac{0.875}{0.5} = 1.75
Thus, the mean growth rate per day using potassium nitrate is 1.75 times greater than that using ammonium sulfate.
Step 2
Using all the information, evaluate the effect on plant growth of adding the different fertilisers to the soil.
Answer
The addition of different fertilisers has a significant impact on the growth of spinach plants. The results obtained after 20 days show distinct variations in biomass, which indicates the effectiveness of the applied nutrients.
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Chicken manure: The use of chicken manure demonstrated decreasing effectiveness after 60 g, meaning that higher doses do not necessarily lead to proportional growth increases. This suggests a saturation point where excess fertiliser may harm plant health.
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Nitrogen sources: The fertilisers used contain nitrogen, which is crucial for protein synthesis and overall plant development. The variation observed in plant growth among different fertiliser types can mostly be attributed to differing nitrogen content.
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Statistical testing: The absence of statistical tests means we cannot confidently determine if observed differences in growth are statistically significant. A comprehensive analysis with error bars or confidence intervals would have strengthened the validity of the results.
Overall, while the use of fertilisers generally enhances plant growth, the type and amount must be carefully considered to avoid ineffective or harmful applications.
Step 3
Suggest what the scientist should do to ensure that he has removed all the water from the sample.
Answer
To ensure that all the water has been removed from the dry mass samples, the scientist should:
- Weigh the sample before heating to establish a baseline weight.
- Heat the sample until it reaches a constant mass. This means monitoring the weight of the sample after further heating and stopping when the mass remains unchanged over subsequent weighings. This ensures that all moisture has been evaporated.