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Figure 2 shows one type of calorimeter - AQA - A-Level Biology - Question 3 - 2020 - Paper 2
Question 3
Figure 2 shows one type of calorimeter. A calorimeter can be used to determine the chemical energy store of biomass. A known mass of biomass is fully combusted in a... show full transcript
Worked Solution & Example Answer:Figure 2 shows one type of calorimeter - AQA - A-Level Biology - Question 3 - 2020 - Paper 2
Step 1
Other than the thermometer, explain how two features of the calorimeter shown in Figure 2 would enable a valid measurement of the total heat energy released.
Answer
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The stirrer distributes heat evenly throughout the water, helping to ensure that the entire body of water reaches a uniform temperature. This is crucial for accurate readings of the temperature change.
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The insulation around the calorimeter reduces heat loss to the environment, ensuring that more heat energy from the biomass combustion is retained in the system. This helps to provide a more accurate measurement of the total heat energy released.
Step 2
A 2 g sample of biomass was fully combusted in a calorimeter. Use this information to calculate the heat energy released in kJ per g of biomass.
Answer
To calculate the heat energy released, we can use the formula:
Heat energy (J) = mass of water (g) × specific heat capacity (J/g°C) × temperature change (°C)
Given:
- Volume of water = 100 cm³ = 100 g (since the density of water is 1 g/cm³)
- Specific heat capacity = 4.18 J/g°C
- Temperature change = 15.7 °C
Heat energy (J) = 100 g × 4.18 J/g°C × 15.7 °C = 6566 J
To convert to kJ and per g of biomass:
Heat energy (kJ) = 6566 J / 1000 = 6.566 kJ
Since the sample mass is 2 g:
Heat released per g = 6.566 kJ / 2 g = 3.283 kJ/g.
Step 3
Suggest two reasons why most of the light falling on producers is not used in photosynthesis.
Answer
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Light is reflected by leaf surfaces, which means it is not absorbed for photosynthesis.
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The light might not be of the correct wavelength or frequency that is required by chlorophyll, thus not contributing effectively to the process of photosynthesis.
Step 4
Step 5
Give your answer in standard form. Show your working.
Answer
We start with 2000 Chlorella cells, which double every 90 minutes.
In 24 hours, there are:
- 24 hours = 24 × 60 = 1440 minutes
- Number of divisions = 1440 minutes / 90 minutes = 16 divisions
Final number of cells = initial cells × 2^number of divisions = 2000 × 2^{16}
Calculating this: Final number of cells = 2000 × 65536 = 131072000
In standard form: 1.31 × 10^8 cells.