igcse model questions vol1 2022 biology | Practical

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Question 1 View Details
A student prepares a slide of an onion (Allium cepa) epidermal peel, stains it with iodine solution and examines the cells under a light microscope at 40× objective. The lengths and widths of ten intact cells are measured with an ocular micrometer as shown in the table below. | Cell | Length (µm) | Width (µm) | |------|-------------|------------| | 1 | 45 | 30 | | 2 | 48 | 32 | | 3 | 44 | 31 | | 4 | 46 | 29 | | 5 | 47 | 33 | | 6 | 45 | 30 | | 7 | 49 | 31 | | 8 | 46 | 32 | | 9 | 44 | 29 | |10 | 48 | 30 | The textbook gives an average area of a typical onion epidermal cell as 1500 µm².
Question Parts
(a)
Calculate the average area of the ten cells measured. Show the calculation steps.
(b)
Compare the calculated average area with the textbook value and suggest two possible reasons for any discrepancy.
(c)
Suggest one improvement to the experimental procedure that could reduce the error identified in part (b).
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Question 2 View Details
A student investigates mitosis in the root tip of an onion (Allium cepa) using the squash technique. After fixing the root tip in Carnoy's solution, staining with aceto‑orcein, and preparing a slide, the student examines a random field of view at 100× objective and records the following numbers of cells in each stage of mitosis. - Prophase: 30 cells - Metaphase: 20 cells - Anaphase: 15 cells - Telophase: 10 cells - Interphase (non‑dividing cells): 125 cells The total number of cells counted in the field is therefore 200.
Question Parts
(a)
Calculate the mitotic index for the root tip sample. Show your working.
(b)
Explain what a high mitotic index indicates about the growth activity of the tissue observed.
(c)
Identify two sources of error that could affect the reliability of the mitotic index obtained and suggest one way to minimise each error.
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Question 3 View Details
You are given a set of data from a practical investigation that measured the blood glucose concentration of three volunteers before and after a 30‑minute moderate‑intensity walk. The concentrations were recorded using a calibrated glucometer. The data are shown in the table below. | Volunteer | Glucose before walk (mmol L⁻¹) | Glucose after walk (mmol L⁻¹) | |-----------|-------------------------------|------------------------------| | 1 | 5.4 | 4.9 | | 2 | 6.1 | 5.5 | | 3 | 5.8 | 5.2 | Using this information answer the questions that follow.
Question Parts
(a)
Calculate the mean glucose concentration before the walk and the mean concentration after the walk.
(b)
Determine the percentage change in the mean glucose concentration as a result of the walk. Show your working.
(c)
Identify two possible sources of error that could affect the reliability of the results and suggest one way to minimise each error.
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Question 4 View Details
You carried out an experiment to compare the rate of respiration in germinating beans kept in light and in darkness. A sealed 50 mL gas syringe was connected to a container holding 5 g of beans. The volume change (increase in gas) was recorded every 5 min for 30 min at a constant temperature of 25 °C. The data obtained are shown. | Time (min) | Volume change – Light (mL) | Volume change – Dark (mL) | |------------|----------------------------|---------------------------| | 5 | 3.2 | 1.8 | | 10 | 6.5 | 3.5 | | 15 | 9.9 | 5.1 | | 20 | 13.1 | 6.6 | | 25 | 16.4 | 8.0 | | 30 | 19.6 | 9.3 | Assume the pressure remains constant and that at 25 °C one mole of gas occupies 24 L. Answer the following questions.
Question Parts
(a)
Calculate the total volume of CO₂ produced in each condition (light and dark) over the 30 minute period.
(b)
Using the ideal‑gas relationship given, calculate the moles of CO₂ produced per gram of beans for each condition. Show your working and give your answer to three significant figures.
(c)
Determine the percentage increase in the respiration rate (moles g⁻¹) in light compared with darkness.
(d)
Discuss two physiological reasons why light might affect the rate of respiration in germinating beans and suggest one improvement to the experimental design that would give more accurate results.
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