igcse model questions vol1 2019 biology | Practical

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Question 1 View Details
You are given a prepared slide of human cheek epithelial cells stained with methylene blue. Using a light microscope equipped with an ocular micrometer (scale = 0.01 mm per division) you observe five cells and record the longest diameter of each cell as shown in the table. | Cell | Diameter (mm) | |------|----------------| | 1 | 0.058 | | 2 | 0.062 | | 3 | 0.055 | | 4 | 0.060 | | 5 | 0.057 | Assume the cells are approximately spherical.
Question Parts
(a)
Calculate the mean (average) diameter of the five cells.
(b)
Assuming a spherical shape, estimate the average volume of a cell in mm³. (Use V = 4/3 π r³, where r = diameter/2.)
(c)
Calculate the surface‑area‑to‑volume ratio (SA:V) for the average cell. (Use SA = 4 π r².) Express your answer in mm⁻¹ and give one decimal place.
(d)
Briefly explain why a high surface‑area‑to‑volume ratio is advantageous for cells that carry out absorption.
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Question 2 View Details
A sample of rapidly growing onion (Allium cepa) root tip is fixed in Carnoy's solution and stained with 2% aceto‑orcein. Under a light microscope you examine five fields and record the number of cells observed in each stage of mitosis as shown. | Field | Prophase | Metaphase | Anaphase | Telophase | Interphase | |-------|----------|-----------|----------|-----------|------------| | 1 | 12 | 8 | 5 | 4 | 71 | | 2 | 10 | 9 | 6 | 5 | 70 | | 3 | 11 | 7 | 4 | 6 | 72 | | 4 | 13 | 8 | 5 | 5 | 69 | | 5 | 9 | 10 | 5 | 4 | 71 | Assume that the five fields together represent a random, unbiased sample of the root‑tip cells.
Question Parts
(a)
Calculate the percentage of cells in each mitotic phase (prophase, metaphase, anaphase, telophase) relative to the total number of cells observed.
(b)
Determine the mitotic index (percentage of cells in any mitotic phase) and comment on what the value indicates about the growth status of the root tip.
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Question 3 View Details
A group of students carried out a nutrition analysis of three locally available food items using standard laboratory methods. The items were: - Sample A: boiled rice - Sample B: roasted groundnuts - Sample C: fried plantain For each sample a 10.0 g portion was dried and then the following masses were obtained after the respective extractions: | Sample | Carbohydrate extracted (g) | Protein extracted (g) | Fat extracted (g) | |--------|----------------------------|-----------------------|-------------------| | A | 4.5 | 1.2 | 2.0 | | B | 2.0 | 3.5 | 5.0 | | C | 5.5 | 0.8 | 3.0 | Using the conversion factors 1 g carbohydrate = 4 kcal, 1 g protein = 4 kcal and 1 g fat = 9 kcal, answer the following:
Question Parts
(a)
Calculate the percentage of carbohydrate in sample B.
(b)
Calculate the total energy (in kCal) supplied by 100 g of sample C.
(c)
Rank the three samples from highest to lowest in terms of total energy per 100 g.
(d)
Which sample would be the most suitable source of protein for a school lunch? Justify your answer with calculations.
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Question 4 View Details
A sealed respirometer containing five germinating beans was used to measure the rate of cellular respiration at three different temperatures. The volume of CO₂ collected over a period of 30 minutes was recorded as follows: | Temperature (°C) | CO₂ volume collected (ml) | |------------------|---------------------------| | 20 | 12.0 | | 30 | 24.0 | | 40 | 36.0 | Assume the gas collected is pure CO₂ and that the temperature of the gas remains constant during each measurement. Answer the questions below:
Question Parts
(a)
Calculate the rate of respiration (ml CO₂ h⁻¹) for each temperature.
(b)
Describe the relationship between temperature and the rate of respiration. State the type of graph you would draw and the expected shape of the curve.
(c)
Using the data for 20 °C and 30 °C, calculate the temperature coefficient Q₁₀ for the respiration process. (Formula: Q₁₀ = (R₂ / R₁) ^ [10 / (T₂ – T₁)])
(d)
Identify two possible sources of error in this experiment and explain how each could affect the measured rates of respiration.
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