ijmb model questions vol1 2025 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 compound microscope equipped with an ocular micrometer calibrated at 0.01 mm per division, you measure the diameter of five randomly selected cells. The recorded diameters are: 0.058 mm, 0.062 mm, 0.060 mm, 0.059 mm and 0.061 mm. Assume the cells are approximately spherical.
Question Parts
(a)
Calculate the mean cell diameter (to three significant figures) and state the corresponding mean radius.
(b)
Assuming a spherical shape, calculate the average surface area and volume of the cells (both to two significant figures) and then compute the surface‑area‑to‑volume (SA:V) ratio.
(c)
Briefly discuss why a high surface‑area‑to‑volume ratio is advantageous for epithelial cells and list two possible sources of error in the diameter measurements.
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Question 2 View Details
A sample of onion (Allium cepa) root tip is collected, fixed in Carnoy's solution, stained with aceto‑orcein and a squash preparation is examined under a compound microscope. From a randomly chosen field you count a total of 300 cells and record the number of cells in each stage of mitosis as follows: Prophase – 45 cells, Metaphase – 60 cells, Anaphase – 30 cells, Telophase – 15 cells, Interphase – 150 cells.
Question Parts
(a)
Calculate the mitotic index, expressed as the percentage of cells that are in any stage of mitosis.
(b)
Determine the percentage distribution of each mitotic phase (Prophase, Metaphase, Anaphase, Telophase) relative to the total number of mitotic cells.
(c)
Explain what the mitotic index reveals about the growth activity of the onion root tip.
(d)
Identify two procedural factors that could lead to an under‑estimation of the mitotic index and suggest a method to minimise each factor.
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Question 3 View Details
A student is required to determine the carbohydrate content of a powdered food sample using the phenol‑sulfuric acid method. The procedure involves preparing a series of glucose standards, measuring their absorbance at 490 nm, and constructing a calibration curve. The data obtained are:
Question Parts
(a)
Write a concise step‑by‑step procedure for preparing the sample extract and performing the phenol‑sulfuric acid assay.
(b)
Using the standard data below, construct the calibration equation (assume a linear relationship passing through the origin) and determine the concentration of carbohydrate in the sample extract (expressed in mg mL⁻¹).
(c)
Calculate the percentage (w/w) of carbohydrate in the original food sample.
(d)
State two possible sources of experimental error in this assay and suggest a method to minimise each error.
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Question 4 View Details
A group of students investigates the effect of metabolic inhibitors on the rate of cellular respiration in germinating pea seeds using a sealed gas syringe to collect the CO₂ evolved over 30 minutes.
Question Parts
(a)
Describe the experimental set‑up, including the preparation of the pea samples, the gas‑syringe system and the method of recording CO₂ volume.
(b)
Given the CO₂ volumes recorded after 30 min are: control = 12.5 mL, sodium azide = 4.2 mL, cyanide = 2.8 mL, calculate the respiration rate in mL CO₂ g⁻¹ min⁻¹ for each treatment.
(c)
Determine the percent inhibition of respiration for each inhibitor relative to the control.
(d)
Explain why cyanide produces a greater inhibition of respiration than sodium azide under the conditions of this experiment.
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