ijmb model questions vol1 2023 biology | Practical

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Question 1 View Details
A prepared slide of an unknown eukaryotic tissue was examined under a light microscope equipped with an ocular micrometer calibrated at 0.5 µm per division. Five cells were randomly selected and the following measurements were recorded: | Cell | Cell diameter (µm) | Nucleus diameter (µm) | |------|--------------------|-----------------------| | 1 | 20 | 10.0 | | 2 | 22 | 11.0 | | 3 | 19 | 9.0 | | 4 | 21 | 10.5 | | 5 | 23 | 11.0 | No rigid cell wall was visible in any of the observed cells.
Question Parts
(a)
Calculate the mean cell diameter and the mean nucleus diameter (in µm).
(b)
For each cell, compute the nuclear‑cytoplasmic ratio (NCR) defined as nucleus diameter ÷ (cell diameter – nucleus diameter). Then determine the mean NCR for the five cells (expressed to two decimal places).
(c)
Using the mean NCR obtained and the observation that no cell wall was visible, infer whether the unknown tissue is of animal or plant origin. Justify your conclusion with two relevant points.
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Question 2 View Details
A root‑tip squash of an onion (Allium cepa) was prepared and examined under a light microscope. From a random field of view, 200 cells were counted and classified according to the stage of mitosis observed. The results are shown below: | Stage | Number of cells | |------------|-----------------| | Prophase | 30 | | Metaphase | 25 | | Anaphase | 20 | | Telophase | 15 | | Interphase | 110 | All counts are whole numbers and the total of the five categories equals 200.
Question Parts
(a)
Calculate the mitotic index (MI) for the sample, expressed as a percentage to one decimal place. MI = (total number of cells in mitosis / total number of cells observed) × 100.
(b)
Determine the percentage of cells in each mitotic phase (prophase, metaphase, anaphase, telophase) relative to the total number of mitotic cells. Express each percentage to one decimal place.
(c)
A researcher treats a comparable onion root tip with auxin, a plant growth hormone known to stimulate cell division. Predict qualitatively how the mitotic index and the distribution of mitotic phases would change compared with the untreated sample, and give a brief explanation (maximum two sentences).
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Question 3 View Details
A sample of an unknown food item weighing 5.00 g was subjected to a series of standard gravimetric analyses to determine its major nutritional components. The following observations were recorded: - Moisture loss after drying at 105 °C: 0.60 g - Ash obtained after incineration at 550 °C: 0.45 g - Crude fat extracted by Soxhlet extraction with petroleum ether: 0.75 g The remaining mass after accounting for moisture, ash and fat is assumed to be crude protein.
Question Parts
(a)
Calculate the percentage (w/w) of moisture, ash, crude fat and crude protein in the sample.
(b)
A 70 kg adult requires protein at 0.8 g kg⁻¹ day⁻¹. Based on the protein content you have calculated, determine how many grams of the food sample must be consumed to meet the daily protein requirement.
(c)
Identify two possible sources of error that could affect the accuracy of the crude fat determination by Soxhlet extraction.
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Question 4 View Details
A closed respirometer was used to measure the rate of aerobic respiration of a suspension of baker's yeast (Saccharomyces cerevisiae) at three different temperatures. The volume of oxygen evolved was recorded over a fixed period of 5 min as shown in the table below. | Temperature (°C) | O₂ evolved in 5 min (mL) | |------------------|--------------------------| | 20 | 12.0 | | 30 | 18.5 | | 40 | 28.0 | Assume the gas is collected at 25 °C and 1 atm and that the volume recorded is directly proportional to the amount of O₂ produced.
Question Parts
(a)
Calculate the rate of oxygen evolution (mL O₂ min⁻¹) at each temperature.
(b)
Using the rates obtained, calculate the temperature coefficient Q₁₀ for the interval 20 °C–30 °C and for 30 °C–40 °C. Use Q₁₀ = (R₂/R₁)^{10/(T₂‑T₁)}.
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