ijmb model questions vol1 2024 biology | Practical

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Question 1 View Details
You are given a prepared slide of an onion epidermal cell that has been stained with iodine. The microscope available has an ocular lens of 10× and objective lenses of 4×, 10× and 40×. An ocular micrometer is fitted to the eyepiece; each division on the micrometer corresponds to 0.01 mm on the stage micrometer. Using the 40× objective, you are to observe the cell and record measurements.
Question Parts
(a)
State the total magnification at which the cell is being observed.
(b)
Identify three distinct structures that are clearly visible in the preparation and give a brief function for each.
(c)
You measured the length of the same cell in three separate fields of view, obtaining 45, 48 and 46 micrometer‑scale divisions respectively. Calculate the average cell length in micrometres (µm).
(d)
Discuss two possible sources of error that could affect the accuracy of your length measurement.
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Question 2 View Details
A smear of onion root tip cells has been prepared and stained with aceto‑orcein. Using a light microscope, you examined five fields of view, each field containing exactly 100 cells. The numbers of cells observed in each mitotic phase are recorded below: Field 1: Prophase 12, Metaphase 8, Anaphase 5, Telophase 3 Field 2: Prophase 15, Metaphase 7, Anaphase 4, Telophase 2 Field 3: Prophase 10, Metaphase 9, Anaphase 6, Telophase 4 Field 4: Prophase 13, Metaphase 6, Anaphase 5, Telophase 3 Field 5: Prophase 14, Metaphase 8, Anaphase 5, Telophase 2 The cover slip used is 5 µm thick and the area of each field of view is 0.02 mm².
Question Parts
(a)
Calculate the mitotic index (percentage of cells in mitosis) for the whole slide.
(b)
Identify the most frequently observed mitotic phase and explain what this suggests about the cell population in the root tip.
(c)
Using the given field area and cover‑slip thickness, calculate the volume of the smear observed in one field of view. Express your answer in cubic millimetres (mm³) and in nanolitres (nL).
(d)
Suggest two practical improvements that could reduce counting errors in the determination of the mitotic index.
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Question 3 View Details
A student is investigating the carbohydrate content of a commercial orange juice using the phenol‑sulfuric acid method. The procedure is as follows: 1. Prepare glucose standard solutions of concentrations 0.20, 0.40, 0.60 and 0.80 g per 100 mL. 2. Add 1 mL of each standard to separate test tubes, add 1 mL of phenol solution and 5 mL of concentrated H₂SO₄, mix and allow colour to develop for 10 min. 3. Measure the absorbance of each tube at 490 nm against a reagent blank. 4. Treat 10 mL of the orange‑juice sample in the same way and record its absorbance. The absorbance readings obtained are: | Glucose concentration (g / 100 mL) | Absorbance (490 nm) | |-----------------------------------|----------------------| | 0.20 | 0.120 | | 0.40 | 0.245 | | 0.60 | 0.365 | | 0.80 | 0.485 | The orange‑juice sample gave an absorbance of 0.312. The density of the juice is 1.05 g mL⁻¹. Using this information, answer the questions below.
Question Parts
(a)
Construct the calibration curve by determining the linear equation (Absorbance = m × Concentration + c) from the four standard points.
(b)
Using the calibration equation, calculate the concentration of glucose (g / 100 mL) present in the orange‑juice sample.
(c)
Determine the percentage (w/w) of carbohydrate in the orange‑juice sample. (Assume that all carbohydrate present reacts as glucose.)
(d)
Identify two possible sources of error in this experiment and suggest one practical improvement for each.
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Question 4 View Details
A group of students set up a closed‑system respirometer to study the effect of temperature on the rate of respiration in germinating beans. The apparatus consists of a 200 mL airtight flask containing 5.0 g of freshly soaked beans immersed in 50 mL of water. The flask is connected to a manometer that records the internal pressure. The system is first equilibrated at 25 °C, then the pressure is recorded after 30 min; the reading falls from 760 mmHg to 750 mmHg. The experiment is repeated at 35 °C, and after 30 min the pressure drops from 760 mmHg to 740 mmHg. Assume the temperature of the gas inside the flask remains constant at the bath temperature, the volume of the flask does not change, and the gas behaves ideally. Using the data provided, answer the following questions.
Question Parts
(a)
Calculate the rate of O₂ consumption at 25 °C in millilitres of O₂ per minute per gram of bean tissue.
(b)
Repeat the calculation for the 35 °C experiment.
(c)
Determine the Q₁₀ temperature coefficient for the respiration process over the 10 °C interval.
(d)
Explain why the Q₁₀ value obtained is useful for understanding metabolic adaptation of seeds to temperature changes.
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