ijmb model questions vol1 2022 biology | Practical

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Question 1 View Details
You are given a prepared slide of an onion (Allium cepa) epidermal cell. Using a light microscope fitted with a 10× ocular and a 40× objective, observe the cell and record your findings.
Question Parts
(a)
Draw a clear, labelled diagram of a typical onion epidermal cell as seen under the microscope. Include the cell wall, cell membrane, cytoplasm, nucleus, large central vacuole and any chloroplasts that may be visible. State the total magnification used for the observation.
(b)
Using the ocular micrometer, record the number of divisions that span the length of the cell from one outer edge of the cell wall to the opposite edge. The ocular micrometer has 100 divisions and the calibrated eyepiece scale indicates that 1 division = 2 µm at 400× total magnification.
(c)
Calculate the actual length of the cell in micrometres (µm) using the reading obtained in part (b). Show your working.
(d)
Identify two possible sources of error in the measurement obtained in part (b) and suggest one method to minimise each error.
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Question 2 View Details
You are to examine a prepared slide of an onion (Allium cepa) root tip that has been stained with aceto‑orcein to reveal chromosomes during mitosis. Use the same microscope (10× ocular, 40× objective).
Question Parts
(a)
Describe how you locate the region of the root tip where mitotic figures are most abundant. State the characteristic features you use to identify this meristematic zone.
(b)
From a single field of view, count 200 cells and record how many are in each stage of mitosis: prophase, metaphase, anaphase, telophase, and interphase. The observed numbers are: prophase 30, metaphase 50, anaphase 40, telophase 20, interphase 60. Verify that the total count is correct.
(c)
Calculate the mitotic index (MI) using the formula MI = (Number of cells in mitosis / Total cells observed) × 100. Show your working.
(d)
Interpret the mitotic index obtained. What does a high or low mitotic index indicate about the growth activity of the root tip?
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Question 3 View Details
A food sample is being analysed for its carbohydrate content using the Benedict’s test followed by spectrophotometric measurement at 420 nm. The procedure is as follows: 1. Prepare standard glucose solutions of known concentrations and record their absorbance values as shown in the table below. 2. Prepare an extract of the food sample by grinding 2.00 g of the sample, adding 50 mL distilled water, stirring for 5 min and filtering. 3. Pipette 10.0 mL of the extract into a test tube, add 5.0 mL of Benedict’s reagent, heat in a boiling water bath for 5 min, cool and measure the absorbance of the resulting solution. 4. Use the calibration curve obtained from the standards to determine the carbohydrate concentration in the test mixture and calculate the percentage carbohydrate in the original food sample. Standard data: | Glucose concentration (g dL⁻¹) | Absorbance (A) | |-------------------------------|----------------| | 0.00 | 0.00 | | 0.20 | 0.11 | | 0.40 | 0.23 | | 0.60 | 0.34 | | 0.80 | 0.46 | Absorbance of the test mixture: **0.29**.
Question Parts
(a)
Using the standard data, derive the linear equation that relates absorbance (A) to carbohydrate concentration (C) in g dL⁻¹. State the slope and intercept to two decimal places.
(b)
Calculate the carbohydrate concentration (C) in the test mixture from the observed absorbance of 0.29.
(c)
Determine the percentage carbohydrate in the original food sample (expressed to one decimal place).
(d)
Identify two possible sources of experimental error in this procedure and suggest a practical way to minimise each error.
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Question 4 View Details
The rate of respiration in germinating beans is being investigated by measuring the volume of carbon dioxide (CO₂) evolved in a sealed respiration chamber. The procedure is: 1. Weigh 5.00 g of dry beans, soak them in water for 12 h, then place the soaked beans in a 250 mL airtight chamber containing 150 mL of distilled water. 2. The chamber is kept at a constant temperature and the CO₂ produced displaces water in a graduated tube. 3. The volume of displaced water is recorded after 30 min. Two experiments are performed at different temperatures. Data: - At 25 °C: displaced water volume = 12.5 mL. - At 35 °C: displaced water volume = 18.2 mL. Atmospheric pressure = 760 mmHg. Water‑vapour pressure: 23.8 mmHg at 25 °C and 38.0 mmHg at 35 °C. Assume ideal gas behaviour (R = 0.0821 L·atm·mol⁻¹).
Question Parts
(a)
Calculate the volume of dry CO₂ (i.e., corrected for water vapour) collected at each temperature.
(b)
Determine the respiration rate expressed as µmol CO₂ · g⁻¹ · min⁻¹ for each temperature.
(c)
Explain the observed difference in respiration rates with reference to the effect of temperature on enzyme activity.
(d)
Suggest two improvements to the experimental set‑up that would increase the reliability of the respiration rate data.
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