ijmb model questions vol1 2018 biology | Practical

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Question 1 View Details
You are given a prepared slide of onion (Allium cepa) epidermal cells and an ocular micrometer that has been calibrated as 100 divisions = 0.5 mm. Using the microscope you measure the length of a typical cell as 45 divisions and its width as 30 divisions. The average thickness of the cell (measured from a different preparation) is 0.02 mm. Answer the following:
Question Parts
(a)
Convert the observed divisions to the actual length and width of the cell in millimetres.
(b)
Assuming the cell is a rectangular prism of thickness 0.02 mm, calculate its volume in mm³.
(c)
Calculate the total external surface area of the cell (excluding the cell wall thickness) in mm².
(d)
Determine the surface‑area‑to‑volume (SA:V) ratio and briefly discuss how this ratio influences the rate of diffusion of nutrients into the cell.
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Question 2 View Details
You are investigating mitotic activity in the root tip of an onion (Allium cepa). A slide is prepared using the squash technique and stained with aceto‑orcein. Under the microscope you examine a random field and count a total of 500 cells. The numbers of cells observed in each stage of mitosis are: prophase 30, metaphase 20, anaphase 15, telophase 10. Answer the following:
Question Parts
(a)
Calculate the mitotic index (percentage of cells in mitosis).
(b)
Determine the percentage of the total cells that are in each individual phase of mitosis.
(c)
The normal mitotic index for a healthy onion root tip is 3–5%. State whether the observed index is within the normal range and give a possible biological explanation for the result.
(d)
Suggest one procedural precaution that could reduce error when counting mitotic cells on the slide.
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Question 3 View Details
A group of students carried out an experiment to compare the effect of three carbohydrate sources on the rise in blood glucose level after simulated digestion. The procedure was as follows: 1. Prepare 100 mL of each carbohydrate solution: 5 % (w/v) glucose solution, 5 % (w/v) sucrose solution and 5 % (w/v) soluble starch solution. 2. Add 2 mL of α‑amylase (10 U mL⁻¹) to each tube and incubate at 37 °C for 30 min. 3. After incubation, cool the tubes and determine the glucose concentration of each sample using a calibrated glucose test strip (readings in mmol L⁻¹). 4. Record three independent readings for each carbohydrate source. The recorded glucose concentrations (mmol L⁻¹) are: | Carbohydrate | Trial 1 | Trial 2 | Trial 3 | |--------------|--------|--------|--------| | Glucose (control) | 5.2 | 5.4 | 5.3 | | Sucrose | 7.1 | 6.9 | 7.0 | | Starch | 6.2 | 6.4 | 6.3 | Using the data above, answer the following:
Question Parts
(a)
Calculate the mean glucose concentration for each carbohydrate source.
(b)
Express the increase in mean glucose concentration for sucrose and starch as a percentage of the control (glucose) mean.
(c)
Identify which carbohydrate source produced the greatest rise in blood glucose and give a brief physiological explanation for this observation.
(d)
List two possible sources of experimental error that could affect the reliability of the results and suggest one way to minimise each error.
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Question 4 View Details
Students investigated the effect of sugar concentration on the rate of cellular respiration in baker's yeast. The procedure was: 1. Prepare three fermentation broths (250 mL each) containing 0 % (control), 2 % (w/v) and 5 % (w/v) glucose respectively. 2. Add 5 g of active dry yeast to each broth, seal the flask with a rubber stopper fitted with a graduated gas‑collecting tube (water displaced), and place the flasks in a water bath at 30 °C. 3. After 30 min, record the volume of CO₂ collected (mL) in each tube. Three independent trials were performed for each concentration. The recorded volumes are: | Glucose concentration | Trial 1 | Trial 2 | Trial 3 | |-----------------------|--------|--------|--------| | 0 % (water control) | 0.2 | 0.1 | 0.15 | | 2 % | 1.8 | 1.9 | 1.7 | | 5 % | 1.2 | 1.1 | 1.3 | Using the data above, answer the following:
Question Parts
(a)
Calculate the mean volume of CO₂ produced for each glucose concentration and the corresponding respiration rate in mL min⁻¹ (use the 30 min incubation period).
(b)
From the calculated rates, state which glucose concentration gives the maximum respiration rate and explain why a higher concentration (5 %) does not produce a higher rate.
(c)
Calculate the percentage inhibition of respiration at 5 % glucose relative to the optimum rate (2 %).
(d)
Suggest one procedural improvement that could reduce experimental error in measuring CO₂ volume.
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