neco model questions vol1 2018 biology | Practical

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Question 1 View Details
A student prepares a squashed slide of cheek epithelial cells stained with methylene blue. Using an ocular micrometer calibrated at 0.01 mm per division, the longest diameter of ten cells is measured as follows (in mm): 0.12, 0.13, 0.11, 0.12, 0.14, 0.13, 0.12, 0.13, 0.11, 0.12. Assume the cells are approximately spherical.
Question Parts
(a)
Calculate the mean cell diameter.
(b)
Using the mean diameter, estimate the average cell volume (V = 4⁄3 π r³) and surface area (A = 4 π r²). Give each answer to two decimal places and express the results in µm³ for volume and µm² for surface area.
(c)
Discuss how a high surface‑area‑to‑volume (SA:V) ratio benefits diffusion of nutrients in epithelial cells.
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Question 2 View Details
A student prepares fresh root‑tip squashes of Allium cepa (onion). In an untreated sample 500 cells are examined and the following numbers of cells are recorded in each mitotic phase: prophase 120, metaphase 80, anaphase 50, telophase 30 (the remaining cells are in interphase). A second set of root tips is treated with 0.01 % colchicine solution for 4 h before fixation; 400 cells are examined and the distribution is: prophase 60, metaphase 150, anaphase 80, telophase 40, interphase 70.
Question Parts
(a)
Calculate the mitotic index (MI = (number of cells in mitosis ÷ total cells) × 100) for the untreated and colchicine‑treated samples.
(b)
Determine the percentage of cells in each mitotic phase (prophase, metaphase, anaphase, telophase, interphase) for both samples.
(c)
Explain the effect of colchicine on the cell cycle, using the results obtained.
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Question 3 View Details
A group of students carried out a qualitative test for reducing sugars in three food samples (A, B and C) using Benedict’s reagent. The sample that gave a positive result was then quantified by spectrophotometric analysis. The spectrophotometer was calibrated with standard glucose solutions as shown in the table below. **Standard glucose solutions** | % (w/v) glucose | Absorbance (A) | |----------------|----------------| | 0.2 | 0.12 | | 0.4 | 0.24 | | 0.6 | 0.36 | | 0.8 | 0.48 | The unknown sample gave an absorbance of 0.33. The unknown was prepared by dissolving 2.0 g of the food in 100 mL of distilled water. Answer the following:
Question Parts
(a)
State the observation for each of the three food samples when Benedict’s reagent was added and identify which sample contains reducing sugars.
(b)
Using the standard curve (assume a linear relationship passing through the origin), calculate the concentration of reducing sugar in the unknown sample in % (w/v). Show all steps.
(c)
If the original sample was prepared by dissolving 2.0 g of the food in 100 mL of water, estimate the percentage (w/w) of reducing sugar in the food sample.
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Question 4 View Details
Students investigated the effect of temperature on the rate of cellular respiration in germinating mung bean seeds using a closed gas‑collection system. The volume of CO₂ produced after 10 minutes at each temperature is shown in the table. **Rate of CO₂ evolution (control)** | Temperature (°C) | Volume of CO₂ (mL) | |------------------|--------------------| | 20 | 12 | | 30 | 22 | | 40 | 35 | | 50 | 30 | **Rate of CO₂ evolution (with cyanide inhibitor)** | Temperature (°C) | Volume of CO₂ (mL) | |------------------|--------------------| | 20 | 5 | | 30 | 6 | | 40 | 7 | | 50 | 6 | Answer the following:
Question Parts
(a)
Calculate the rate of CO₂ evolution (in mL min⁻¹) for each temperature in both the control and the cyanide‑treated samples.
(b)
From the rates obtained, describe the trend with temperature for the control and explain at which temperature the maximum rate occurs.
(c)
Explain why the rate of respiration falls at 50 °C despite the higher temperature.
(d)
Identify two possible sources of experimental error in this investigation and suggest a method to minimise each error.
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