neco model questions vol1 2019 biology | Practical

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Question 1 View Details
You are given a prepared slide of an onion (Allium cepa) epidermal peel and a compound microscope equipped with an ocular micrometer calibrated at 0.01 mm per division.
Question Parts
(a)
Identify three cellular structures that can be observed in the slide and state one function of each.
(b)
A student measures the length of a typical rectangular epidermal cell as 45 divisions and its width as 30 divisions on the ocular micrometer. Calculate the actual length and width of the cell in micrometres (µm). Show all steps.
(c)
Determine the overall magnification used if the objective lens is 40× and the ocular lens is 10×. Then calculate the linear size of the cell as it appears on the screen (apparent size) in millimetres.
(d)
List two sources of error that could affect the accuracy of the measurements and suggest one way to minimise each error.
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Question 2 View Details
A sample of rapidly growing root tip of a garden pea (Pisum sativum) is collected, fixed, stained with Feulgen stain, and a slide is prepared. Under the microscope, a student examines five fields of view and records the number of cells in each stage of mitosis as shown in the table below. Field | Prophase | Metaphase | Anaphase | Telophase | Interphase ------|----------|-----------|----------|-----------|----------- 1 | 12 | 8 | 5 | 3 | 22 2 | 10 | 9 | 6 | 4 | 21 3 | 11 | 7 | 5 | 2 | 25 4 | 13 | 8 | 4 | 3 | 22 5 | 9 | 10 | 7 | 5 | 19
Question Parts
(a)
Calculate the total number of cells observed and the total number of cells in mitosis (i.e., sum of prophase, metaphase, anaphase and telophase) across all fields.
(b)
Determine the mitotic index (percentage of cells in mitosis) for the sample. Show your calculation.
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Question 3 View Details
A group of students carried out an experiment to determine the carbohydrate content of an unknown food sample using the Benedict’s test. They prepared a series of glucose standards and recorded the absorbance at 620 nm as follows: Standard (g/100 mL) : 0.2 0.4 0.6 0.8 1.0 Absorbance (A) : 0.12 0.24 0.36 0.48 0.60 The unknown solution (prepared by dissolving the extracted food in water) gave an absorbance of 0.42. The students extracted 2.5 g of the food in 25 mL of distilled water before the test. Answer the following questions:
Question Parts
(a)
Construct the calibration curve by determining the linear relationship between absorbance (A) and carbohydrate concentration (C) in g/100 mL.
(b)
Using the equation obtained in (a), calculate the carbohydrate concentration of the unknown solution (in g/100 mL).
(c)
Determine the percentage of carbohydrate in the original food sample.
(d)
Identify two possible sources of error in this experiment and suggest a way to minimise each.
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Question 4 View Details
Students investigated the effect of temperature on the rate of respiration in germinating pea seeds using a closed respirometer. Each respirometer contained 0.5 g of freshly germinated peas, 50 mL of water and was sealed with a gas‑collecting syringe. The ambient temperature of the water bath was set at three values and the volume of gas collected after 10 min was recorded as follows: Temperature (°C) : 15  25  35 Collected gas (mL) : 12  20  28 Atmospheric pressure = 760 mm Hg. The water‑vapour pressures at the three temperatures are: 15 °C – 12.8 mm Hg, 25 °C – 23.8 mm Hg, 35 °C – 42.2 mm Hg. Answer the following questions:
Question Parts
(a)
Correct each measured gas volume for water vapour to obtain the dry CO₂ volume at each temperature.
(b)
Calculate the respiration rate expressed as mL CO₂ min⁻¹ g⁻¹ of tissue for each temperature.
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