neco model questions vol1 2021 biology | Practical

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Question 1 View Details
A student prepares a temporary wet mount of an onion (Allium cepa) epidermal peel to observe cell structure under the microscope. The ocular micrometer has been calibrated with a stage micrometer such that 1 mm = 100 divisions.
Question Parts
(a)
List three distinct cell structures that can be clearly identified in the preparation and state one function for each.
(b)
The student measures the length of five adjacent cells as follows (in ocular divisions): 28, 30, 27, 31, 29. Calculate the average cell length in micrometres (µm). Show all steps.
(c)
Assuming the cells are approximately rectangular and the average width measured from the same field is 12 divisions, calculate the average cell area in µm². Then estimate how many such cells would be required to line up to cover a leaf surface area of 2.5 cm². (1 cm = 10,000 µm)
(d)
Identify two sources of error that could affect the accuracy of the measurements and suggest one precaution for each.
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Question 2 View Details
A student prepares a squash preparation of an onion root tip to study mitosis. The root tip is stained with 1% acetocarmine before squashing.
Question Parts
(a)
Describe the steps involved in preparing the squash slide, including any reagents used.
(b)
In the prepared slide the student counts a total of 800 cells distributed as follows: Prophase 120, Metaphase 150, Anaphase 80, Telophase 100, Interphase 350. Calculate the mitotic index (percentage of cells in mitosis) and the percentage of cells in each mitotic phase. Show all calculations.
(c)
The normal mitotic index for healthy onion root tip cells is between 2% and 5%. Based on the calculated index, discuss whether the sample is likely to be from healthy tissue or affected by a factor such as a toxin. Provide a brief justification.
(d)
Suggest one improvement to the experimental procedure that could increase the accuracy of the mitotic index determination.
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Question 3 View Details
A student is required to determine the carbohydrate content of a commercial cereal sample using the Benedict’s test.
Question Parts
(a)
Outline the procedure for preparing a standard glucose curve using Benedict’s reagent, specifying the concentrations of the five standard solutions.
(b)
Using the data below, determine the concentration of carbohydrate in the cereal extract. (No graph is required – use linear interpolation.) Standard glucose solutions: | Concentration (g L⁻¹) | Precipitate volume (mL) | |-----------------------|--------------------------| | 0 | 0.0 | | 2 | 1.2 | | 4 | 2.4 | | 6 | 3.6 | | 8 | 4.8 | Cereal extract (5.0 mL of extract was mixed with 2 mL Benedict’s reagent) gave a precipitate volume of 3.0 mL.
(c)
Calculate the percentage (w/w) of carbohydrate in the cereal sample, given that 2.00 g of the powdered sample was extracted in 50.0 mL of water and 5.0 mL of the extract was used for the test.
(d)
List two possible sources of error in this experiment and suggest how each could be minimised.
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Question 4 View Details
A student investigates the effect of temperature on the rate of respiration in germinating beans using a closed respirometer.
Question Parts
(a)
Describe the set‑up of the closed respirometer and the procedure for measuring the volume of gas evolved during respiration.
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