waec model questions vol1 2021 biology | Practical

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Question 1 View Details
A student is required to prepare a permanent slide of an onion epidermal cell for observation under a light microscope.
Question Parts
(a)
List the correct order of steps the student should follow to prepare the permanent slide, starting from obtaining the specimen to mounting the slide.
(b)
After staining with iodine solution, the student observes the cell under 400× magnification and records the following measurements: length of the cell = 0.12 mm, width = 0.04 mm. Assuming the cell is a rectangular prism whose thickness equals half its width, calculate the approximate surface area of the cell. Show your working.
(c)
Identify three structures that the student is likely to see in the stained epidermal cell and state one function for each.
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Question 2 View Details
A student investigates cell division in the root tip of a fast‑growing bean (Phaseolus vulgaris) using a fresh squash preparation stained with acetocarmine.
Question Parts
(a)
Describe the procedure for preparing a fresh squash of the root tip suitable for observing mitosis.
(b)
The student counts a total of 500 cells in five randomly selected fields of view. The numbers of cells in each phase of mitosis observed are: prophase 120, metaphase 80, anaphase 60, telophase 40, and interphase 200. Calculate:
() The mitotic index (percentage of cells undergoing mitosis).
() The percentage of cells in each mitotic phase (prophase, metaphase, anaphase, telophase).
(c)
Based on the percentages obtained, discuss what the results suggest about the growth activity of the root tip.
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Question 3 View Details
A group of students carried out a quantitative analysis of carbohydrate in a cooked rice sample using the Benedict’s test. The procedure was as follows: 10 g of the cooked rice was homogenised in 100 mL of distilled water, filtered and the filtrate was made up to the mark. From this solution, 10 mL was taken and mixed with an excess of Benedict’s reagent. The mixture was heated in a water‑bath for 5 minutes and the volume of Benedict’s reagent required to give the first distinct brick‑red colour was recorded. The data obtained from a series of glucose standards are shown in the table below. | Glucose (mg) | Volume of Benedict’s reagent (mL) | |--------------|-----------------------------------| | 0 | 5.0 | | 200 | 7.0 | | 400 | 9.0 | | 600 | 11.0 | The rice sample required 9.5 mL of Benedict’s reagent to develop the colour.
Question Parts
(a)
State the chemical principle behind the Benedict’s test for reducing sugars.
(b)
Using the data in the table, determine the amount of glucose (in milligrams) present in the 10 mL aliquot taken from the rice extract.
(c)
Calculate the percentage of carbohydrate (as glucose) in the original 10 g rice sample.
(d)
List two possible sources of error in this experiment and suggest a method to minimise each error.
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Question 4 View Details
Students investigated the effect of temperature on the rate of respiration in germinating mung bean seeds using a closed respirometer. The seeds were placed in the respirometer and the volume of gas produced was measured over a period of 5 minutes at three different temperatures. The data obtained are shown in the table. | Temperature (°C) | Volume of gas collected in 5 min (mL) | |------------------|----------------------------------------| | 20 | 12.0 | | 30 | 18.0 | | 40 | 27.0 | Assume the gas collected is CO₂ produced by respiration.
Question Parts
(a)
Calculate the rate of respiration (in mL CO₂ min⁻¹) at each temperature.
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