waec model questions vol1 2017 biology | Practical

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Question 1 View Details
You are provided with a fresh leaf peel of Elodea and a compound microscope equipped with a 10× ocular lens and a 40× objective lens. The microscope is set up on a laboratory bench and a clean glass slide and cover slip are available.
Question Parts
(a)
State the sequence of steps you would follow to prepare the slide and obtain a clear view of the cells.
(b)
Draw a labelled diagram of the observed cell showing the nucleus, cell wall, plasma membrane, chloroplast and vacuole. Indicate the relative size of each structure.
(c)
Briefly state the function of each labelled structure.
(d)
Mention two possible sources of error that could affect the observation and suggest one way to minimise each error.
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Question 2 View Details
You are to investigate the mitotic activity in the root tip of an onion (Allium cepa). The laboratory provides fresh onion roots, a microscope with 10× ocular and 40× objective lenses, a fixing solution (3% acetic acid), a staining solution (0.5% acetocarmine), and the usual slide‑preparation materials.
Question Parts
(a)
Outline the complete procedure for preparing a root‑tip slide suitable for observing mitosis, including any pretreatment of the root tip.
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Question 3 View Details
A group of students carried out an experiment to determine the carbohydrate content of a commercial fruit‑juice sample using the dinitrosalicylic acid (DNS) method.
Question Parts
(a)
Describe the procedure for preparing a series of glucose standard solutions (0, 2, 4, 6 and 8 mg mL⁻¹) and for measuring their absorbance at 540 nm.
(b)
The absorbance readings obtained were: 0 mg mL⁻¹ – 0.012, 2 mg mL⁻¹ – 0.158, 4 mg mL⁻¹ – 0.301, 6 mg mL⁻¹ – 0.452, 8 mg mL⁻¹ – 0.603. State the equation of the best‑fit straight line and calculate the carbohydrate concentration in the diluted juice sample that gave an absorbance of 0.375.
(c)
The diluted juice sample was prepared by mixing 2.00 mL of the juice with 8.00 mL of distilled water. Using the concentration obtained in (b), calculate the percentage (w/v) of carbohydrate in the original undiluted juice. Show all steps, including the dilution factor.
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Question 4 View Details
Students investigated the effect of temperature on the rate of respiration of germinating wheat seeds using a closed respirometer containing a potassium hydroxide (KOH) solution to absorb CO₂.
Question Parts
(a)
Explain the purpose of KOH in the set‑up and describe how the change in gas volume is recorded during the experiment.
(b)
At 25 °C the gas volume fell from 100 mL to 78 mL in 10 min. At 35 °C the fall was from 100 mL to 70 mL in the same period. Assuming ideal‑gas behaviour and constant temperature during each trial, calculate the rate of CO₂ production (in mL min⁻¹) at each temperature.
(c)
Using the rates obtained in (b), calculate the Q₁₀ temperature coefficient for respiration between 25 °C and 35 °C. Use Q₁₀ = (R₂/R₁)^{10/(T₂‑T₁)}.
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