neco 2023 biology | Practical

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Question 1 View Details
You are given a slide of a peeled epidermal layer of an onion leaf. Using a compound microscope at 400× magnification, you observe rectangular cells. You record the length and width of five randomly selected cells as shown in the table below (values in µm).
Question Parts
(a)
Calculate the mean length and the mean width of the five cells.
(b)
Assuming each cell is a rectangular prism with a uniform thickness of 10 µm, calculate the average volume of a cell using the mean dimensions obtained in part (a).
(c)
Using the average dimensions, calculate the surface‑area‑to‑volume ratio (SA:V) of a typical cell. (Surface area = 2(lw + lh + wh); volume = l × w × h)
(d)
Explain why a relatively high SA:V ratio is advantageous for the metabolic activities of a plant cell.
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Question 2 View Details
You are investigating the rate of cell division in the root tip of a fast‑growing bean plant (Phaseolus vulgaris). A fresh root tip is fixed, stained and squashed. Under a microscope at 1000× magnification you examine 200 cells and record the number of cells in each stage of mitosis as shown below.
Question Parts
(a)
Calculate the mitotic index (MI) using the formula MI = (Number of cells in mitosis / Total observed cells) × 100.
(b)
Determine the percentage of cells in each mitotic stage (relative frequency) and present the data in a table.
(c)
Based on the percentages obtained, identify which mitotic stage is longest in duration and justify your answer.
(d)
Discuss two possible sources of error that could affect the accuracy of the mitotic index you have calculated.
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Question 3 View Details
A group of students carried out a nutrition analysis of three locally available foods. The data obtained are shown in the table below. | Food | Sample mass (g) | % Carbohydrate | % Protein | % Fat | |--------------------|-----------------|----------------|-----------|-------| | Boiled plantain | 150 | 30 | 2 | 0.2 | | Roasted groundnuts | 50 | 15 | 25 | 45 | | Fermented milk | 200 (ml) | 5 | 3 | 2 | (Assume the density of fermented milk is 1 g ml⁻¹. Energy values: carbohydrate = 4 kcal g⁻¹, protein = 4 kcal g⁻¹, fat = 9 kcal g⁻¹.) Answer the following questions:
Question Parts
(a)
Calculate the total caloric value of a meal consisting of the whole sample of each food listed in the table. Show all working.
(b)
Identify which food contributes the greatest amount of protein to the meal and state the amount of protein (in grams) supplied by that food.
(c)
The recommended daily energy intake for a 15‑year‑old adolescent is 2500 kcal. Calculate the percentage of this requirement supplied by the meal and comment on whether the meal is adequate as a single meal.
(d)
Suggest one modification to the meal that will increase its protein content by at least 10 g without raising the total caloric value by more than 200 kcal. Justify your suggestion.
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Question 4 View Details
Students investigated the effect of temperature on the rate of respiration in *Saccharomyces cerevisiae* (baker's yeast) using a closed respirometer. The procedure was as follows: 1. 5 g of dried yeast was added to 100 ml of 5 % (w/v) glucose solution in a 250 ml sealed flask. 2. The flask was connected to a gas syringe that was initially set to 0 ml (zeroed). The system was placed in a water bath. 3. The flask was first kept at 30 °C for 30 minutes; the volume of gas displaced was recorded. 4. The temperature was then raised to 40 °C and the flask was kept for a further 30 minutes; the cumulative gas volume was recorded. The observations were: - After 30 min at 30 °C, the gas syringe read 45 ml. - After a further 30 min at 40 °C (total 60 min), the gas syringe read 120 ml. Assume the gas collected is CO₂ and that the mass of yeast remains constant throughout the experiment. Answer the following:
Question Parts
(a)
Calculate the rate of respiration (ml CO₂ produced per gram of yeast per minute) at 30 °C.
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