neco model questions vol1 2024 biology | Practical

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Question 1 View Details
You are given a prepared slide of human cheek cells stained with methylene blue and an ocular micrometer attached to a compound microscope. The ocular lens has a magnification of 10× and the objective lens used is 40×. One division on the ocular micrometer corresponds to 0.01 mm.
Question Parts
(a)
State the total magnification of the microscope.
(b)
You measured the diameter of a typical nucleus to be 25 divisions on the ocular micrometer. Calculate the actual diameter of the nucleus in micrometres (µm). Show all working.
(c)
Draw a labelled diagram of a typical cheek cell as observed, indicating the nucleus, cell membrane, cytoplasm and any other visible structures.
(d)
List three possible sources of error that could affect the measurement obtained in part (b) and suggest one way to minimise each error.
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Question 2 View Details
You are investigating mitosis in onion (Allium cepa) root tip cells using the squash technique. Five fields were examined and the numbers of cells observed in each stage of the cell cycle are recorded in the table below. | Field | Prophase | Metaphase | Anaphase | Telophase | Interphase | |-------|----------|-----------|----------|-----------|------------| | 1 | 12 | 8 | 4 | 2 | 24 | | 2 | 10 | 9 | 5 | 1 | 25 | | 3 | 11 | 7 | 6 | 2 | 24 | | 4 | 13 | 8 | 3 | 3 | 23 | | 5 | 9 | 10 | 5 | 2 | 24 |
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 five fields.
(b)
Determine the mitotic index (MI) as a percentage using the formula MI = (Number of cells in mitosis / Total number of cells) × 100. Show your working and give the answer to one decimal place.
(c)
Identify which phase of mitosis is most frequent in the sample and discuss what this may indicate about the rate of cell division in the onion root tip.
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Question 3 View Details
A student carried out a Benedict’s test to estimate the carbohydrate content of a commercial fruit juice. The procedure was: 1. Weigh 5.00 g of the juice. 2. Dilute with 10 mL distilled water and filter. 3. Pipette 2.00 mL of the filtrate into a test tube, add 2.00 mL of Benedict’s reagent and heat in a boiling water bath for 5 minutes. 4. Cool the mixture, filter the reddish‑brown precipitate, wash with a small amount of cold water and dry to constant mass. The mass of the dried precipitate (Cu₂O) was 0.108 g. The reaction stoichiometry is such that 1.0 g of Cu₂O corresponds to 5.0 g of reducing sugar present in the original sample. The juice label states that it contains 12 % (w/v) carbohydrate (i.e. 12 g per 100 mL). The density of the juice is 1.05 g mL⁻¹. Using the data above, answer the following:
Question Parts
(a)
Calculate the percentage (w/v) of carbohydrate in the juice sample obtained from the experiment. Give your answer to one decimal place.
(b)
State whether the experimental value agrees with the label claim, using an acceptance limit of ±2 % (absolute difference).
(c)
Identify two possible sources of systematic error in the procedure and suggest one method to minimise each error.
(d)
Explain why Benedict’s test measures only reducing sugars and not non‑reducing polysaccharides such as starch.
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Question 4 View Details
A group of students investigated the rate of respiration in germinating beans using a closed‑system respirometer. The set‑up consisted of a sealed 250 mL bottle containing 10 germinating beans immersed in 50 mL of water. The bottle was connected to a graduated tube filled with water; as the beans respired, O₂ was consumed and the water level in the tube fell, indicating the volume of gas taken up. Two experiments were performed: • At 25 °C the water level fell 12 mL in 5 minutes. • At 35 °C the water level fell 18 mL in 5 minutes. Assume that the volume of water displaced is equal to the volume of O₂ consumed, and that the gas behaves ideally at the experimental temperature and pressure. Use 22.4 L as the molar volume of an ideal gas at STP (0 °C, 1 atm) and the molar mass of CO₂ = 44 g mol⁻¹. Answer the following:
Question Parts
(a)
Calculate the rate of O₂ consumption (in mL min⁻¹) at 25 °C.
(b)
Using the data at 35 °C, calculate the mass of CO₂ produced per minute (in mg min⁻¹). Show all steps.
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