neco model questions vol1 2017 biology | Practical

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Question 1 View Details
A prepared slide of an onion epidermal peel is examined under a light microscope. The ocular micrometer is calibrated at 0.01 mm per division. The lengths of five successive cells measured in divisions are: 45, 48, 44, 47 and 46.
Question Parts
(a)
Calculate the average length of the cells in millimetres.
(b)
Identify any three cell organelles that can be seen in the preparation and state one function of each.
(c)
Suggest one precaution that should be observed to avoid distortion of cell size during measurement.
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Question 2 View Details
A student prepared a fresh root tip of Vicia faba (broad bean) for microscopic observation. From a single field of view, the student counted 1,200 cells, of which 48 were observed in the stages of mitosis (prophase, metaphase, anaphase or telophase).
Question Parts
(a)
Calculate the mitotic index (percentage of cells in mitosis).
(b)
If the student estimates that 5 % of the mitotic cells were missed because they overlapped with other cells, recalculate the corrected mitotic index.
(c)
Explain how the mitotic index can be used to assess the effect of a growth regulator applied to the plant, and describe the trend that would indicate inhibition of cell division.
(d)
List two possible sources of error in the preparation and counting procedure and suggest a method to minimise each error.
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Question 3 View Details
A student is investigating the carbohydrate content of a 5.00 g sample of boiled rice using the Benedict’s test. The procedure is as follows: 1. Prepare standard glucose solutions of known concentrations (0, 2, 4 and 6 mg ml⁻¹) and add 2 ml of each to separate test tubes. 2. Add 2 ml of Benedict’s reagent to each tube, heat in a boiling water bath for 5 min and cool. 3. Measure the absorbance of each coloured solution at 540 nm using a colour‑meter. The recorded absorbances are: - 0 mg ml⁻¹ : 0.000 - 2 mg ml⁻¹ : 0.210 - 4 mg ml⁻¹ : 0.415 - 6 mg ml⁻¹ : 0.620 4. Prepare an extract of the rice sample by boiling 5.00 g of the rice in 50 ml of distilled water, filtering and taking 2 ml of the filtrate for the test. The absorbance of the rice extract after adding Benedict’s reagent and heating is 0.425. Answer the following questions:
Question Parts
(a)
Construct a calibration curve for glucose concentration versus absorbance and derive the linear equation (y = mx + c) that relates absorbance (y) to concentration (x).
(b)
Using the equation obtained in (a), calculate the concentration of glucose in the rice extract (in mg ml⁻¹).
(c)
Determine the percentage of carbohydrate (as glucose) present in the original 5.00 g rice sample.
(d)
State two possible sources of error in this experiment and suggest how each could be minimised.
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Question 4 View Details
A group of students is studying the effect of temperature and a metabolic inhibitor on the rate of respiration in germinating beans using a closed‑system respirometer. The procedure is as follows: 1. Place 10 germinating beans in the respirometer chamber containing 50 ml of water. 2. Connect the chamber to a graduated tube filled with water; the displaced water volume indicates the amount of CO₂ produced. 3. Record the volume of displaced water after 5 min at three different temperatures (the water bath is allowed to stabilise before each measurement). The data obtained are: - 20 °C : 12 ml displaced - 30 °C : 18 ml displaced - 40 °C : 30 ml displaced 4. After the 30 °C measurement, a drop of potassium cyanide solution (a known inhibitor of cytochrome oxidase) is added to the chamber and the experiment is repeated at 30 °C. The displaced volume after 5 min is 6 ml. Answer the following questions:
Question Parts
(a)
Calculate the rate of respiration (in ml min⁻¹) at each temperature before the inhibitor was added.
(b)
Using the rates at 20 °C and 30 °C, determine the temperature coefficient Q₁₀ for respiration between these temperatures.
(c)
Explain the effect of potassium cyanide on the respiration rate observed at 30 °C and give a biochemical reason for this effect.
(d)
List two precautions that should be observed to obtain reliable respiration measurements with this apparatus.
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