neco 2017 biology | Practical

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Question 1 View Details
You are given a prepared slide of an unknown plant cell and a compound microscope with an ocular lens of 10× and objective lenses of 4×, 10× and 40×. A stage micrometer with divisions of 0.01 mm is placed on the stage. Perform the tasks described below.
Question Parts
(a)
State the total magnification when the 40× objective is used.
(b)
The micrometer shows that 25 divisions correspond to 0.25 mm in reality. On the same field, the length of the observed cell spans 150 divisions of the reticle. Calculate the actual length of the cell in micrometres (µm).
(c)
Draw a labelled diagram of the cell showing at least five organelles. Include the cell wall, plasma membrane, nucleus, vacuole and chloroplast. Indicate the relative positions of the organelles clearly.
(d)
Mention two precautions that should be observed when preparing the slide to avoid artefacts.
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Question 2 View Details
A fresh onion root tip is collected, fixed in 1% acetic acid, stained with Feulgen stain and a squash preparation is made. Using the 40× objective of a compound microscope, you examine 200 cells and record the following numbers in each stage of mitosis: Prophase – 30 cells, Metaphase – 50 cells, Anaphase – 20 cells, Telophase – 10 cells, Interphase – 90 cells.
Question Parts
(a)
Calculate the mitotic index (percentage of cells undergoing mitosis).
(b)
Determine the percentage of the total cells that are in each individual phase of mitosis.
(c)
Discuss what the relatively high proportion of cells in metaphase may indicate about the effect of the Feulgen stain on the cell cycle.
(d)
Identify two possible sources of error that could affect the accuracy of the mitotic index and suggest a method to minimise each error.
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Question 3 View Details
A group of five secondary school students each prepared a 250 g serving of a mixed meal consisting of rice, beans and fried plantain. The following data were recorded for each food item per serving: | Food item | Mass (g) | Carbohydrate (%) | Protein (%) | Fat (%) | |-----------|----------|------------------|-------------|---------| | Rice | 120 | 80 | 8 | 2 | | Beans | 80 | 60 | 20 | 2 | | Fried plantain | 50 | 70 | 2 | 8 | Use the conversion factors: 4 kcal per gram of carbohydrate, 4 kcal per gram of protein and 9 kcal per gram of fat. Answer the following:
Question Parts
(a)
Calculate the total calories contributed by each macronutrient (carbohydrate, protein, fat) in one serving of the meal.
(b)
Determine the total caloric content of the meal per serving and compare it with the recommended daily allowance (RDA) of 2500 kcal for an adolescent. State whether the meal meets, exceeds or falls short of the RDA and by how many kilocalories.
(c)
If the meal is to be adjusted to meet exactly the RDA without changing the total mass of the meal, suggest the percentage change required for the component that contributes the highest excess calories. Show your calculation.
(d)
Identify two possible sources of experimental error in the determination of the macronutrient percentages and suggest a method to minimise each error.
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Question 4 View Details
A simple closed respirometer was used to measure the rate of respiration of germinating mung beans at two temperatures. The apparatus consisted of a sealed bottle containing 50 mL of water and a set of 10 germinating beans. The volume of gas collected (as displaced water) was recorded every 5 minutes for 30 minutes at each temperature. Data recorded: **At 25 °C** | Time (min) | Volume displaced (mL) | |------------|-----------------------| | 0 | 0 | | 5 | 2.8 | | 10 | 5.6 | | 15 | 8.4 | | 20 | 11.2 | | 25 | 14.0 | | 30 | 16.8 | **At 35 °C** | Time (min) | Volume displaced (mL) | |------------|-----------------------| | 0 | 0 | | 5 | 4.5 | | 10 | 9.0 | | 15 | 13.5 | | 20 | 18.0 | | 25 | 22.5 | | 30 | 27.0 | Answer the following:
Question Parts
(a)
Calculate the rate of respiration (mL CO₂ per minute) at each temperature using the linear portion of the data.
(b)
Determine the Q₁₀ temperature coefficient for the respiration process between 25 °C and 35 °C. Use the formula Q₁₀ = (R₂/R₁)^(10/(T₂‑T₁)), where R₁ and R₂ are the respiration rates at T₁ and T₂ respectively.
(c)
Discuss two physiological reasons why the rate of respiration in the beans increases with temperature.
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