Practical Skills: Written Assessment (OCR AS Biology)

Assumption A relates to step .............

Assumption B relates to step .............

Assumption C relates to step .............

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Fig. 20.1

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A student investigated the heart rates of smokers and non-smokers.

• Each test subject had their resting heart rate measured using an electronic heart rate monitor.
• They ran 1km on a running track and their heart rate after running 500m was recorded.
• Their heart rate was recorded for a third time 3 minutes after the completion of the exercise.

All test subjects were 18 years old. Subjects were tested between 9am and 4pm on one day, one at a time. Each test lasted approximately 20 minutes in total. The tests were repeated one week later using the same method. Mean heart rates were calculated for each subject.

The student’s plan was to compare the heart rates of smokers and non-smokers using Student’s t-test.

The student’s results are shown in Table 6.

Table 6

Suggest and explain improvements that the student could make to his experimental method and his presentation of data.

In your answer you should explain the benefits of your suggested improvements.

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Water moves by osmosis in living organisms.

Fig. 16

When the capillary tube with visking tubing bag was placed in solution Y, the level of solution X inside the capillary tube rose from 10.5mm to 26.5mm.

uncertainty = ............................. % [2]

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• Cut pieces of plant material of equal surface area ensuring no skin is present.
• Rinse to remove cell debris.
• Gently pat the plant pieces dry with a paper towel.
• Weigh each piece and record mass.
• Put the plant piece in a 200cm³ beaker.
• Cover plant piece with 50cm³ of sucrose solution.
• Use sucrose solutions of 0, 0.1, 0.3, 0.5, 0.7moldm^–3.
• Leave for 24h.
• Remove the piece of plant material.
• Dry carefully using a paper towel.
• Weigh the plant piece and record the mass.
• Calculate the percentage change in mass for each piece.
• Repeat twice for each sucrose concentration.

The students investigated material from three different plants: carrot, courgette and potato.
Their results are shown in Table 16.

Table 16

Fig. 2.3 shows the relationship between body mass and lifespan in a range of mammal species.

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The Madidi National Park, in the South American rainforest, is home to a wide variety of species.
The largest predator in the area is the jaguar. These large cats are well camouflaged and hunt mostly at night. A single individual can cover a very large area.

• Digital camera traps were placed in areas that jaguars were likely to visit.
• If an infrared beam was broken by an animal, the camera was activated.
• The camera then took a photograph of the animal.

• 100 camera traps were set up covering an area of 271km².
• 28 images of 9 different jaguars were recorded.

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The potato plant, Solanum tuberosum, is a staple food plant in many parts of the world.

Potatoes are susceptible to infection by a pathogen called Phytophthora infestans, which causes a disease known as potato late blight. The most visible sign of the disease is a brown discolouration of the leaves.

Some varieties of potato are resistant to infection by P. infestans.

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• Three different clones, A, B and C, of S. tuberosum were used.
• The clones were grown in adjacent fields over the same time period.
• The percentage of leaf area affected by the disease was estimated at regular intervals.

The results are shown in Fig. 18.

Fig. 18

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The effect of wave action on the height of the shells of the dog whelk (Nucella lapillus) was investigated by comparing an exposed shore and a sheltered shore.

• A random sampling technique was used to collect 50 shells from an exposed shore.
• The shell height was measured from the base to the conical tip. The whelk was returned to its location.
• The process was repeated for the sheltered shore.
• All the results were recorded in Table 3.1.

Table 3.1

The t test can be used to determine the significance of the differences between shell height on the exposed shore and the sheltered shore.

Calculate the t value for the data using the formula:

where,

is the difference in mean values of sample 1 and sample 2

and are the squares of the standard deviations of the samples

n₁ and n₂ are the sample sizes.

Give your answer to two decimal places.

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The null hypothesis is that there is no difference between the means of the two shell populations.

The critical values at 98 degrees of freedom are shown in Table 3.2.

Table 3.2

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Sheltered shore			Exposed shore
Height (mm)	Tally	Total	Height (mm)	Tally	Total
23–26		5	11–14		4
27–30		22	15–18		7
31–34		11	19–22		12
35–38		9	23–26		12
39–42		3	27–30		4

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A student wanted to investigate how length of day period affects the rate of plant growth. She decided to use common bean plants and set up her experiment in a room in the school laboratory. 

Explain how the student could carry out her experiment in the laboratory. Give details of how she could collect data.

List three control variables in this experiment AND explain how each could be controlled. 

Suggest the most appropriate way to present the data.

Two students wanted to test the effects of light intensity on the rate of photosynthesis in pond weed. 

Student 1 used the setup in Figure 2.1, while Student 2 used the setup in Figure 2.2. 

Figure 2.1

Figure 2.2

Compare how the two experimental setups would affect the validity and accuracy of the results. Give reasons for your answers.

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Suggest how the students could adapt the experiment to test the effects of temperature on photosynthesis.

A student wanted to use a 0.5 m x 0.5 m quadrat to carry out a line transect up a 300 m stretch of shore perpendicularly to the water line. They carried out quadrats every 5 metres along the transect.

Calculate the total area covered by the transect quadrats in cm².

A student investigated the effects of surface area on osmosis in different sized potato cubes. They cut sets of cubes of the following sizes:

• 1 cm³
• Sides of 5 mm each
• Sides of 0.25 cm each

They then weighed equal masses of each cube size and put them in different sugar solutions for 10 minutes. They then removed the cubes from the solution, dabbed off the excess moisture with tissue paper and weighed each set of cubes. 

[3]

In a clinical trial for a new drug affecting insulin sensitivity, 20 subjects were given 100 mg tablets of either the drug or a placebo. Subjects’ blood glucose response was tested before and after the medication. 

Calculate how many tablets would be needed to provide a drug dose of 5 mg per kilo for an 80 kg man. 

The scientists found that this dose was too low to produce a significant effect. In a previous experiment 1000 mg was found to be effective but created too many side effects. 

Design an experiment to test what the lowest effective dose would be. Include the variables that should be controlled.

The glucose monitors used to measure subjects’ insulin responses had a percentage error of 6%. 

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An ecologist wanted to study the change in arthropod species in a 100 m x 100 m woodland over the course of 5 years. Each year, they conducted sweep-net samples and pitfall trap samples and recorded the mean abundance of 4 key species across 10 randomly-selected 1 m² sample sites. Their results are presented in Table 1 below.

Table 1

Explain the measures the ecologist could take to ensure that their data was valid.

Describe the trends that can be observed in the data over time.

The ecologist wanted to use their data to understand changes in species abundance over the whole study site.

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