Practical Skills: Endorsement Assessment (OCR A Level Biology)

The photograph below shows a blood smear.
Which row correctly lists the cells that are visible in the smear?

Scientists wanted to estimate the number of E.coli bacteria in a 25 cm³ sample.

They carried out a serial dilution with a dilution factor of 10³ and then transferred 0.1 cm³ of the solution to an agar plate to obtain a countable sample.

75 colonies grew on the agar plate.

Which number provides the best estimate for the number of E.coli bacteria found in the original 25 cm³ solution?

The image below shows the stages involved in growing a culture of a bacterial species usually found in the mouth.

Which option correctly explains the reason for incubating the petri dish at 25 °C and no higher?

Some students are dissecting a sheep's heart.

Before they cut into the heart they decided to examine the structure as a whole and to investigate the action of the valves.

Stage 1: The students ran water in through the vena cava and pulmonary vein.

Stage 2: They squeezed the heart from the bottom so that the water moved out through the aorta and pulmonary artery.

Which of the following correctly describes the position of the valves inside the heart during this process.

A student investigated the effect of temperature on the cells of beetroot. The method followed by the student was as follows:

1. Cut 6 discs of equal size from beetroot
2. Place the discs into 6 test tubes with distilled water
3. Maintain the temperature of the tubes at 20 °C, 30 °C, 40 °C, 50 °C, 60 °C and 70 °C
4. After 30 minutes remove the beetroot discs and use a colorimeter to measure the percentage of light passing through the water (transmission)

Which of the following graphs most accurately represents the results the student should expect using this method?

A student was using a light microscope to study some cells from an onion. They used an eyepiece graticule and a stage micrometer; the smallest divisions on the micrometer measured 10 μm.

The image below shows the view through the eyepiece as seen by the students.

What is the length of the complete cell in the image?

Some students used a mark-release-recapture method to estimate the size of an insect population at two different sites in the UK:

• Site 1 was a natural meadow situated 10 m from a busy motorway.
• Site 2 was a natural meadow situated 1000 m from the nearest major road.

The table below shows their results:

What is the difference in the population estimates of the two sites?

Some students carried out a series of biochemical tests on some unknown solutions to identify their contents.

Which solution contained sucrose?

A leafy shoot was attached to a potometer and the time taken for the meniscus to move along the capillary tubing was recorded. The capillary tube had a 0.5 mm diameter.

In one session the student measured bubble movement at a rate of 3 mm min^-1

The volume of a cylinder can be calculated using the following formula:

V = πr²l

To two significant figures, how much water would the plant absorb in 30 minutes at this rate?

Two agar blocks of different sizes are cut. The agar contains universal indicator, giving it a purple colour.

The cubes were then placed in hydrochloric acid solution.

Which of the following statements correctly explains the observations made by the student?

A student uses a potometer to investigate the effect of temperature on the rate of transpiration in a plant cutting. All the potometers were left for the same length of time during the investigation.

The results from the investigation are shown below:

Which of the following is the correct rate of transpiration at 15°C?

The population of roe deer in a woodland area are estimated using the mark-release-capture method. They were captured and marked with a small plastic ear-tag before being released. After 12 months the population was sampled again.

The data collected from this study is shown below:

Which of the answers below is the correct estimate of the roe deer population in this area?

Which of the following statements explain why membrane permeability increases as temperature increases?

Which of the answers below explains why a mixture of solvents is used as the mobile phase of chromatography when separating a mixture of amino acids?

An investigation was completed into the effect of water potential on potato cylinders. The potato cylinders all began with a length of 5cm. The data gathered is shown below:

Which of the following observations and conclusions would not be made for potato cylinders C and D?