ASBiologyOCRExam Questions1. Development of Practical Skills in Biology1.2 Practical Skills: Endorsement Assessment

Practical Skills: Endorsement Assessment (OCR AS Biology)

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1a
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A class of students wanted to carry out a dissection of a sheep’s kidney in their school laboratory.

(i)

Name three examples of dissecting equipment that they might need to successfully carry out the dissection.

[3]

(ii)

Name two safety precautions that should be followed while carrying out the dissection.

[2]

(iii)
Give one reason for your answer at (a)(ii).
[1]

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1b
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Several of the students decided not to take part in the dissection on ethical grounds.

Suggest one reason why they might have made this choice.

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1c
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The students observed their dissections with the naked eye.

State two limitations of a dissection such as this for understanding the function of a kidney.

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2a
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A group of students were sent to do Ecology fieldwork in a mixed grassland habitat near their school. They were equipped with:

  • Quadrats
  • Tape measures
  • Pooters

One group of students decided to investigate the frequency of an orchid species in the study area. 

(i)
Identify the piece of equipment that would be required to carry out this study.

[1]

(ii)

Orchids are not very common in the study area. 

State the most appropriate way to calculate the abundance of orchids.

[1]

(iii)
Describe the method that should be used for choosing sample sites.
[2]

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2b
Sme Calculator6 marks

Another group of students wanted to investigate the arthropod diversity in the area.

(i)
State what piece of equipment from the list provided would be most suitable.

[1]

(ii)
They selected ten study sites of 1 m2 each in the meadow to take samples in.
Suggest how they might have ensured that the sampling was fair between sites.

[1]

(iii)
They found 120 woodlice and 40 earwigs across the study sites.
Calculate the species density of woodlice and earwigs per m2.

[2]

(iv)
The meadow was 100 m x 100 m. Use your answer to (b)(iii) to calculate how many woodlice would be estimated to be present in the entire meadow.
[2]

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3a
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A dye was separated into its component molecules using paper chromatography. The results are shown in Figure 3.1.ocr-a-1-2-sq-e-q3-paper-chromatography

Figure 3.1

(i)
State how many different solutes the dye contains.

[1]

(ii)
Identify the colour solute that has the smallest molecules.

[1]

(iii)

The Rf value of a solute is:

 The distance travelled by the solute ÷ distance travelled by the solvent. 

Calculate the Rf value of the purple dye solute.

[2]

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3b
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(i)
Aside from molecule size, state one other factor that might affect how far a solute travels.

[1]

(ii)
Name two precautions that must be taken when setting up the solvent and starting line for a chromatogram. 

[2]

(iii)
Describe how this procedure might be used to compare the components of the unknown dye sample with a dye of known components.
[2]

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3c
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A chromatogram was made using a mixed sample of amino acids.

Describe how the component amino acids could be visualised.

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4a
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Students wanted to investigate the effect of temperature on the membrane permeability of beetroot cells. They used a scalpel to cut cubes of beetroot and placed them in test tubes of water in water baths at 20 ⁰C, 30 ⁰C and 40 ⁰C before testing the amount of pigment released into the water. 

(i)
State what other piece of apparatus they could have used to cut pieces of beetroot.

 [1]

(ii)
Describe two control variables for this experiment.

  [2]

(iii)

Name the piece of apparatus the students should use to measure the amount of pigment that was released.

  [1]

(iv)
State what the students should do between each reading on the piece of apparatus in your answer to (a)(iii).
  [1]

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4b
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(i)
State and explain the relationship between the light absorbance of the water samples and the permeability of the beetroot cell membranes. 

[2]
(ii)

Explain two reasons why an increase in temperature increases membrane permeability.

[2]

(iii)
State how the students might ensure that their results were reliable.
[1]

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5a
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A student wanted to determine the water potential of potato cells. They cut pieces of potato with a cork borer, weighed them, and placed them in sugar solutions of different concentrations for 30 minutes, then weighed them again. Three different sugar solutions were used: 0.1 M, 1 M and 1.5 M.

State the variables the student should control.

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5b
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If a potato cell cytoplasm has a solute concentration of 0.8 M, state what you would expect to happen to the mass of the potato pieces in the: 

(i)
0.1 M solution

[1]

(ii)
1 M solution

[1]

(iii)
1.5 M solution

[1]

(iv)
Name the process responsible for the changes in mass of the potato pieces.

[1]

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5c
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The student wanted to find out the exact concentration of the potato cells.

Describe how they could use their results to do this.

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1a1 mark

Two students investigated the growth of bacteria at different temperatures.

Three flasks containing identical solutions of nutrient broth were used.

  • Flask 1: inoculated with 1cm3 of broth containing the bacterium Bacillus subtilis and incubated at 20°C.
  • Flask 2: inoculated with 1cm3 of broth containing B. subtilis and incubated at 30°C.
  • Flask 3: inoculated with 1cm3 of broth containing no bacteria and incubated at 30°C.

Aseptic techniques were used throughout.

At set times over the next 3 days the students removed samples from each flask and measured the number of viable bacteria present.

(a)
State one further variable the students should have controlled in their investigation in order to produce valid results.
[1]

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1b5 marks
(b)
The students used the following procedure to determine the number of viable bacteria in each flask at a given time.

From each flask, 0.1cm3 was removed and mixed with 9.9cm3 of sterile water in a test tube.
This was labelled Tube A. A serial dilution then proceeded, as shown in Table 19.1.

Tube Contents
B 1cm3 of Tube A mixture 9cm3 of sterile water
C 1cm3 of Tube B mixture  9cm3 of sterile water
D 1cm3 of Tube C mixture  9cm3 of sterile water
E 1cm3 of Tube D mixture  9cm3 of sterile water
F 1cm3 of Tube E mixture  9cm3 of sterile water

Table 19.1

From each tube, A–F, 0.1cm3 of mixture was cultured on nutrient agar for 24 hours at 30°C.

The results from Flask 2 after 7 hours of incubation are shown in Fig. 19.

q19b-paper-2-june-2018-ocr-a-level-biology

Fig. 19

The students used Tube F to calculate the number of viable bacteria present in the original sample.

(i)
Use Tube F to calculate the number of viable bacteria present in the original 0.1cm3 sample from Flask 2 after 7 hours of incubation.

Give your answer in standard form.
[2]
(ii)
The students disagreed about which tube’s result to use as a starting point for their calculation.

Discuss whether the petri dish resulting from Tube F was the most appropriate for them to use.
[3]

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1c12 marks
(c)
The processed results from the students’ investigation are shown in Table 19.2.

Time after incubation started (hours)

 Number of viable bacteria present in Flask 1 at 20°C Number of viable bacteria present in Flask 2 at 30°C
0 7.0 × 102 7.1 × 102
2 6.8 × 102 7.4 × 102
4 4.7 × 104 2.5 × 106
8 6.5 × 107 9.2 × 1010
12 2.4 × 109 1.8 × 1011
18 7.8 × 1010 1.8 × 1011
24 9.2 × 1010 5.5 × 108
36 8.6 × 1010 4.2 × 104
48 6.0 × 109 6.7 × 102
60 5.7 × 107 5.2 × 102
72 1.3 × 105 3.1 × 102

Table 19.2

(i)
Using the information in Table 19.2, compare and explain the patterns of growth seen at 20°C and at 30°C.
[6]
(ii)
No bacteria were detected at any time in the flask that was inoculated with nutrient broth that did not contain bacteria.
Explain the purpose of this flask.
[2]
(iii)
The teacher told the students they should not investigate the growth of bacteria at 35°C.
Suggest why the teacher told them not to grow bacteria at 35°C.
[1]
(iv)
The teacher also suggested that the students should have carried out the investigation using three flasks at each temperature.
Explain how this suggestion would have improved the students’ investigation.
[3]

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2a
Sme Calculator5 marks
(a)
Fig. 1.1 shows the structure of the amino acid leucine.
 
(i)
On Fig. 1.1, draw a circle around the R group of leucine.
q1ai-paper-3-june-2017-ocr-a-level-biology
Fig. 1.1

[1]
(ii)
Students used thin layer chromatography to separate leucine from other amino acids.
The chromatogram they produced is shown in Fig. 1.2.
ocr-a-level-june-2017-paper-3-q1aiii
Fig. 1.2

What can you conclude about the chemical properties of leucine and amino acid X?
[1]

(iii)
Amino acid Z was in the mixture analysed by the students. It is not shown on the chromatogram in Fig. 1.2. Amino acid Z has an Rf value that is 0.20 lower than that of amino acid Y.

Place a dot on the chromatogram in Fig. 1.2 to show the distance moved by amino acid Z. A ruler has been added to the image to assist with your measurements.

Show your working.

[3]

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2b
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(b)
Thin layer chromatography can also be used to separate photosynthetic pigments.

(i)
State a material that can be used as the stationary phase in thin layer chromatography.
[1]

(ii)
State the precise location of photosynthetic pigments in a chloroplast.
[2]

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2c
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(c)
When sequencing DNA, fragments of DNA are separated by electrophoresis.

Describe three differences between the process of thin layer chromatography and the form of electrophoresis used to sequence DNA.

[3]

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3
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(a)
Plants lose water by transpiration.

The rate of transpiration varies between different species of plant.

The rate of transpiration can be measured using a potometer.

Plan an investigation into the rate of transpiration in two species of plant that would allow valid data to be collected.

Details of how to set up a potometer are not required.

[6]

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4
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(a)
A student planned to carry out a dissection of insect and fish gaseous exchange systems.

The student planned to complete diagrams of the different tissues. They were advised to observe the following guidelines:
  • use a sharp pencil
  • use ruled label lines
  • include a scale bar.

Suggest two further guidelines for the student to follow to ensure they present their diagrams clearly and accurately.

1 ..........................................................

2 ..........................................................

[2]

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5
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(a)
Lactose is a reducing sugar.

Benedict’s reagent can be used to detect the presence of lactose in a solution.

A colorimeter can be used to measure the concentration of lactose.

The colorimeter first needs to be calibrated.

Describe how a method that uses Benedict’s reagent and a colorimeter could be calibrated to measure the concentration of lactose in an unknown sample.
 [4]

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1a
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Some students wanted to test an unknown solution for reducing sugars in the school laboratory. 

Describe a method they could use to carry out a qualitative test for reducing sugars on the unknown solution and state the results of a positive test. 

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1b
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The students got a positive result for their qualitative test. They wanted to carry out a quantitative test on the solution using a colorimeter.

(i)
Describe how the students could make a calibration curve using a colorimeter. 

[4]

(ii)
Explain how the students could use the calibration curve to identify the concentration of reducing sugar in the unknown solution. 
[2]

How did you do?

1c
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Explain why a colorimeter is more accurate than judging the Benedict’s test result wit the naked eye.

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2a
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 A group of students wanted to test an unknown solid sample for proteins. 

(i)
Describe how they could carry out a test for proteins and state the results of a positive test.

[4]

(ii)
The students found it difficult to tell whether the test was positive.
Suggest two ways in which they could better distinguish a positive result. 
[2]

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2b
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Explain why the unknown sample might still contain amino acids even if there is a negative result.

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3a
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Lipids include triglycerides and phospholipids, which are found in cell membranes.  

An emulsion test can be used to test for lipids in a sample. The sample is shaken with ethanol before water is added. If lipids are present, a cloudy emulsion appears. 

(i)
Explain why lipids cannot dissolve in water. 
[1]
(ii)
Explain why an emulsion appears after water is added.
[1]

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3b
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Organic solvents affect the permeability of cell membranes. A student wanted to investigate how solvent concentration affected the permeability of beetroot cell membranes. Beetroot cells contain a red-violet pigment called betacyanin. They cut cubes of beetroot and put them in a range of ethanol solutions of different concentrations, then measured the amount of pigment that left the cells using a colorimeter. 

(i)

Describe two limitations of this experiment. 

[2]

(ii)
The results of the experiment are presented in Figure 3.1.ocr-a-1-2-sq-h-q3-beetroot-membrane-permeability

Figure 3.1

Describe and explain the shape of the graph.

[4]

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4a
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Computer simulations can be used to model the effects of natural selection on populations. A scientist wanted to test the effects of selection on a population of white butterflies. 

Suggest the effect on the butterfly population if the scientist changed the abiotic environment in the simulation. 

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4b
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The scientist added a dominant mutation into the butterfly population making it bright red and toxic to a predator in the simulation environment.
Explain what would likely happen to the mutation in the simulation.

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4c
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The scientist changed the mutation to be recessive.

Explain how the simulation with this allele would differ from your answer in (b).

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4d
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Discuss the advantages of using computer modelling for studying natural selection.

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5a
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A scientist wanted to determine the concentration of a stock bacterial suspension. They created a serial dilution, taking 1 ml of stock solution, adding 9 ml of nutrient broth. This was repeated 6 times, as shown in Figure 5.1. 

ocr-a-1-2-sq-h-q5-serial-dilution

Figure 5.1

1 ml of each dilution was plated on an agar plate and the number of colonies was counted. 

The number of colonies from Dilution 5 was 3.

Calculate the estimated number of bacterial colonies in the entire Dilution 4 tube.

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5b
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Dilution 3 had 311 colonies.

Calculate the concentration of bacterial colonies of the stock solution. Write your answer in standard form.

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5c
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(i)
Suggest why the scientist used the number of colonies from Dilution 3 to calculate the concentration of the stock solution.

[2]

(ii)
The scientist wanted to determine the rate of bacterial growth in Dilution 5.
Describe how they could do this. 

[3]

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